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<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"/><title>1.10 Managing Control Arrows: "arrow.rkt"</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> Teachpacks</a></td></tr></table></div><div class="tocviewsublisttop" style="display: none;" id="tocview_0"><table cellspacing="0" cellpadding="0"><tr><td align="right">1 </td><td><a href="htdp.html" class="tocviewselflink" data-pltdoc="x">Ht<span class="mywbr"> </span>DP Teachpacks</a></td></tr><tr><td align="right">2 </td><td><a href="2htdp2htdp.html" class="tocviewlink" data-pltdoc="x">Ht<span class="mywbr"> </span>DP/<span class="mywbr"> </span>2e Teachpacks</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>1 </td><td><a href="htdp.html" class="tocviewlink" data-pltdoc="x">Ht<span class="mywbr"> </span>DP Teachpacks</a></td></tr></table><div class="tocviewsublistbottom" style="display: block;" id="tocview_1"><table cellspacing="0" cellpadding="0"><tr><td align="right">1.1 </td><td><a href="image.html" class="tocviewlink" data-pltdoc="x">Manipulating Images:<span class="mywbr"> </span> <span class="stt">"image.rkt"</span><a name="(idx._(gentag._0._(lib._teachpack/teachpack..scrbl)))"></a></a></td></tr><tr><td align="right">1.2 </td><td><a href="world.html" class="tocviewlink" data-pltdoc="x">Simulations and Animations:<span class="mywbr"> </span> <span class="stt">"world.rkt"</span><a name="(idx._(gentag._1._(lib._teachpack/teachpack..scrbl)))"></a></a></td></tr><tr><td align="right">1.3 </td><td><a href="convert.html" class="tocviewlink" data-pltdoc="x">Converting Temperatures:<span class="mywbr"> </span> <span class="stt">"convert.rkt"</span><a name="(idx._(gentag._2._(lib._teachpack/teachpack..scrbl)))"></a></a></td></tr><tr><td align="right">1.4 </td><td><a href="guess.html" class="tocviewlink" data-pltdoc="x">Guessing Numbers:<span class="mywbr"> </span> <span class="stt">"guess.rkt"</span><a name="(idx._(gentag._3._(lib._teachpack/teachpack..scrbl)))"></a></a></td></tr><tr><td align="right">1.5 </td><td><a href="master.html" class="tocviewlink" data-pltdoc="x">Master<span class="mywbr"> </span>Minding:<span class="mywbr"> </span> <span class="stt">"master.rkt"</span><a name="(idx._(gentag._4._(lib._teachpack/teachpack..scrbl)))"></a></a></td></tr><tr><td align="right">1.6 </td><td><a href="master-play.html" class="tocviewlink" data-pltdoc="x">Playing Master<span class="mywbr"> </span>Mind:<span class="mywbr"> </span> <span class="stt">"master-<wbr></wbr>play.rkt"</span><a name="(idx._(gentag._5._(lib._teachpack/teachpack..scrbl)))"></a></a></td></tr><tr><td align="right">1.7 </td><td><a href="draw.html" class="tocviewlink" data-pltdoc="x">Simple Drawing:<span class="mywbr"> </span> <span class="stt">"draw.rkt"</span><a name="(idx._(gentag._6._(lib._teachpack/teachpack..scrbl)))"></a></a></td></tr><tr><td align="right">1.8 </td><td><a href="hangman.html" class="tocviewlink" data-pltdoc="x">Hangman:<span class="mywbr"> </span> <span class="stt">"hangman.rkt"</span><a name="(idx._(gentag._7._(lib._teachpack/teachpack..scrbl)))"></a></a></td></tr><tr><td align="right">1.9 </td><td><a href="hangman-play.html" class="tocviewlink" data-pltdoc="x">Playing Hangman:<span class="mywbr"> </span> <span class="stt">"hangman-<wbr></wbr>play.rkt"</span><a name="(idx._(gentag._8._(lib._teachpack/teachpack..scrbl)))"></a></a></td></tr><tr><td align="right">1.10 </td><td><a href="" class="tocviewselflink" data-pltdoc="x">Managing Control Arrows:<span class="mywbr"> </span> <span class="stt">"arrow.rkt"</span><a name="(idx._(gentag._9._(lib._teachpack/teachpack..scrbl)))"></a></a></td></tr><tr><td align="right">1.11 </td><td><a href="docs.html" class="tocviewlink" data-pltdoc="x">Manipulating Simple HTML Documents:<span class="mywbr"> </span> <span class="stt">"docs.rkt"</span><a name="(idx._(gentag._10._(lib._teachpack/teachpack..scrbl)))"></a></a></td></tr><tr><td align="right">1.12 </td><td><a href="dir.html" class="tocviewlink" data-pltdoc="x">Working with Files and Directories:<span class="mywbr"> </span> <span class="stt">"dir.rkt"</span><a name="(idx._(gentag._11._(lib._teachpack/teachpack..scrbl)))"></a></a></td></tr><tr><td align="right">1.13 </td><td><a href="graphing.html" class="tocviewlink" data-pltdoc="x">Graphing Functions:<span class="mywbr"> </span> <span class="stt">"graphing.rkt"</span><a name="(idx._(gentag._12._(lib._teachpack/teachpack..scrbl)))"></a></a></td></tr><tr><td align="right">1.14 </td><td><a href="gui.html" class="tocviewlink" data-pltdoc="x">Simple Graphical User Interfaces:<span class="mywbr"> </span> <span class="stt">"gui.rkt"</span><a name="(idx._(gentag._13._(lib._teachpack/teachpack..scrbl)))"></a></a></td></tr><tr><td align="right">1.15 </td><td><a href="arrow-gui.html" class="tocviewlink" data-pltdoc="x">An Arrow GUI:<span class="mywbr"> </span> <span class="stt">"arrow-<wbr></wbr>gui.rkt"</span><a name="(idx._(gentag._14._(lib._teachpack/teachpack..scrbl)))"></a></a></td></tr><tr><td align="right">1.16 </td><td><a href="elevator.html" class="tocviewlink" data-pltdoc="x">Controlling an Elevator:<span class="mywbr"> </span> <span class="stt">"elevator.rkt"</span><a name="(idx._(gentag._15._(lib._teachpack/teachpack..scrbl)))"></a></a></td></tr><tr><td align="right">1.17 </td><td><a href="lkup-gui.html" class="tocviewlink" data-pltdoc="x">Lookup GUI:<span class="mywbr"> </span> <span class="stt">"lkup-<wbr></wbr>gui.rkt"</span><a name="(idx._(gentag._16._(lib._teachpack/teachpack..scrbl)))"></a></a></td></tr><tr><td align="right">1.18 </td><td><a href="guess-gui.html" class="tocviewlink" data-pltdoc="x">Guess GUI:<span class="mywbr"> </span> <span class="stt">"guess-<wbr></wbr>gui.rkt"</span><a name="(idx._(gentag._17._(lib._teachpack/teachpack..scrbl)))"></a></a></td></tr><tr><td align="right">1.19 </td><td><a href="show-queen.html" class="tocviewlink" data-pltdoc="x">Queens:<span class="mywbr"> </span> <span class="stt">"show-<wbr></wbr>queen.rkt"</span><a name="(idx._(gentag._18._(lib._teachpack/teachpack..scrbl)))"></a></a></td></tr><tr><td align="right">1.20 </td><td><a href="matrix.html" class="tocviewlink" data-pltdoc="x">Matrix Functions:<span class="mywbr"> </span> <span class="stt">"matrix.rkt"</span><a name="(idx._(gentag._19._(lib._teachpack/teachpack..scrbl)))"></a></a></td></tr></table></div></div></div><div class="tocsub"><div class="tocsubtitle">On this page:</div><table class="tocsublist" cellspacing="0"><tr><td><a href="#%28def._%28%28lib._htdp%2Farrow..rkt%29._control-left-right%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">control-<wbr></wbr>left-<wbr></wbr>right</span></span></a></td></tr><tr><td><a href="#%28def._%28%28lib._htdp%2Farrow..rkt%29._control-up-down%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">control-<wbr></wbr>up-<wbr></wbr>down</span></span></a></td></tr><tr><td><a href="#%28def._%28%28lib._htdp%2Farrow..rkt%29._control%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">control</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, "6.7", "../");" 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("6.7");">top</a></span><span class="navright"> <a href="hangman-play.html" title="backward to "1.9 Playing Hangman: "hangman-play.rkt""" data-pltdoc="x">← prev</a> <a href="htdp.html" title="up to "1 HtDP Teachpacks"" data-pltdoc="x">up</a> <a href="docs.html" title="forward to "1.11 Manipulating Simple HTML Documents: "docs.rkt""" data-pltdoc="x">next →</a></span> </div><h4 x-source-module="(lib "teachpack/teachpack.scrbl")" x-source-pkg="htdp-doc" x-part-tag=""arrow"">1.10<tt> </tt><a name="(part._arrow)"></a><a name="(mod-path._htdp/arrow)"></a>Managing Control Arrows: <span class="stt">"arrow.rkt"</span><a name="(idx._(gentag._9._(lib._teachpack/teachpack..scrbl)))"></a></h4><p><table cellspacing="0" cellpadding="0" class="defmodule"><tr><td align="left"><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/docs/6.7/html/local-redirect/index.html?doc=htdp-langs&rel=beginner.html%23%2528form._%2528%2528lib._lang%252Fhtdp-beginner..rkt%2529._require%2529%2529&version=6.7" class="RktStxLink Sq" data-pltdoc="x">require</a></span><span class="stt"> </span><a href="" class="RktModLink" data-pltdoc="x"><span class="RktSym">htdp/arrow</span></a><span class="RktPn">)</span></td><td align="right"><span class="RpackageSpec"><span class="Smaller"> package:</span> <span class="stt">htdp-lib</span></span></td></tr></table></p><p>The teachpack implements a controller for moving shapes across a canvass.</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>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._htdp/arrow..rkt)._control-left-right))"></a><span title="Provided from: htdp/arrow | Package: htdp-lib"><span class="RktSym"><a href="#%28def._%28%28lib._htdp%2Farrow..rkt%29._control-left-right%29%29" class="RktValDef RktValLink" data-pltdoc="x">control-left-right</a></span></span><span class="hspace"> </span><span class="RktVar">shape</span><span class="hspace"> </span><span class="RktVar">n</span><span class="hspace"> </span><span class="RktVar">move</span><span class="hspace"> </span><span class="RktVar">draw</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="https://download.racket-lang.org/docs/6.7/html/local-redirect/index.html?doc=reference&rel=booleans.html%23%2528def._%2528%2528lib._racket%252Fbool..rkt%2529._true%2529%2529&version=6.7" class="RktValLink Sq" data-pltdoc="x">true</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">shape</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">Shape</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">n</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="https://download.racket-lang.org/docs/6.7/html/local-redirect/index.html?doc=reference&rel=number-types.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._number%7E3f%2529%2529&version=6.7" class="RktValLink Sq" data-pltdoc="x">number?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">move</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/docs/6.7/html/local-redirect/index.html?doc=reference&rel=function-contracts.html%23%2528form._%2528%2528lib._racket%252Fcontract%252Fbase..rkt%2529._-%7E3e%2529%2529&version=6.7" class="RktStxLink Sq" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="hspace"> </span><span class="RktSym"><a href="https://download.racket-lang.org/docs/6.7/html/local-redirect/index.html?doc=reference&rel=number-types.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._number%7E3f%2529%2529&version=6.7" class="RktValLink Sq" data-pltdoc="x">number?</a></span><span class="hspace"> </span><span class="RktSym">Shape</span><span class="hspace"> </span><span class="RktSym">Shape</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">draw</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/docs/6.7/html/local-redirect/index.html?doc=reference&rel=function-contracts.html%23%2528form._%2528%2528lib._racket%252Fcontract%252Fbase..rkt%2529._-%7E3e%2529%2529&version=6.7" class="RktStxLink Sq" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="hspace"> </span><span class="RktSym">Shape</span><span class="hspace"> </span><span class="RktSym"><a href="https://download.racket-lang.org/docs/6.7/html/local-redirect/index.html?doc=reference&rel=booleans.html%23%2528def._%2528%2528lib._racket%252Fbool..rkt%2529._true%2529%2529&version=6.7" class="RktValLink Sq" data-pltdoc="x">true</a></span><span class="RktPn">)</span></td></tr></table></blockquote></div><div class="SIntrapara">Moves shape <span class="RktVar">n</span> pixels left
(negative) or right (positive).</div></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>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._htdp/arrow..rkt)._control-up-down))"></a><span title="Provided from: htdp/arrow | Package: htdp-lib"><span class="RktSym"><a href="#%28def._%28%28lib._htdp%2Farrow..rkt%29._control-up-down%29%29" class="RktValDef RktValLink" data-pltdoc="x">control-up-down</a></span></span><span class="hspace"> </span><span class="RktVar">shape</span><span class="hspace"> </span><span class="RktVar">n</span><span class="hspace"> </span><span class="RktVar">move</span><span class="hspace"> </span><span class="RktVar">draw</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="https://download.racket-lang.org/docs/6.7/html/local-redirect/index.html?doc=reference&rel=booleans.html%23%2528def._%2528%2528lib._racket%252Fbool..rkt%2529._true%2529%2529&version=6.7" class="RktValLink Sq" data-pltdoc="x">true</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">shape</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">Shape</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">n</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="https://download.racket-lang.org/docs/6.7/html/local-redirect/index.html?doc=reference&rel=number-types.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._number%7E3f%2529%2529&version=6.7" class="RktValLink Sq" data-pltdoc="x">number?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">move</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/docs/6.7/html/local-redirect/index.html?doc=reference&rel=function-contracts.html%23%2528form._%2528%2528lib._racket%252Fcontract%252Fbase..rkt%2529._-%7E3e%2529%2529&version=6.7" class="RktStxLink Sq" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="hspace"> </span><span class="RktSym"><a href="https://download.racket-lang.org/docs/6.7/html/local-redirect/index.html?doc=reference&rel=number-types.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._number%7E3f%2529%2529&version=6.7" class="RktValLink Sq" data-pltdoc="x">number?</a></span><span class="hspace"> </span><span class="RktSym">Shape</span><span class="hspace"> </span><span class="RktSym">Shape</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">draw</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/docs/6.7/html/local-redirect/index.html?doc=reference&rel=function-contracts.html%23%2528form._%2528%2528lib._racket%252Fcontract%252Fbase..rkt%2529._-%7E3e%2529%2529&version=6.7" class="RktStxLink Sq" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="hspace"> </span><span class="RktSym">Shape</span><span class="hspace"> </span><span class="RktSym"><a href="https://download.racket-lang.org/docs/6.7/html/local-redirect/index.html?doc=reference&rel=booleans.html%23%2528def._%2528%2528lib._racket%252Fbool..rkt%2529._true%2529%2529&version=6.7" class="RktValLink Sq" data-pltdoc="x">true</a></span><span class="RktPn">)</span></td></tr></table></blockquote></div><div class="SIntrapara">Moves shape <span class="RktVar">n</span> pixels up
(negative) or down (positive).</div></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>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._htdp/arrow..rkt)._control))"></a><span title="Provided from: htdp/arrow | Package: htdp-lib"><span class="RktSym"><a href="#%28def._%28%28lib._htdp%2Farrow..rkt%29._control%29%29" class="RktValDef RktValLink" data-pltdoc="x">control</a></span></span><span class="hspace"> </span><span class="RktVar">shape</span><span class="hspace"> </span><span class="RktVar">n</span><span class="hspace"> </span><span class="RktVar">move-lr</span><span class="hspace"> </span><span class="RktVar">move-ud</span><span class="hspace"> </span><span class="RktVar">draw</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="https://download.racket-lang.org/docs/6.7/html/local-redirect/index.html?doc=reference&rel=booleans.html%23%2528def._%2528%2528lib._racket%252Fbool..rkt%2529._true%2529%2529&version=6.7" class="RktValLink Sq" data-pltdoc="x">true</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">shape</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">Shape</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">n</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="https://download.racket-lang.org/docs/6.7/html/local-redirect/index.html?doc=reference&rel=number-types.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._number%7E3f%2529%2529&version=6.7" class="RktValLink Sq" data-pltdoc="x">number?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">move-lr</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/docs/6.7/html/local-redirect/index.html?doc=reference&rel=function-contracts.html%23%2528form._%2528%2528lib._racket%252Fcontract%252Fbase..rkt%2529._-%7E3e%2529%2529&version=6.7" class="RktStxLink Sq" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="hspace"> </span><span class="RktSym"><a href="https://download.racket-lang.org/docs/6.7/html/local-redirect/index.html?doc=reference&rel=number-types.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._number%7E3f%2529%2529&version=6.7" class="RktValLink Sq" data-pltdoc="x">number?</a></span><span class="hspace"> </span><span class="RktSym">Shape</span><span class="hspace"> </span><span class="RktSym">Shape</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">move-ud</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/docs/6.7/html/local-redirect/index.html?doc=reference&rel=function-contracts.html%23%2528form._%2528%2528lib._racket%252Fcontract%252Fbase..rkt%2529._-%7E3e%2529%2529&version=6.7" class="RktStxLink Sq" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="hspace"> </span><span class="RktSym"><a href="https://download.racket-lang.org/docs/6.7/html/local-redirect/index.html?doc=reference&rel=number-types.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._number%7E3f%2529%2529&version=6.7" class="RktValLink Sq" data-pltdoc="x">number?</a></span><span class="hspace"> </span><span class="RktSym">Shape</span><span class="hspace"> </span><span class="RktSym">Shape</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">draw</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/docs/6.7/html/local-redirect/index.html?doc=reference&rel=function-contracts.html%23%2528form._%2528%2528lib._racket%252Fcontract%252Fbase..rkt%2529._-%7E3e%2529%2529&version=6.7" class="RktStxLink Sq" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="hspace"> </span><span class="RktSym">Shape</span><span class="hspace"> </span><span class="RktSym"><a href="https://download.racket-lang.org/docs/6.7/html/local-redirect/index.html?doc=reference&rel=booleans.html%23%2528def._%2528%2528lib._racket%252Fbool..rkt%2529._true%2529%2529&version=6.7" class="RktValLink Sq" data-pltdoc="x">true</a></span><span class="RktPn">)</span></td></tr></table></blockquote></div><div class="SIntrapara">Moves shape <span class="RktSym">N</span> pixels left or right and up or down, respectively.</div></p><p><div class="SIntrapara">Example:
</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">A shape is a structure:</span></td></tr><tr><td><span class="RktCmt">;</span><span class="RktCmt"> </span><span class="hspace"> </span><span class="RktCmt">(make-posn num num)</span></td></tr><tr><td><span class="hspace"> </span></td></tr><tr><td><span class="RktCmt">;</span><span class="RktCmt"> </span><span class="RktCmt">RAD : the radius of the simple disk moving across a canvas</span></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/docs/6.7/html/local-redirect/index.html?doc=reference&rel=define.html%23%2528form._%2528%2528lib._racket%252Fprivate%252Fbase..rkt%2529._define%2529%2529&version=6.7" class="RktStxLink Sq" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktSym">RAD</span><span class="hspace"> </span><span class="RktVal">10</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">move : number shape -> shape or false</span></td></tr><tr><td><span class="RktCmt">;</span><span class="RktCmt"> </span><span class="RktCmt">to move a shape by delta according to translate</span></td></tr><tr><td><span class="RktCmt">;</span><span class="RktCmt"> </span><span class="RktCmt">effect: to redraw it</span></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/docs/6.7/html/local-redirect/index.html?doc=reference&rel=define.html%23%2528form._%2528%2528lib._racket%252Fprivate%252Fbase..rkt%2529._define%2529%2529&version=6.7" class="RktStxLink Sq" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">move</span><span class="hspace"> </span><span class="RktSym">delta</span><span class="hspace"> </span><span class="RktSym">sh</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/docs/6.7/html/local-redirect/index.html?doc=reference&rel=if.html%23%2528form._%2528%2528lib._racket%252Fprivate%252Fletstx-scheme..rkt%2529._cond%2529%2529&version=6.7" class="RktStxLink Sq" 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="https://download.racket-lang.org/docs/6.7/html/local-redirect/index.html?doc=reference&rel=if.html%23%2528form._%2528%2528lib._racket%252Fprivate%252Fletstx-scheme..rkt%2529._and%2529%2529&version=6.7" class="RktStxLink Sq" data-pltdoc="x">and</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">clear-solid-disk</span><span class="hspace"> </span><span class="RktSym">sh</span><span class="hspace"> </span><span class="RktSym">RAD</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">draw-solid-disk</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">translate</span><span class="hspace"> </span><span class="RktSym">sh</span><span class="hspace"> </span><span class="RktSym">delta</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym">RAD</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">translate</span><span class="hspace"> </span><span class="RktSym">sh</span><span class="hspace"> </span><span class="RktSym">delta</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="https://download.racket-lang.org/docs/6.7/html/local-redirect/index.html?doc=reference&rel=if.html%23%2528form._%2528%2528lib._racket%252Fprivate%252Fletstx-scheme..rkt%2529._else%2529%2529&version=6.7" class="RktStxLink Sq" data-pltdoc="x">else</a></span><span class="hspace"> </span><span class="RktSym"><a href="https://download.racket-lang.org/docs/6.7/html/local-redirect/index.html?doc=reference&rel=booleans.html%23%2528def._%2528%2528lib._racket%252Fbool..rkt%2529._false%2529%2529&version=6.7" class="RktValLink Sq" data-pltdoc="x">false</a></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="RktCmt">;</span><span class="RktCmt"> </span><span class="RktCmt">translate : shape number -> shape</span></td></tr><tr><td><span class="RktCmt">;</span><span class="RktCmt"> </span><span class="RktCmt">to translate a shape by delta in the x direction</span></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/docs/6.7/html/local-redirect/index.html?doc=reference&rel=define.html%23%2528form._%2528%2528lib._racket%252Fprivate%252Fbase..rkt%2529._define%2529%2529&version=6.7" class="RktStxLink Sq" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">translate</span><span class="hspace"> </span><span class="RktSym">sh</span><span class="hspace"> </span><span class="RktSym">delta</span><span class="RktPn">)</span></td></tr><tr><td><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"><a href="https://download.racket-lang.org/docs/6.7/html/local-redirect/index.html?doc=reference&rel=generic-numbers.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._%252B%2529%2529&version=6.7" class="RktValLink Sq" data-pltdoc="x">+</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">posn-x</span><span class="hspace"> </span><span class="RktSym">sh</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym">delta</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">posn-y</span><span class="hspace"> </span><span class="RktSym">sh</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="RktCmt">;</span><span class="RktCmt"> </span><span class="RktCmt">draw-it : shape -> true</span></td></tr><tr><td><span class="RktCmt">;</span><span class="RktCmt"> </span><span class="RktCmt">to draw a shape on the canvas: a disk with radius</span></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/docs/6.7/html/local-redirect/index.html?doc=reference&rel=define.html%23%2528form._%2528%2528lib._racket%252Fprivate%252Fbase..rkt%2529._define%2529%2529&version=6.7" class="RktStxLink Sq" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">draw-it</span><span class="hspace"> </span><span class="RktSym">sh</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">draw-solid-disk</span><span class="hspace"> </span><span class="RktSym">sh</span><span class="hspace"> </span><span class="RktSym">RAD</span><span class="RktPn">)</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">Run:</span></td></tr><tr><td><span class="hspace"> </span></td></tr><tr><td><span class="RktCmt">;</span><span class="RktCmt"> </span><span class="RktCmt">this creates the canvas</span></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym">start</span><span class="hspace"> </span><span class="RktVal">100</span><span class="hspace"> </span><span class="RktVal">50</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">this creates the controller GUI</span></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="#%28def._%28%28lib._htdp%2Farrow..rkt%29._control-left-right%29%29" class="RktValLink" data-pltdoc="x">control-left-right</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">make-posn</span><span class="hspace"> </span><span class="RktVal">10</span><span class="hspace"> </span><span class="RktVal">20</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVal">10</span><span class="hspace"> </span><span class="RktSym">move</span><span class="hspace"> </span><span class="RktSym">draw-it</span><span class="RktPn">)</span></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, "6.7", "../");" 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("6.7");">top</a></span><span class="navright"> <a href="hangman-play.html" title="backward to "1.9 Playing Hangman: "hangman-play.rkt""" data-pltdoc="x">← prev</a> <a 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