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<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"/><title>2 Beginning Student with List Abbreviations</title><link rel="stylesheet" type="text/css" href="../scribble.css" title="default"/><link rel="stylesheet" type="text/css" href="../racket.css" title="default"/><link rel="stylesheet" type="text/css" href="../manual-style.css" title="default"/><link rel="stylesheet" type="text/css" href="../manual-racket.css" title="default"/><link rel="stylesheet" type="text/css" href="../doc-site.css" title="default"/><script type="text/javascript" src="../scribble-common.js"></script><script type="text/javascript" src="../manual-racket.js"></script><script type="text/javascript" src="../doc-site.js"></script><script type="text/javascript" src="../local-redirect/local-redirect.js"></script><script type="text/javascript" src="../local-redirect/local-user-redirect.js"></script><!--[if IE 6]><style type="text/css">.SIEHidden { overflow: hidden; }</style><![endif]--></head><body id="doc-racket-lang-org"><div class="tocset"><div class="tocview"><div class="tocviewlist tocviewlisttopspace"><div class="tocviewtitle"><table cellspacing="0" cellpadding="0"><tr><td style="width: 1em;"><a href="javascript:void(0);" title="Expand/Collapse" class="tocviewtoggle" onclick="TocviewToggle(this,"tocview_0");">▼</a></td><td></td><td><a href="index.html" class="tocviewlink" data-pltdoc="x"><span style="font-style: italic">How to Design Programs</span> Languages</a></td></tr></table></div><div class="tocviewsublisttop" style="display: block;" id="tocview_0"><table cellspacing="0" cellpadding="0"><tr><td align="right">1 </td><td><a href="beginner.html" class="tocviewlink" data-pltdoc="x">Beginning Student</a></td></tr><tr><td align="right">2 </td><td><a href="" class="tocviewselflink" data-pltdoc="x">Beginning Student with List Abbreviations</a></td></tr><tr><td align="right">3 </td><td><a href="intermediate.html" class="tocviewlink" data-pltdoc="x">Intermediate Student</a></td></tr><tr><td align="right">4 </td><td><a href="intermediate-lam.html" class="tocviewlink" data-pltdoc="x">Intermediate Student with Lambda</a></td></tr><tr><td align="right">5 </td><td><a href="advanced.html" class="tocviewlink" data-pltdoc="x">Advanced Student</a></td></tr></table></div></div><div class="tocviewlist"><table cellspacing="0" cellpadding="0"><tr><td style="width: 1em;"><a href="javascript:void(0);" title="Expand/Collapse" class="tocviewtoggle" onclick="TocviewToggle(this,"tocview_1");">►</a></td><td>2 </td><td><a href="" class="tocviewselflink" data-pltdoc="x">Beginning Student with List Abbreviations</a></td></tr></table><div class="tocviewsublistbottom" style="display: none;" id="tocview_1"><table cellspacing="0" cellpadding="0"><tr><td align="right">2.1 </td><td><a href="#%28part._beginner-abbr._.Pre-.Defined._.Variables%29" class="tocviewlink" data-pltdoc="x">Pre-<wbr></wbr>Defined Variables</a></td></tr><tr><td align="right">2.2 </td><td><a href="#%28part._beginner-abbr._.Template._.Variables%29" class="tocviewlink" data-pltdoc="x">Template Variables</a></td></tr><tr><td align="right">2.3 </td><td><a href="#%28part._beginner-abbr-syntax%29" class="tocviewlink" data-pltdoc="x">Syntaxes for Beginning Student with List Abbreviations</a></td></tr><tr><td align="right">2.4 </td><td><a href="#%28part._beginner-abbr-common-syntax%29" class="tocviewlink" data-pltdoc="x">Common Syntaxes</a></td></tr><tr><td align="right">2.5 </td><td><a href="#%28part._beginner-abbr-pre-defined%29" class="tocviewlink" data-pltdoc="x">Pre-<wbr></wbr>defined Functions</a></td></tr><tr><td align="right">2.6 </td><td><a href="#%28part._htdp-beginner-abbr._.Numbers__.Integers__.Rationals__.Reals__.Complex__.Exacts__.Inexacts%29" class="tocviewlink" data-pltdoc="x">Numbers:<span class="mywbr"> </span> Integers, Rationals, Reals, Complex, Exacts, Inexacts</a></td></tr><tr><td align="right">2.7 </td><td><a href="#%28part._htdp-beginner-abbr._.Booleans%29" class="tocviewlink" data-pltdoc="x">Booleans</a></td></tr><tr><td align="right">2.8 </td><td><a href="#%28part._htdp-beginner-abbr._.Symbols%29" class="tocviewlink" data-pltdoc="x">Symbols</a></td></tr><tr><td align="right">2.9 </td><td><a href="#%28part._htdp-beginner-abbr._.Lists%29" class="tocviewlink" data-pltdoc="x">Lists</a></td></tr><tr><td align="right">2.10 </td><td><a href="#%28part._htdp-beginner-abbr._.Posns%29" class="tocviewlink" data-pltdoc="x">Posns</a></td></tr><tr><td align="right">2.11 </td><td><a href="#%28part._htdp-beginner-abbr._.Characters%29" class="tocviewlink" data-pltdoc="x">Characters</a></td></tr><tr><td align="right">2.12 </td><td><a href="#%28part._htdp-beginner-abbr._.Strings%29" class="tocviewlink" data-pltdoc="x">Strings</a></td></tr><tr><td align="right">2.13 </td><td><a href="#%28part._htdp-beginner-abbr._.Images%29" class="tocviewlink" data-pltdoc="x">Images</a></td></tr><tr><td align="right">2.14 </td><td><a href="#%28part._htdp-beginner-abbr._.Misc%29" class="tocviewlink" data-pltdoc="x">Misc</a></td></tr></table></div></div></div><div class="tocsub"><div class="tocsubtitle">On this page:</div><table class="tocsublist" cellspacing="0"><tr><td><span class="tocsublinknumber">2.1<tt> </tt></span><a href="#%28part._beginner-abbr._.Pre-.Defined._.Variables%29" class="tocsubseclink" data-pltdoc="x">Pre-<wbr></wbr>Defined Variables</a></td></tr><tr><td><a href="#%28def._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._empty%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">empty</span></span></a></td></tr><tr><td><a href="#%28def._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._true%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">true</span></span></a></td></tr><tr><td><a href="#%28def._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._false%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">false</span></span></a></td></tr><tr><td><span class="tocsublinknumber">2.2<tt> </tt></span><a href="#%28part._beginner-abbr._.Template._.Variables%29" class="tocsubseclink" data-pltdoc="x">Template Variables</a></td></tr><tr><td><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._....%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">..</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._......%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktMeta"><span class="RktStxLink">...</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._........%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">....</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._..........%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">.....</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._............%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">......</span></span></a></td></tr><tr><td><span class="tocsublinknumber">2.3<tt> </tt></span><a href="#%28part._beginner-abbr-syntax%29" class="tocsubseclink" data-pltdoc="x">Syntaxes for Beginning Student with List Abbreviations</a></td></tr><tr><td><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._quote%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">quote</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._quasiquote%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">quasiquote</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._unquote%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">unquote</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._unquote-splicing%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">unquote-<wbr></wbr>splicing</span></span></a></td></tr><tr><td><span class="tocsublinknumber">2.4<tt> </tt></span><a href="#%28part._beginner-abbr-common-syntax%29" class="tocsubseclink" data-pltdoc="x">Common Syntaxes</a></td></tr><tr><td><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._define%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">define</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._lambda%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">lambda</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._define-struct%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">define-<wbr></wbr>struct</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._cond%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">cond</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._else%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">else</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._if%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">if</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._and%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">and</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._or%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">or</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._check-expect%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">check-<wbr></wbr>expect</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._check-random%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">check-<wbr></wbr>random</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._check-within%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">check-<wbr></wbr>within</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._check-error%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">check-<wbr></wbr>error</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._check-member-of%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">check-<wbr></wbr>member-<wbr></wbr>of</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._check-range%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">check-<wbr></wbr>range</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._require%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">require</span></span></a></td></tr><tr><td><span class="tocsublinknumber">2.5<tt> </tt></span><a href="#%28part._beginner-abbr-pre-defined%29" class="tocsubseclink" data-pltdoc="x">Pre-<wbr></wbr>defined Functions</a></td></tr><tr><td><span class="tocsublinknumber">2.6<tt> </tt></span><a href="#%28part._htdp-beginner-abbr._.Numbers__.Integers__.Rationals__.Reals__.Complex__.Exacts__.Inexacts%29" class="tocsubseclink" data-pltdoc="x">Numbers:<span class="mywbr"> </span> Integers, Rationals, Reals, Complex, Exacts, Inexacts</a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._%2A%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">*</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._%2B%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">+</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._-%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink"><span class="nobreak">-</span></span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._%2F%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">/</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._~3c%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink"><</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._~3c~3d%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink"><=</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._~3d%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">=</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._~3e%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">></span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._~3e~3d%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">>=</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._abs%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">abs</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._acos%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">acos</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._add1%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">add1</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._angle%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">angle</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._asin%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">asin</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._atan%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">atan</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._ceiling%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">ceiling</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._complex~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">complex?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._conjugate%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">conjugate</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._cos%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">cos</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._cosh%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">cosh</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._current-seconds%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">current-<wbr></wbr>seconds</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._denominator%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">denominator</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._e%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">e</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._even~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">even?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._exact-~3einexact%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">exact-<wbr></wbr>>inexact</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._exact~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">exact?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._exp%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">exp</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._expt%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">expt</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._floor%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">floor</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._gcd%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">gcd</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._imag-part%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">imag-<wbr></wbr>part</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._inexact-~3eexact%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">inexact-<wbr></wbr>>exact</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._inexact~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">inexact?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._integer-~3echar%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">integer-<wbr></wbr>>char</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._integer-sqrt%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">integer-<wbr></wbr>sqrt</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._integer~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">integer?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._lcm%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">lcm</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._log%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">log</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._magnitude%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">magnitude</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._make-polar%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">make-<wbr></wbr>polar</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._make-rectangular%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">make-<wbr></wbr>rectangular</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._max%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">max</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._min%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">min</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._modulo%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">modulo</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._negative~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">negative?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._number-~3estring%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">number-<wbr></wbr>>string</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._number~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">number?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._numerator%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">numerator</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._odd~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">odd?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._pi%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">pi</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._positive~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">positive?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._quotient%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">quotient</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._random%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">random</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._rational~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">rational?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._real-part%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">real-<wbr></wbr>part</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._real~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">real?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._remainder%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">remainder</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._round%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">round</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._sgn%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">sgn</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._sin%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">sin</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._sinh%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">sinh</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._sqr%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">sqr</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._sqrt%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">sqrt</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._sub1%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">sub1</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._tan%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">tan</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._zero~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">zero?</span></span></a></td></tr><tr><td><span class="tocsublinknumber">2.7<tt> </tt></span><a href="#%28part._htdp-beginner-abbr._.Booleans%29" class="tocsubseclink" data-pltdoc="x">Booleans</a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._boolean~3d~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">boolean=?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._boolean~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">boolean?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._false~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">false?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._not%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">not</span></span></a></td></tr><tr><td><span class="tocsublinknumber">2.8<tt> </tt></span><a href="#%28part._htdp-beginner-abbr._.Symbols%29" class="tocsubseclink" data-pltdoc="x">Symbols</a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._symbol-~3estring%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">symbol-<wbr></wbr>>string</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._symbol~3d~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">symbol=?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._symbol~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">symbol?</span></span></a></td></tr><tr><td><span class="tocsublinknumber">2.9<tt> </tt></span><a href="#%28part._htdp-beginner-abbr._.Lists%29" class="tocsubseclink" data-pltdoc="x">Lists</a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._append%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">append</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._assq%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">assq</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._caaar%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">caaar</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._caadr%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">caadr</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._caar%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">caar</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._cadar%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">cadar</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._cadddr%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">cadddr</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._caddr%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">caddr</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._cadr%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">cadr</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._car%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">car</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._cdaar%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">cdaar</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._cdadr%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">cdadr</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._cdar%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">cdar</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._cddar%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">cddar</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._cdddr%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">cdddr</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._cddr%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">cddr</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._cdr%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">cdr</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._cons%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">cons</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._cons~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">cons?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._eighth%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">eighth</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._empty~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">empty?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._fifth%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">fifth</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._first%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">first</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._fourth%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">fourth</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._length%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">length</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._list%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">list</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._list%2A%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">list*</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._list-ref%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">list-<wbr></wbr>ref</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._make-list%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">make-<wbr></wbr>list</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._member%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">member</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._member~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">member?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._memq%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">memq</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._memq~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">memq?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._memv%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">memv</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._null%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">null</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._null~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">null?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._range%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">range</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._remove%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">remove</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._rest%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">rest</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._reverse%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">reverse</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._second%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">second</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._seventh%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">seventh</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._sixth%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">sixth</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._third%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">third</span></span></a></td></tr><tr><td><span class="tocsublinknumber">2.10<tt> </tt></span><a href="#%28part._htdp-beginner-abbr._.Posns%29" class="tocsubseclink" data-pltdoc="x">Posns</a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._make-posn%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">make-<wbr></wbr>posn</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._posn%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">posn</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._posn-x%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">posn-<wbr></wbr>x</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._posn-y%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">posn-<wbr></wbr>y</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._posn~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">posn?</span></span></a></td></tr><tr><td><span class="tocsublinknumber">2.11<tt> </tt></span><a href="#%28part._htdp-beginner-abbr._.Characters%29" class="tocsubseclink" data-pltdoc="x">Characters</a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._char-~3einteger%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">char-<wbr></wbr>>integer</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._char-alphabetic~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">char-<wbr></wbr>alphabetic?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._char-ci~3c~3d~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">char-<wbr></wbr>ci<=?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._char-ci~3c~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">char-<wbr></wbr>ci<?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._char-ci~3d~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">char-<wbr></wbr>ci=?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._char-ci~3e~3d~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">char-<wbr></wbr>ci>=?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._char-ci~3e~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">char-<wbr></wbr>ci>?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._char-downcase%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">char-<wbr></wbr>downcase</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._char-lower-case~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">char-<wbr></wbr>lower-<wbr></wbr>case?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._char-numeric~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">char-<wbr></wbr>numeric?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._char-upcase%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">char-<wbr></wbr>upcase</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._char-upper-case~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">char-<wbr></wbr>upper-<wbr></wbr>case?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._char-whitespace~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">char-<wbr></wbr>whitespace?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._char~3c~3d~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">char<=?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._char~3c~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">char<?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._char~3d~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">char=?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._char~3e~3d~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">char>=?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._char~3e~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">char>?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._char~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">char?</span></span></a></td></tr><tr><td><span class="tocsublinknumber">2.12<tt> </tt></span><a href="#%28part._htdp-beginner-abbr._.Strings%29" class="tocsubseclink" data-pltdoc="x">Strings</a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._explode%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">explode</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._format%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">format</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._implode%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">implode</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._int-~3estring%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">int-<wbr></wbr>>string</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._list-~3estring%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">list-<wbr></wbr>>string</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._make-string%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">make-<wbr></wbr>string</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._replicate%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">replicate</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">string</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string-~3eint%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">string-<wbr></wbr>>int</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string-~3elist%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">string-<wbr></wbr>>list</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string-~3enumber%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">string-<wbr></wbr>>number</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string-~3esymbol%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">string-<wbr></wbr>>symbol</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string-alphabetic~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">string-<wbr></wbr>alphabetic?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string-append%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">string-<wbr></wbr>append</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string-ci~3c~3d~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">string-<wbr></wbr>ci<=?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string-ci~3c~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">string-<wbr></wbr>ci<?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string-ci~3d~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">string-<wbr></wbr>ci=?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string-ci~3e~3d~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">string-<wbr></wbr>ci>=?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string-ci~3e~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">string-<wbr></wbr>ci>?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string-contains~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">string-<wbr></wbr>contains?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string-copy%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">string-<wbr></wbr>copy</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string-ith%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">string-<wbr></wbr>ith</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string-length%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">string-<wbr></wbr>length</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string-lower-case~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">string-<wbr></wbr>lower-<wbr></wbr>case?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string-numeric~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">string-<wbr></wbr>numeric?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string-ref%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">string-<wbr></wbr>ref</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string-upper-case~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">string-<wbr></wbr>upper-<wbr></wbr>case?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string-whitespace~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">string-<wbr></wbr>whitespace?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string~3c~3d~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">string<=?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string~3c~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">string<?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string~3d~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">string=?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string~3e~3d~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">string>=?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string~3e~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">string>?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">string?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._substring%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">substring</span></span></a></td></tr><tr><td><span class="tocsublinknumber">2.13<tt> </tt></span><a href="#%28part._htdp-beginner-abbr._.Images%29" class="tocsubseclink" data-pltdoc="x">Images</a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._image~3d~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">image=?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._image~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">image?</span></span></a></td></tr><tr><td><span class="tocsublinknumber">2.14<tt> </tt></span><a href="#%28part._htdp-beginner-abbr._.Misc%29" class="tocsubseclink" data-pltdoc="x">Misc</a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._~3d~7e%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">=~</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._eof%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">eof</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._eof-object~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">eof-<wbr></wbr>object?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._eq~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">eq?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._equal~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">equal?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._equal~7e~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">equal~?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._eqv~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">eqv?</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._error%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">error</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._exit%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">exit</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._identity%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">identity</span></span></a></td></tr><tr><td><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._struct~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">struct?</span></span></a></td></tr></table></div></div><div class="maincolumn"><div class="main"><div class="navsettop"><span class="navleft"><form class="searchform"><input class="searchbox" style="color: #888;" type="text" value="...search manuals..." title="Enter a search string to search the manuals" onkeypress="return DoSearchKey(event, this, "6.1", "../");" onfocus="this.style.color="black"; this.style.textAlign="left"; if (this.value == "...search manuals...") this.value="";" onblur="if (this.value.match(/^ *$/)) { this.style.color="#888"; this.style.textAlign="center"; this.value="...search manuals..."; }"/></form> <a href="../index.html" title="up to the documentation top" data-pltdoc="x" onclick="return GotoPLTRoot("6.1");">top</a></span><span class="navright"> <a href="beginner.html" title="backward to "1 Beginning Student"" data-pltdoc="x">← prev</a> <a href="index.html" title="up to "How to Design Programs Languages"" data-pltdoc="x">up</a> <a href="intermediate.html" title="forward to "3 Intermediate Student"" data-pltdoc="x">next →</a></span> </div><h3 x-source-module="(lib "scribblings/htdp-langs/htdp-langs.scrbl")" x-part-tag=""beginner-abbr"">2<tt> </tt><a name="(part._beginner-abbr)"></a>Beginning Student with List Abbreviations</h3><p><table cellspacing="0" cellpadding="0"><tr><td align="right" valign="baseline"><span class="hspace"> </span><span class="RktVar">program</span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">=</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktVar">def-or-expr</span><span class="hspace"> </span><span class="RktSym">...</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td></tr><tr><td align="right" valign="baseline"><span class="hspace"> </span><span class="RktVar">def-or-expr</span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">=</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktVar">definition</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktVar">expr</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktVar">test-case</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktVar">library-require</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td></tr><tr><td align="right" valign="baseline"><span class="hspace"> </span><span class="RktVar">definition</span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">=</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktVar">name</span><span class="hspace"> </span><span class="RktVar">variable</span><span class="hspace"> </span><span class="RktVar">variable</span><span class="hspace"> </span><span class="RktSym">...</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVar">expr</span><span class="RktPn">)</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktVar">name</span><span class="hspace"> </span><span class="RktVar">expr</span><span class="RktPn">)</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktVar">name</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._lambda%29%29" class="RktStxLink" data-pltdoc="x">lambda</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktVar">variable</span><span class="hspace"> </span><span class="RktVar">variable</span><span class="hspace"> </span><span class="RktSym">...</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVar">expr</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._define-struct%29%29" class="RktStxLink" data-pltdoc="x">define-struct</a></span><span class="hspace"> </span><span class="RktVar">name</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktVar">name</span><span class="hspace"> </span><span class="RktSym">...</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td></tr><tr><td align="right" valign="baseline"><span class="hspace"> </span><span class="RktVar">expr</span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">=</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">(</span><span class="RktVar">name</span><span class="hspace"> </span><span class="RktVar">expr</span><span class="hspace"> </span><span class="RktVar">expr</span><span class="hspace"> </span><span class="RktSym">...</span><span class="RktPn">)</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">(</span><span class="RktVar">prim-op</span><span class="hspace"> </span><span class="RktVar">expr</span><span class="hspace"> </span><span class="RktSym">...</span><span class="RktPn">)</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._cond%29%29" class="RktStxLink" data-pltdoc="x">cond</a></span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktVar">expr</span><span class="hspace"> </span><span class="RktVar">expr</span><span class="RktPn">]</span><span class="hspace"> </span><span class="RktSym">...</span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktVar">expr</span><span class="hspace"> </span><span class="RktVar">expr</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._cond%29%29" class="RktStxLink" data-pltdoc="x">cond</a></span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktVar">expr</span><span class="hspace"> </span><span class="RktVar">expr</span><span class="RktPn">]</span><span class="hspace"> </span><span class="RktSym">...</span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._else%29%29" class="RktStxLink" data-pltdoc="x">else</a></span><span class="hspace"> </span><span class="RktVar">expr</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._if%29%29" class="RktStxLink" data-pltdoc="x">if</a></span><span class="hspace"> </span><span class="RktVar">expr</span><span class="hspace"> </span><span class="RktVar">expr</span><span class="hspace"> </span><span class="RktVar">expr</span><span class="RktPn">)</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._and%29%29" class="RktStxLink" data-pltdoc="x">and</a></span><span class="hspace"> </span><span class="RktVar">expr</span><span class="hspace"> </span><span class="RktVar">expr</span><span class="hspace"> </span><span class="RktVar">expr</span><span class="hspace"> </span><span class="RktSym">...</span><span class="RktPn">)</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._or%29%29" class="RktStxLink" data-pltdoc="x">or</a></span><span class="hspace"> </span><span class="RktVar">expr</span><span class="hspace"> </span><span class="RktVar">expr</span><span class="hspace"> </span><span class="RktVar">expr</span><span class="hspace"> </span><span class="RktSym">...</span><span class="RktPn">)</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktVar">name</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktVal">’</span><span class="RktVar">quoted</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktVal">‘</span><span class="RktVar">quasiquoted</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktVar">number</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktVar">boolean</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktVar">string</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktVar">character</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td></tr><tr><td align="right" valign="baseline"><span class="hspace"> </span><span class="RktVar">quoted</span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">=</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktVar">name</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktVar">number</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktVar">string</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktVar">character</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">(</span><span class="RktVar">quoted</span><span class="stt"> </span><span class="RktSym">...</span><span class="RktPn">)</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktVal">’</span><span class="RktVar">quoted</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktVal">‘</span><span class="RktVar">quoted</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt">,</span><span class="RktVar">quoted</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt">,@</span><span class="RktVar">quoted</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td></tr><tr><td align="right" valign="baseline"><span class="hspace"> </span><span class="RktVar">quasiquoted</span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">=</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktVar">name</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktVar">number</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktVar">string</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktVar">character</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">(</span><span class="RktVar">quasiquoted</span><span class="stt"> </span><span class="RktSym">...</span><span class="RktPn">)</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktVal">’</span><span class="RktVar">quasiquoted</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktVal">‘</span><span class="RktVar">quasiquoted</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt">,</span><span class="RktSym">expr</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt">,@</span><span class="RktSym">expr</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td></tr><tr><td align="right" valign="baseline"><span class="hspace"> </span><span class="RktVar">test-case</span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">=</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._check-expect%29%29" class="RktStxLink" data-pltdoc="x">check-expect</a></span><span class="stt"> </span><span class="RktSym">expr</span><span class="stt"> </span><span class="RktSym">expr</span><span class="RktPn">)</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._check-random%29%29" class="RktStxLink" data-pltdoc="x">check-random</a></span><span class="stt"> </span><span class="RktSym">expr</span><span class="stt"> </span><span class="RktSym">expr</span><span class="RktPn">)</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._check-within%29%29" class="RktStxLink" data-pltdoc="x">check-within</a></span><span class="stt"> </span><span class="RktSym">expr</span><span class="stt"> </span><span class="RktSym">expr</span><span class="stt"> </span><span class="RktSym">expr</span><span class="RktPn">)</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._check-member-of%29%29" class="RktStxLink" data-pltdoc="x">check-member-of</a></span><span class="stt"> </span><span class="RktSym">expr</span><span class="stt"> </span><span class="RktSym">expr</span><span class="stt"> </span><span class="RktSym">...</span><span class="RktPn">)</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._check-range%29%29" class="RktStxLink" data-pltdoc="x">check-range</a></span><span class="stt"> </span><span class="RktSym">expr</span><span class="stt"> </span><span class="RktSym">expr</span><span class="stt"> </span><span class="RktSym">expr</span><span class="RktPn">)</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._check-error%29%29" class="RktStxLink" data-pltdoc="x">check-error</a></span><span class="stt"> </span><span class="RktSym">expr</span><span class="stt"> </span><span class="RktSym">expr</span><span class="RktPn">)</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._check-error%29%29" class="RktStxLink" data-pltdoc="x">check-error</a></span><span class="stt"> </span><span class="RktSym">expr</span><span class="RktPn">)</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td></tr><tr><td align="right" valign="baseline"><span class="hspace"> </span><span class="RktVar">library-require</span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">=</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._require%29%29" class="RktStxLink" data-pltdoc="x">require</a></span><span class="stt"> </span><span class="RktSym">string</span><span class="RktPn">)</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._require%29%29" class="RktStxLink" data-pltdoc="x">require</a></span><span class="stt"> </span><span class="RktPn">(</span><span class="RktSym">lib</span><span class="stt"> </span><span class="RktSym">string</span><span class="stt"> </span><span class="RktSym">string</span><span class="stt"> </span><span class="RktSym">...</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._require%29%29" class="RktStxLink" data-pltdoc="x">require</a></span><span class="stt"> </span><span class="RktPn">(</span><span class="RktSym">planet</span><span class="stt"> </span><span class="RktSym">string</span><span class="stt"> </span><span class="RktVar">package</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td></tr><tr><td align="right" valign="baseline"><span class="hspace"> </span><span class="RktVar">package</span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">=</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">(</span><span class="RktSym">string</span><span class="stt"> </span><span class="RktSym">string</span><span class="stt"> </span><span class="RktSym">number</span><span class="stt"> </span><span class="RktSym">number</span><span class="RktPn">)</span></td></tr></table></p><p><div class="SIntrapara">An <span class="RktVar">name</span> or a <span class="RktVar">variable</span> is a sequence of characters
not including a space or one of the following:</div><div class="SIntrapara"><span class="hspace"> </span> <span class="RktInBG"><span class="hspace"></span><span class="RktIn">"</span><span class="hspace"></span></span> <span class="RktInBG"><span class="hspace"></span><span class="RktIn">,</span><span class="hspace"></span></span> <span class="RktInBG"><span class="hspace"></span><span class="RktIn">'</span><span class="hspace"></span></span> <span class="RktInBG"><span class="hspace"></span><span class="RktIn">`</span><span class="hspace"></span></span>
<span class="RktInBG"><span class="hspace"></span><span class="RktIn">(</span><span class="hspace"></span></span> <span class="RktInBG"><span class="hspace"></span><span class="RktIn">)</span><span class="hspace"></span></span> <span class="RktInBG"><span class="hspace"></span><span class="RktIn">[</span><span class="hspace"></span></span> <span class="RktInBG"><span class="hspace"></span><span class="RktIn">]</span><span class="hspace"></span></span>
<span class="RktInBG"><span class="hspace"></span><span class="RktIn">{</span><span class="hspace"></span></span> <span class="RktInBG"><span class="hspace"></span><span class="RktIn">}</span><span class="hspace"></span></span> <span class="RktInBG"><span class="hspace"></span><span class="RktIn">|</span><span class="hspace"></span></span> <span class="RktInBG"><span class="hspace"></span><span class="RktIn">;</span><span class="hspace"></span></span>
<span class="RktInBG"><span class="hspace"></span><span class="RktIn">#</span><span class="hspace"></span></span></div><div class="SIntrapara">A <span class="RktVar">number</span> is a number such as <span class="RktVal">123</span>, <span class="RktVal">3/2</span>, or
<span class="RktVal">5.5</span>.</div><div class="SIntrapara">A <span class="RktVar">boolean</span> is one of: <span class="RktSym">true</span>, <span class="RktSym">false</span>,
<span class="RktVal">#t</span>, <span class="RktVal">#f</span>, <span class="RktVal">#true</span><span class="RktMeta"></span>, or <span class="RktVal">#false</span><span class="RktMeta"></span>.</div><div class="SIntrapara">A <span class="RktVar">symbol</span> is a quote character followed by a name. A
symbol is a value, just like 0 or empty.</div><div class="SIntrapara">A <span class="RktVar">string</span> is enclosed by a pair of <span class="RktInBG"><span class="hspace"></span><span class="RktIn">"</span><span class="hspace"></span></span>. Unlike
symbols, strings may be split into characters and manipulated by a
variety of functions. For example, <span class="RktVal">"abcdef"</span>,
<span class="RktVal">"This is a string"</span>, and <span class="RktVal">"This is a string with \" inside"</span> are all strings.</div><div class="SIntrapara">A <span class="RktVar">character</span> begins with <span class="RktInBG"><span class="hspace"></span><span class="RktIn">#\</span><span class="hspace"></span></span> and has the
name of the character. For example, <span class="RktVal">#\a</span>, <span class="RktVal">#\b</span>,
and <span class="RktVal">#\space</span> are characters.</div><div class="SIntrapara">In <a href="#%28part._beginner-abbr-syntax%29" data-pltdoc="x">function calls</a>, the function appearing
immediatly after the open parenthesis can be any functions defined
with <span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span> or <span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._define-struct%29%29" class="RktStxLink" data-pltdoc="x">define-struct</a></span>, or any one of the
<a href="#%28part._beginner-abbr-pre-defined%29" data-pltdoc="x">pre-defined functions</a>.</div></p><h4 x-source-module="(lib "scribblings/htdp-langs/htdp-langs.scrbl")" x-part-tag=""beginner-abbr Pre-Defined Variables"">2.1<tt> </tt><a name="(part._beginner-abbr._.Pre-.Defined._.Variables)"></a>Pre-Defined Variables</h4><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>value</p></div></div><p class="RForeground"><a name="(def._((lib._lang/htdp-beginner-abbr..rkt)._empty))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._empty%29%29" class="RktValDef RktValLink" data-pltdoc="x">empty</a></span></span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="intermediate.html#%28def._htdp-intermediate._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._empty~3f%29%29" class="RktValLink" data-pltdoc="x">empty?</a></span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">The empty list.</div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>value</p></div></div><p class="RForeground"><a name="(def._((lib._lang/htdp-beginner-abbr..rkt)._true))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._true%29%29" class="RktValDef RktValLink" data-pltdoc="x">true</a></span></span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="intermediate.html#%28def._htdp-intermediate._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._boolean~3f%29%29" class="RktValLink" data-pltdoc="x">boolean?</a></span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">The true value.</div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>value</p></div></div><p class="RForeground"><a name="(def._((lib._lang/htdp-beginner-abbr..rkt)._false))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._false%29%29" class="RktValDef RktValLink" data-pltdoc="x">false</a></span></span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="intermediate.html#%28def._htdp-intermediate._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._boolean~3f%29%29" class="RktValLink" data-pltdoc="x">boolean?</a></span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">The false value.</div></p><h4 x-source-module="(lib "scribblings/htdp-langs/htdp-langs.scrbl")" x-part-tag=""beginner-abbr Template Variables"">2.2<tt> </tt><a name="(part._beginner-abbr._.Template._.Variables)"></a>Template Variables</h4><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><a name="(form._((lib._lang/htdp-beginner-abbr..rkt)._....))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._....%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">..</a></span></span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">A placeholder for indicating that a definition is a template.</div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><a name="(form._((lib._lang/htdp-beginner-abbr..rkt)._......))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktMeta"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._......%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">...</a></span></span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">A placeholder for indicating that a definition is a template.</div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><a name="(form._((lib._lang/htdp-beginner-abbr..rkt)._........))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._........%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">....</a></span></span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">A placeholder for indicating that a definition is a template.</div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><a name="(form._((lib._lang/htdp-beginner-abbr..rkt)._..........))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._..........%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">.....</a></span></span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">A placeholder for indicating that a definition is a template.</div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><a name="(form._((lib._lang/htdp-beginner-abbr..rkt)._............))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._............%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">......</a></span></span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">A placeholder for indicating that a definition is a template.</div></p><h4 x-source-module="(lib "scribblings/htdp-langs/htdp-langs.scrbl")" x-part-tag=""beginner-abbr-syntax"">2.3<tt> </tt><a name="(part._beginner-abbr-syntax)"></a>Syntaxes for Beginning Student with List Abbreviations</h4><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><table cellspacing="0" cellpadding="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktVal">’</span><span class="RktVar">name</span></p></blockquote></td></tr></table></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktVal">’</span><span class="RktVar">part</span></p></blockquote></td></tr></table></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._lang/htdp-beginner-abbr..rkt)._quote))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._quote%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">quote</a></span></span><span class="hspace"> </span><span class="RktVar">name</span><span class="RktPn">)</span></p></blockquote></td></tr></table></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._quote%29%29" class="RktStxLink" data-pltdoc="x">quote</a></span><span class="hspace"> </span><span class="RktVar">part</span><span class="RktPn">)</span></p></blockquote></td></tr></table></td></tr></table></blockquote></div><div class="SIntrapara">A quoted name is a symbol. A quoted part is an abbreviation for a nested lists.</div></p><p><div class="SIntrapara">Normally, this quotation is written with a <span class="RktInBG"><span class="hspace"></span><span class="RktIn">'</span><span class="hspace"></span></span>, like
<span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">apple</span><span class="stt"> </span><span class="RktVal">banana</span><span class="RktVal">)</span>, but it can also be written with
<span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._quote%29%29" class="RktStxLink" data-pltdoc="x">quote</a></span>, like <span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._quote%29%29" class="RktStxLink" data-pltdoc="x">quote</a></span><span class="stt"> </span><span class="RktPn">(</span><span class="RktSym">apple</span><span class="stt"> </span><span class="RktSym">banana</span><span class="RktPn">)</span><span class="RktPn">)</span>.</div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><table cellspacing="0" cellpadding="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktVal">‘</span><span class="RktVar">name</span></p></blockquote></td></tr></table></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktVal">‘</span><span class="RktVar">part</span></p></blockquote></td></tr></table></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._lang/htdp-beginner-abbr..rkt)._quasiquote))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._quasiquote%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">quasiquote</a></span></span><span class="hspace"> </span><span class="RktVar">name</span><span class="RktPn">)</span></p></blockquote></td></tr></table></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._quasiquote%29%29" class="RktStxLink" data-pltdoc="x">quasiquote</a></span><span class="hspace"> </span><span class="RktVar">part</span><span class="RktPn">)</span></p></blockquote></td></tr></table></td></tr></table></blockquote></div><div class="SIntrapara">Like <span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._quote%29%29" class="RktStxLink" data-pltdoc="x">quote</a></span>, but also allows escaping to expression
“unquotes.”</div></p><p><div class="SIntrapara">Normally, quasi-quotations are written with a backquote,
<span class="RktInBG"><span class="hspace"></span><span class="RktIn">`</span><span class="hspace"></span></span>, like <span class="RktVal">`</span><span class="RktVal">(</span><span class="RktVal">apple</span><span class="stt"> </span><span class="RktRdr">,</span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28def._htdp-intermediate._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._%2B%29%29" class="RktValLink" data-pltdoc="x">+</a></span><span class="stt"> </span><span class="RktVal">1</span><span class="stt"> </span><span class="RktVal">2</span><span class="RktPn">)</span><span class="RktVal">)</span>, but they can also be
written with <span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._quasiquote%29%29" class="RktStxLink" data-pltdoc="x">quasiquote</a></span>, like
<span class="RktPn">(</span><span class="RktSym">quasiquote-elem</span><span class="stt"> </span><span class="RktPn">(</span><span class="RktSym">apple</span><span class="stt"> </span><span class="RktRdr">,</span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28def._htdp-intermediate._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._%2B%29%29" class="RktValLink" data-pltdoc="x">+</a></span><span class="stt"> </span><span class="RktVal">1</span><span class="stt"> </span><span class="RktVal">2</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span>.</div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><table cellspacing="0" cellpadding="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktVal">,</span><span class="RktVar">expression</span></p></blockquote></td></tr></table></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._lang/htdp-beginner-abbr..rkt)._unquote))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._unquote%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">unquote</a></span></span><span class="hspace"> </span><span class="RktVar">expression</span><span class="RktPn">)</span></p></blockquote></td></tr></table></td></tr></table></blockquote></div><div class="SIntrapara">Under a single quasiquote, <span class="stt">,</span><span class="RktVar">expression</span>
escapes from the quote to include an evaluated expression whose
result is inserted into the abbreviated list.</div></p><p>Under multiple quasiquotes, <span class="stt">,</span><span class="RktVar">expression</span> is
really the literal <span class="stt">,</span><span class="RktVar">expression</span>, decrementing
the quasiquote count by one for <span class="RktVar">expression</span>.</p><p><div class="SIntrapara">Normally, an unquote is written with <span class="RktInBG"><span class="hspace"></span><span class="RktIn">,</span><span class="hspace"></span></span>, but it can also be
written with <span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._unquote%29%29" class="RktStxLink" data-pltdoc="x">unquote</a></span>.</div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><table cellspacing="0" cellpadding="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktVal">,@</span><span class="RktVar">expression</span></p></blockquote></td></tr></table></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._lang/htdp-beginner-abbr..rkt)._unquote-splicing))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._unquote-splicing%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">unquote-splicing</a></span></span><span class="hspace"> </span><span class="RktVar">expression</span><span class="RktPn">)</span></p></blockquote></td></tr></table></td></tr></table></blockquote></div><div class="SIntrapara">Under a single quasiquote, <span class="stt">,@</span><span class="RktVar">expression</span>
escapes from the quote to include an evaluated expression whose
result is a list to splice into the abbreviated list.</div></p><p>Under multiple quasiquotes, a splicing unquote is like an unquote;
that is, it decrements the quasiquote count by one.</p><p>Normally, a splicing unquote is written with <span class="RktInBG"><span class="hspace"></span><span class="RktIn">,</span><span class="hspace"></span></span>, but it
can also be written with <span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._unquote-splicing%29%29" class="RktStxLink" data-pltdoc="x">unquote-splicing</a></span>.</p><h4 x-source-module="(lib "scribblings/htdp-langs/htdp-langs.scrbl")" x-part-tag=""beginner-abbr-common-syntax"">2.4<tt> </tt><a name="(part._beginner-abbr-common-syntax)"></a>Common Syntaxes</h4><p>The following syntaxes behave the same in the <span style="font-style: italic">Beginner with List
Abbreviations</span> level as they did in the <a href="beginner.html" data-pltdoc="x">Beginning Student</a> level.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._lang/htdp-beginner-abbr..rkt)._define))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._define%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">define</a></span></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktVar">name</span><span class="hspace"> </span><span class="RktVar">variable</span><span class="hspace"> </span><span class="RktVar">variable</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVar">expression</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Defines a function named <span class="RktVar">name</span>. The <span class="RktVar">expression</span> is the body
of the function. When the function is called,
the values of the arguments are inserted into the body in place of the
<span class="RktVar">variable</span>s. The function returns the value of that new expression.</div></p><p><div class="SIntrapara">The function name’s cannot be the same as that of another function or
variable.</div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktVar">name</span><span class="hspace"> </span><span class="RktVar">expression</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Defines a variable called <span class="RktVar">name</span> with the the value of
<span class="RktVar">expression</span>. The variable name’s cannot be the same as that of
another function or variable, and <span class="RktVar">name</span> itself must not appear in
<span class="RktVar">expression</span>.
</div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktVar">name</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._lambda%29%29" class="RktStxLink" data-pltdoc="x">lambda</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktVar">variable</span><span class="hspace"> </span><span class="RktVar">variable</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVar">expression</span><span class="RktPn">)</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">An alternate way on defining functions. The <span class="RktVar">name</span> is the name of
the function, which cannot be the same as that of another function or
variable.</div></p><p>A <a name="(form._((lib._lang/htdp-beginner-abbr..rkt)._lambda))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._lambda%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">lambda</a></span></span> cannot be used outside of this alternate syntax.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._lang/htdp-beginner-abbr..rkt)._define-struct))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._define-struct%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">define-struct</a></span></span><span class="hspace"> </span><span class="RktVar">structure-name</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktVar">field-name</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Defines a new structure called <span class="RktVar">structure-name</span>. The structure’s fields are
named by the <span class="RktVar">field-name</span>s. After the <span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._define-struct%29%29" class="RktStxLink" data-pltdoc="x">define-struct</a></span>, the following new
functions are available:</div></p><ul><li><p><span class="RktSym">make-</span><span class="RktVar">structure-name</span> : takes a number of
arguments equal to the number of fields in the structure,
and creates a new instance of that structure.</p></li><li><p><span class="RktVar">structure-name</span><span class="RktSym">-</span><span class="RktVar">field-name</span> : takes an
instance of the structure and returns the value in the field named by
<span class="RktVar">field-name</span>.</p></li><li><p><span class="RktVar">structure-name</span><span class="RktSym">?</span> : takes any value, and returns
<span class="RktSym"><a href="#%28def._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._true%29%29" class="RktValLink" data-pltdoc="x">true</a></span> if the value is an instance of the structure.</p></li></ul><p>The name of the new functions introduced by <span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._define-struct%29%29" class="RktStxLink" data-pltdoc="x">define-struct</a></span>
must not be the same as that of other functions or variables,
otherwise <span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._define-struct%29%29" class="RktStxLink" data-pltdoc="x">define-struct</a></span> reports an error.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><span class="RktVar">name</span><span class="hspace"> </span><span class="RktVar">expression</span><span class="hspace"> </span><span class="RktVar">expression</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Calls the function named <span class="RktVar">name</span>. The value of the call is the
value of <span class="RktVar">name</span>’s body when every one of the function’s
variables are replaced by the values of the corresponding
<span class="RktVar">expression</span>s.</div></p><p><div class="SIntrapara">The function named <span class="RktVar">name</span> must defined before it can be called. The
number of argument <span class="RktVar">expression</span>s must be the same as the number of arguments
expected by the function.</div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._lang/htdp-beginner-abbr..rkt)._cond))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._cond%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">cond</a></span></span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktVar">question-expression</span><span class="hspace"> </span><span class="RktVar">answer-expression</span><span class="RktPn">]</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._cond%29%29" class="RktStxLink" data-pltdoc="x">cond</a></span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktVar">question-expression</span><span class="hspace"> </span><span class="RktVar">answer-expression</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace"> </span><span class="RktMeta">...</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">[</span><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._else%29%29" class="RktStxLink" data-pltdoc="x">else</a></span><span class="hspace"> </span><span class="RktVar">answer-expression</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr></table></blockquote></div><div class="SIntrapara">Chooses a clause based on some condition. <span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._cond%29%29" class="RktStxLink" data-pltdoc="x">cond</a></span> finds the first
<span class="RktVar">question-expression</span> that evaluates to <span class="RktSym"><a href="#%28def._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._true%29%29" class="RktValLink" data-pltdoc="x">true</a></span>, then
evaluates the corresponding <span class="RktVar">answer-expression</span>.</div></p><p>If none of the <span class="RktVar">question-expression</span>s evaluates to <span class="RktSym"><a href="#%28def._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._true%29%29" class="RktValLink" data-pltdoc="x">true</a></span>,
<span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._cond%29%29" class="RktStxLink" data-pltdoc="x">cond</a></span>’s value is the <span class="RktVar">answer-expression</span> of the
<span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._else%29%29" class="RktStxLink" data-pltdoc="x">else</a></span> clause. If there is no <span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._else%29%29" class="RktStxLink" data-pltdoc="x">else</a></span>, <span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._cond%29%29" class="RktStxLink" data-pltdoc="x">cond</a></span> reports
an error. If the result of a <span class="RktVar">question-expression</span> is neither
<span class="RktSym"><a href="#%28def._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._true%29%29" class="RktValLink" data-pltdoc="x">true</a></span> nor <span class="RktSym"><a href="#%28def._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._false%29%29" class="RktValLink" data-pltdoc="x">false</a></span>, <span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._cond%29%29" class="RktStxLink" data-pltdoc="x">cond</a></span> also reports an error.</p><p><div class="SIntrapara"><a name="(form._((lib._lang/htdp-beginner-abbr..rkt)._else))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._else%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">else</a></span></span> cannot be used outside of <span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._cond%29%29" class="RktStxLink" data-pltdoc="x">cond</a></span>.</div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._lang/htdp-beginner-abbr..rkt)._if))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._if%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">if</a></span></span><span class="hspace"> </span><span class="RktVar">test-expression</span><span class="hspace"> </span><span class="RktVar">then-expression</span><span class="hspace"> </span><span class="RktVar">else-expression</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">When the value of the <span class="RktVar">test-expression</span> is <span class="RktSym"><a href="#%28def._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._true%29%29" class="RktValLink" data-pltdoc="x">true</a></span>,
<span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._if%29%29" class="RktStxLink" data-pltdoc="x">if</a></span> evaluates the <span class="RktVar">then-expression</span>. When the test is
<span class="RktSym"><a href="#%28def._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._false%29%29" class="RktValLink" data-pltdoc="x">false</a></span>, <span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._if%29%29" class="RktStxLink" data-pltdoc="x">if</a></span> evaluates the <span class="RktVar">else-expression</span>.</div></p><p><div class="SIntrapara">If the <span class="RktVar">test-expression</span> is neither <span class="RktSym"><a href="#%28def._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._true%29%29" class="RktValLink" data-pltdoc="x">true</a></span> nor
<span class="RktSym"><a href="#%28def._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._false%29%29" class="RktValLink" data-pltdoc="x">false</a></span>, <span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._if%29%29" class="RktStxLink" data-pltdoc="x">if</a></span> reports an error.</div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._lang/htdp-beginner-abbr..rkt)._and))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._and%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">and</a></span></span><span class="hspace"> </span><span class="RktVar">expression</span><span class="hspace"> </span><span class="RktVar">expression</span><span class="hspace"> </span><span class="RktVar">expression</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Evaluates to <span class="RktSym"><a href="#%28def._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._true%29%29" class="RktValLink" data-pltdoc="x">true</a></span> if all the <span class="RktVar">expression</span>s are
<span class="RktSym"><a href="#%28def._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._true%29%29" class="RktValLink" data-pltdoc="x">true</a></span>. If any <span class="RktVar">expression</span> is <span class="RktSym"><a href="#%28def._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._false%29%29" class="RktValLink" data-pltdoc="x">false</a></span>, the <span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._and%29%29" class="RktStxLink" data-pltdoc="x">and</a></span>
expression evaluates to <span class="RktSym"><a href="#%28def._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._false%29%29" class="RktValLink" data-pltdoc="x">false</a></span> (and the expressions to the
right of that expression are not evaluated.)</div></p><p><div class="SIntrapara">If any of the expressions evaluate to a value other than <span class="RktSym"><a href="#%28def._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._true%29%29" class="RktValLink" data-pltdoc="x">true</a></span> or
<span class="RktSym"><a href="#%28def._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._false%29%29" class="RktValLink" data-pltdoc="x">false</a></span>, <span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._and%29%29" class="RktStxLink" data-pltdoc="x">and</a></span> reports an error.</div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._lang/htdp-beginner-abbr..rkt)._or))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._or%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">or</a></span></span><span class="hspace"> </span><span class="RktVar">expression</span><span class="hspace"> </span><span class="RktVar">expression</span><span class="hspace"> </span><span class="RktVar">expression</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Evaluates to <span class="RktSym"><a href="#%28def._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._true%29%29" class="RktValLink" data-pltdoc="x">true</a></span> as soon as one of the
<span class="RktVar">expression</span>s is <span class="RktSym"><a href="#%28def._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._true%29%29" class="RktValLink" data-pltdoc="x">true</a></span> (and the expressions to the right of that
expression are not evaluated.) If all of the <span class="RktVar">expression</span>s are <span class="RktSym"><a href="#%28def._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._false%29%29" class="RktValLink" data-pltdoc="x">false</a></span>,
the <span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._or%29%29" class="RktStxLink" data-pltdoc="x">or</a></span> expression evaluates to <span class="RktSym"><a href="#%28def._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._false%29%29" class="RktValLink" data-pltdoc="x">false</a></span>.</div></p><p><div class="SIntrapara">If any of the expressions evaluate to a value other than <span class="RktSym"><a href="#%28def._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._true%29%29" class="RktValLink" data-pltdoc="x">true</a></span> or
<span class="RktSym"><a href="#%28def._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._false%29%29" class="RktValLink" data-pltdoc="x">false</a></span>, <span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._or%29%29" class="RktStxLink" data-pltdoc="x">or</a></span> reports an error.</div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._lang/htdp-beginner-abbr..rkt)._check-expect))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._check-expect%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">check-expect</a></span></span><span class="hspace"> </span><span class="RktVar">expression</span><span class="hspace"> </span><span class="RktVar">expected-expression</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Checks that the first <span class="RktVar">expression</span> evaluates to the same value as the
<span class="RktVar">expected-expression</span>.</div></p><p><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._check-expect%29%29" class="RktStxLink" data-pltdoc="x">check-expect</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">fahrenheit->celsius</span><span class="hspace"> </span><span class="RktVal">212</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVal">100</span><span class="RktPn">)</span></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._check-expect%29%29" class="RktStxLink" data-pltdoc="x">check-expect</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">fahrenheit->celsius</span><span class="hspace"> </span><span class="RktVal"><span class="nobreak">-4</span>0</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVal"><span class="nobreak">-4</span>0</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">fahrenheit->celsius</span><span class="hspace"> </span><span class="RktSym">f</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28def._htdp-intermediate._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._%2A%29%29" class="RktValLink" data-pltdoc="x">*</a></span><span class="hspace"> </span><span class="RktVal">5/9</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28def._htdp-intermediate._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._-%29%29" class="RktValLink" data-pltdoc="x"><span class="nobreak">-</span></a></span><span class="hspace"> </span><span class="RktSym">f</span><span class="hspace"> </span><span class="RktVal">32</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></blockquote></div><div class="SIntrapara">A <span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._check-expect%29%29" class="RktStxLink" data-pltdoc="x">check-expect</a></span> expression must be placed at the top-level of a
student program. Also it may show up anywhere in the program, including
ahead of the tested function definition. By placing <span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._check-expect%29%29" class="RktStxLink" data-pltdoc="x">check-expect</a></span>s
there, a programmer conveys to a future reader the intention behind the
program with working examples, thus making it often superfluous to read
the function definition proper.</div></p><p><div class="SIntrapara">It is an error for <span class="RktSym">expr</span> or <span class="RktSym">expected-expr</span> to produce an
inexact number or a function value. As for inexact numbers, it is
<span style="font-style: italic">morally</span> wrong to compare them for plain equality. Instead one
tests whether they are both within a small interval; see
<span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._check-within%29%29" class="RktStxLink" data-pltdoc="x">check-within</a></span>. As for functions (see Intermediate and up), it is
provably impossible to compare functions.</div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._lang/htdp-beginner-abbr..rkt)._check-random))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._check-random%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">check-random</a></span></span><span class="hspace"> </span><span class="RktVar">expression</span><span class="hspace"> </span><span class="RktVar">expected-expression</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Checks that the first <span class="RktVar">expression</span> evaluates to the same value as the
<span class="RktVar">expected-expression</span>.</div></p><p>The form supplies the same random-number generator to both parts. If both
parts request <span class="RktSym"><a href="intermediate.html#%28def._htdp-intermediate._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._random%29%29" class="RktValLink" data-pltdoc="x">random</a></span> numbers from the same interval in the same
order, they receive the same random numbers.</p><p><div class="SIntrapara">Here is a simple example of where <span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._check-random%29%29" class="RktStxLink" data-pltdoc="x">check-random</a></span> is useful:
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktSym">WIDTH</span><span class="hspace"> </span><span class="RktVal">100</span><span class="RktPn">)</span></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktSym">HEIGHT</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28def._htdp-intermediate._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._%2A%29%29" class="RktValLink" data-pltdoc="x">*</a></span><span class="hspace"> </span><span class="RktVal">2</span><span class="hspace"> </span><span class="RktSym">WIDTH</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._define-struct%29%29" class="RktStxLink" data-pltdoc="x">define-struct</a></span><span class="hspace"> </span><span class="RktSym">player</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">name</span><span class="hspace"> </span><span class="RktSym">x</span><span class="hspace"> </span><span class="RktSym">y</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="RktCmt">;</span><span class="RktCmt"> </span><span class="RktCmt">A </span><span style="font-style: italic">Player</span><span class="RktCmt"> is </span><span class="RktPn">(</span><span class="RktSym">make-player</span><span class="stt"> </span><span class="RktSym">String</span><span class="stt"> </span><span class="RktSym">Nat</span><span class="stt"> </span><span class="RktSym">Nat</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span></td></tr><tr><td><span class="RktCmt">;</span><span class="RktCmt"> </span><span class="RktCmt">String -> Player </span></td></tr><tr><td><span class="hspace"> </span></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._check-random%29%29" class="RktStxLink" data-pltdoc="x">check-random</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">create-randomly-placed-player</span><span class="hspace"> </span><span class="RktVal">"David Van Horn"</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">make-player</span><span class="hspace"> </span><span class="RktVal">"David Van Horn"</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28def._htdp-intermediate._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._random%29%29" class="RktValLink" data-pltdoc="x">random</a></span><span class="hspace"> </span><span class="RktSym">WIDTH</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28def._htdp-intermediate._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._random%29%29" class="RktValLink" data-pltdoc="x">random</a></span><span class="hspace"> </span><span class="RktSym">HEIGHT</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">create-randomly-placed-player</span><span class="hspace"> </span><span class="RktSym">name</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">make-player</span><span class="hspace"> </span><span class="RktSym">name</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28def._htdp-intermediate._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._random%29%29" class="RktValLink" data-pltdoc="x">random</a></span><span class="hspace"> </span><span class="RktSym">WIDTH</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28def._htdp-intermediate._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._random%29%29" class="RktValLink" data-pltdoc="x">random</a></span><span class="hspace"> </span><span class="RktSym">HEIGHT</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></blockquote></div><div class="SIntrapara">Note how <span class="RktSym"><a href="intermediate.html#%28def._htdp-intermediate._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._random%29%29" class="RktValLink" data-pltdoc="x">random</a></span> is called on the same numbers in the same order in
both parts of <span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._check-random%29%29" class="RktStxLink" data-pltdoc="x">check-random</a></span>. If the two parts call <span class="RktSym"><a href="intermediate.html#%28def._htdp-intermediate._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._random%29%29" class="RktValLink" data-pltdoc="x">random</a></span>
for different intervals, they are likely to fail:
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="RktCmt">;</span><span class="RktCmt"> </span><span class="RktCmt">String -> </span><span style="font-style: italic">Player</span></td></tr><tr><td><span class="hspace"> </span></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._check-random%29%29" class="RktStxLink" data-pltdoc="x">check-random</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">create-randomly-placed-player</span><span class="hspace"> </span><span class="RktVal">"David Van Horn"</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">make-player</span><span class="hspace"> </span><span class="RktVal">"David Van Horn"</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28def._htdp-intermediate._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._random%29%29" class="RktValLink" data-pltdoc="x">random</a></span><span class="hspace"> </span><span class="RktSym">WIDTH</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28def._htdp-intermediate._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._random%29%29" class="RktValLink" data-pltdoc="x">random</a></span><span class="hspace"> </span><span class="RktSym">HEIGHT</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">create-randomly-placed-player</span><span class="hspace"> </span><span class="RktSym">name</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._local%29%29" class="RktStxLink" data-pltdoc="x">local</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktSym">h</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28def._htdp-intermediate._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._random%29%29" class="RktValLink" data-pltdoc="x">random</a></span><span class="hspace"> </span><span class="RktSym">HEIGHT</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktSym">w</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28def._htdp-intermediate._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._random%29%29" class="RktValLink" data-pltdoc="x">random</a></span><span class="hspace"> </span><span class="RktSym">WIDTH</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">make-player</span><span class="hspace"> </span><span class="RktSym">name</span><span class="hspace"> </span><span class="RktSym">w</span><span class="hspace"> </span><span class="RktSym">h</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></blockquote></div></p><p><div class="SIntrapara">It is an error for <span class="RktSym">expr</span> or <span class="RktSym">expected-expr</span> to produce a function
value or an inexact number; see note on <span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._check-expect%29%29" class="RktStxLink" data-pltdoc="x">check-expect</a></span> for details.</div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._lang/htdp-beginner-abbr..rkt)._check-within))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._check-within%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">check-within</a></span></span><span class="hspace"> </span><span class="RktVar">expression</span><span class="hspace"> </span><span class="RktVar">expected-expression</span><span class="hspace"> </span><span class="RktVar">delta</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Checks whether the value of the <span class="RktVar">expression</span> expression is
structurally equal to the value produced by the
<span class="RktVar">expected-expression</span> expression; every number in the first
expression must be within <span class="RktVar">delta</span> of the corresponding number in
the second expression.</div></p><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._define-struct%29%29" class="RktStxLink" data-pltdoc="x">define-struct</a></span><span class="hspace"> </span><span class="RktSym">roots</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">x</span><span class="hspace"> </span><span class="RktSym"><a href="intermediate.html#%28def._htdp-intermediate._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._sqrt%29%29" class="RktValLink" data-pltdoc="x">sqrt</a></span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="RktCmt">;</span><span class="RktCmt"> </span><span class="RktCmt">RT is [List-of (make-roots Number Number)]</span></td></tr><tr><td><span class="hspace"> </span></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">roots-table</span><span class="hspace"> </span><span class="RktSym">xs</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28def._htdp-intermediate._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._map%29%29" class="RktValLink" data-pltdoc="x">map</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._lambda%29%29" class="RktStxLink" data-pltdoc="x">lambda</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">a</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">make-roots</span><span class="hspace"> </span><span class="RktSym">a</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28def._htdp-intermediate._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._sqrt%29%29" class="RktValLink" data-pltdoc="x">sqrt</a></span><span class="hspace"> </span><span class="RktSym">a</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym">xs</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></blockquote><p><div class="SIntrapara">Due to the presence of inexact numbers in nested data, <span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._check-within%29%29" class="RktStxLink" data-pltdoc="x">check-within</a></span> is the
correct choice for testing, and the test succeeds if <span class="RktVar">delta</span> is reasonably
large:
</div><div class="SIntrapara"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><p>Example:</p></td></tr><tr><td><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._check-within%29%29" class="RktStxLink" data-pltdoc="x">check-within</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">roots-table</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28def._htdp-intermediate._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktVal">1.0</span><span class="hspace"> </span><span class="RktVal">2.0</span><span class="hspace"> </span><span class="RktVal">3.0</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28def._htdp-intermediate._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">make-roots</span><span class="hspace"> </span><span class="RktVal">1.0</span><span class="hspace"> </span><span class="RktVal">1.0</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">make-roots</span><span class="hspace"> </span><span class="RktVal">2</span><span class="hspace"> </span><span class="RktVal">1.414</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">make-roots</span><span class="hspace"> </span><span class="RktVal">3</span><span class="hspace"> </span><span class="RktVal">1.713</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktVal">0.1</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktOut">The only test passed!</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0"><tr><td></td></tr></table></td></tr></table></blockquote></td></tr></table></div><div class="SIntrapara">In contrast, when <span class="RktVar">delta</span> is small, the test fails:
</div><div class="SIntrapara"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><p>Example:</p></td></tr><tr><td><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._check-within%29%29" class="RktStxLink" data-pltdoc="x">check-within</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">roots-table</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28def._htdp-intermediate._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktVal">2.0</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28def._htdp-intermediate._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">make-roots</span><span class="hspace"> </span><span class="RktVal">2</span><span class="hspace"> </span><span class="RktVal">1.414</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktVal">1e-05</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><table cellspacing="0" cellpadding="0"><tr><td><p><span class="RktOut">Ran 1 check.</span></p></td></tr><tr><td><p><span class="RktOut">0 checks passed.</span></p></td></tr><tr><td><p><span class="RktOut"> Actual value ((make-roots 2.0 1.4142135623730951)) is not within 1e-05 of expected value ((make-roots 2 1.414)).</span></p></td></tr><tr><td><p><span class="RktOut"></span><span class="hspace"> </span><span class="RktOut">At line 5 column 0</span></p></td></tr></table></td></tr><tr><td><table cellspacing="0" cellpadding="0"><tr><td></td></tr></table></td></tr></table></blockquote></td></tr></table></div></p><p>It is an error for <span class="RktSym">expressions</span> or <span class="RktVar">expected-expression</span>
to produce a function value; see note on <span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._check-expect%29%29" class="RktStxLink" data-pltdoc="x">check-expect</a></span> for details.</p><p><div class="SIntrapara">If <span class="RktVar">delta</span> is not a number, <span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._check-within%29%29" class="RktStxLink" data-pltdoc="x">check-within</a></span> reports an error.</div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._lang/htdp-beginner-abbr..rkt)._check-error))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._check-error%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">check-error</a></span></span><span class="hspace"> </span><span class="RktVar">expression</span><span class="hspace"> </span><span class="RktVar">expected-error-message</span><span class="RktPn">)</span></p></blockquote></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._check-error%29%29" class="RktStxLink" data-pltdoc="x">check-error</a></span><span class="hspace"> </span><span class="RktVar">expression</span><span class="RktPn">)</span></td></tr></table></blockquote></div><div class="SIntrapara">Checks that the <span class="RktVar">expression</span> reports an error, where the error messages
matches the value of <span class="RktVar">expected-error-message</span>, if it is present.</div></p><p><div class="SIntrapara">Here is a typical beginner example that calls for a use of <span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._check-error%29%29" class="RktStxLink" data-pltdoc="x">check-error</a></span>:
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktSym">sample-table</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">(</span><span class="RktVal">"matthias"</span><span class="hspace"> </span><span class="RktVal">10</span><span class="RktVal">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVal">(</span><span class="RktVal">"matthew"</span><span class="hspace"> </span><span class="RktVal">20</span><span class="RktVal">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVal">(</span><span class="RktVal">"robby"</span><span class="hspace"> </span><span class="RktVal"><span class="nobreak">-1</span></span><span class="RktVal">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVal">(</span><span class="RktVal">"shriram"</span><span class="hspace"> </span><span class="RktVal">18</span><span class="RktVal">)</span><span class="RktVal">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span></td></tr><tr><td><span class="RktCmt">;</span><span class="RktCmt"> </span><span class="RktCmt">[List-of [list String Number]] String -> Number </span></td></tr><tr><td><span class="RktCmt">;</span><span class="RktCmt"> </span><span class="RktCmt">determine the number associated with </span><span class="RktSym">s</span><span class="RktCmt"> in </span><span class="RktSym">table</span><span class="RktCmt"> </span></td></tr><tr><td><span class="hspace"> </span></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">lookup</span><span class="hspace"> </span><span class="RktSym">table</span><span class="hspace"> </span><span class="RktSym">s</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._cond%29%29" class="RktStxLink" data-pltdoc="x">cond</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28def._htdp-intermediate._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._empty~3f%29%29" class="RktValLink" data-pltdoc="x">empty?</a></span><span class="hspace"> </span><span class="RktSym">table</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28def._htdp-intermediate._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._error%29%29" class="RktValLink" data-pltdoc="x">error</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28def._htdp-intermediate._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._string-append%29%29" class="RktValLink" data-pltdoc="x">string-append</a></span><span class="hspace"> </span><span class="RktSym">s</span><span class="hspace"> </span><span class="RktVal">" not found"</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">[</span><span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._else%29%29" class="RktStxLink" data-pltdoc="x">else</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._if%29%29" class="RktStxLink" data-pltdoc="x">if</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28def._htdp-intermediate._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._string~3d~3f%29%29" class="RktValLink" data-pltdoc="x">string=?</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28def._htdp-intermediate._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._first%29%29" class="RktValLink" data-pltdoc="x">first</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28def._htdp-intermediate._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._first%29%29" class="RktValLink" data-pltdoc="x">first</a></span><span class="hspace"> </span><span class="RktSym">table</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym">s</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28def._htdp-intermediate._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._second%29%29" class="RktValLink" data-pltdoc="x">second</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28def._htdp-intermediate._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._first%29%29" class="RktValLink" data-pltdoc="x">first</a></span><span class="hspace"> </span><span class="RktSym">table</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">lookup</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28def._htdp-intermediate._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._rest%29%29" class="RktValLink" data-pltdoc="x">rest</a></span><span class="hspace"> </span><span class="RktSym">table</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></blockquote></div></p><p>Consider the following two examples in this context:</p><p><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><p>Example:</p></td></tr><tr><td><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._check-expect%29%29" class="RktStxLink" data-pltdoc="x">check-expect</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">lookup</span><span class="hspace"> </span><span class="RktSym">sample-table</span><span class="hspace"> </span><span class="RktVal">"matthew"</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVal">20</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktOut">The only test passed!</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0"><tr><td></td></tr></table></td></tr></table></blockquote></td></tr></table></p><p><div class="SIntrapara"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><p>Example:</p></td></tr><tr><td><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._check-error%29%29" class="RktStxLink" data-pltdoc="x">check-error</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">lookup</span><span class="hspace"> </span><span class="RktSym">sample-table</span><span class="hspace"> </span><span class="RktVal">"kathi"</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVal">"kathi not found"</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktOut">The only test passed!</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0"><tr><td></td></tr></table></td></tr></table></blockquote></td></tr></table></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._lang/htdp-beginner-abbr..rkt)._check-member-of))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._check-member-of%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">check-member-of</a></span></span><span class="hspace"> </span><span class="RktVar">expression</span><span class="hspace"> </span><span class="RktVar">expression</span><span class="hspace"> </span><span class="RktVar">expression</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Checks that the value of the first <span class="RktVar">expression</span> as that of
one of the following <span class="RktVar">expression</span>s.</div></p><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="RktCmt">;</span><span class="RktCmt"> </span><span class="RktCmt">[List-of X] -> X </span></td></tr><tr><td><span class="RktCmt">;</span><span class="RktCmt"> </span><span class="RktCmt">pick a random element from the given list </span><span class="RktSym">l</span></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">pick-one</span><span class="hspace"> </span><span class="RktSym">l</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28def._htdp-intermediate._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._list-ref%29%29" class="RktValLink" data-pltdoc="x">list-ref</a></span><span class="hspace"> </span><span class="RktSym">l</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28def._htdp-intermediate._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._random%29%29" class="RktValLink" data-pltdoc="x">random</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28def._htdp-intermediate._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._length%29%29" class="RktValLink" data-pltdoc="x">length</a></span><span class="hspace"> </span><span class="RktSym">l</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></blockquote><p><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><p>Example:</p></td></tr><tr><td><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._check-member-of%29%29" class="RktStxLink" data-pltdoc="x">check-member-of</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">pick-one</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">"a"</span><span class="hspace"> </span><span class="RktVal">"b"</span><span class="hspace"> </span><span class="RktVal">"c"</span><span class="RktVal">)</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVal">"a"</span><span class="hspace"> </span><span class="RktVal">"b"</span><span class="hspace"> </span><span class="RktVal">"c"</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktOut">The only test passed!</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0"><tr><td></td></tr></table></td></tr></table></blockquote></td></tr></table></p><p><div class="SIntrapara">It is an error for any of <span class="RktSym">expressions</span> to produce a function value; see
note on <span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._check-expect%29%29" class="RktStxLink" data-pltdoc="x">check-expect</a></span> for details.</div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._lang/htdp-beginner-abbr..rkt)._check-range))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._check-range%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">check-range</a></span></span><span class="hspace"> </span><span class="RktVar">expression</span><span class="hspace"> </span><span class="RktVar">low-expression</span><span class="hspace"> </span><span class="RktVar">high-expression</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Checks that the value of the first <span class="RktVar">expression</span> is a number in
between the value of the <span class="RktVar">low-expression</span> and the
<span class="RktVar">high-expression</span>, inclusive.</div></p><p><div class="SIntrapara">A <span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._check-range%29%29" class="RktStxLink" data-pltdoc="x">check-range</a></span> form is best used to delimit the possible results of
functions that compute inexact numbers:
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="RktCmt">;</span><span class="RktCmt"> </span><span class="RktCmt">[Real -> Real] Real -> Real </span></td></tr><tr><td><span class="RktCmt">;</span><span class="RktCmt"> </span><span class="RktCmt">what is the slope of </span><span class="RktSym">f</span><span class="RktCmt"> at </span><span class="RktSym">x</span><span class="RktCmt">?</span></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">differentiate</span><span class="hspace"> </span><span class="RktSym">f</span><span class="hspace"> </span><span class="RktSym">x</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._local%29%29" class="RktStxLink" data-pltdoc="x">local</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktSym">epsilon</span><span class="hspace"> </span><span class="RktVal">0.001</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktSym">left</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28def._htdp-intermediate._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._-%29%29" class="RktValLink" data-pltdoc="x"><span class="nobreak">-</span></a></span><span class="hspace"> </span><span class="RktSym">x</span><span class="hspace"> </span><span class="RktSym">epsilon</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktSym">right</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28def._htdp-intermediate._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._%2B%29%29" class="RktValLink" data-pltdoc="x">+</a></span><span class="hspace"> </span><span class="RktSym">x</span><span class="hspace"> </span><span class="RktSym">epsilon</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktSym">slope</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28def._htdp-intermediate._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._%2F%29%29" class="RktValLink" data-pltdoc="x">/</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28def._htdp-intermediate._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._-%29%29" class="RktValLink" data-pltdoc="x"><span class="nobreak">-</span></a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">f</span><span class="hspace"> </span><span class="RktSym">right</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">f</span><span class="hspace"> </span><span class="RktSym">left</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVal">2</span><span class="hspace"> </span><span class="RktSym">epsilon</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktSym">slope</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._check-range%29%29" class="RktStxLink" data-pltdoc="x">check-range</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">differentiate</span><span class="hspace"> </span><span class="RktSym"><a href="intermediate.html#%28def._htdp-intermediate._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._sin%29%29" class="RktValLink" data-pltdoc="x">sin</a></span><span class="hspace"> </span><span class="RktVal">0</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVal">0.99</span><span class="hspace"> </span><span class="RktVal">1.0</span><span class="RktPn">)</span></td></tr></table></blockquote></div></p><p><div class="SIntrapara">It is an error for <span class="RktVar">expression</span>, <span class="RktVar">low-expression</span>, or
<span class="RktVar">high-expression</span> to produce a function value or an inexact number;
see note on <span class="RktSym"><a href="intermediate.html#%28form._%28%28lib._lang%2Fhtdp-intermediate..rkt%29._check-expect%29%29" class="RktStxLink" data-pltdoc="x">check-expect</a></span> for details. </div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._lang/htdp-beginner-abbr..rkt)._require))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._require%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">require</a></span></span><span class="hspace"> </span><span class="RktVar">string</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Makes the definitions of the module specified by <span class="RktVar">string</span>
available in the current module (i.e., the current file), where
<span class="RktVar">string</span> refers to a file relative to the current file.</div></p><p><div class="SIntrapara">The <span class="RktVar">string</span> is constrained in several ways to avoid
problems with different path conventions on different platforms: a
<span class="RktInBG"><span class="hspace"></span><span class="RktIn">/</span><span class="hspace"></span></span> is a directory separator, <span class="RktInBG"><span class="hspace"></span><span class="RktIn">.</span><span class="hspace"></span></span> always means the
current directory, <span class="RktInBG"><span class="hspace"></span><span class="RktIn">..</span><span class="hspace"></span></span> always means the parent directory,
path elements can use only <span class="RktInBG"><span class="hspace"></span><span class="RktIn">a</span><span class="hspace"></span></span> through <span class="RktInBG"><span class="hspace"></span><span class="RktIn">z</span><span class="hspace"></span></span>
(uppercase or lowercase), <span class="RktInBG"><span class="hspace"></span><span class="RktIn">0</span><span class="hspace"></span></span> through <span class="RktInBG"><span class="hspace"></span><span class="RktIn">9</span><span class="hspace"></span></span>,
<span class="RktInBG"><span class="hspace"></span><span class="RktIn">-</span><span class="hspace"></span></span>, <span class="RktInBG"><span class="hspace"></span><span class="RktIn">_</span><span class="hspace"></span></span>, and <span class="RktInBG"><span class="hspace"></span><span class="RktIn">.</span><span class="hspace"></span></span>, and the string cannot be
empty or contain a leading or trailing <span class="RktInBG"><span class="hspace"></span><span class="RktIn">/</span><span class="hspace"></span></span>.</div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._require%29%29" class="RktStxLink" data-pltdoc="x">require</a></span><span class="hspace"> </span><span class="RktVar">module-name</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Accesses a file in an installed library. The library name is an
identifier with the same constraints as for a relative-path string
(though without the quotes), with the additional constraint that it
must not contain a <span class="RktInBG"><span class="hspace"></span><span class="RktIn">.</span><span class="hspace"></span></span>.</div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._require%29%29" class="RktStxLink" data-pltdoc="x">require</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktVar">lib</span><span class="hspace"> </span><span class="RktVar">string</span><span class="hspace"> </span><span class="RktVar">string</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Accesses a file in an installed library, making its definitions
available in the current module (i.e., the current file). The first
<span class="RktVar">string</span> names the library file, and the remaining
<span class="RktVar">string</span>s name the collection (and sub-collection, and so on)
where the file is installed. Each string is constrained in the same
way as for the <span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._require%29%29" class="RktStxLink" data-pltdoc="x">require</a></span><span class="stt"> </span><span class="RktVar">string</span><span class="RktPn">)</span> form.</div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><table cellspacing="0" cellpadding="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._require%29%29" class="RktStxLink" data-pltdoc="x">require</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">planet</span><span class="hspace"> </span><span class="RktVar">string</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktVar">string</span><span class="hspace"> </span><span class="RktVar">string</span><span class="hspace"> </span><span class="RktVar">number</span><span class="hspace"> </span><span class="RktVar">number</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></p></blockquote></td></tr></table></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._require%29%29" class="RktStxLink" data-pltdoc="x">require</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">planet</span><span class="hspace"> </span><span class="RktVar">id</span><span class="RktPn">)</span><span class="RktPn">)</span></p></blockquote></td></tr></table></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._require%29%29" class="RktStxLink" data-pltdoc="x">require</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">planet</span><span class="hspace"> </span><span class="RktVar">string</span><span class="RktPn">)</span><span class="RktPn">)</span></p></blockquote></td></tr></table></td></tr></table></blockquote></div><div class="SIntrapara">Accesses a library that is distributed on the internet via the
<span class="planetName">PLaneT</span> server, making it definitions available in the current module
(i.e., current file).</div></p><p>The full grammar for planet requires is given in
<a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=require.html&version=6.1" class="Sq" data-pltdoc="x">Importing and Exporting: <span class="RktSym"><span class="RktStxLink">require</span></span> and <span class="RktSym"><span class="RktStxLink">provide</span></span></a>, but
the best place to find examples of the syntax is on the
<a href="http://planet.racket-lang.org">the <span class="planetName">PLaneT</span> server</a>, in the
description of a specific package.</p><h4 x-source-module="(lib "scribblings/htdp-langs/htdp-langs.scrbl")" x-part-tag=""beginner-abbr-pre-defined"">2.5<tt> </tt><a name="(part._beginner-abbr-pre-defined)"></a>Pre-defined Functions</h4><h4 x-source-module="(lib "scribblings/htdp-langs/htdp-langs.scrbl")" x-part-tag=""Numbers__Integers__Rationals__Reals__Complex__Exacts__Inexacts"">2.6<tt> </tt><a name="(part._htdp-beginner-abbr._.Numbers__.Integers__.Rationals__.Reals__.Complex__.Exacts__.Inexacts)"></a>Numbers: Integers, Rationals, Reals, Complex, Exacts, Inexacts</h4><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._*))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._%2A%29%29" class="RktValDef RktValLink" data-pltdoc="x">*</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span><span class="RktVar">z</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">number</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">z</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr></table></blockquote></div><div class="SIntrapara"><a name="(idx._htdp-beginner-abbr._(gentag._15._(lib._scribblings/htdp-langs/htdp-langs..scrbl)._htdp-beginner-abbr))"></a><a name="(idx._htdp-beginner-abbr._(gentag._16._(lib._scribblings/htdp-langs/htdp-langs..scrbl)._htdp-beginner-abbr))"></a><a name="(idx._htdp-beginner-abbr._(gentag._17._(lib._scribblings/htdp-langs/htdp-langs..scrbl)._htdp-beginner-abbr))"></a>Multiplies all numbers.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">*</span><span class="hspace"> </span><span class="RktVal">5</span><span class="hspace"> </span><span class="RktVal">3</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">15</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">*</span><span class="hspace"> </span><span class="RktVal">5</span><span class="hspace"> </span><span class="RktVal">3</span><span class="hspace"> </span><span class="RktVal">2</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">30</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._+))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._%2B%29%29" class="RktValDef RktValLink" data-pltdoc="x">+</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span><span class="RktVar">z</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">number</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">z</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr></table></blockquote></div><div class="SIntrapara"><a name="(idx._htdp-beginner-abbr._(gentag._18._(lib._scribblings/htdp-langs/htdp-langs..scrbl)._htdp-beginner-abbr))"></a><a name="(idx._htdp-beginner-abbr._(gentag._19._(lib._scribblings/htdp-langs/htdp-langs..scrbl)._htdp-beginner-abbr))"></a>Adds up all numbers.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">+</span><span class="hspace"> </span><span class="RktVal">2/3</span><span class="hspace"> </span><span class="RktVal">1/16</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">35/48</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">+</span><span class="hspace"> </span><span class="RktVal">3</span><span class="hspace"> </span><span class="RktVal">2</span><span class="hspace"> </span><span class="RktVal">5</span><span class="hspace"> </span><span class="RktVal">8</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">18</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._-))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._-%29%29" class="RktValDef RktValLink" data-pltdoc="x"><span class="nobreak">-</span></a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">number</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr></table></blockquote></div><div class="SIntrapara"><a name="(idx._htdp-beginner-abbr._(gentag._20._(lib._scribblings/htdp-langs/htdp-langs..scrbl)._htdp-beginner-abbr))"></a>Subtracts the second (and following) number(s) from the first ;
negates the number if there is only one argument.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><span class="nobreak">-</span></span><span class="hspace"> </span><span class="RktVal">5</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">-5</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><span class="nobreak">-</span></span><span class="hspace"> </span><span class="RktVal">5</span><span class="hspace"> </span><span class="RktVal">3</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">2</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><span class="nobreak">-</span></span><span class="hspace"> </span><span class="RktVal">5</span><span class="hspace"> </span><span class="RktVal">3</span><span class="hspace"> </span><span class="RktVal">1</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">1</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._/))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._%2F%29%29" class="RktValDef RktValLink" data-pltdoc="x">/</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span><span class="RktVar">z</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">number</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">z</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr></table></blockquote></div><div class="SIntrapara"><a name="(idx._htdp-beginner-abbr._(gentag._21._(lib._scribblings/htdp-langs/htdp-langs..scrbl)._htdp-beginner-abbr))"></a>Divides the first by the second (and all following) number(s).
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">/</span><span class="hspace"> </span><span class="RktVal">12</span><span class="hspace"> </span><span class="RktVal">2</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">6</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">/</span><span class="hspace"> </span><span class="RktVal">12</span><span class="hspace"> </span><span class="RktVal">2</span><span class="hspace"> </span><span class="RktVal">3</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">2</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._~3c))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._~3c%29%29" class="RktValDef RktValLink" data-pltdoc="x"><</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span><span class="RktVar">z</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">real</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">real</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">z</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">real</span></td></tr></table></blockquote></div><div class="SIntrapara">Compares (real) numbers for less-than.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><</span><span class="hspace"> </span><span class="RktVal">42</span><span class="hspace"> </span><span class="RktVal">2/5</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">false</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._~3c~3d))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._~3c~3d%29%29" class="RktValDef RktValLink" data-pltdoc="x"><=</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span><span class="RktVar">z</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">real</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">real</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">z</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">real</span></td></tr></table></blockquote></div><div class="SIntrapara">Compares (real) numbers for less-than or equality.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><=</span><span class="hspace"> </span><span class="RktVal">42</span><span class="hspace"> </span><span class="RktVal">2/5</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">false</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._~3d))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._~3d%29%29" class="RktValDef RktValLink" data-pltdoc="x">=</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span><span class="RktVar">z</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">z</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr></table></blockquote></div><div class="SIntrapara">Compares numbers for equality.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">=</span><span class="hspace"> </span><span class="RktVal">42</span><span class="hspace"> </span><span class="RktVal">2/5</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">false</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._~3e))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._~3e%29%29" class="RktValDef RktValLink" data-pltdoc="x">></a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span><span class="RktVar">z</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">real</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">real</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">z</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">real</span></td></tr></table></blockquote></div><div class="SIntrapara">Compares (real) numbers for greater-than.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">></span><span class="hspace"> </span><span class="RktVal">42</span><span class="hspace"> </span><span class="RktVal">2/5</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._~3e~3d))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._~3e~3d%29%29" class="RktValDef RktValLink" data-pltdoc="x">>=</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span><span class="RktVar">z</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">real</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">real</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">z</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">real</span></td></tr></table></blockquote></div><div class="SIntrapara">Compares (real) numbers for greater-than or equality.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">>=</span><span class="hspace"> </span><span class="RktVal">42</span><span class="hspace"> </span><span class="RktVal">42</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._abs))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._abs%29%29" class="RktValDef RktValLink" data-pltdoc="x">abs</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">real</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">real</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines the absolute value of a real number.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">abs</span><span class="hspace"> </span><span class="RktVal"><span class="nobreak">-1</span>2</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">12</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._acos))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._acos%29%29" class="RktValDef RktValLink" data-pltdoc="x">acos</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">number</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr></table></blockquote></div><div class="SIntrapara">Computes the arccosine (inverse of cos) of a number.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">acos</span><span class="hspace"> </span><span class="RktVal">0</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#i1.5707963267948966</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._add1))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._add1%29%29" class="RktValDef RktValLink" data-pltdoc="x">add1</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">number</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr></table></blockquote></div><div class="SIntrapara">Incrementes the given number.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">add1</span><span class="hspace"> </span><span class="RktVal">2</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">3</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._angle))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._angle%29%29" class="RktValDef RktValLink" data-pltdoc="x">angle</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">real</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr></table></blockquote></div><div class="SIntrapara">Extracts the angle from a complex number.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">angle</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">make-polar</span><span class="hspace"> </span><span class="RktVal">3</span><span class="hspace"> </span><span class="RktVal">4</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#i-2.2831853071795867</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._asin))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._asin%29%29" class="RktValDef RktValLink" data-pltdoc="x">asin</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">number</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr></table></blockquote></div><div class="SIntrapara">Computes the arcsine (inverse of sin) of a number.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">asin</span><span class="hspace"> </span><span class="RktVal">0</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">0</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._atan))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._atan%29%29" class="RktValDef RktValLink" data-pltdoc="x">atan</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">number</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr></table></blockquote></div><div class="SIntrapara">Computes the arctangent of the given number:
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">atan</span><span class="hspace"> </span><span class="RktVal">0</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">0</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">atan</span><span class="hspace"> </span><span class="RktVal">0.5</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#i0.4636476090008061</span></p></td></tr></table></blockquote></div></p><p><div class="SIntrapara">Also comes in a two-argument version where <span class="RktPn">(</span><span class="RktSym">atan</span><span class="stt"> </span><span class="RktVar">x</span><span class="stt"> </span><span class="RktSym">y</span><span class="RktPn">)</span> computes
<span class="RktPn">(</span><span class="RktSym">atan</span><span class="stt"> </span><span class="RktPn">(</span><span class="RktSym">/</span><span class="stt"> </span><span class="RktVar">x</span><span class="stt"> </span><span class="RktSym">y</span><span class="RktPn">)</span><span class="RktPn">)</span> but the signs of <span class="RktVar">x</span> and <span class="RktSym">y</span>
determine the quadrant of the result and the result tends to be more
accurate than that of the 1-argument version in borderline cases:
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">atan</span><span class="hspace"> </span><span class="RktVal">3</span><span class="hspace"> </span><span class="RktVal">4</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#i0.6435011087932844</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">atan</span><span class="hspace"> </span><span class="RktVal"><span class="nobreak">-2</span></span><span class="hspace"> </span><span class="RktVal"><span class="nobreak">-1</span></span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#i-2.0344439357957027</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._ceiling))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._ceiling%29%29" class="RktValDef RktValLink" data-pltdoc="x">ceiling</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">integer</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">real</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines the closest integer (exact or inexact) above a real
number. See <span class="RktSym">round</span>.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">ceiling</span><span class="hspace"> </span><span class="RktVal">12.3</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#i13.0</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._complex~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._complex~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">complex?</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">any/c</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether some value is complex.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">real?</span><span class="hspace"> </span><span class="RktVal">1-2i</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">false</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._conjugate))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._conjugate%29%29" class="RktValDef RktValLink" data-pltdoc="x">conjugate</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">number</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr></table></blockquote></div><div class="SIntrapara">Extracts the conjugate of a complex number.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">conjugate</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">make-polar</span><span class="hspace"> </span><span class="RktVal">3</span><span class="hspace"> </span><span class="RktVal">4</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#i-1.960930862590836+2.2704074859237844i</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._cos))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._cos%29%29" class="RktValDef RktValLink" data-pltdoc="x">cos</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">number</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr></table></blockquote></div><div class="SIntrapara">Computes the <a name="(idx._htdp-beginner-abbr._(gentag._22._(lib._scribblings/htdp-langs/htdp-langs..scrbl)._htdp-beginner-abbr))"></a>cosine of a number (radians).
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">cos</span><span class="hspace"> </span><span class="RktSym">pi</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#i-1.0</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._cosh))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._cosh%29%29" class="RktValDef RktValLink" data-pltdoc="x">cosh</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">number</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr></table></blockquote></div><div class="SIntrapara">Computes the hyperbolic cosine of a number.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">cosh</span><span class="hspace"> </span><span class="RktVal">10</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#i11013.232920103324</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._current-seconds))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._current-seconds%29%29" class="RktValDef RktValLink" data-pltdoc="x">current-seconds</a></span></span><span class="RktPn"></span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">integer</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Determines the current time in seconds elapsed (since a platform-specific starting date).
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">current-seconds</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">1414141626</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._denominator))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._denominator%29%29" class="RktValDef RktValLink" data-pltdoc="x">denominator</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">integer</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">rational?</span></td></tr></table></blockquote></div><div class="SIntrapara">Computees the denominator of a rational.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">denominator</span><span class="hspace"> </span><span class="RktVal">2/3</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">3</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>value</p></div></div><p class="RForeground"><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._e))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._e%29%29" class="RktValDef RktValLink" data-pltdoc="x">e</a></span></span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">real</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Euler’s number.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktSym">e</span></td></tr><tr><td><p><span class="RktRes">#i2.718281828459045</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._even~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._even~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">even?</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">integer</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines if some integer (exact or inexact) is even or not.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">even?</span><span class="hspace"> </span><span class="RktVal">2</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._exact-~3einexact))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._exact-~3einexact%29%29" class="RktValDef RktValLink" data-pltdoc="x">exact->inexact</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">number</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr></table></blockquote></div><div class="SIntrapara">Converts an exact number to an inexact one.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">exact->inexact</span><span class="hspace"> </span><span class="RktVal">12</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#i12.0</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._exact~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._exact~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">exact?</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether some number is exact.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">exact?</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">sqrt</span><span class="hspace"> </span><span class="RktVal">2</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">false</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._exp))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._exp%29%29" class="RktValDef RktValLink" data-pltdoc="x">exp</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">number</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines e raised to a number.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">exp</span><span class="hspace"> </span><span class="RktVal"><span class="nobreak">-2</span></span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#i0.1353352832366127</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._expt))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._expt%29%29" class="RktValDef RktValLink" data-pltdoc="x">expt</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktVar">y</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">number</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr></table></blockquote></div><div class="SIntrapara">Computes the power of the first to the second number.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">expt</span><span class="hspace"> </span><span class="RktVal">16</span><span class="hspace"> </span><span class="RktVal">1/2</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">4</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">expt</span><span class="hspace"> </span><span class="RktVal">3</span><span class="hspace"> </span><span class="RktVal"><span class="nobreak">-4</span></span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">1/81</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._floor))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._floor%29%29" class="RktValDef RktValLink" data-pltdoc="x">floor</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">integer</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">real</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines the closest integer (exact or inexact) below a real
number. See <span class="RktSym">round</span>.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">floor</span><span class="hspace"> </span><span class="RktVal">12.3</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#i12.0</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._gcd))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._gcd%29%29" class="RktValDef RktValLink" data-pltdoc="x">gcd</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">integer</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">integer</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">integer</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines the greatest common divisior of two integers (exact or inexact).
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">gcd</span><span class="hspace"> </span><span class="RktVal">6</span><span class="hspace"> </span><span class="RktVal">12</span><span class="hspace"> </span><span class="RktVal">8</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">2</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._imag-part))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._imag-part%29%29" class="RktValDef RktValLink" data-pltdoc="x">imag-part</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">real</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr></table></blockquote></div><div class="SIntrapara">Extracts the imaginary part from a complex number.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">imag-part</span><span class="hspace"> </span><span class="RktVal">3+4i</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">4</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._inexact-~3eexact))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._inexact-~3eexact%29%29" class="RktValDef RktValLink" data-pltdoc="x">inexact->exact</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">number</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr></table></blockquote></div><div class="SIntrapara">Approximates an inexact number by an exact one.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">inexact->exact</span><span class="hspace"> </span><span class="RktVal">12.0</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">12</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._inexact~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._inexact~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">inexact?</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether some number is inexact.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">inexact?</span><span class="hspace"> </span><span class="RktVal">1-2i</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">false</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._integer-~3echar))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._integer-~3echar%29%29" class="RktValDef RktValLink" data-pltdoc="x">integer->char</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">char</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">exact-integer?</span></td></tr></table></blockquote></div><div class="SIntrapara">Lookups the character that corresponds to the given exact integer in the ASCII table (if any).
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">integer->char</span><span class="hspace"> </span><span class="RktVal">42</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#\*</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._integer-sqrt))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._integer-sqrt%29%29" class="RktValDef RktValLink" data-pltdoc="x">integer-sqrt</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">integer</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr></table></blockquote></div><div class="SIntrapara">Computes the integer (exact or inexact) square root of a number.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">sqrt</span><span class="hspace"> </span><span class="RktVal">11</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#i3.3166247903554</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._integer~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._integer~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">integer?</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">any/c</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether some value is an integer (exact or inexact).
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">integer?</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">sqrt</span><span class="hspace"> </span><span class="RktVal">2</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">false</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._lcm))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._lcm%29%29" class="RktValDef RktValLink" data-pltdoc="x">lcm</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">integer</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">integer</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">integer</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines the least common multiple of two integers (exact or inexact).
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">lcm</span><span class="hspace"> </span><span class="RktVal">6</span><span class="hspace"> </span><span class="RktVal">12</span><span class="hspace"> </span><span class="RktVal">8</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">24</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._log))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._log%29%29" class="RktValDef RktValLink" data-pltdoc="x">log</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">number</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines the base-e logarithm of a number.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">log</span><span class="hspace"> </span><span class="RktVal">12</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#i2.4849066497880004</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._magnitude))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._magnitude%29%29" class="RktValDef RktValLink" data-pltdoc="x">magnitude</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">real</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines the magnitude of a complex number.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">magnitude</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">make-polar</span><span class="hspace"> </span><span class="RktVal">3</span><span class="hspace"> </span><span class="RktVal">4</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#i3.0</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._make-polar))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._make-polar%29%29" class="RktValDef RktValLink" data-pltdoc="x">make-polar</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktVar">y</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">number</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">real</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">real</span></td></tr></table></blockquote></div><div class="SIntrapara">Creates a complex from a magnitude and angle.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">make-polar</span><span class="hspace"> </span><span class="RktVal">3</span><span class="hspace"> </span><span class="RktVal">4</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#i-1.960930862590836-2.2704074859237844i</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._make-rectangular))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._make-rectangular%29%29" class="RktValDef RktValLink" data-pltdoc="x">make-rectangular</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktVar">y</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">number</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">real</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">real</span></td></tr></table></blockquote></div><div class="SIntrapara">Creates a complex from a real and an imaginary part.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">make-rectangular</span><span class="hspace"> </span><span class="RktVal">3</span><span class="hspace"> </span><span class="RktVal">4</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">3+4i</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._max))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._max%29%29" class="RktValDef RktValLink" data-pltdoc="x">max</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">real</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">real</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">real</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines the largest number—<wbr></wbr>aka, the <a name="(idx._htdp-beginner-abbr._(gentag._23._(lib._scribblings/htdp-langs/htdp-langs..scrbl)._htdp-beginner-abbr))"></a>maxiumum.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">max</span><span class="hspace"> </span><span class="RktVal">3</span><span class="hspace"> </span><span class="RktVal">2</span><span class="hspace"> </span><span class="RktVal">8</span><span class="hspace"> </span><span class="RktVal">7</span><span class="hspace"> </span><span class="RktVal">2</span><span class="hspace"> </span><span class="RktVal">9</span><span class="hspace"> </span><span class="RktVal">0</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">9</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._min))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._min%29%29" class="RktValDef RktValLink" data-pltdoc="x">min</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">real</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">real</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">real</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines the smallest number—<wbr></wbr>aka, the <a name="(idx._htdp-beginner-abbr._(gentag._24._(lib._scribblings/htdp-langs/htdp-langs..scrbl)._htdp-beginner-abbr))"></a>miniumum.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">min</span><span class="hspace"> </span><span class="RktVal">3</span><span class="hspace"> </span><span class="RktVal">2</span><span class="hspace"> </span><span class="RktVal">8</span><span class="hspace"> </span><span class="RktVal">7</span><span class="hspace"> </span><span class="RktVal">2</span><span class="hspace"> </span><span class="RktVal">9</span><span class="hspace"> </span><span class="RktVal">0</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">0</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._modulo))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._modulo%29%29" class="RktValDef RktValLink" data-pltdoc="x">modulo</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktVar">y</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">integer</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">integer</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">integer</span></td></tr></table></blockquote></div><div class="SIntrapara">Finds the remainder of the division of the first number by the second:
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">modulo</span><span class="hspace"> </span><span class="RktVal">9</span><span class="hspace"> </span><span class="RktVal">2</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">1</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">modulo</span><span class="hspace"> </span><span class="RktVal">3</span><span class="hspace"> </span><span class="RktVal"><span class="nobreak">-4</span></span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">-1</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._negative~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._negative~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">negative?</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines if some value is strictly smaller than zero.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">negative?</span><span class="hspace"> </span><span class="RktVal"><span class="nobreak">-2</span></span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._number-~3estring))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._number-~3estring%29%29" class="RktValDef RktValLink" data-pltdoc="x">number->string</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">string</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr></table></blockquote></div><div class="SIntrapara">Converts a number to a string.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">number->string</span><span class="hspace"> </span><span class="RktVal">42</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">"42"</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._number~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._number~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">number?</a></span></span><span class="hspace"> </span><span class="RktVar">n</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">n</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">any/c</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether some value is a number:
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">number?</span><span class="hspace"> </span><span class="RktVal">"hello world"</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">false</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">number?</span><span class="hspace"> </span><span class="RktVal">42</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._numerator))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._numerator%29%29" class="RktValDef RktValLink" data-pltdoc="x">numerator</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">integer</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">rational?</span></td></tr></table></blockquote></div><div class="SIntrapara">Computes the numerator of a rational.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">numerator</span><span class="hspace"> </span><span class="RktVal">2/3</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">2</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._odd~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._odd~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">odd?</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">integer</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines if some integer (exact or inexact) is odd or not.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">odd?</span><span class="hspace"> </span><span class="RktVal">2</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">false</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>value</p></div></div><p class="RForeground"><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._pi))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._pi%29%29" class="RktValDef RktValLink" data-pltdoc="x">pi</a></span></span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">real</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">The ratio of a circle’s circumference to its diameter.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktSym">pi</span></td></tr><tr><td><p><span class="RktRes">#i3.141592653589793</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._positive~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._positive~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">positive?</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines if some value is strictly larger than zero.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">positive?</span><span class="hspace"> </span><span class="RktVal"><span class="nobreak">-2</span></span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">false</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._quotient))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._quotient%29%29" class="RktValDef RktValLink" data-pltdoc="x">quotient</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktVar">y</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">integer</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">integer</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">integer</span></td></tr></table></blockquote></div><div class="SIntrapara">Divides the second integer—<wbr></wbr>also called divisor—<wbr></wbr>into the first—<wbr></wbr>known as
dividend—<wbr></wbr>to obtain the <a name="(idx._htdp-beginner-abbr._(gentag._25._(lib._scribblings/htdp-langs/htdp-langs..scrbl)._htdp-beginner-abbr))"></a>quotient.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">quotient</span><span class="hspace"> </span><span class="RktVal">9</span><span class="hspace"> </span><span class="RktVal">2</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">4</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">quotient</span><span class="hspace"> </span><span class="RktVal">3</span><span class="hspace"> </span><span class="RktVal">4</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">0</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._random))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._random%29%29" class="RktValDef RktValLink" data-pltdoc="x">random</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">natural</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">natural</span></td></tr></table></blockquote></div><div class="SIntrapara">Generates a random natural number less than some given exact natural.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">random</span><span class="hspace"> </span><span class="RktVal">42</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">9</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._rational~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._rational~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">rational?</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">any/c</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether some value is a rational number.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">rational?</span><span class="hspace"> </span><span class="RktVal">1-2i</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">false</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._real-part))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._real-part%29%29" class="RktValDef RktValLink" data-pltdoc="x">real-part</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">real</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr></table></blockquote></div><div class="SIntrapara">Extracts the real part from a complex number.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">real-part</span><span class="hspace"> </span><span class="RktVal">3+4i</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">3</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._real~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._real~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">real?</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">any/c</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether some value is a real number.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">real?</span><span class="hspace"> </span><span class="RktVal">1-2i</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">false</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._remainder))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._remainder%29%29" class="RktValDef RktValLink" data-pltdoc="x">remainder</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktVar">y</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">integer</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">integer</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">integer</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines the <a name="(idx._htdp-beginner-abbr._(gentag._26._(lib._scribblings/htdp-langs/htdp-langs..scrbl)._htdp-beginner-abbr))"></a>remainder of dividing the first by the second integer
(exact or inexact).
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">remainder</span><span class="hspace"> </span><span class="RktVal">9</span><span class="hspace"> </span><span class="RktVal">2</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">1</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">remainder</span><span class="hspace"> </span><span class="RktVal">3</span><span class="hspace"> </span><span class="RktVal">4</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">3</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._round))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._round%29%29" class="RktValDef RktValLink" data-pltdoc="x">round</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">integer</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">real</span></td></tr></table></blockquote></div><div class="SIntrapara">Rounds a real number to an integer (rounds to even to break ties). See
<span class="RktSym">floor</span> and <span class="RktSym">ceiling</span>.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">round</span><span class="hspace"> </span><span class="RktVal">12.3</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#i12.0</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._sgn))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._sgn%29%29" class="RktValDef RktValLink" data-pltdoc="x">sgn</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">union</span><span class="hspace"> </span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktVal">1.0</span><span class="hspace"> </span><span class="RktVal">0</span><span class="hspace"> </span><span class="RktVal">0.0</span><span class="hspace"> </span><span class="RktVal"><span class="nobreak">-1</span></span><span class="hspace"> </span><span class="RktVal"><span class="nobreak">-1</span>.0</span><span class="RktPn">)</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">real</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines the sign of a real number.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">sgn</span><span class="hspace"> </span><span class="RktVal"><span class="nobreak">-1</span>2</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">-1</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._sin))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._sin%29%29" class="RktValDef RktValLink" data-pltdoc="x">sin</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">number</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr></table></blockquote></div><div class="SIntrapara">Computes the <a name="(idx._htdp-beginner-abbr._(gentag._27._(lib._scribblings/htdp-langs/htdp-langs..scrbl)._htdp-beginner-abbr))"></a>sine of a number (radians).
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">sin</span><span class="hspace"> </span><span class="RktSym">pi</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#i1.2246467991473532e-16</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._sinh))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._sinh%29%29" class="RktValDef RktValLink" data-pltdoc="x">sinh</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">number</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr></table></blockquote></div><div class="SIntrapara">Computes the hyperbolic sine of a number.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">sinh</span><span class="hspace"> </span><span class="RktVal">10</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#i11013.232874703393</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._sqr))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._sqr%29%29" class="RktValDef RktValLink" data-pltdoc="x">sqr</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">number</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr></table></blockquote></div><div class="SIntrapara">Computes the <a name="(idx._htdp-beginner-abbr._(gentag._28._(lib._scribblings/htdp-langs/htdp-langs..scrbl)._htdp-beginner-abbr))"></a>square of a number.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">sqr</span><span class="hspace"> </span><span class="RktVal">8</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">64</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._sqrt))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._sqrt%29%29" class="RktValDef RktValLink" data-pltdoc="x">sqrt</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">number</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr></table></blockquote></div><div class="SIntrapara">Computes the square root of a number.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">sqrt</span><span class="hspace"> </span><span class="RktVal">9</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">3</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">sqrt</span><span class="hspace"> </span><span class="RktVal">2</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#i1.4142135623730951</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._sub1))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._sub1%29%29" class="RktValDef RktValLink" data-pltdoc="x">sub1</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">number</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr></table></blockquote></div><div class="SIntrapara">Decrements the given number.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">sub1</span><span class="hspace"> </span><span class="RktVal">2</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">1</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._tan))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._tan%29%29" class="RktValDef RktValLink" data-pltdoc="x">tan</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">number</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr></table></blockquote></div><div class="SIntrapara">Computes the <a name="(idx._htdp-beginner-abbr._(gentag._29._(lib._scribblings/htdp-langs/htdp-langs..scrbl)._htdp-beginner-abbr))"></a>tangent of a number (radians).
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">tan</span><span class="hspace"> </span><span class="RktSym">pi</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#i-1.2246467991473532e-16</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._zero~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._zero~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">zero?</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines if some value is zero or not.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">zero?</span><span class="hspace"> </span><span class="RktVal">2</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">false</span></p></td></tr></table></blockquote></div></p><h4 x-source-module="(lib "scribblings/htdp-langs/htdp-langs.scrbl")" x-part-tag=""Booleans"">2.7<tt> </tt><a name="(part._htdp-beginner-abbr._.Booleans)"></a>Booleans</h4><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._boolean~3d~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._boolean~3d~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">boolean=?</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktVar">y</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">boolean?</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">boolean?</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether two booleans are equal.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">boolean=?</span><span class="hspace"> </span><span class="RktSym">true</span><span class="hspace"> </span><span class="RktSym">false</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">false</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._boolean~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._boolean~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">boolean?</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">any/c</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether some value is a boolean.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">boolean?</span><span class="hspace"> </span><span class="RktVal">42</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">false</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">boolean?</span><span class="hspace"> </span><span class="RktSym">false</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._false~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._false~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">false?</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">any/c</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether a value is false.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">false?</span><span class="hspace"> </span><span class="RktSym">false</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._not))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._not%29%29" class="RktValDef RktValLink" data-pltdoc="x">not</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">boolean?</span></td></tr></table></blockquote></div><div class="SIntrapara">Negates a boolean value.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">not</span><span class="hspace"> </span><span class="RktSym">false</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div></p><h4 x-source-module="(lib "scribblings/htdp-langs/htdp-langs.scrbl")" x-part-tag=""Symbols"">2.8<tt> </tt><a name="(part._htdp-beginner-abbr._.Symbols)"></a>Symbols</h4><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._symbol-~3estring))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._symbol-~3estring%29%29" class="RktValDef RktValLink" data-pltdoc="x">symbol->string</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">string</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">symbol</span></td></tr></table></blockquote></div><div class="SIntrapara">Converts a symbol to a string.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">symbol->string</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">c</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">"c"</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._symbol~3d~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._symbol~3d~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">symbol=?</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktVar">y</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">symbol</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">symbol</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether two symbols are equal.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">symbol=?</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">a</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">b</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">false</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._symbol~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._symbol~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">symbol?</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">any/c</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether some value is a symbol.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">symbol?</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">a</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div></p><h4 x-source-module="(lib "scribblings/htdp-langs/htdp-langs.scrbl")" x-part-tag=""Lists"">2.9<tt> </tt><a name="(part._htdp-beginner-abbr._.Lists)"></a>Lists</h4><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._append))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._append%29%29" class="RktValDef RktValLink" data-pltdoc="x">append</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span><span class="RktVar">z</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">list?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">list?</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">list?</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">z</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">list?</span></td></tr></table></blockquote></div><div class="SIntrapara">Creates a single list from several, by juxtaposition of the items.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">append</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">cons</span><span class="hspace"> </span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">cons</span><span class="hspace"> </span><span class="RktVal">2</span><span class="hspace"> </span><span class="RktSym">empty</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">cons</span><span class="hspace"> </span><span class="RktVal">"a"</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">cons</span><span class="hspace"> </span><span class="RktVal">"b"</span><span class="hspace"> </span><span class="RktSym">empty</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">(list 1 2 "a" "b")</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._assq))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._assq%29%29" class="RktValDef RktValLink" data-pltdoc="x">assq</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktVar">l</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">union</span><span class="hspace"> </span><span class="RktSym">false</span><span class="hspace"> </span><span class="RktSym">cons?</span><span class="RktPn">)</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">any/c</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">l</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">list?</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether some item is the first item of a pair in a list of
pairs. (It compares the items with <span class="RktSym">eq?</span>.)
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktSym">a</span></td></tr><tr><td><p><span class="RktRes">(list (list 'a 22) (list 'b 8) (list 'c 70))</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">assq</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">b</span><span class="hspace"> </span><span class="RktSym">a</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">(list 'b 8)</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._caaar))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._caaar%29%29" class="RktValDef RktValLink" data-pltdoc="x">caaar</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">any/c</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">list?</span></td></tr></table></blockquote></div><div class="SIntrapara">LISP-style selector: <span class="RktPn">(</span><span class="RktSym">car</span><span class="stt"> </span><span class="RktPn">(</span><span class="RktSym">car</span><span class="stt"> </span><span class="RktPn">(</span><span class="RktSym">car</span><span class="stt"> </span><span class="RktPn">(</span><span class="RktSym">car</span><span class="stt"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span>.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktSym">w</span></td></tr><tr><td><p><span class="RktRes">(list (list (list (list "bye") 3) true) 42)</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">caaar</span><span class="hspace"> </span><span class="RktSym">w</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">(list "bye")</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._caadr))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._caadr%29%29" class="RktValDef RktValLink" data-pltdoc="x">caadr</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">any/c</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">list?</span></td></tr></table></blockquote></div><div class="SIntrapara">LISP-style selector: <span class="RktPn">(</span><span class="RktSym">car</span><span class="stt"> </span><span class="RktPn">(</span><span class="RktSym">car</span><span class="stt"> </span><span class="RktPn">(</span><span class="RktSym">cdr</span><span class="stt"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span>.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktSym">z</span></td></tr><tr><td><p><span class="RktRes">(list (list (list (list 'a 'b) 2 3)) (list false true) "world")</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">caadr</span><span class="hspace"> </span><span class="RktSym">z</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">false</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._caar))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._caar%29%29" class="RktValDef RktValLink" data-pltdoc="x">caar</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">any/c</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">list?</span></td></tr></table></blockquote></div><div class="SIntrapara">LISP-style selector: <span class="RktPn">(</span><span class="RktSym">car</span><span class="stt"> </span><span class="RktPn">(</span><span class="RktSym">car</span><span class="stt"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="RktPn">)</span>.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktSym">y</span></td></tr><tr><td><p><span class="RktRes">(list (list (list 1 2 3) false "world"))</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">caar</span><span class="hspace"> </span><span class="RktSym">y</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">(list 1 2 3)</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._cadar))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._cadar%29%29" class="RktValDef RktValLink" data-pltdoc="x">cadar</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">any/c</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">list?</span></td></tr></table></blockquote></div><div class="SIntrapara">LISP-style selector: <span class="RktPn">(</span><span class="RktSym">car</span><span class="stt"> </span><span class="RktPn">(</span><span class="RktSym">cdr</span><span class="stt"> </span><span class="RktPn">(</span><span class="RktSym">car</span><span class="stt"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span>.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktSym">w</span></td></tr><tr><td><p><span class="RktRes">(list (list (list (list "bye") 3) true) 42)</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">cadar</span><span class="hspace"> </span><span class="RktSym">w</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._cadddr))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._cadddr%29%29" class="RktValDef RktValLink" data-pltdoc="x">cadddr</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">any/c</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">list?</span></td></tr></table></blockquote></div><div class="SIntrapara">LISP-style selector: <span class="RktPn">(</span><span class="RktSym">car</span><span class="stt"> </span><span class="RktPn">(</span><span class="RktSym">cdr</span><span class="stt"> </span><span class="RktPn">(</span><span class="RktSym">cdr</span><span class="stt"> </span><span class="RktPn">(</span><span class="RktSym">cdr</span><span class="stt"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span>.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktSym">v</span></td></tr><tr><td><p><span class="RktRes">(list 1 2 3 4 5 6 7 8 9 'A)</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">cadddr</span><span class="hspace"> </span><span class="RktSym">v</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">4</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._caddr))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._caddr%29%29" class="RktValDef RktValLink" data-pltdoc="x">caddr</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">any/c</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">list?</span></td></tr></table></blockquote></div><div class="SIntrapara">LISP-style selector: <span class="RktPn">(</span><span class="RktSym">car</span><span class="stt"> </span><span class="RktPn">(</span><span class="RktSym">cdr</span><span class="stt"> </span><span class="RktPn">(</span><span class="RktSym">cdr</span><span class="stt"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span>.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktVar">x</span></td></tr><tr><td><p><span class="RktRes">(list 2 "hello" true)</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">caddr</span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._cadr))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._cadr%29%29" class="RktValDef RktValLink" data-pltdoc="x">cadr</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">any/c</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">list?</span></td></tr></table></blockquote></div><div class="SIntrapara">LISP-style selector: <span class="RktPn">(</span><span class="RktSym">car</span><span class="stt"> </span><span class="RktPn">(</span><span class="RktSym">cdr</span><span class="stt"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="RktPn">)</span>.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktVar">x</span></td></tr><tr><td><p><span class="RktRes">(list 2 "hello" true)</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">cadr</span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">"hello"</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._car))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._car%29%29" class="RktValDef RktValLink" data-pltdoc="x">car</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">any/c</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">cons?</span></td></tr></table></blockquote></div><div class="SIntrapara">Selects the first item of a non-empty list.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktVar">x</span></td></tr><tr><td><p><span class="RktRes">(list 2 "hello" true)</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">car</span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">2</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._cdaar))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._cdaar%29%29" class="RktValDef RktValLink" data-pltdoc="x">cdaar</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">any/c</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">list?</span></td></tr></table></blockquote></div><div class="SIntrapara">LISP-style selector: <span class="RktPn">(</span><span class="RktSym">cdr</span><span class="stt"> </span><span class="RktPn">(</span><span class="RktSym">car</span><span class="stt"> </span><span class="RktPn">(</span><span class="RktSym">car</span><span class="stt"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span>.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktSym">w</span></td></tr><tr><td><p><span class="RktRes">(list (list (list (list "bye") 3) true) 42)</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">cdaar</span><span class="hspace"> </span><span class="RktSym">w</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">(list 3)</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._cdadr))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._cdadr%29%29" class="RktValDef RktValLink" data-pltdoc="x">cdadr</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">any/c</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">list?</span></td></tr></table></blockquote></div><div class="SIntrapara">LISP-style selector: <span class="RktPn">(</span><span class="RktSym">cdr</span><span class="stt"> </span><span class="RktPn">(</span><span class="RktSym">car</span><span class="stt"> </span><span class="RktPn">(</span><span class="RktSym">cdr</span><span class="stt"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span>.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktSym">z</span></td></tr><tr><td><p><span class="RktRes">(list (list (list (list 'a 'b) 2 3)) (list false true) "world")</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">cdadr</span><span class="hspace"> </span><span class="RktSym">z</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">(list true)</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._cdar))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._cdar%29%29" class="RktValDef RktValLink" data-pltdoc="x">cdar</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">list?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">list?</span></td></tr></table></blockquote></div><div class="SIntrapara">LISP-style selector: <span class="RktPn">(</span><span class="RktSym">cdr</span><span class="stt"> </span><span class="RktPn">(</span><span class="RktSym">car</span><span class="stt"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="RktPn">)</span>.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktSym">y</span></td></tr><tr><td><p><span class="RktRes">(list (list (list 1 2 3) false "world"))</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">cdar</span><span class="hspace"> </span><span class="RktSym">y</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">(list false "world")</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._cddar))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._cddar%29%29" class="RktValDef RktValLink" data-pltdoc="x">cddar</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">any/c</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">list?</span></td></tr></table></blockquote></div><div class="SIntrapara">LISP-style selector: <span class="RktPn">(</span><span class="RktSym">cdr</span><span class="stt"> </span><span class="RktPn">(</span><span class="RktSym">cdr</span><span class="stt"> </span><span class="RktPn">(</span><span class="RktSym">car</span><span class="stt"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span>
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktSym">w</span></td></tr><tr><td><p><span class="RktRes">(list (list (list (list "bye") 3) true) 42)</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">cddar</span><span class="hspace"> </span><span class="RktSym">w</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">empty</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._cdddr))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._cdddr%29%29" class="RktValDef RktValLink" data-pltdoc="x">cdddr</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">any/c</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">list?</span></td></tr></table></blockquote></div><div class="SIntrapara">LISP-style selector: <span class="RktPn">(</span><span class="RktSym">cdr</span><span class="stt"> </span><span class="RktPn">(</span><span class="RktSym">cdr</span><span class="stt"> </span><span class="RktPn">(</span><span class="RktSym">cdr</span><span class="stt"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span>.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktSym">v</span></td></tr><tr><td><p><span class="RktRes">(list 1 2 3 4 5 6 7 8 9 'A)</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">cdddr</span><span class="hspace"> </span><span class="RktSym">v</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">(list 4 5 6 7 8 9 'A)</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._cddr))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._cddr%29%29" class="RktValDef RktValLink" data-pltdoc="x">cddr</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">list?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">list?</span></td></tr></table></blockquote></div><div class="SIntrapara">LISP-style selector: <span class="RktPn">(</span><span class="RktSym">cdr</span><span class="stt"> </span><span class="RktPn">(</span><span class="RktSym">cdr</span><span class="stt"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="RktPn">)</span>.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktVar">x</span></td></tr><tr><td><p><span class="RktRes">(list 2 "hello" true)</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">cddr</span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">(list true)</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._cdr))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._cdr%29%29" class="RktValDef RktValLink" data-pltdoc="x">cdr</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">any/c</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">cons?</span></td></tr></table></blockquote></div><div class="SIntrapara">Selects the rest of a non-empty list.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktVar">x</span></td></tr><tr><td><p><span class="RktRes">(list 2 "hello" true)</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">cdr</span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">(list "hello" true)</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._cons))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._cons%29%29" class="RktValDef RktValLink" data-pltdoc="x">cons</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktVar">y</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">list?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">any/x</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">list?</span></td></tr></table></blockquote></div><div class="SIntrapara">Constructs a list.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">cons</span><span class="hspace"> </span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktSym">empty</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">(cons 1 empty)</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._cons~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._cons~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">cons?</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">any/c</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether some value is a constructed list.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">cons?</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">cons</span><span class="hspace"> </span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktSym">empty</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">cons?</span><span class="hspace"> </span><span class="RktVal">42</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">false</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._eighth))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._eighth%29%29" class="RktValDef RktValLink" data-pltdoc="x">eighth</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">any/c</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">list?</span></td></tr></table></blockquote></div><div class="SIntrapara">Selects the eighth item of a non-empty list.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktSym">v</span></td></tr><tr><td><p><span class="RktRes">(list 1 2 3 4 5 6 7 8 9 'A)</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">eighth</span><span class="hspace"> </span><span class="RktSym">v</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">8</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._empty~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._empty~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">empty?</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">any/c</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether some value is the empty list.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">empty?</span><span class="hspace"> </span><span class="RktSym">empty</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">empty?</span><span class="hspace"> </span><span class="RktVal">42</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">false</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._fifth))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._fifth%29%29" class="RktValDef RktValLink" data-pltdoc="x">fifth</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">any/c</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">list?</span></td></tr></table></blockquote></div><div class="SIntrapara">Selects the fifth item of a non-empty list.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktSym">v</span></td></tr><tr><td><p><span class="RktRes">(list 1 2 3 4 5 6 7 8 9 'A)</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">fifth</span><span class="hspace"> </span><span class="RktSym">v</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">5</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._first))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._first%29%29" class="RktValDef RktValLink" data-pltdoc="x">first</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">any/c</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">cons?</span></td></tr></table></blockquote></div><div class="SIntrapara">Selects the first item of a non-empty list.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktVar">x</span></td></tr><tr><td><p><span class="RktRes">(list 2 "hello" true)</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">first</span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">2</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._fourth))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._fourth%29%29" class="RktValDef RktValLink" data-pltdoc="x">fourth</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">any/c</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">list?</span></td></tr></table></blockquote></div><div class="SIntrapara">Selects the fourth item of a non-empty list.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktSym">v</span></td></tr><tr><td><p><span class="RktRes">(list 1 2 3 4 5 6 7 8 9 'A)</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">fourth</span><span class="hspace"> </span><span class="RktSym">v</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">4</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._length))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._length%29%29" class="RktValDef RktValLink" data-pltdoc="x">length</a></span></span><span class="hspace"> </span><span class="RktVar">l</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">natural-number?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">l</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">list?</span></td></tr></table></blockquote></div><div class="SIntrapara">Evaluates the number of items on a list.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktSym">x</span></td></tr><tr><td><p><span class="RktRes">(list 2 "hello" true)</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">length</span><span class="hspace"> </span><span class="RktSym">x</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">3</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._list))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._list%29%29" class="RktValDef RktValLink" data-pltdoc="x">list</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">list?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">any/c</span></td></tr></table></blockquote></div><div class="SIntrapara">Constructs a list of its arguments.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">list</span><span class="hspace"> </span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktVal">2</span><span class="hspace"> </span><span class="RktVal">3</span><span class="hspace"> </span><span class="RktVal">4</span><span class="hspace"> </span><span class="RktVal">5</span><span class="hspace"> </span><span class="RktVal">6</span><span class="hspace"> </span><span class="RktVal">7</span><span class="hspace"> </span><span class="RktVal">8</span><span class="hspace"> </span><span class="RktVal">9</span><span class="hspace"> </span><span class="RktVal">0</span><span class="RktPn">)</span></td></tr><tr><td><table cellspacing="0" cellpadding="0"><tr><td><p><span class="RktRes">(cons</span></p></td></tr><tr><td><p><span class="RktRes"></span><span class="hspace"> </span><span class="RktRes">1</span></p></td></tr><tr><td><p><span class="RktRes"></span><span class="hspace"> </span><span class="RktRes">(cons</span></p></td></tr><tr><td><p><span class="RktRes"></span><span class="hspace"> </span><span class="RktRes">2</span></p></td></tr><tr><td><p><span class="RktRes"></span><span class="hspace"> </span><span class="RktRes">(cons</span></p></td></tr><tr><td><p><span class="RktRes"></span><span class="hspace"> </span><span class="RktRes"></span><span class="hspace"> </span><span class="RktRes">3</span></p></td></tr><tr><td><p><span class="RktRes"></span><span class="hspace"> </span><span class="RktRes"></span><span class="hspace"> </span><span class="RktRes">(cons</span></p></td></tr><tr><td><p><span class="RktRes"></span><span class="hspace"> </span><span class="RktRes"></span><span class="hspace"> </span><span class="RktRes">4</span></p></td></tr><tr><td><p><span class="RktRes"></span><span class="hspace"> </span><span class="RktRes"></span><span class="hspace"> </span><span class="RktRes">(cons</span></p></td></tr><tr><td><p><span class="RktRes"></span><span class="hspace"> </span><span class="RktRes"></span><span class="hspace"> </span><span class="RktRes"></span><span class="hspace"> </span><span class="RktRes">5</span></p></td></tr><tr><td><p><span class="RktRes"></span><span class="hspace"> </span><span class="RktRes"></span><span class="hspace"> </span><span class="RktRes"></span><span class="hspace"> </span><span class="RktRes">(cons 6 (cons 7 (cons 8 (cons 9 (cons 0 empty))))))))))</span></p></td></tr></table></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._list*))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._list%2A%29%29" class="RktValDef RktValLink" data-pltdoc="x">list*</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="hspace"> </span><span class="RktVar">l</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">list?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">any/c</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">l</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">list?</span></td></tr></table></blockquote></div><div class="SIntrapara">Constructs a list by adding multiple items to a list.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktVar">x</span></td></tr><tr><td><p><span class="RktRes">(cons 2 (cons "hello" (cons true empty)))</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">list*</span><span class="hspace"> </span><span class="RktVal">4</span><span class="hspace"> </span><span class="RktVal">3</span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">(cons 4 (cons 3 (cons 2 (cons "hello" (cons true empty)))))</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._list-ref))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._list-ref%29%29" class="RktValDef RktValLink" data-pltdoc="x">list-ref</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktVar">i</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">any/c</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">list?</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">i</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">natural?</span></td></tr></table></blockquote></div><div class="SIntrapara">Extracts the indexed item from the list.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktSym">v</span></td></tr><tr><td><p><span class="RktRes">(list 1 2 3 4 5 6 7 8 9 'A)</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">list-ref</span><span class="hspace"> </span><span class="RktSym">v</span><span class="hspace"> </span><span class="RktVal">9</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">'A</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._make-list))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._make-list%29%29" class="RktValDef RktValLink" data-pltdoc="x">make-list</a></span></span><span class="hspace"> </span><span class="RktVar">i</span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">list?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">i</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">natural-number</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">any/c</span></td></tr></table></blockquote></div><div class="SIntrapara">Constructs a list of <span class="RktVar">i</span> copies of <span class="RktVar">x</span>.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">make-list</span><span class="hspace"> </span><span class="RktVal">3</span><span class="hspace"> </span><span class="RktVal">"hello"</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">(cons "hello" (cons "hello" (cons "hello" empty)))</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._member))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._member%29%29" class="RktValDef RktValLink" data-pltdoc="x">member</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktVar">l</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">any/c</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">l</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">list?</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether some value is on the list (comparing values with equal?).
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktVar">x</span></td></tr><tr><td><p><span class="RktRes">(list 2 "hello" true)</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">member</span><span class="hspace"> </span><span class="RktVal">"hello"</span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._member~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._member~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">member?</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktVar">l</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">any/c</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">l</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">list?</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether some value is on the list (comparing values with equal?).
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktVar">x</span></td></tr><tr><td><p><span class="RktRes">(list 2 "hello" true)</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">member?</span><span class="hspace"> </span><span class="RktVal">"hello"</span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._memq))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._memq%29%29" class="RktValDef RktValLink" data-pltdoc="x">memq</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktVar">l</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">any/c</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">l</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">list?</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether some value <span class="RktVar">x</span> is on some list <span class="RktVar">l</span>,
using <span class="RktSym">eq?</span> to compare <span class="RktVar">x</span> with items on <span class="RktVar">l</span>.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktVar">x</span></td></tr><tr><td><p><span class="RktRes">(list 2 "hello" true)</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">memq</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">list</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">list</span><span class="hspace"> </span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktVal">2</span><span class="hspace"> </span><span class="RktVal">3</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">false</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._memq~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._memq~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">memq?</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktVar">l</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">any/c</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">l</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">list?</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether some value <span class="RktVar">x</span> is on some list <span class="RktVar">l</span>,
using <span class="RktSym">eq?</span> to compare <span class="RktVar">x</span> with items on <span class="RktVar">l</span>.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktVar">x</span></td></tr><tr><td><p><span class="RktRes">(list 2 "hello" true)</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">memq?</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">list</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">list</span><span class="hspace"> </span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktVal">2</span><span class="hspace"> </span><span class="RktVal">3</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">false</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._memv))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._memv%29%29" class="RktValDef RktValLink" data-pltdoc="x">memv</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktVar">l</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">or/c</span><span class="hspace"> </span><span class="RktSym">false</span><span class="hspace"> </span><span class="RktSym">list</span><span class="RktPn">)</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">any/c</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">l</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">list?</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether some value is on the list if so, it produces the
suffix of the list that starts with x if not, it produces false. (It
compares values with the eqv? predicate.)
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktVar">x</span></td></tr><tr><td><p><span class="RktRes">(list 2 "hello" true)</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">memv</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">list</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">list</span><span class="hspace"> </span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktVal">2</span><span class="hspace"> </span><span class="RktVal">3</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">false</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>value</p></div></div><p class="RForeground"><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._null))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._null%29%29" class="RktValDef RktValLink" data-pltdoc="x">null</a></span></span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">list</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Another name for the empty list
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktSym">null</span></td></tr><tr><td><p><span class="RktRes">empty</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._null~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._null~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">null?</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">any/c</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether some value is the empty list.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">null?</span><span class="hspace"> </span><span class="RktSym">empty</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">null?</span><span class="hspace"> </span><span class="RktVal">42</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">false</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._range))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._range%29%29" class="RktValDef RktValLink" data-pltdoc="x">range</a></span></span><span class="hspace"> </span><span class="RktVar">start</span><span class="hspace"> </span><span class="RktVar">end</span><span class="hspace"> </span><span class="RktVar">step</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">list?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">start</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">end</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">step</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr></table></blockquote></div><div class="SIntrapara">Constructs a list of numbers by <span class="RktVar">step</span>ping from <span class="RktVar">start</span>
to <span class="RktVar">end</span>.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">range</span><span class="hspace"> </span><span class="RktVal">0</span><span class="hspace"> </span><span class="RktVal">10</span><span class="hspace"> </span><span class="RktVal">2</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">(cons 0 (cons 2 (cons 4 (cons 6 (cons 8 empty)))))</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._remove))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._remove%29%29" class="RktValDef RktValLink" data-pltdoc="x">remove</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktVar">l</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">list?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">any/c</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">l</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">list?</span></td></tr></table></blockquote></div><div class="SIntrapara">Constructs a list like the given one with the first occurrence of the
given item removed (comparing values with equal?).
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktVar">x</span></td></tr><tr><td><p><span class="RktRes">(list 2 "hello" true)</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">remove</span><span class="hspace"> </span><span class="RktVal">"hello"</span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">(list 2 true)</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._rest))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._rest%29%29" class="RktValDef RktValLink" data-pltdoc="x">rest</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">any/c</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">cons?</span></td></tr></table></blockquote></div><div class="SIntrapara">Selects the rest of a non-empty list.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktVar">x</span></td></tr><tr><td><p><span class="RktRes">(list 2 "hello" true)</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">rest</span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">(list "hello" true)</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._reverse))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._reverse%29%29" class="RktValDef RktValLink" data-pltdoc="x">reverse</a></span></span><span class="hspace"> </span><span class="RktVar">l</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">list</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">l</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">list?</span></td></tr></table></blockquote></div><div class="SIntrapara">Creates a reversed version of a list.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktSym">x</span></td></tr><tr><td><p><span class="RktRes">(list 2 "hello" true)</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">reverse</span><span class="hspace"> </span><span class="RktSym">x</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">(list true "hello" 2)</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._second))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._second%29%29" class="RktValDef RktValLink" data-pltdoc="x">second</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">any/c</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">list?</span></td></tr></table></blockquote></div><div class="SIntrapara">Selects the second item of a non-empty list.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktVar">x</span></td></tr><tr><td><p><span class="RktRes">(list 2 "hello" true)</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">second</span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">"hello"</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._seventh))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._seventh%29%29" class="RktValDef RktValLink" data-pltdoc="x">seventh</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">any/c</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">list?</span></td></tr></table></blockquote></div><div class="SIntrapara">Selects the seventh item of a non-empty list.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktSym">v</span></td></tr><tr><td><p><span class="RktRes">(list 1 2 3 4 5 6 7 8 9 'A)</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">seventh</span><span class="hspace"> </span><span class="RktSym">v</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">7</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._sixth))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._sixth%29%29" class="RktValDef RktValLink" data-pltdoc="x">sixth</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">any/c</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">list?</span></td></tr></table></blockquote></div><div class="SIntrapara">Selects the sixth item of a non-empty list.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktSym">v</span></td></tr><tr><td><p><span class="RktRes">(list 1 2 3 4 5 6 7 8 9 'A)</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">sixth</span><span class="hspace"> </span><span class="RktSym">v</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">6</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._third))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._third%29%29" class="RktValDef RktValLink" data-pltdoc="x">third</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">any/c</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">list?</span></td></tr></table></blockquote></div><div class="SIntrapara">Selects the third item of a non-empty list.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktVar">x</span></td></tr><tr><td><p><span class="RktRes">(list 2 "hello" true)</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">third</span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div></p><h4 x-source-module="(lib "scribblings/htdp-langs/htdp-langs.scrbl")" x-part-tag=""Posns"">2.10<tt> </tt><a name="(part._htdp-beginner-abbr._.Posns)"></a>Posns</h4><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._make-posn))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._make-posn%29%29" class="RktValDef RktValLink" data-pltdoc="x">make-posn</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktVar">y</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">posn</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">any/c</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">any/c</span></td></tr></table></blockquote></div><div class="SIntrapara">Constructs a posn from two arbitrary values.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">make-posn</span><span class="hspace"> </span><span class="RktVal">3</span><span class="hspace"> </span><span class="RktVal">3</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">(posn 3 3)</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">make-posn</span><span class="hspace"> </span><span class="RktVal">"hello"</span><span class="hspace"> </span><span class="RktSym">true</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">(posn "hello" true)</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._posn))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._posn%29%29" class="RktValDef RktValLink" data-pltdoc="x">posn</a></span></span><span class="RktPn"></span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">signature</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Signature for posns.</div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._posn-x))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._posn-x%29%29" class="RktValDef RktValLink" data-pltdoc="x">posn-x</a></span></span><span class="hspace"> </span><span class="RktVar">p</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">any</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">p</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">posn</span></td></tr></table></blockquote></div><div class="SIntrapara">Extracts the x component of a posn.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktVar">p</span></td></tr><tr><td><p><span class="RktRes">(posn 2 -3)</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">posn-x</span><span class="hspace"> </span><span class="RktVar">p</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">2</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._posn-y))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._posn-y%29%29" class="RktValDef RktValLink" data-pltdoc="x">posn-y</a></span></span><span class="hspace"> </span><span class="RktVar">p</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">any</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">p</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">posn</span></td></tr></table></blockquote></div><div class="SIntrapara">Extracts the y component of a posn.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktVar">p</span></td></tr><tr><td><p><span class="RktRes">(posn 2 -3)</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">posn-y</span><span class="hspace"> </span><span class="RktVar">p</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">-3</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._posn~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._posn~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">posn?</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">any/c</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines if its input is a posn.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktSym">q</span></td></tr><tr><td><p><span class="RktRes">(posn "bye" 2)</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">posn?</span><span class="hspace"> </span><span class="RktSym">q</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">posn?</span><span class="hspace"> </span><span class="RktVal">42</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">false</span></p></td></tr></table></blockquote></div></p><h4 x-source-module="(lib "scribblings/htdp-langs/htdp-langs.scrbl")" x-part-tag=""Characters"">2.11<tt> </tt><a name="(part._htdp-beginner-abbr._.Characters)"></a>Characters</h4><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._char-~3einteger))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._char-~3einteger%29%29" class="RktValDef RktValLink" data-pltdoc="x">char->integer</a></span></span><span class="hspace"> </span><span class="RktVar">c</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">integer</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">char</span></td></tr></table></blockquote></div><div class="SIntrapara">Lookups the number that corresponds to the given character in the ASCII table (if any).
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">char->integer</span><span class="hspace"> </span><span class="RktVal">#\a</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">97</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">char->integer</span><span class="hspace"> </span><span class="RktVal">#\z</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">122</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._char-alphabetic~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._char-alphabetic~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">char-alphabetic?</a></span></span><span class="hspace"> </span><span class="RktVar">c</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">char</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether a character represents an alphabetic character.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">char-alphabetic?</span><span class="hspace"> </span><span class="RktVal">#\Q</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._char-ci~3c~3d~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._char-ci~3c~3d~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">char-ci<=?</a></span></span><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span><span class="RktVar">d</span><span class="hspace"> </span><span class="RktVar">e</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">char</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">d</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">char</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">e</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">char</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether the characterc are ordered in an increasing and case-insensitive manner.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">char-ci<=?</span><span class="hspace"> </span><span class="RktVal">#\b</span><span class="hspace"> </span><span class="RktVal">#\B</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">char<=?</span><span class="hspace"> </span><span class="RktVal">#\b</span><span class="hspace"> </span><span class="RktVal">#\B</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">false</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._char-ci~3c~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._char-ci~3c~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">char-ci<?</a></span></span><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span><span class="RktVar">d</span><span class="hspace"> </span><span class="RktVar">e</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">char</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">d</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">char</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">e</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">char</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether the characterc are ordered in a strictly increasing and case-insensitive manner.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">char-ci<?</span><span class="hspace"> </span><span class="RktVal">#\B</span><span class="hspace"> </span><span class="RktVal">#\c</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">char<?</span><span class="hspace"> </span><span class="RktVal">#\b</span><span class="hspace"> </span><span class="RktVal">#\B</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">false</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._char-ci~3d~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._char-ci~3d~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">char-ci=?</a></span></span><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span><span class="RktVar">d</span><span class="hspace"> </span><span class="RktVar">e</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">char</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">d</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">char</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">e</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">char</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether two characters are equal in a case-insensitive
manner.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">char-ci=?</span><span class="hspace"> </span><span class="RktVal">#\b</span><span class="hspace"> </span><span class="RktVal">#\B</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._char-ci~3e~3d~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._char-ci~3e~3d~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">char-ci>=?</a></span></span><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span><span class="RktVar">d</span><span class="hspace"> </span><span class="RktVar">e</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">char</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">d</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">char</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">e</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">char</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether the characters are sorted in a decreasing and case-insensitive manner.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">char-ci>=?</span><span class="hspace"> </span><span class="RktVal">#\b</span><span class="hspace"> </span><span class="RktVal">#\C</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">false</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">char>=?</span><span class="hspace"> </span><span class="RktVal">#\b</span><span class="hspace"> </span><span class="RktVal">#\C</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._char-ci~3e~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._char-ci~3e~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">char-ci>?</a></span></span><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span><span class="RktVar">d</span><span class="hspace"> </span><span class="RktVar">e</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">char</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">d</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">char</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">e</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">char</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether the characters are sorted in a strictly decreasing and case-insensitive manner.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">char-ci>?</span><span class="hspace"> </span><span class="RktVal">#\b</span><span class="hspace"> </span><span class="RktVal">#\B</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">false</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">char>?</span><span class="hspace"> </span><span class="RktVal">#\b</span><span class="hspace"> </span><span class="RktVal">#\B</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._char-downcase))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._char-downcase%29%29" class="RktValDef RktValLink" data-pltdoc="x">char-downcase</a></span></span><span class="hspace"> </span><span class="RktVar">c</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">char</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">char</span></td></tr></table></blockquote></div><div class="SIntrapara">Produces the equivalent lower-case character.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">char-downcase</span><span class="hspace"> </span><span class="RktVal">#\T</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#\t</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._char-lower-case~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._char-lower-case~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">char-lower-case?</a></span></span><span class="hspace"> </span><span class="RktVar">c</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">char</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether a character is a lower-case character.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">char-lower-case?</span><span class="hspace"> </span><span class="RktVal">#\T</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">false</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._char-numeric~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._char-numeric~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">char-numeric?</a></span></span><span class="hspace"> </span><span class="RktVar">c</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">char</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether a character represents a digit.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">char-numeric?</span><span class="hspace"> </span><span class="RktVal">#\9</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._char-upcase))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._char-upcase%29%29" class="RktValDef RktValLink" data-pltdoc="x">char-upcase</a></span></span><span class="hspace"> </span><span class="RktVar">c</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">char</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">char</span></td></tr></table></blockquote></div><div class="SIntrapara">Produces the equivalent upper-case character.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">char-upcase</span><span class="hspace"> </span><span class="RktVal">#\t</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#\T</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._char-upper-case~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._char-upper-case~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">char-upper-case?</a></span></span><span class="hspace"> </span><span class="RktVar">c</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">char</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether a character is an upper-case character.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">char-upper-case?</span><span class="hspace"> </span><span class="RktVal">#\T</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._char-whitespace~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._char-whitespace~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">char-whitespace?</a></span></span><span class="hspace"> </span><span class="RktVar">c</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">char</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether a character represents space.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">char-whitespace?</span><span class="hspace"> </span><span class="RktVal">#\tab</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._char~3c~3d~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._char~3c~3d~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">char<=?</a></span></span><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span><span class="RktVar">d</span><span class="hspace"> </span><span class="RktVar">e</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">char</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">d</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">char</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">e</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">char</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether the characterc are ordered in a strictly increasing manner.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">char<=?</span><span class="hspace"> </span><span class="RktVal">#\a</span><span class="hspace"> </span><span class="RktVal">#\a</span><span class="hspace"> </span><span class="RktVal">#\b</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._char~3c~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._char~3c~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">char<?</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktVar">d</span><span class="hspace"> </span><span class="RktVar">e</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">char</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">d</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">char</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">e</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">char</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether the characterc are ordered in a strictly increasing manner.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">char<?</span><span class="hspace"> </span><span class="RktVal">#\a</span><span class="hspace"> </span><span class="RktVal">#\b</span><span class="hspace"> </span><span class="RktVal">#\c</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._char~3d~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._char~3d~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">char=?</a></span></span><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span><span class="RktVar">d</span><span class="hspace"> </span><span class="RktVar">e</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">char</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">d</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">char</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">e</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">char</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether the characters are equal.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">char=?</span><span class="hspace"> </span><span class="RktVal">#\b</span><span class="hspace"> </span><span class="RktVal">#\a</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">false</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._char~3e~3d~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._char~3e~3d~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">char>=?</a></span></span><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span><span class="RktVar">d</span><span class="hspace"> </span><span class="RktVar">e</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">char</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">d</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">char</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">e</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">char</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether the characters are sorted in a decreasing manner.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">char>=?</span><span class="hspace"> </span><span class="RktVal">#\b</span><span class="hspace"> </span><span class="RktVal">#\b</span><span class="hspace"> </span><span class="RktVal">#\a</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._char~3e~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._char~3e~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">char>?</a></span></span><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span><span class="RktVar">d</span><span class="hspace"> </span><span class="RktVar">e</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">char</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">d</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">char</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">e</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">char</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether the characters are sorted in a strictly decreasing manner.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">char>?</span><span class="hspace"> </span><span class="RktVal">#\A</span><span class="hspace"> </span><span class="RktVal">#\z</span><span class="hspace"> </span><span class="RktVal">#\a</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">false</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._char~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._char~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">char?</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">any/c</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether a value is a character.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">char?</span><span class="hspace"> </span><span class="RktVal">"a"</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">false</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">char?</span><span class="hspace"> </span><span class="RktVal">#\a</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div></p><h4 x-source-module="(lib "scribblings/htdp-langs/htdp-langs.scrbl")" x-part-tag=""Strings"">2.12<tt> </tt><a name="(part._htdp-beginner-abbr._.Strings)"></a>Strings</h4><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._explode))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._explode%29%29" class="RktValDef RktValLink" data-pltdoc="x">explode</a></span></span><span class="hspace"> </span><span class="RktVar">s</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">listof</span><span class="hspace"> </span><span class="RktSym">string</span><span class="RktPn">)</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr></table></blockquote></div><div class="SIntrapara">Translates a string into a list of 1-letter strings.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">explode</span><span class="hspace"> </span><span class="RktVal">"cat"</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">(list "c" "a" "t")</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._format))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._format%29%29" class="RktValDef RktValLink" data-pltdoc="x">format</a></span></span><span class="hspace"> </span><span class="RktVar">f</span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">string</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">f</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">any/c</span></td></tr></table></blockquote></div><div class="SIntrapara">Formats a string, possibly embedding values.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">format</span><span class="hspace"> </span><span class="RktVal">"Dear Dr. ~a:"</span><span class="hspace"> </span><span class="RktVal">"Flatt"</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">"Dear Dr. Flatt:"</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">format</span><span class="hspace"> </span><span class="RktVal">"Dear Dr. ~s:"</span><span class="hspace"> </span><span class="RktVal">"Flatt"</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">"Dear Dr. \"Flatt\":"</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">format</span><span class="hspace"> </span><span class="RktVal">"the value of ~s is ~a"</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">+</span><span class="hspace"> </span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktVal">1</span><span class="RktVal">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">+</span><span class="hspace"> </span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktVal">1</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">"the value of (+ 1 1) is 2"</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._implode))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._implode%29%29" class="RktValDef RktValLink" data-pltdoc="x">implode</a></span></span><span class="hspace"> </span><span class="RktVar">l</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">string</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">l</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">list?</span></td></tr></table></blockquote></div><div class="SIntrapara">Concatenates the list of 1-letter strings into one string.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">implode</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">cons</span><span class="hspace"> </span><span class="RktVal">"c"</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">cons</span><span class="hspace"> </span><span class="RktVal">"a"</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">cons</span><span class="hspace"> </span><span class="RktVal">"t"</span><span class="hspace"> </span><span class="RktSym">empty</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">"cat"</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._int-~3estring))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._int-~3estring%29%29" class="RktValDef RktValLink" data-pltdoc="x">int->string</a></span></span><span class="hspace"> </span><span class="RktVar">i</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">string</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">i</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">integer</span></td></tr></table></blockquote></div><div class="SIntrapara">Converts an integer in [0,55295] or [57344 1114111] to a 1-letter string.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">int->string</span><span class="hspace"> </span><span class="RktVal">65</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">"A"</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._list-~3estring))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._list-~3estring%29%29" class="RktValDef RktValLink" data-pltdoc="x">list->string</a></span></span><span class="hspace"> </span><span class="RktVar">l</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">string</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">l</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">list?</span></td></tr></table></blockquote></div><div class="SIntrapara">Converts a s list of characters into a string.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">list->string</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">cons</span><span class="hspace"> </span><span class="RktVal">#\c</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">cons</span><span class="hspace"> </span><span class="RktVal">#\a</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">cons</span><span class="hspace"> </span><span class="RktVal">#\t</span><span class="hspace"> </span><span class="RktSym">empty</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">"cat"</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._make-string))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._make-string%29%29" class="RktValDef RktValLink" data-pltdoc="x">make-string</a></span></span><span class="hspace"> </span><span class="RktVar">i</span><span class="hspace"> </span><span class="RktVar">c</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">string</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">i</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">natural-number</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">char</span></td></tr></table></blockquote></div><div class="SIntrapara">Produces a string of length <span class="RktVar">i</span> from <span class="RktVar">c</span>.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">make-string</span><span class="hspace"> </span><span class="RktVal">3</span><span class="hspace"> </span><span class="RktVal">#\d</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">"ddd"</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._replicate))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._replicate%29%29" class="RktValDef RktValLink" data-pltdoc="x">replicate</a></span></span><span class="hspace"> </span><span class="RktVar">i</span><span class="hspace"> </span><span class="RktVar">s</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">string</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">i</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">natural-number</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr></table></blockquote></div><div class="SIntrapara">Replicates <span class="RktVar">s</span> <span class="RktVar">i</span> times.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">replicate</span><span class="hspace"> </span><span class="RktVal">3</span><span class="hspace"> </span><span class="RktVal">"h"</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">"hhh"</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._string))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string%29%29" class="RktValDef RktValLink" data-pltdoc="x">string</a></span></span><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">string?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">char</span></td></tr></table></blockquote></div><div class="SIntrapara">Builds a string of the given characters.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">string</span><span class="hspace"> </span><span class="RktVal">#\d</span><span class="hspace"> </span><span class="RktVal">#\o</span><span class="hspace"> </span><span class="RktVal">#\g</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">"dog"</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._string-~3eint))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string-~3eint%29%29" class="RktValDef RktValLink" data-pltdoc="x">string->int</a></span></span><span class="hspace"> </span><span class="RktVar">s</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">integer</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr></table></blockquote></div><div class="SIntrapara">Converts a 1-letter string to an integer in [0,55295] or [57344, 1114111].
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">string->int</span><span class="hspace"> </span><span class="RktVal">"a"</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">97</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._string-~3elist))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string-~3elist%29%29" class="RktValDef RktValLink" data-pltdoc="x">string->list</a></span></span><span class="hspace"> </span><span class="RktVar">s</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">listof</span><span class="hspace"> </span><span class="RktSym">char</span><span class="RktPn">)</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr></table></blockquote></div><div class="SIntrapara">Converts a string into a list of characters.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">string->list</span><span class="hspace"> </span><span class="RktVal">"hello"</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">(list #\h #\e #\l #\l #\o)</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._string-~3enumber))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string-~3enumber%29%29" class="RktValDef RktValLink" data-pltdoc="x">string->number</a></span></span><span class="hspace"> </span><span class="RktVar">s</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">union</span><span class="hspace"> </span><span class="RktSym">number</span><span class="hspace"> </span><span class="RktSym">false</span><span class="RktPn">)</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr></table></blockquote></div><div class="SIntrapara">Converts a string into a number, produce false if impossible.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">string->number</span><span class="hspace"> </span><span class="RktVal">"-2.03"</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#i-2.03</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">string->number</span><span class="hspace"> </span><span class="RktVal">"1-2i"</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">1-2i</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._string-~3esymbol))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string-~3esymbol%29%29" class="RktValDef RktValLink" data-pltdoc="x">string->symbol</a></span></span><span class="hspace"> </span><span class="RktVar">s</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">symbol</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr></table></blockquote></div><div class="SIntrapara">Converts a string into a symbol.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">string->symbol</span><span class="hspace"> </span><span class="RktVal">"hello"</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">'hello</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._string-alphabetic~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string-alphabetic~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">string-alphabetic?</a></span></span><span class="hspace"> </span><span class="RktVar">s</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether all ’letters’ in the string are alphabetic.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">string-alphabetic?</span><span class="hspace"> </span><span class="RktVal">"123"</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">false</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">string-alphabetic?</span><span class="hspace"> </span><span class="RktVal">"cat"</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._string-append))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string-append%29%29" class="RktValDef RktValLink" data-pltdoc="x">string-append</a></span></span><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">string</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr></table></blockquote></div><div class="SIntrapara">Juxtaposes the characters of several strings.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">string-append</span><span class="hspace"> </span><span class="RktVal">"hello"</span><span class="hspace"> </span><span class="RktVal">" "</span><span class="hspace"> </span><span class="RktVal">"world"</span><span class="hspace"> </span><span class="RktVal">" "</span><span class="hspace"> </span><span class="RktVal">"good bye"</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">"hello world good bye"</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._string-ci~3c~3d~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string-ci~3c~3d~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">string-ci<=?</a></span></span><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span><span class="RktVar">t</span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">t</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether the strings are ordered in a lexicographically increasing and case-insensitive manner.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">string-ci<=?</span><span class="hspace"> </span><span class="RktVal">"hello"</span><span class="hspace"> </span><span class="RktVal">"WORLD"</span><span class="hspace"> </span><span class="RktVal">"zoo"</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._string-ci~3c~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string-ci~3c~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">string-ci<?</a></span></span><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span><span class="RktVar">t</span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">t</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether the strings are ordered in a lexicographically strictly increasing and case-insensitive manner.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">string-ci<?</span><span class="hspace"> </span><span class="RktVal">"hello"</span><span class="hspace"> </span><span class="RktVal">"WORLD"</span><span class="hspace"> </span><span class="RktVal">"zoo"</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._string-ci~3d~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string-ci~3d~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">string-ci=?</a></span></span><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span><span class="RktVar">t</span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">t</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether all strings are equal, character for character, regardless of case.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">string-ci=?</span><span class="hspace"> </span><span class="RktVal">"hello"</span><span class="hspace"> </span><span class="RktVal">"HellO"</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._string-ci~3e~3d~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string-ci~3e~3d~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">string-ci>=?</a></span></span><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span><span class="RktVar">t</span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">t</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether the strings are ordered in a lexicographically decreasing and case-insensitive manner.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">string-ci>?</span><span class="hspace"> </span><span class="RktVal">"zoo"</span><span class="hspace"> </span><span class="RktVal">"WORLD"</span><span class="hspace"> </span><span class="RktVal">"hello"</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._string-ci~3e~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string-ci~3e~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">string-ci>?</a></span></span><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span><span class="RktVar">t</span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">t</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether the strings are ordered in a lexicographically strictly decreasing and case-insensitive manner.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">string-ci>?</span><span class="hspace"> </span><span class="RktVal">"zoo"</span><span class="hspace"> </span><span class="RktVal">"WORLD"</span><span class="hspace"> </span><span class="RktVal">"hello"</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._string-contains~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string-contains~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">string-contains?</a></span></span><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span><span class="RktVar">t</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">t</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether the first string appears literally in the second one.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">string-contains?</span><span class="hspace"> </span><span class="RktVal">"at"</span><span class="hspace"> </span><span class="RktVal">"cat"</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._string-copy))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string-copy%29%29" class="RktValDef RktValLink" data-pltdoc="x">string-copy</a></span></span><span class="hspace"> </span><span class="RktVar">s</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">string</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr></table></blockquote></div><div class="SIntrapara">Copies a string. </div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">string-copy</span><span class="hspace"> </span><span class="RktVal">"hello"</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">"hello"</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._string-ith))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string-ith%29%29" class="RktValDef RktValLink" data-pltdoc="x">string-ith</a></span></span><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span><span class="RktVar">i</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">1string?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">i</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">natural-number</span></td></tr></table></blockquote></div><div class="SIntrapara">Extracts the <span class="RktVar">i</span>th 1-letter substring from <span class="RktVar">s</span>.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">string-ith</span><span class="hspace"> </span><span class="RktVal">"hello world"</span><span class="hspace"> </span><span class="RktVal">1</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">"e"</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._string-length))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string-length%29%29" class="RktValDef RktValLink" data-pltdoc="x">string-length</a></span></span><span class="hspace"> </span><span class="RktVar">s</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">nat</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines the length of a string.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">string-length</span><span class="hspace"> </span><span class="RktVal">"hello world"</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">11</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._string-lower-case~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string-lower-case~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">string-lower-case?</a></span></span><span class="hspace"> </span><span class="RktVar">s</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether all ’letters’ in the string are lower case.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">string-lower-case?</span><span class="hspace"> </span><span class="RktVal">"CAT"</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">false</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._string-numeric~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string-numeric~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">string-numeric?</a></span></span><span class="hspace"> </span><span class="RktVar">s</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether all ’letters’ in the string are numeric.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">string-numeric?</span><span class="hspace"> </span><span class="RktVal">"123"</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">string-numeric?</span><span class="hspace"> </span><span class="RktVal">"1-2i"</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">false</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._string-ref))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string-ref%29%29" class="RktValDef RktValLink" data-pltdoc="x">string-ref</a></span></span><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span><span class="RktVar">i</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">char</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">i</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">natural-number</span></td></tr></table></blockquote></div><div class="SIntrapara">Extracts the <span class="RktVar">i</span>th character from <span class="RktVar">s</span>.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">string-ref</span><span class="hspace"> </span><span class="RktVal">"cat"</span><span class="hspace"> </span><span class="RktVal">2</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#\t</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._string-upper-case~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string-upper-case~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">string-upper-case?</a></span></span><span class="hspace"> </span><span class="RktVar">s</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether all ’letters’ in the string are upper case.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">string-upper-case?</span><span class="hspace"> </span><span class="RktVal">"CAT"</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._string-whitespace~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string-whitespace~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">string-whitespace?</a></span></span><span class="hspace"> </span><span class="RktVar">s</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether all ’letters’ in the string are white space.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">string-whitespace?</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">string-append</span><span class="hspace"> </span><span class="RktVal">" "</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">string</span><span class="hspace"> </span><span class="RktVal">#\tab</span><span class="hspace"> </span><span class="RktVal">#\newline</span><span class="hspace"> </span><span class="RktVal">#\return</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._string~3c~3d~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string~3c~3d~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">string<=?</a></span></span><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span><span class="RktVar">t</span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">t</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether the strings are ordered in a lexicographically increasing manner.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">string<=?</span><span class="hspace"> </span><span class="RktVal">"hello"</span><span class="hspace"> </span><span class="RktVal">"hello"</span><span class="hspace"> </span><span class="RktVal">"world"</span><span class="hspace"> </span><span class="RktVal">"zoo"</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._string~3c~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string~3c~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">string<?</a></span></span><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span><span class="RktVar">t</span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">t</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether the strings are ordered in a lexicographically strictly increasing manner.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">string<?</span><span class="hspace"> </span><span class="RktVal">"hello"</span><span class="hspace"> </span><span class="RktVal">"world"</span><span class="hspace"> </span><span class="RktVal">"zoo"</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._string~3d~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string~3d~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">string=?</a></span></span><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span><span class="RktVar">t</span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">t</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether all strings are equal, character for character.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">string=?</span><span class="hspace"> </span><span class="RktVal">"hello"</span><span class="hspace"> </span><span class="RktVal">"world"</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">false</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">string=?</span><span class="hspace"> </span><span class="RktVal">"bye"</span><span class="hspace"> </span><span class="RktVal">"bye"</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._string~3e~3d~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string~3e~3d~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">string>=?</a></span></span><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span><span class="RktVar">t</span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">t</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether the strings are ordered in a lexicographically decreasing manner.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">string>=?</span><span class="hspace"> </span><span class="RktVal">"zoo"</span><span class="hspace"> </span><span class="RktVal">"zoo"</span><span class="hspace"> </span><span class="RktVal">"world"</span><span class="hspace"> </span><span class="RktVal">"hello"</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._string~3e~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string~3e~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">string>?</a></span></span><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span><span class="RktVar">t</span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">t</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether the strings are ordered in a lexicographically strictly decreasing manner.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">string>?</span><span class="hspace"> </span><span class="RktVal">"zoo"</span><span class="hspace"> </span><span class="RktVal">"world"</span><span class="hspace"> </span><span class="RktVal">"hello"</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._string~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._string~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">string?</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">any/c</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether a value is a string.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">string?</span><span class="hspace"> </span><span class="RktVal">"hello world"</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">string?</span><span class="hspace"> </span><span class="RktVal">42</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">false</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._substring))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._substring%29%29" class="RktValDef RktValLink" data-pltdoc="x">substring</a></span></span><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span><span class="RktVar">i</span><span class="hspace"> </span><span class="RktVar">j</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">string</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">string</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">i</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">natural-number</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">j</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">natural-number</span></td></tr></table></blockquote></div><div class="SIntrapara">Extracts the substring starting at <span class="RktVar">i</span> up to <span class="RktVar">j</span> (or the
end if <span class="RktVar">j</span> is not provided).
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">substring</span><span class="hspace"> </span><span class="RktVal">"hello world"</span><span class="hspace"> </span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktVal">5</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">"ello"</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">substring</span><span class="hspace"> </span><span class="RktVal">"hello world"</span><span class="hspace"> </span><span class="RktVal">4</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">"o world"</span></p></td></tr></table></blockquote></div></p><h4 x-source-module="(lib "scribblings/htdp-langs/htdp-langs.scrbl")" x-part-tag=""Images"">2.13<tt> </tt><a name="(part._htdp-beginner-abbr._.Images)"></a>Images</h4><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._image~3d~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._image~3d~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">image=?</a></span></span><span class="hspace"> </span><span class="RktVar">i</span><span class="hspace"> </span><span class="RktVar">j</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">i</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">image</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">j</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">image</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether two images are equal.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktSym">c1</span></td></tr><tr><td><p><img src="pict_4.png" alt="image" width="21" height="21"/></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">image=?</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">circle</span><span class="hspace"> </span><span class="RktVal">5</span><span class="hspace"> </span><span class="RktVal">"solid"</span><span class="hspace"> </span><span class="RktVal">"green"</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym">c1</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">false</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">image=?</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">circle</span><span class="hspace"> </span><span class="RktVal">10</span><span class="hspace"> </span><span class="RktVal">"solid"</span><span class="hspace"> </span><span class="RktVal">"green"</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym">c1</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._image~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._image~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">image?</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">any/c</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether a value is an image.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktSym">c1</span></td></tr><tr><td><p><img src="pict_5.png" alt="image" width="21" height="21"/></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">image?</span><span class="hspace"> </span><span class="RktSym">c1</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div></p><h4 x-source-module="(lib "scribblings/htdp-langs/htdp-langs.scrbl")" x-part-tag=""Misc"">2.14<tt> </tt><a name="(part._htdp-beginner-abbr._.Misc)"></a>Misc</h4><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._~3d~7e))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._~3d~7e%29%29" class="RktValDef RktValLink" data-pltdoc="x">=~</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span><span class="RktVar">z</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">number</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">z</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">non-negative-real</span></td></tr></table></blockquote></div><div class="SIntrapara">Checks whether <span class="RktVar">x</span> and <span class="RktVar">y</span> are within <span class="RktVar">z</span> of either other.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">=~</span><span class="hspace"> </span><span class="RktVal">1.01</span><span class="hspace"> </span><span class="RktVal">1.0</span><span class="hspace"> </span><span class="RktVal">0.1</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">=~</span><span class="hspace"> </span><span class="RktVal">1.01</span><span class="hspace"> </span><span class="RktVal">1.5</span><span class="hspace"> </span><span class="RktVal">0.1</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">false</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>value</p></div></div><p class="RForeground"><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._eof))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._eof%29%29" class="RktValDef RktValLink" data-pltdoc="x">eof</a></span></span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">eof-object?</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">A value that represents the end of a file:
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktSym">eof</span></td></tr><tr><td><p><span class="RktRes">#<eof></span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._eof-object~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._eof-object~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">eof-object?</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">any/c</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether some value is the end-of-file value.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">eof-object?</span><span class="hspace"> </span><span class="RktSym">eof</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">eof-object?</span><span class="hspace"> </span><span class="RktVal">42</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">false</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._eq~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._eq~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">eq?</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktVar">y</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">any/c</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">any/c</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether two values are equivalent from the computer’s perspective (intensional).
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">eq?</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">cons</span><span class="hspace"> </span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktSym">empty</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">cons</span><span class="hspace"> </span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktSym">empty</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">false</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktSym">one</span></td></tr><tr><td><p><span class="RktRes">(list 1)</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">eq?</span><span class="hspace"> </span><span class="RktSym">one</span><span class="hspace"> </span><span class="RktSym">one</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._equal~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._equal~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">equal?</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktVar">y</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">any/c</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">any/c</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether two values are structurally equal where basic values
are compared with the eqv? predicate.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">equal?</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">make-posn</span><span class="hspace"> </span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktVal">2</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">make-posn</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><span class="nobreak">-</span></span><span class="hspace"> </span><span class="RktVal">2</span><span class="hspace"> </span><span class="RktVal">1</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">+</span><span class="hspace"> </span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktVal">1</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._equal~7e~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._equal~7e~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">equal~?</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span><span class="RktVar">z</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">any/c</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">any/c</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">z</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">non-negative-real</span></td></tr></table></blockquote></div><div class="SIntrapara">Compares <span class="RktVar">x</span> and <span class="RktVar">y</span> like <span class="RktSym">equal?</span> but uses =~ in the case of numbers.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">equal~?</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">make-posn</span><span class="hspace"> </span><span class="RktVal">1.01</span><span class="hspace"> </span><span class="RktVal">1.0</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">make-posn</span><span class="hspace"> </span><span class="RktVal">1.01</span><span class="hspace"> </span><span class="RktVal">0.99</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVal">0.2</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._eqv~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._eqv~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">eqv?</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktVar">y</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">any/c</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">y</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">any/c</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether two values are equivalent from the perspective of all functions that can be applied to it (extensional).
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">eqv?</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">cons</span><span class="hspace"> </span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktSym">empty</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">cons</span><span class="hspace"> </span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktSym">empty</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">false</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktSym">one</span></td></tr><tr><td><p><span class="RktRes">(list 1)</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">eqv?</span><span class="hspace"> </span><span class="RktSym">one</span><span class="hspace"> </span><span class="RktSym">one</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._error))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._error%29%29" class="RktValDef RktValLink" data-pltdoc="x">error</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">void?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">any/c</span></td></tr></table></blockquote></div><div class="SIntrapara">Signals an error, combining the given values
into an error message. If any of the values’
printed representations is too long, it is
truncated and “...” is put into the string.
If the first value is a symbol, it is suffixed with a colon and the
result pre-pended on to the error message.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktSym">zero</span></td></tr><tr><td><p><span class="RktRes">0</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">if</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">=</span><span class="hspace"> </span><span class="RktSym">zero</span><span class="hspace"> </span><span class="RktVal">0</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">error</span><span class="hspace"> </span><span class="RktVal">"can't divide by 0"</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">/</span><span class="hspace"> </span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktSym">zero</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktErr">can't divide by 0</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._exit))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._exit%29%29" class="RktValDef RktValLink" data-pltdoc="x">exit</a></span></span><span class="RktPn"></span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">void</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Evaluating <span class="RktPn">(</span><span class="RktSym">exit</span><span class="RktPn">)</span> terminates the running program.</div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._identity))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._identity%29%29" class="RktValDef RktValLink" data-pltdoc="x">identity</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">any</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">any/c</span></td></tr></table></blockquote></div><div class="SIntrapara">Returns <span class="RktVar">x</span>.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">identity</span><span class="hspace"> </span><span class="RktVal">42</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">42</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">identity</span><span class="hspace"> </span><span class="RktSym">c1</span><span class="RktPn">)</span></td></tr><tr><td><p><img src="pict_6.png" alt="image" width="21" height="21"/></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">identity</span><span class="hspace"> </span><span class="RktVal">"hello"</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">"hello"</span></p></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._htdp-beginner-abbr._((lib._lang/htdp-beginner-abbr..rkt)._struct~3f))"></a><span title="Provided from: lang/htdp-beginner-abbr | Package: htdp-lib"><span class="RktSym"><a href="#%28def._htdp-beginner-abbr._%28%28lib._lang%2Fhtdp-beginner-abbr..rkt%29._struct~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">struct?</a></span></span><span class="hspace"> </span><span class="RktVar">x</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">boolean?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">x</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">any/c</span></td></tr></table></blockquote></div><div class="SIntrapara">Determines whether some value is a structure.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">struct?</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">make-posn</span><span class="hspace"> </span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktVal">2</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">true</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">struct?</span><span class="hspace"> </span><span class="RktVal">43</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">false</span></p></td></tr></table></blockquote></div></p><div class="navsetbottom"><span class="navleft"><form class="searchform"><input class="searchbox" style="color: #888;" type="text" value="...search manuals..." title="Enter a search string to search the manuals" onkeypress="return DoSearchKey(event, this, "6.1", "../");" onfocus="this.style.color="black"; this.style.textAlign="left"; if (this.value == "...search manuals...") this.value="";" onblur="if (this.value.match(/^ *$/)) { this.style.color="#888"; this.style.textAlign="center"; this.value="...search manuals..."; }"/></form> <a href="../index.html" title="up to the documentation top" data-pltdoc="x" onclick="return GotoPLTRoot("6.1");">top</a></span><span class="navright"> <a href="beginner.html" title="backward to "1 Beginning Student"" data-pltdoc="x">← prev</a> <a href="index.html" title="up to "How to Design Programs Languages"" data-pltdoc="x">up</a> <a href="intermediate.html" title="forward to "3 Intermediate Student"" data-pltdoc="x">next →</a></span> </div></div></div><div id="contextindicator"> </div></body></html>
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