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<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"/><title>3 Syntactic Forms</title><link rel="stylesheet" type="text/css" href="../scribble.css" title="default"/><link rel="stylesheet" type="text/css" href="extras.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="../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="../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-weight: bold">The Racket Reference</span></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="model.html" class="tocviewlink" data-pltdoc="x">Language Model</a></td></tr><tr><td align="right">2 </td><td><a href="notation.html" class="tocviewlink" data-pltdoc="x">Notation for Documentation</a></td></tr><tr><td align="right">3 </td><td><a href="" class="tocviewselflink" data-pltdoc="x">Syntactic Forms</a></td></tr><tr><td align="right">4 </td><td><a href="data.html" class="tocviewlink" data-pltdoc="x">Datatypes</a></td></tr><tr><td align="right">5 </td><td><a href="structures.html" class="tocviewlink" data-pltdoc="x">Structures</a></td></tr><tr><td align="right">6 </td><td><a href="mzlib_class.html" class="tocviewlink" data-pltdoc="x">Classes and Objects</a></td></tr><tr><td align="right">7 </td><td><a href="mzlib_unit.html" class="tocviewlink" data-pltdoc="x">Units</a></td></tr><tr><td align="right">8 </td><td><a href="contracts.html" class="tocviewlink" data-pltdoc="x">Contracts</a></td></tr><tr><td align="right">9 </td><td><a href="match.html" class="tocviewlink" data-pltdoc="x">Pattern Matching</a></td></tr><tr><td align="right">10 </td><td><a href="control.html" class="tocviewlink" data-pltdoc="x">Control Flow</a></td></tr><tr><td align="right">11 </td><td><a href="concurrency.html" class="tocviewlink" data-pltdoc="x">Concurrency and Parallelism</a></td></tr><tr><td align="right">12 </td><td><a href="Macros.html" class="tocviewlink" data-pltdoc="x">Macros</a></td></tr><tr><td align="right">13 </td><td><a href="input-and-output.html" class="tocviewlink" data-pltdoc="x">Input and Output</a></td></tr><tr><td align="right">14 </td><td><a href="security.html" class="tocviewlink" data-pltdoc="x">Reflection and Security</a></td></tr><tr><td align="right">15 </td><td><a href="os.html" class="tocviewlink" data-pltdoc="x">Operating System</a></td></tr><tr><td align="right">16 </td><td><a href="memory.html" class="tocviewlink" data-pltdoc="x">Memory Management</a></td></tr><tr><td align="right">17 </td><td><a href="unsafe.html" class="tocviewlink" data-pltdoc="x">Unsafe Operations</a></td></tr><tr><td align="right">18 </td><td><a href="running.html" class="tocviewlink" data-pltdoc="x">Running Racket</a></td></tr><tr><td align="right"></td><td><a href="doc-bibliography.html" class="tocviewlink" data-pltdoc="x">Bibliography</a></td></tr><tr><td align="right"></td><td><a href="doc-index.html" class="tocviewlink" data-pltdoc="x">Index</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>3 </td><td><a href="" class="tocviewselflink" data-pltdoc="x">Syntactic Forms</a></td></tr></table><div class="tocviewsublistbottom" style="display: block;" id="tocview_1"><table cellspacing="0" cellpadding="0"><tr><td align="right">3.1 </td><td><a href="module.html" class="tocviewlink" data-pltdoc="x">Modules:<span class="mywbr"> </span> <span class="RktSym"><span class="RktStxLink">module</span></span>, <span class="RktSym"><span class="RktStxLink">module*</span></span>, ...</a></td></tr><tr><td align="right">3.2 </td><td><a href="require.html" class="tocviewlink" data-pltdoc="x">Importing and Exporting:<span class="mywbr"> </span> <span class="RktSym"><span class="RktStxLink">require</span></span> and <span class="RktSym"><span class="RktStxLink">provide</span></span></a></td></tr><tr><td align="right">3.3 </td><td><a href="quote.html" class="tocviewlink" data-pltdoc="x">Literals:<span class="mywbr"> </span> <span class="RktSym"><span class="RktStxLink">quote</span></span> and <span class="RktSym"><span class="RktStxLink">#%datum</span></span></a></td></tr><tr><td align="right">3.4 </td><td><a href="__expression.html" class="tocviewlink" data-pltdoc="x">Expression Wrapper:<span class="mywbr"> </span> <span class="RktSym"><span class="RktStxLink">#%expression</span></span></a></td></tr><tr><td align="right">3.5 </td><td><a href="__top.html" class="tocviewlink" data-pltdoc="x">Variable References and <span class="RktSym"><span class="RktStxLink">#%top</span></span></a></td></tr><tr><td align="right">3.6 </td><td><a href="Locations____variable-reference.html" class="tocviewlink" data-pltdoc="x">Locations:<span class="mywbr"> </span> <span class="RktSym"><span class="RktStxLink">#%variable-<wbr></wbr>reference</span></span></a></td></tr><tr><td align="right">3.7 </td><td><a href="application.html" class="tocviewlink" data-pltdoc="x">Procedure Applications and <span class="RktSym"><span class="RktStxLink">#%app</span></span></a></td></tr><tr><td align="right">3.8 </td><td><a href="lambda.html" class="tocviewlink" data-pltdoc="x">Procedure Expressions:<span class="mywbr"> </span> <span class="RktSym"><span class="RktStxLink">lambda</span></span> and <span class="RktSym"><span class="RktStxLink">case-<wbr></wbr>lambda</span></span></a></td></tr><tr><td align="right">3.9 </td><td><a href="let.html" class="tocviewlink" data-pltdoc="x">Local Binding:<span class="mywbr"> </span> <span class="RktSym"><span class="RktStxLink">let</span></span>, <span class="RktSym"><span class="RktStxLink">let*</span></span>, <span class="RktSym"><span class="RktStxLink">letrec</span></span>, ...</a></td></tr><tr><td align="right">3.10 </td><td><a href="local.html" class="tocviewlink" data-pltdoc="x">Local Definitions:<span class="mywbr"> </span> <span class="RktSym"><span class="RktStxLink">local</span></span></a></td></tr><tr><td align="right">3.11 </td><td><a href="shared.html" class="tocviewlink" data-pltdoc="x">Constructing Graphs:<span class="mywbr"> </span> <span class="RktSym"><span class="RktStxLink">shared</span></span></a></td></tr><tr><td align="right">3.12 </td><td><a href="if.html" class="tocviewlink" data-pltdoc="x">Conditionals:<span class="mywbr"> </span> <span class="RktSym"><span class="RktStxLink">if</span></span>, <span class="RktSym"><span class="RktStxLink">cond</span></span>, <span class="RktSym"><span class="RktStxLink">and</span></span>, and <span class="RktSym"><span class="RktStxLink">or</span></span></a></td></tr><tr><td align="right">3.13 </td><td><a href="case.html" class="tocviewlink" data-pltdoc="x">Dispatch:<span class="mywbr"> </span> <span class="RktSym"><span class="RktStxLink">case</span></span></a></td></tr><tr><td align="right">3.14 </td><td><a href="define.html" class="tocviewlink" data-pltdoc="x">Definitions:<span class="mywbr"> </span> <span class="RktSym"><span class="RktStxLink">define</span></span>, <span class="RktSym"><span class="RktStxLink">define-<wbr></wbr>syntax</span></span>, ...</a></td></tr><tr><td align="right">3.15 </td><td><a href="begin.html" class="tocviewlink" data-pltdoc="x">Sequencing:<span class="mywbr"> </span> <span class="RktSym"><span class="RktStxLink">begin</span></span>, <span class="RktSym"><span class="RktStxLink">begin0</span></span>, and <span class="RktSym"><span class="RktStxLink">begin-<wbr></wbr>for-<wbr></wbr>syntax</span></span></a></td></tr><tr><td align="right">3.16 </td><td><a href="when_unless.html" class="tocviewlink" data-pltdoc="x">Guarded Evaluation:<span class="mywbr"> </span> <span class="RktSym"><span class="RktStxLink">when</span></span> and <span class="RktSym"><span class="RktStxLink">unless</span></span></a></td></tr><tr><td align="right">3.17 </td><td><a href="set_.html" class="tocviewlink" data-pltdoc="x">Assignment:<span class="mywbr"> </span> <span class="RktSym"><span class="RktStxLink">set!</span></span> and <span class="RktSym"><span class="RktStxLink">set!-<wbr></wbr>values</span></span></a></td></tr><tr><td align="right">3.18 </td><td><a href="for.html" class="tocviewlink" data-pltdoc="x">Iterations and Comprehensions:<span class="mywbr"> </span> <span class="RktSym"><span class="RktStxLink">for</span></span>, <span class="RktSym"><span class="RktStxLink">for/<span class="mywbr"> </span>list</span></span>, ...</a></td></tr><tr><td align="right">3.19 </td><td><a href="wcm.html" class="tocviewlink" data-pltdoc="x">Continuation Marks:<span class="mywbr"> </span> <span class="RktSym"><span class="RktStxLink">with-<wbr></wbr>continuation-<wbr></wbr>mark</span></span></a></td></tr><tr><td align="right">3.20 </td><td><a href="quasiquote.html" class="tocviewlink" data-pltdoc="x">Quasiquoting:<span class="mywbr"> </span> <span class="RktSym"><span class="RktStxLink">quasiquote</span></span>, <span class="RktSym"><span class="RktStxLink">unquote</span></span>, and <span class="RktSym"><span class="RktStxLink">unquote-<wbr></wbr>splicing</span></span></a></td></tr><tr><td align="right">3.21 </td><td><a href="Syntax_Quoting__quote-syntax.html" class="tocviewlink" data-pltdoc="x">Syntax Quoting:<span class="mywbr"> </span> <span class="RktSym"><span class="RktStxLink">quote-<wbr></wbr>syntax</span></span></a></td></tr><tr><td align="right">3.22 </td><td><a href="__top-interaction.html" class="tocviewlink" data-pltdoc="x">Interaction Wrapper:<span class="mywbr"> </span> <span class="RktSym"><span class="RktStxLink">#%top-<wbr></wbr>interaction</span></span></a></td></tr><tr><td align="right">3.23 </td><td><a href="block.html" class="tocviewlink" data-pltdoc="x">Blocks:<span class="mywbr"> </span> <span class="RktSym"><span class="RktStxLink">block</span></span></a></td></tr><tr><td align="right">3.24 </td><td><a href="stratified-body.html" class="tocviewlink" data-pltdoc="x">Internal-<wbr></wbr>Definition Limiting:<span class="mywbr"> </span> <span class="RktSym"><span class="RktStxLink">#%stratified-<wbr></wbr>body</span></span></a></td></tr><tr><td align="right">3.25 </td><td><a href="performance-hint.html" class="tocviewlink" data-pltdoc="x">Performance Hints:<span class="mywbr"> </span> <span class="RktSym"><span class="RktStxLink">begin-<wbr></wbr>encourage-<wbr></wbr>inline</span></span></a></td></tr><tr><td align="right">3.26 </td><td><a href="lazy-require.html" class="tocviewlink" data-pltdoc="x">Importing Modules Lazily:<span class="mywbr"> </span> <span class="RktSym"><span class="RktStxLink">lazy-<wbr></wbr>require</span></span></a></td></tr></table></div></div></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="notation.html" title="backward to "2 Notation for Documentation"" data-pltdoc="x">← prev</a> <a href="index.html" title="up to "The Racket Reference"" data-pltdoc="x">up</a> <a href="module.html" title="forward to "3.1 Modules: module, module*, ..."" data-pltdoc="x">next →</a></span> </div><h3 x-source-module="(lib "scribblings/reference/reference.scrbl")" x-source-pkg="racket-doc" x-part-tag=""syntax"">3<tt> </tt><a name="(part._syntax)"></a>Syntactic Forms</h3><p>This section describes the core syntax forms that appear in a fully
expanded expression, plus many closely related non-core forms.
See <a href="syntax-model.html#%28part._fully-expanded%29" data-pltdoc="x">Fully Expanded Programs</a> for the core grammar.</p><table cellspacing="0" cellpadding="0"><tr><td><p><span class="hspace"> </span><a href="module.html" class="toclink" data-pltdoc="x">3.1<span class="hspace"> </span>Modules: <span class="RktSym"><span class="RktStxLink">module</span></span>, <span class="RktSym"><span class="RktStxLink">module*</span></span>, ...</a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="require.html" class="toclink" data-pltdoc="x">3.2<span class="hspace"> </span>Importing and Exporting: <span class="RktSym"><span class="RktStxLink">require</span></span> and <span class="RktSym"><span class="RktStxLink">provide</span></span></a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="require.html#%28part._.Additional_require_.Forms%29" class="toclink" data-pltdoc="x">3.2.1<span class="hspace"> </span>Additional <span class="RktSym"><span class="RktStxLink">require</span></span> Forms</a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="require.html#%28part._.Additional_provide_.Forms%29" class="toclink" data-pltdoc="x">3.2.2<span class="hspace"> </span>Additional <span class="RktSym"><span class="RktStxLink">provide</span></span> Forms</a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="quote.html" class="toclink" data-pltdoc="x">3.3<span class="hspace"> </span>Literals: <span class="RktSym"><span class="RktStxLink">quote</span></span> and <span class="RktSym"><span class="RktStxLink">#%datum</span></span></a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="__expression.html" class="toclink" data-pltdoc="x">3.4<span class="hspace"> </span>Expression Wrapper: <span class="RktSym"><span class="RktStxLink">#%expression</span></span></a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="__top.html" class="toclink" data-pltdoc="x">3.5<span class="hspace"> </span>Variable References and <span class="RktSym"><span class="RktStxLink">#%top</span></span></a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="Locations____variable-reference.html" class="toclink" data-pltdoc="x">3.6<span class="hspace"> </span>Locations: <span class="RktSym"><span class="RktStxLink">#%variable-reference</span></span></a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="application.html" class="toclink" data-pltdoc="x">3.7<span class="hspace"> </span>Procedure Applications and <span class="RktSym"><span class="RktStxLink">#%app</span></span></a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="lambda.html" class="toclink" data-pltdoc="x">3.8<span class="hspace"> </span>Procedure Expressions: <span class="RktSym"><span class="RktStxLink">lambda</span></span> and <span class="RktSym"><span class="RktStxLink">case-lambda</span></span></a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="let.html" class="toclink" data-pltdoc="x">3.9<span class="hspace"> </span>Local Binding: <span class="RktSym"><span class="RktStxLink">let</span></span>, <span class="RktSym"><span class="RktStxLink">let*</span></span>, <span class="RktSym"><span class="RktStxLink">letrec</span></span>, ...</a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="local.html" class="toclink" data-pltdoc="x">3.10<span class="hspace"> </span>Local Definitions: <span class="RktSym"><span class="RktStxLink">local</span></span></a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="shared.html" class="toclink" data-pltdoc="x">3.11<span class="hspace"> </span>Constructing Graphs: <span class="RktSym"><span class="RktStxLink">shared</span></span></a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="if.html" class="toclink" data-pltdoc="x">3.12<span class="hspace"> </span>Conditionals: <span class="RktSym"><span class="RktStxLink">if</span></span>, <span class="RktSym"><span class="RktStxLink">cond</span></span>, <span class="RktSym"><span class="RktStxLink">and</span></span>, and <span class="RktSym"><span class="RktStxLink">or</span></span></a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="case.html" class="toclink" data-pltdoc="x">3.13<span class="hspace"> </span>Dispatch: <span class="RktSym"><span class="RktStxLink">case</span></span></a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="define.html" class="toclink" data-pltdoc="x">3.14<span class="hspace"> </span>Definitions: <span class="RktSym"><span class="RktStxLink">define</span></span>, <span class="RktSym"><span class="RktStxLink">define-syntax</span></span>, ...</a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="define.html#%28part._require-syntax%29" class="toclink" data-pltdoc="x">3.14.1<span class="hspace"> </span><span class="RktSym"><span class="RktStxLink">require</span></span> Macros</a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="define.html#%28part._provide-syntax%29" class="toclink" data-pltdoc="x">3.14.2<span class="hspace"> </span><span class="RktSym"><span class="RktStxLink">provide</span></span> Macros</a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="begin.html" class="toclink" data-pltdoc="x">3.15<span class="hspace"> </span>Sequencing: <span class="RktSym"><span class="RktStxLink">begin</span></span>, <span class="RktSym"><span class="RktStxLink">begin0</span></span>, and <span class="RktSym"><span class="RktStxLink">begin-for-syntax</span></span></a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="when_unless.html" class="toclink" data-pltdoc="x">3.16<span class="hspace"> </span>Guarded Evaluation: <span class="RktSym"><span class="RktStxLink">when</span></span> and <span class="RktSym"><span class="RktStxLink">unless</span></span></a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="set_.html" class="toclink" data-pltdoc="x">3.17<span class="hspace"> </span>Assignment: <span class="RktSym"><span class="RktStxLink">set!</span></span> and <span class="RktSym"><span class="RktStxLink">set!-values</span></span></a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="for.html" class="toclink" data-pltdoc="x">3.18<span class="hspace"> </span>Iterations and Comprehensions: <span class="RktSym"><span class="RktStxLink">for</span></span>, <span class="RktSym"><span class="RktStxLink">for/list</span></span>, ...</a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="for.html#%28part._.Iteration_and_.Comprehension_.Forms%29" class="toclink" data-pltdoc="x">3.18.1<span class="hspace"> </span>Iteration and Comprehension Forms</a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="for.html#%28part._.Deriving_.New_.Iteration_.Forms%29" class="toclink" data-pltdoc="x">3.18.2<span class="hspace"> </span>Deriving New Iteration Forms</a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="for.html#%28part._.Do_.Loops%29" class="toclink" data-pltdoc="x">3.18.3<span class="hspace"> </span>Do Loops</a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="wcm.html" class="toclink" data-pltdoc="x">3.19<span class="hspace"> </span>Continuation Marks: <span class="RktSym"><span class="RktStxLink">with-continuation-mark</span></span></a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="quasiquote.html" class="toclink" data-pltdoc="x">3.20<span class="hspace"> </span>Quasiquoting: <span class="RktSym"><span class="RktStxLink">quasiquote</span></span>, <span class="RktSym"><span class="RktStxLink">unquote</span></span>, and <span class="RktSym"><span class="RktStxLink">unquote-splicing</span></span></a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="Syntax_Quoting__quote-syntax.html" class="toclink" data-pltdoc="x">3.21<span class="hspace"> </span>Syntax Quoting: <span class="RktSym"><span class="RktStxLink">quote-syntax</span></span></a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="__top-interaction.html" class="toclink" data-pltdoc="x">3.22<span class="hspace"> </span>Interaction Wrapper: <span class="RktSym"><span class="RktStxLink">#%top-interaction</span></span></a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="block.html" class="toclink" data-pltdoc="x">3.23<span class="hspace"> </span>Blocks: <span class="RktSym"><span class="RktStxLink">block</span></span></a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="stratified-body.html" class="toclink" data-pltdoc="x">3.24<span class="hspace"> </span>Internal-Definition Limiting: <span class="RktSym"><span class="RktStxLink">#%stratified-body</span></span></a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="performance-hint.html" class="toclink" data-pltdoc="x">3.25<span class="hspace"> </span>Performance Hints: <span class="RktSym"><span class="RktStxLink">begin-encourage-inline</span></span></a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="lazy-require.html" class="toclink" data-pltdoc="x">3.26<span class="hspace"> </span>Importing Modules Lazily: <span class="RktSym"><span class="RktStxLink">lazy-require</span></span></a></p></td></tr></table><p><span class="SSubSubSubSection">Notation</span></p><p>Each syntactic form is described by a BNF-like notation that describes
a combination of (syntax-wrapped) pairs, symbols, and other data (not
a sequence of characters). These grammatical specifications are shown
as in the following specification of a <span class="RktKw">something</span>
form:</p><blockquote class="leftindent"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><span class="RktPn">(</span><span class="RktKw">something</span><span class="hspace"> </span><span class="RktVar">id</span><span class="hspace"> </span><span class="RktVar">thing-expr</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></td></tr><tr><td><span class="stt"> </span></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="argcontract"><tr><td><span class="hspace"> </span></td><td><span class="RktVar">thing-expr</span></td><td><span class="hspace"> </span></td><td>:</td><td><span class="hspace"> </span></td><td><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._number~3f%29%29" class="RktValLink" data-pltdoc="x">number?</a></span></td></tr></table></td></tr></table></blockquote></blockquote><p>Within such specifications,</p><ul><li><p><span class="RktSym"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span> indicates zero or more repetitions of the
preceding datum; more generally, <span style="font-style: italic">N</span> consecutive
<span class="RktSym"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span>s a row indicate a consecutive repetition of the
preceding <span style="font-style: italic">N</span> datums.</p></li><li><p><span class="RktSym"><a href="https://download.racket-lang.org/docs/6.7/html/local-redirect/index.html?doc=syntax&rel=stxparse-patterns.html%23%2528form._%2528%2528lib._syntax%252Fparse..rkt%2529._......%252B%2529%2529&version=6.7" class="RktStxLink Sq" data-pltdoc="x">...+</a></span> indicates one or more repetitions of the
preceding datum.</p></li><li><p>Italic meta-identifiers play the role of non-terminals. Some
meta-identifier names imply syntactic constraints:</p><ul><li><p>A meta-identifier that ends in <span class="RktVar">id</span> stands for an
identifier.</p></li><li><p>A meta-identifier that ends in <span class="RktVar">keyword</span> stands
for a keyword.</p></li><li><p>A meta-identifier that ends with <span class="RktVar">expr</span> (such as
<span class="RktVar">thing-expr</span>) stands for a sub-form that is
expanded as an expression.</p></li><li><p>A meta-identifier that ends with <span class="RktVar">body</span> stands
for a sub-form that is expanded in an
internal-definition context (see
<a href="syntax-model.html#%28part._intdef-body%29" data-pltdoc="x">Internal Definitions</a>).</p></li></ul></li><li><p>Contracts indicate constraints on sub-expression results. For
example, <span class="RktVar">thing-expr</span><span class="stt"> </span>:<span class="stt"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._number~3f%29%29" class="RktValLink" data-pltdoc="x">number?</a></span> indicates that
the expression <span class="RktVar">thing-expr</span> must produce a number.</p></li></ul><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="notation.html" title="backward to "2 Notation for Documentation"" data-pltdoc="x">← prev</a> <a href="index.html" title="up to "The Racket Reference"" data-pltdoc="x">up</a> <a href="module.html" title="forward to "3.1 Modules: module, module*, ..."" data-pltdoc="x">next →</a></span> </div></div></div><div id="contextindicator"> </div></body></html>
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