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<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"/><meta name="viewport" content="width=device-width, initial-scale=0.8"/><title>4 Expressions and Definitions</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="../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">The Racket Guide</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="intro.html" class="tocviewlink" data-pltdoc="x">Welcome to Racket</a></td></tr><tr><td align="right">2 </td><td><a href="to-scheme.html" class="tocviewlink" data-pltdoc="x">Racket Essentials</a></td></tr><tr><td align="right">3 </td><td><a href="datatypes.html" class="tocviewlink" data-pltdoc="x">Built-<wbr></wbr>In Datatypes</a></td></tr><tr><td align="right">4 </td><td><a href="scheme-forms.html" class="tocviewselflink" data-pltdoc="x">Expressions and Definitions</a></td></tr><tr><td align="right">5 </td><td><a href="define-struct.html" class="tocviewlink" data-pltdoc="x">Programmer-<wbr></wbr>Defined Datatypes</a></td></tr><tr><td align="right">6 </td><td><a href="modules.html" class="tocviewlink" data-pltdoc="x">Modules</a></td></tr><tr><td align="right">7 </td><td><a href="contracts.html" class="tocviewlink" data-pltdoc="x">Contracts</a></td></tr><tr><td align="right">8 </td><td><a href="i_o.html" class="tocviewlink" data-pltdoc="x">Input and Output</a></td></tr><tr><td align="right">9 </td><td><a href="regexp.html" class="tocviewlink" data-pltdoc="x">Regular Expressions</a></td></tr><tr><td align="right">10 </td><td><a href="control.html" class="tocviewlink" data-pltdoc="x">Exceptions and Control</a></td></tr><tr><td align="right">11 </td><td><a href="for.html" class="tocviewlink" data-pltdoc="x">Iterations and Comprehensions</a></td></tr><tr><td align="right">12 </td><td><a href="match.html" class="tocviewlink" data-pltdoc="x">Pattern Matching</a></td></tr><tr><td align="right">13 </td><td><a href="classes.html" class="tocviewlink" data-pltdoc="x">Classes and Objects</a></td></tr><tr><td align="right">14 </td><td><a href="units.html" class="tocviewlink" data-pltdoc="x">Units</a></td></tr><tr><td align="right">15 </td><td><a href="reflection.html" class="tocviewlink" data-pltdoc="x">Reflection and Dynamic Evaluation</a></td></tr><tr><td align="right">16 </td><td><a href="macros.html" class="tocviewlink" data-pltdoc="x">Macros</a></td></tr><tr><td align="right">17 </td><td><a href="languages.html" class="tocviewlink" data-pltdoc="x">Creating Languages</a></td></tr><tr><td align="right">18 </td><td><a 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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>4 </td><td><a href="scheme-forms.html" class="tocviewselflink" data-pltdoc="x">Expressions and Definitions</a></td></tr></table><div class="tocviewsublistbottom" style="display: block;" id="tocview_1"><table cellspacing="0" cellpadding="0"><tr><td align="right">4.1 </td><td><a href="syntax-notation.html" class="tocviewlink" data-pltdoc="x">Notation</a></td></tr><tr><td align="right">4.2 </td><td><a href="binding.html" class="tocviewlink" data-pltdoc="x">Identifiers and Binding</a></td></tr><tr><td align="right">4.3 </td><td><a href="application.html" class="tocviewlink" data-pltdoc="x">Function Calls</a></td></tr><tr><td align="right">4.4 </td><td><a href="lambda.html" class="tocviewlink" data-pltdoc="x">Functions:<span class="mywbr"> </span> <span class="RktSym"><span class="RktStxLink">lambda</span></span></a></td></tr><tr><td align="right">4.5 </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></a></td></tr><tr><td align="right">4.6 </td><td><a href="let.html" class="tocviewlink" data-pltdoc="x">Local Binding</a></td></tr><tr><td align="right">4.7 </td><td><a href="conditionals.html" class="tocviewlink" data-pltdoc="x">Conditionals</a></td></tr><tr><td align="right">4.8 </td><td><a href="begin.html" class="tocviewlink" data-pltdoc="x">Sequencing</a></td></tr><tr><td align="right">4.9 </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></a></td></tr><tr><td align="right">4.10 </td><td><a href="quote.html" class="tocviewlink" data-pltdoc="x">Quoting:<span class="mywbr"> </span> <span class="RktSym"><span class="RktStxLink">quote</span></span> and <span class="RktVal">’</span></a></td></tr><tr><td align="right">4.11 </td><td><a href="qq.html" class="tocviewlink" data-pltdoc="x">Quasiquoting:<span class="mywbr"> </span> <span class="RktSym"><span class="RktStxLink">quasiquote</span></span> and <span class="RktVal">‘</span></a></td></tr><tr><td align="right">4.12 </td><td><a href="case.html" class="tocviewlink" data-pltdoc="x">Simple Dispatch:<span class="mywbr"> </span> <span class="RktSym"><span class="RktStxLink">case</span></span></a></td></tr><tr><td align="right">4.13 </td><td><a href="parameterize.html" class="tocviewlink" data-pltdoc="x">Dynamic Binding:<span class="mywbr"> </span> <span class="RktSym"><span class="RktStxLink">parameterize</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" id="searchbox" type="text" tabindex="1" placeholder="...search manuals..." title="Enter a search string to search the manuals" onkeypress="return DoSearchKey(event, this, "8.6", "../");"/></form> <a href="https://docs.racket-lang.org/index.html" title="up to the documentation top" data-pltdoc="x" onclick="return GotoPLTRoot("8.6");">top</a><span class="tocsettoggle"> <a href="javascript:void(0);" title="show/hide table of contents" onclick="TocsetToggle();">contents</a></span></span><span class="navright"> <a href="void_undefined.html" title="backward to "3.12 Void and Undefined"" data-pltdoc="x">← prev</a> <a href="index.html" title="up to "The Racket Guide"" data-pltdoc="x">up</a> <a href="syntax-notation.html" title="forward to "4.1 Notation"" data-pltdoc="x">next →</a></span> </div><h3 x-source-module="(lib "scribblings/guide/guide.scrbl")" x-source-pkg="racket-doc" x-part-tag=""scheme-forms"">4<tt> </tt><a name="(part._scheme-forms)"></a>Expressions and Definitions</h3><p>The <a href="to-scheme.html" data-pltdoc="x">Racket Essentials</a> chapter introduced some of Racket’s syntactic
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forms: definitions, procedure applications, conditionals, and so
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on. This section provides more details on those forms, plus a few
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additional basic forms.</p><table cellspacing="0" cellpadding="0"><tr><td><p><span class="hspace"> </span><a href="syntax-notation.html" class="toclink" data-pltdoc="x">4.1<span class="hspace"> </span>Notation</a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="binding.html" class="toclink" data-pltdoc="x">4.2<span class="hspace"> </span>Identifiers and Binding</a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="application.html" class="toclink" data-pltdoc="x">4.3<span class="hspace"> </span>Function Calls (Procedure Applications)</a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="application.html#%28part._.Evaluation_.Order_and_.Arity%29" class="toclink" data-pltdoc="x">4.3.1<span class="hspace"> </span>Evaluation Order and Arity</a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="application.html#%28part._keyword-args%29" class="toclink" data-pltdoc="x">4.3.2<span class="hspace"> </span>Keyword Arguments</a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="application.html#%28part._apply%29" class="toclink" data-pltdoc="x">4.3.3<span class="hspace"> </span>The <span class="RktSym"><span class="RktValLink">apply</span></span> Function</a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="lambda.html" class="toclink" data-pltdoc="x">4.4<span class="hspace"> </span>Functions (Procedures): <span class="RktSym"><span class="RktStxLink">lambda</span></span></a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="lambda.html#%28part._rest-args%29" class="toclink" data-pltdoc="x">4.4.1<span class="hspace"> </span>Declaring a Rest Argument</a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="lambda.html#%28part._.Declaring_.Optional_.Arguments%29" class="toclink" data-pltdoc="x">4.4.2<span class="hspace"> </span>Declaring Optional Arguments</a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="lambda.html#%28part._lambda-keywords%29" class="toclink" data-pltdoc="x">4.4.3<span class="hspace"> </span>Declaring Keyword Arguments</a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="lambda.html#%28part._case-lambda%29" class="toclink" data-pltdoc="x">4.4.4<span class="hspace"> </span>Arity-Sensitive Functions: <span class="RktSym"><span class="RktStxLink">case-lambda</span></span></a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="define.html" class="toclink" data-pltdoc="x">4.5<span class="hspace"> </span>Definitions: <span class="RktSym"><span class="RktStxLink">define</span></span></a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="define.html#%28part._.Function_.Shorthand%29" class="toclink" data-pltdoc="x">4.5.1<span class="hspace"> </span>Function Shorthand</a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="define.html#%28part._.Curried_.Function_.Shorthand%29" class="toclink" data-pltdoc="x">4.5.2<span class="hspace"> </span>Curried Function Shorthand</a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="define.html#%28part._multiple-values%29" class="toclink" data-pltdoc="x">4.5.3<span class="hspace"> </span>Multiple Values and <span class="RktSym"><span class="RktStxLink">define-values</span></span></a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="define.html#%28part._intdefs%29" class="toclink" data-pltdoc="x">4.5.4<span class="hspace"> </span>Internal Definitions</a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="let.html" class="toclink" data-pltdoc="x">4.6<span class="hspace"> </span>Local Binding</a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="let.html#%28part._.Parallel_.Binding__let%29" class="toclink" data-pltdoc="x">4.6.1<span class="hspace"> </span>Parallel Binding: <span class="RktSym"><span class="RktStxLink">let</span></span></a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="let.html#%28part._.Sequential_.Binding__let_%29" class="toclink" data-pltdoc="x">4.6.2<span class="hspace"> </span>Sequential Binding: <span class="RktSym"><span class="RktStxLink">let*</span></span></a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="let.html#%28part._.Recursive_.Binding__letrec%29" class="toclink" data-pltdoc="x">4.6.3<span class="hspace"> </span>Recursive Binding: <span class="RktSym"><span class="RktStxLink">letrec</span></span></a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="let.html#%28part._.Named_let%29" class="toclink" data-pltdoc="x">4.6.4<span class="hspace"> </span>Named <span class="RktSym"><span class="RktStxLink">let</span></span></a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="let.html#%28part._.Multiple_.Values__let-values__let_-values__letrec-values%29" class="toclink" data-pltdoc="x">4.6.5<span class="hspace"> </span>Multiple Values: <span class="RktSym"><span class="RktStxLink">let-values</span></span>, <span class="RktSym"><span class="RktStxLink">let*-values</span></span>, <span class="RktSym"><span class="RktStxLink">letrec-values</span></span></a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="conditionals.html" class="toclink" data-pltdoc="x">4.7<span class="hspace"> </span>Conditionals</a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="conditionals.html#%28part._.Simple_.Branching__if%29" class="toclink" data-pltdoc="x">4.7.1<span class="hspace"> </span>Simple Branching: <span class="RktSym"><span class="RktStxLink">if</span></span></a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="conditionals.html#%28part._and%2Bor%29" class="toclink" data-pltdoc="x">4.7.2<span class="hspace"> </span>Combining Tests: <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="conditionals.html#%28part._cond%29" class="toclink" data-pltdoc="x">4.7.3<span class="hspace"> </span>Chaining Tests: <span class="RktSym"><span class="RktStxLink">cond</span></span></a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="begin.html" class="toclink" data-pltdoc="x">4.8<span class="hspace"> </span>Sequencing</a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="begin.html#%28part._.Effects_.Before__begin%29" class="toclink" data-pltdoc="x">4.8.1<span class="hspace"> </span>Effects Before: <span class="RktSym"><span class="RktStxLink">begin</span></span></a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="begin.html#%28part._.Effects_.After__begin0%29" class="toclink" data-pltdoc="x">4.8.2<span class="hspace"> </span>Effects After: <span class="RktSym"><span class="RktStxLink">begin0</span></span></a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="begin.html#%28part._when%2Bunless%29" class="toclink" data-pltdoc="x">4.8.3<span class="hspace"> </span>Effects If...: <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">4.9<span class="hspace"> </span>Assignment: <span class="RktSym"><span class="RktStxLink">set!</span></span></a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="set_.html#%28part._using-set%21%29" class="toclink" data-pltdoc="x">4.9.1<span class="hspace"> </span>Guidelines for Using Assignment</a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="set_.html#%28part._.Multiple_.Values__set_-values%29" class="toclink" data-pltdoc="x">4.9.2<span class="hspace"> </span>Multiple Values: <span class="RktSym"><span class="RktStxLink">set!-values</span></span></a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="quote.html" class="toclink" data-pltdoc="x">4.10<span class="hspace"> </span>Quoting: <span class="RktSym"><span class="RktStxLink">quote</span></span> and <span class="RktVal">’</span></a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="qq.html" class="toclink" data-pltdoc="x">4.11<span class="hspace"> </span>Quasiquoting: <span class="RktSym"><span class="RktStxLink">quasiquote</span></span> and <span class="RktVal">‘</span></a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="case.html" class="toclink" data-pltdoc="x">4.12<span class="hspace"> </span>Simple Dispatch: <span class="RktSym"><span class="RktStxLink">case</span></span></a></p></td></tr><tr><td><p><span class="hspace"> </span><a href="parameterize.html" class="toclink" data-pltdoc="x">4.13<span class="hspace"> </span>Dynamic Binding: <span class="RktSym"><span class="RktStxLink">parameterize</span></span></a></p></td></tr></table><div class="navsetbottom"><span class="navleft"><form class="searchform"><input 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