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<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"/><title>9 Pattern Matching</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="icons.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: block;" 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="syntax.html" class="tocviewlink" 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="" class="tocviewselflink" 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>9 </td><td><a href="" class="tocviewselflink" data-pltdoc="x">Pattern Matching</a></td></tr></table><div class="tocviewsublistbottom" style="display: none;" id="tocview_1"><table cellspacing="0" cellpadding="0"><tr><td align="right">9.1 </td><td><a href="#%28part._.Additional_.Matching_.Forms%29" class="tocviewlink" data-pltdoc="x">Additional Matching Forms</a></td></tr><tr><td align="right">9.2 </td><td><a href="#%28part._.Extending_match%29" class="tocviewlink" data-pltdoc="x">Extending <span class="RktSym"><span class="RktStxLink">match</span></span></a></td></tr><tr><td align="right">9.3 </td><td><a href="#%28part._.Library_.Extensions%29" class="tocviewlink" data-pltdoc="x">Library Extensions</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="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">match</span></span></a></td></tr><tr><td><span class="tocsublinknumber">9.1<tt> </tt></span><a href="#%28part._.Additional_.Matching_.Forms%29" class="tocsubseclink" data-pltdoc="x">Additional Matching Forms</a></td></tr><tr><td><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%2A%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">match*</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%2Fvalues%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">match/<span class="mywbr"> </span>values</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._define%2Fmatch%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">define/<span class="mywbr"> </span>match</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match-lambda%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">match-<wbr></wbr>lambda</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match-lambda%2A%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">match-<wbr></wbr>lambda*</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match-lambda%2A%2A%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">match-<wbr></wbr>lambda**</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match-let%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">match-<wbr></wbr>let</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match-let%2A%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">match-<wbr></wbr>let*</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match-let-values%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">match-<wbr></wbr>let-<wbr></wbr>values</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match-let%2A-values%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">match-<wbr></wbr>let*-<wbr></wbr>values</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match-letrec%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">match-<wbr></wbr>letrec</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match-letrec-values%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">match-<wbr></wbr>letrec-<wbr></wbr>values</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match-define%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">match-<wbr></wbr>define</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match-define-values%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">match-<wbr></wbr>define-<wbr></wbr>values</span></span></a></td></tr><tr><td><a href="#%28def._%28%28lib._racket%2Fmatch..rkt%29._exn~3amisc~3amatch~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">exn:<span class="mywbr"> </span>misc:<span class="mywbr"> </span>match?</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._failure-cont%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">failure-<wbr></wbr>cont</span></span></a></td></tr><tr><td><span class="tocsublinknumber">9.2<tt> </tt></span><a href="#%28part._.Extending_match%29" class="tocsubseclink" data-pltdoc="x">Extending <span class="RktSym"><span class="RktStxLink">match</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._define-match-expander%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">define-<wbr></wbr>match-<wbr></wbr>expander</span></span></a></td></tr><tr><td><a href="#%28def._%28%28lib._racket%2Fmatch..rkt%29._prop~3amatch-expander%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">prop:<span class="mywbr"> </span>match-<wbr></wbr>expander</span></span></a></td></tr><tr><td><a href="#%28def._%28%28lib._racket%2Fmatch..rkt%29._prop~3alegacy-match-expander%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">prop:<span class="mywbr"> </span>legacy-<wbr></wbr>match-<wbr></wbr>expander</span></span></a></td></tr><tr><td><a href="#%28def._%28%28lib._racket%2Fmatch..rkt%29._match-expander~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">match-<wbr></wbr>expander?</span></span></a></td></tr><tr><td><a href="#%28def._%28%28lib._racket%2Fmatch..rkt%29._legacy-match-expander~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">legacy-<wbr></wbr>match-<wbr></wbr>expander?</span></span></a></td></tr><tr><td><a href="#%28def._%28%28lib._racket%2Fmatch..rkt%29._syntax-local-match-introduce%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">syntax-<wbr></wbr>local-<wbr></wbr>match-<wbr></wbr>introduce</span></span></a></td></tr><tr><td><a href="#%28def._%28%28lib._racket%2Fmatch..rkt%29._match-equality-test%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">match-<wbr></wbr>equality-<wbr></wbr>test</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%2Fderived%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">match/<span class="mywbr"> </span>derived</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%2A%2Fderived%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">match*/<span class="mywbr"> </span>derived</span></span></a></td></tr><tr><td><span class="tocsublinknumber">9.3<tt> </tt></span><a href="#%28part._.Library_.Extensions%29" class="tocsubseclink" data-pltdoc="x">Library Extensions</a></td></tr><tr><td><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._~3d~3d%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._racket%2Fmatch..rkt%29._struct%2A%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">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, "6.7", "../");" 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="Random_generation.html" title="backward to "8.11 Random generation"" data-pltdoc="x">← prev</a> <a href="index.html" title="up to "The Racket Reference"" data-pltdoc="x">up</a> <a href="control.html" title="forward to "10 Control Flow"" data-pltdoc="x">next →</a></span> </div><h3 x-source-module="(lib "scribblings/reference/reference.scrbl")" x-source-pkg="racket-doc" x-part-tag=""match"">9<tt> </tt><a name="(part._match)"></a><a name="(mod-path._racket/match)"></a>Pattern Matching</h3><blockquote class="refpara"><blockquote class="refcolumn"><blockquote class="refcontent"><p><span class="imageleft"><img src="finger.png" alt="+" width="24" height="24"/></span><a href="https://download.racket-lang.org/docs/6.7/html/local-redirect/index.html?doc=guide&rel=match.html&version=6.7" class="Sq" data-pltdoc="x">Pattern Matching</a> in <a href="https://download.racket-lang.org/docs/6.7/html/local-redirect/index.html?doc=guide&rel=index.html&version=6.7" class="Sq" data-pltdoc="x"><span style="font-weight: bold">The Racket Guide</span></a> introduces pattern matching.</p></blockquote></blockquote></blockquote><p>The <span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span> form and related forms support general pattern
matching on Racket values. See also <a href="regexp.html" data-pltdoc="x">Regular Expressions</a> for information
on regular-expression matching on strings, bytes, and streams.</p><p><div class="SIntrapara"><table cellspacing="0" cellpadding="0" class="defmodule"><tr><td align="left"><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="require.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._require%29%29" class="RktStxLink" data-pltdoc="x">require</a></span><span class="stt"> </span><a href="" class="RktModLink" data-pltdoc="x"><span class="RktSym">racket/match</span></a><span class="RktPn">)</span></td><td align="right"><span class="RpackageSpec"><span class="Smaller"> package:</span> <span class="stt">base</span></span></td></tr></table></div><div class="SIntrapara">The bindings documented in this section are provided by the <a href="" class="RktModLink" data-pltdoc="x"><span class="RktSym">racket/match</span></a> and <a href="index.html" class="RktModLink" data-pltdoc="x"><span class="RktSym">racket</span></a> libraries, but not <a href="index.html" class="RktModLink" data-pltdoc="x"><span class="RktSym">racket/base</span></a>.</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>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/match..rkt)._match))"></a><span title="Provided from: racket/match, racket | Package: base"><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">match</a></span></span><span class="hspace"> </span><span class="RktVar">val-expr</span><span class="hspace"> </span><span class="RktVar">clause</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr><tr><td><span class="stt"> </span></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="specgrammar"><tr><td align="right" valign="baseline"><span class="RktVar">clause</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">pat</span><span class="hspace"> </span><span class="RktVar">body</span><span class="hspace"> </span><span class="RktMeta">...+</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">pat</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktVar">=></span><span class="hspace"> </span><span class="RktVar">id</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVar">body</span><span class="hspace"> </span><span class="RktMeta">...+</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">pat</span><span class="hspace"> </span><span class="RktPn">#:when</span><span class="hspace"> </span><span class="RktVar">cond-expr</span><span class="hspace"> </span><span class="RktVar">body</span><span class="hspace"> </span><span class="RktMeta">...+</span><span class="RktPn">]</span></td></tr></table></td></tr></table></blockquote></div><div class="SIntrapara">Finds the first <span class="RktVar">pat</span> that matches the result of
<span class="RktVar">val-expr</span>, and evaluates the corresponding <span class="RktVar">body</span>s with
bindings introduced by <span class="RktVar">pat</span> (if any). Bindings introduced by
<span class="RktVar">pat</span> are not available in other parts of <span class="RktVar">pat</span>.
The last <span class="RktVar">body</span>
in the matching clause is evaluated in tail position with respect to
the <span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span> expression.</div></p><p>To find a match, the <span class="RktVar">clause</span>s are tried in order. If no
<span class="RktVar">clause</span> matches, then the <span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fmatch..rkt%29._exn~3amisc~3amatch~3f%29%29" class="RktValLink" data-pltdoc="x">exn:misc:match?</a></span> exception is raised.</p><p>An optional <span class="RktPn">#:when</span><span class="stt"> </span><span class="RktVar">cond-expr</span> specifies that the pattern
should only match if <span class="RktVar">cond-expr</span> produces a true value.
<span class="RktVar">cond-expr</span> is in the scope of all of the variables bound in
<span class="RktVar">pat</span>. <span class="RktVar">cond-expr</span> must not mutate the object being
matched before calling the failure procedure, otherwise the behavior
of matching is unpredictable. See also <span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._failure-cont%29%29" class="RktStxLink" data-pltdoc="x">failure-cont</a></span>, which is
a lower-level mechanism achieving the same ends.</p><p>An optional <span class="RktPn">(</span><span class="RktVar">=></span><span class="stt"> </span><span class="RktVar">id</span><span class="RktPn">)</span> between a <span class="RktVar">pat</span> and the
<span class="RktVar">body</span>s is bound to a <span style="font-style: italic">failure procedure</span> of zero
arguments. If this procedure is invoked, it escapes back to the
pattern matching expression, and resumes the matching process as if
the pattern had failed to match. The <span class="RktVar">body</span>s must not mutate
the object being matched before calling the failure procedure,
otherwise the behavior of matching is unpredictable.</p><p>The grammar of <span class="RktVar">pat</span> is as follows, where non-italicized
identifiers are recognized symbolically (i.e., not by binding).</p><p><table cellspacing="0" cellpadding="0"><tr><td><p><span class="RktVar">pat</span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="stt">::=</span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktVar">id</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match anything, bind identifier</p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktPn">(</span><span class="RktSym">var</span><span class="stt"> </span><span class="RktVar">id</span><span class="RktPn">)</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match anything, bind identifier</p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktSym">_</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match anything</p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktVar">literal</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match literal</p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktPn">(</span><span class="RktSym">quote</span><span class="stt"> </span><span class="RktVar">datum</span><span class="RktPn">)</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match <span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._equal~3f%29%29" class="RktValLink" data-pltdoc="x">equal?</a></span> value</p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktPn">(</span><span class="RktSym">list</span><span class="stt"> </span><span class="RktVar">lvp</span><span class="stt"> </span><span class="RktSym">...</span><span class="RktPn">)</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match sequence of <span class="RktVar">lvp</span>s</p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktPn">(</span><span class="RktSym">list-rest</span><span class="stt"> </span><span class="RktVar">lvp</span><span class="stt"> </span><span class="RktSym">...</span><span class="stt"> </span><span class="RktVar">pat</span><span class="RktPn">)</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match <span class="RktVar">lvp</span>s consed onto a <span class="RktVar">pat</span></p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktPn">(</span><span class="RktSym">list-no-order</span><span class="stt"> </span><span class="RktVar">pat</span><span class="stt"> </span><span class="RktSym">...</span><span class="RktPn">)</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match <span class="RktVar">pat</span>s in any order</p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktPn">(</span><span class="RktSym">list-no-order</span><span class="stt"> </span><span class="RktVar">pat</span><span class="stt"> </span><span class="RktSym">...</span><span class="stt"> </span><span class="RktVar">lvp</span><span class="RktPn">)</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match <span class="RktVar">pat</span>s in any order</p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktPn">(</span><span class="RktSym">vector</span><span class="stt"> </span><span class="RktVar">lvp</span><span class="stt"> </span><span class="RktSym">...</span><span class="RktPn">)</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match vector of <span class="RktVar">pat</span>s</p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktPn">(</span><span class="RktSym">hash-table</span><span class="stt"> </span><span class="RktPn">(</span><span class="RktVar">pat</span><span class="stt"> </span><span class="RktVar">pat</span><span class="RktPn">)</span><span class="stt"> </span><span class="RktSym">...</span><span class="RktPn">)</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match hash table</p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktPn">(</span><span class="RktSym">hash-table</span><span class="stt"> </span><span class="RktPn">(</span><span class="RktVar">pat</span><span class="stt"> </span><span class="RktVar">pat</span><span class="RktPn">)</span><span class="stt"> </span><span class="RktSym">...+</span><span class="stt"> </span><span class="RktVar">ooo</span><span class="RktPn">)</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match hash table</p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktPn">(</span><span class="RktSym">cons</span><span class="stt"> </span><span class="RktVar">pat</span><span class="stt"> </span><span class="RktVar">pat</span><span class="RktPn">)</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match pair of <span class="RktVar">pat</span>s</p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktPn">(</span><span class="RktSym">mcons</span><span class="stt"> </span><span class="RktVar">pat</span><span class="stt"> </span><span class="RktVar">pat</span><span class="RktPn">)</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match mutable pair of <span class="RktVar">pat</span>s</p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktPn">(</span><span class="RktSym">box</span><span class="stt"> </span><span class="RktVar">pat</span><span class="RktPn">)</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match boxed <span class="RktVar">pat</span></p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktPn">(</span><span class="RktVar">struct-id</span><span class="stt"> </span><span class="RktVar">pat</span><span class="stt"> </span><span class="RktSym">...</span><span class="RktPn">)</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match <span class="RktVar">struct-id</span> instance</p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktPn">(</span><span class="RktSym">struct</span><span class="stt"> </span><span class="RktVar">struct-id</span><span class="stt"> </span><span class="RktPn">(</span><span class="RktVar">pat</span><span class="stt"> </span><span class="RktSym">...</span><span class="RktPn">)</span><span class="RktPn">)</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match <span class="RktVar">struct-id</span> instance</p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktPn">(</span><span class="RktSym">regexp</span><span class="stt"> </span><span class="RktVar">rx-expr</span><span class="RktPn">)</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match string</p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktPn">(</span><span class="RktSym">regexp</span><span class="stt"> </span><span class="RktVar">rx-expr</span><span class="stt"> </span><span class="RktVar">pat</span><span class="RktPn">)</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match string, result with <span class="RktVar">pat</span></p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktPn">(</span><span class="RktSym">pregexp</span><span class="stt"> </span><span class="RktVar">px-expr</span><span class="RktPn">)</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match string</p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktPn">(</span><span class="RktSym">pregexp</span><span class="stt"> </span><span class="RktVar">px-expr</span><span class="stt"> </span><span class="RktVar">pat</span><span class="RktPn">)</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match string, result with <span class="RktVar">pat</span></p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktPn">(</span><span class="RktSym">and</span><span class="stt"> </span><span class="RktVar">pat</span><span class="stt"> </span><span class="RktSym">...</span><span class="RktPn">)</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match when all <span class="RktVar">pat</span>s match</p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktPn">(</span><span class="RktSym">or</span><span class="stt"> </span><span class="RktVar">pat</span><span class="stt"> </span><span class="RktSym">...</span><span class="RktPn">)</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match when any <span class="RktVar">pat</span> match</p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktPn">(</span><span class="RktSym">not</span><span class="stt"> </span><span class="RktVar">pat</span><span class="stt"> </span><span class="RktSym">...</span><span class="RktPn">)</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match when no <span class="RktVar">pat</span> matches</p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktPn">(</span><span class="RktSym">app</span><span class="stt"> </span><span class="RktVar">expr</span><span class="stt"> </span><span class="RktSym">pats</span><span class="stt"> </span><span class="RktSym">...</span><span class="RktPn">)</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match <span class="RktPn">(</span><span class="RktVar">expr</span> value<span class="RktPn">)</span> output values to <span class="RktVar">pat</span>s</p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktPn">(</span><span class="RktSym">?</span><span class="stt"> </span><span class="RktVar">expr</span><span class="stt"> </span><span class="RktVar">pat</span><span class="stt"> </span><span class="RktSym">...</span><span class="RktPn">)</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match if <span class="RktPn">(</span><span class="RktVar">expr</span> value<span class="RktPn">)</span> and <span class="RktVar">pat</span>s</p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktPn">(</span><span class="RktSym">quasiquote</span><span class="stt"> </span><span class="RktVar">qp</span><span class="RktPn">)</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match a quasipattern</p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktVar">derived-pattern</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match using extension</p></td></tr><tr><td><p><span class="RktVar">literal</span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="stt">::=</span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktVal">#t</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match true</p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktVal">#f</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match false</p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktVar">string</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match <span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._equal~3f%29%29" class="RktValLink" data-pltdoc="x">equal?</a></span> string</p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktVar">bytes</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match <span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._equal~3f%29%29" class="RktValLink" data-pltdoc="x">equal?</a></span> byte string</p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktVar">number</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match <span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._equal~3f%29%29" class="RktValLink" data-pltdoc="x">equal?</a></span> number</p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktSym">char</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match <span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._equal~3f%29%29" class="RktValLink" data-pltdoc="x">equal?</a></span> character</p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktSym">keyword</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match <span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._equal~3f%29%29" class="RktValLink" data-pltdoc="x">equal?</a></span> keyword</p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktSym">regexp</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match <span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._equal~3f%29%29" class="RktValLink" data-pltdoc="x">equal?</a></span> regexp literal</p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktSym">pregexp</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match <span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._equal~3f%29%29" class="RktValLink" data-pltdoc="x">equal?</a></span> pregexp literal</p></td></tr><tr><td><p><span class="RktVar">lvp</span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="stt">::=</span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktVar">pat</span><span class="stt"> </span><span class="RktVar">ooo</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>greedily match <span class="RktVar">pat</span> instances</p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktVar">pat</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match <span class="RktVar">pat</span></p></td></tr><tr><td><p><span class="RktVar">qp</span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="stt">::=</span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktVar">literal</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match literal</p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktVar">id</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match symbol</p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktPn">(</span><span class="RktVar">qp</span><span class="stt"> </span><span class="RktSym">...</span><span class="RktPn">)</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match sequences of <span class="RktVar">qp</span>s</p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktPn">(</span><span class="RktVar">qp</span><span class="stt"> </span><span class="RktSym">...</span><span class="stt"> </span><span class="RktPn">. </span><span class="RktVar">qp</span><span class="RktPn">)</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match <span class="RktVar">qp</span>s ending <span class="RktVar">qp</span></p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktPn">(</span><span class="RktVar">qp</span><span class="stt"> </span><span class="RktVar">ooo</span><span class="stt"> </span><span class="RktPn">. </span><span class="RktVar">qp</span><span class="RktPn">)</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match <span class="RktVar">qp</span>s beginning with repeated <span class="RktVar">qp</span></p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktVal">#</span><span class="RktVal">(</span><span class="RktVar">qp</span><span class="stt"> </span><span class="RktVal">...</span><span class="RktVal">)</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match vector of <span class="RktVar">qp</span>s</p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktVal">#&</span><span class="RktVar">qp</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match boxed <span class="RktVar">qp</span></p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktVal">#s</span><span class="RktVal">(</span><span class="RktVal">prefab-key</span><span class="stt"> </span><span class="RktVar">qp</span><span class="stt"> </span><span class="RktVal">...</span><span class="RktVal">)</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match prefab struct with <span class="RktVar">qp</span> fields</p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktRdr">,</span><span class="RktVar">pat</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match <span class="RktVar">pat</span></p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktRdr">,@</span><span class="RktPn">(</span><span class="RktSym">list</span><span class="stt"> </span><span class="RktVar">lvp</span><span class="stt"> </span><span class="RktSym">...</span><span class="RktPn">)</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match <span class="RktVar">lvp</span>s, spliced</p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktRdr">,@</span><span class="RktPn">(</span><span class="RktSym">list-rest</span><span class="stt"> </span><span class="RktVar">lvp</span><span class="stt"> </span><span class="RktSym">...</span><span class="stt"> </span><span class="RktVar">pat</span><span class="RktPn">)</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match <span class="RktVar">lvp</span>s plus <span class="RktVar">pat</span>, spliced</p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktRdr">,@</span><span class="RktVal">'</span><span class="RktVar">qp</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>match list-matching <span class="RktVar">qp</span>, spliced</p></td></tr><tr><td><p><span class="RktVar">ooo</span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="stt">::=</span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktSym">...</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>zero or more; <span class="RktSym">...</span> is literal</p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktSym">___</span></p></td><td><p><span class="hspace"> </span></p></td><td><p>zero or more</p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktSym">..</span><span class="RktVar">k</span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktVar">k</span> or more</p></td></tr><tr><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="hspace"> </span><span class="stt">| </span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktSym">__</span><span class="RktVar">k</span></p></td><td><p><span class="hspace"> </span></p></td><td><p><span class="RktVar">k</span> or more</p></td></tr></table></p><p>In more detail, patterns match as follows:</p><ul><li><p><span class="RktVar">id</span> (excluding the reserved names <span class="RktSym">_</span>,
<span class="RktSym">...</span>, <span class="RktSym">.._</span>,
<span class="RktSym">..</span><span class="RktVar">k</span>, and
<span class="RktSym">..</span><span class="RktVar">k</span> for non-negative integers
<span class="RktVar">k</span>) or <span class="RktPn">(</span><span class="RktSym">var</span><span class="stt"> </span><span class="RktVar">id</span><span class="RktPn">)</span> —<wbr></wbr> matches anything, and binds <span class="RktVar">id</span> to the
matching values. If an <span class="RktVar">id</span> is used multiple times
within a pattern, the corresponding matches must be the same
according to <span class="RktPn">(</span><span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fmatch..rkt%29._match-equality-test%29%29" class="RktValLink" data-pltdoc="x">match-equality-test</a></span><span class="RktPn">)</span>, except that
instances of an <span class="RktVar">id</span> in different <span class="RktSym">or</span> and
<span class="RktSym">not</span> sub-patterns are independent. The binding for <span class="RktVar">id</span> is
not available in other parts of the same pattern.</p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><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="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">(</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="RktVal">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktSym">a</span><span class="hspace"> </span><span class="RktSym">b</span><span class="hspace"> </span><span class="RktSym">a</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktSym">a</span><span class="hspace"> </span><span class="RktSym">b</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="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktSym">a</span><span class="hspace"> </span><span class="RktSym">b</span><span class="hspace"> </span><span class="RktSym">c</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktSym">c</span><span class="hspace"> </span><span class="RktSym">b</span><span class="hspace"> </span><span class="RktSym">a</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">'(3 2 1)</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktVal">(</span><span class="RktVal">x</span><span class="hspace"> </span><span class="RktVal">y</span><span class="hspace"> </span><span class="RktVal">z</span><span class="RktVal">)</span><span class="hspace"> </span><span class="RktVal">1</span><span class="RktVal">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktSym">a</span><span class="hspace"> </span><span class="RktSym">b</span><span class="hspace"> </span><span class="RktSym">a</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktSym">a</span><span class="hspace"> </span><span class="RktSym">b</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="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktSym">a</span><span class="hspace"> </span><span class="RktSym">b</span><span class="hspace"> </span><span class="RktSym">c</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktSym">c</span><span class="hspace"> </span><span class="RktSym">b</span><span class="hspace"> </span><span class="RktSym">a</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">'(1 (x y z))</span></p></td></tr></table></blockquote></div></p></li><li><p><span class="RktSym">_</span> —<wbr></wbr> matches anything, without binding any
identifiers.</p><p><div class="SIntrapara">Example:</div><div class="SIntrapara"><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="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">(</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="RktVal">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><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><span class="hspace"> </span><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><span class="hspace"> </span><span class="RktSym">a</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym">a</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">3</span></p></td></tr></table></blockquote></div></p></li><li><p><span class="RktVal">#t</span>, <span class="RktVal">#f</span>, <span class="RktVar">string</span>, <span class="RktVar">bytes</span>,
<span class="RktVar">number</span>, <span class="RktVar">char</span>, or <span class="RktPn">(</span><span class="RktSym">quote</span><span class="stt"> </span><span class="RktVar">datum</span><span class="RktPn">)</span> —<wbr></wbr> matches an <span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._equal~3f%29%29" class="RktValLink" data-pltdoc="x">equal?</a></span> constant.</p><p><div class="SIntrapara">Example:</div><div class="SIntrapara"><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="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span><span class="hspace"> </span><span class="RktVal">"yes"</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktVal">"no"</span><span class="hspace"> </span><span class="RktVal">#f</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktVal">"yes"</span><span class="hspace"> </span><span class="RktVal">#t</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">#t</span></p></td></tr></table></blockquote></div></p></li><li><p><span class="RktPn">(</span><span class="RktSym">list</span><span class="stt"> </span><span class="RktVar">lvp</span><span class="stt"> </span><span class="RktMeta"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span><span class="RktPn">)</span> —<wbr></wbr> matches a list
of elements. In the case of <span class="RktPn">(</span><span class="RktSym">list</span><span class="stt"> </span><span class="RktVar">pat</span><span class="stt"> </span><span class="RktMeta"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span><span class="RktPn">)</span>, the pattern matches a list with as many element as
<span class="RktVar">pat</span>s, and each element must match the corresponding
<span class="RktVar">pat</span>. In the more general case, each <span class="RktVar">lvp</span>
corresponds to a “spliced” list of greedy matches.</p><p>For spliced lists, <span class="RktSym">...</span> and <span class="RktSym">___</span>
are aliases for zero or more matches. The
<span class="RktSym">..</span><span class="RktVar">k</span> and <span class="RktSym">__</span><span class="RktVar">k</span>
forms are also aliases, specifying <span class="RktVar">k</span> or more
matches. Pattern variables that precede these splicing
operators are bound to lists of matching forms.</p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><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="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">(</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="RktVal">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktSym">a</span><span class="hspace"> </span><span class="RktSym">b</span><span class="hspace"> </span><span class="RktSym">c</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktSym">c</span><span class="hspace"> </span><span class="RktSym">b</span><span class="hspace"> </span><span class="RktSym">a</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">'(3 2 1)</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">(</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="RktVal">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktSym">a</span><span class="hspace"> </span><span class="RktMeta"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym">a</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">'(2 3)</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">(</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="RktVal">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktSym">a</span><span class="hspace"> </span><span class="RktSym">..3</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym">a</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="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29.__%29%29" class="RktStxLink" data-pltdoc="x">_</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">else</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">'else</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">(</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="RktVal">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktSym">a</span><span class="hspace"> </span><span class="RktSym">..3</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym">a</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="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29.__%29%29" class="RktStxLink" data-pltdoc="x">_</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">else</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">'(2 3 4)</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">(</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="RktVal">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktSym">a</span><span class="hspace"> </span><span class="RktSym">..3</span><span class="hspace"> </span><span class="RktVal">5</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym">a</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="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29.__%29%29" class="RktStxLink" data-pltdoc="x">_</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">else</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">'(2 3 4)</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktVal">(</span><span class="RktVal">2</span><span class="RktVal">)</span><span class="hspace"> </span><span class="RktVal">(</span><span class="RktVal">2</span><span class="RktVal">)</span><span class="hspace"> </span><span class="RktVal">(</span><span class="RktVal">2</span><span class="RktVal">)</span><span class="hspace"> </span><span class="RktVal">5</span><span class="RktVal">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktSym">a</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym">..3</span><span class="hspace"> </span><span class="RktVal">5</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym">a</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="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29.__%29%29" class="RktStxLink" data-pltdoc="x">_</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">else</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">'(2 2 2)</span></p></td></tr></table></blockquote></div></p></li><li><p><span class="RktPn">(</span><span class="RktSym">list-rest</span><span class="stt"> </span><span class="RktVar">lvp</span><span class="stt"> </span><span class="RktMeta"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span><span class="stt"> </span><span class="RktVar">pat</span><span class="RktPn">)</span> —<wbr></wbr>
similar to a <span class="RktSym">list</span> pattern, but the final
<span class="RktVar">pat</span> matches the “rest” of the list after the last
<span class="RktVar">lvp</span>. In fact, the matched value can be a non-list
chain of pairs (i.e., an “improper list”) if <span class="RktVar">pat</span>
matches non-list values.</p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><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="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">(</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">. </span><span class="RktVal">4</span><span class="RktVal">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym">list-rest</span><span class="hspace"> </span><span class="RktSym">a</span><span class="hspace"> </span><span class="RktSym">b</span><span class="hspace"> </span><span class="RktSym">c</span><span class="hspace"> </span><span class="RktSym">d</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym">d</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">4</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">(</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">. </span><span class="RktVal">4</span><span class="RktVal">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym">list-rest</span><span class="hspace"> </span><span class="RktSym">a</span><span class="hspace"> </span><span class="RktMeta"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span><span class="hspace"> </span><span class="RktSym">d</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktSym">a</span><span class="hspace"> </span><span class="RktSym">d</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">'((1 2 3) 4)</span></p></td></tr></table></blockquote></div></p></li><li><p><span class="RktPn">(</span><span class="RktSym">list-no-order</span><span class="stt"> </span><span class="RktVar">pat</span><span class="stt"> </span><span class="RktMeta"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span><span class="RktPn">)</span> —<wbr></wbr>
similar to a <span class="RktSym">list</span> pattern, but the elements to
match each <span class="RktVar">pat</span> can appear in the list in any order.</p><p><div class="SIntrapara">Example:</div><div class="SIntrapara"><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="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">(</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="RktVal">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym">list-no-order</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="RktSym">x</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym">x</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">1</span></p></td></tr></table></blockquote></div></p></li><li><p><span class="RktPn">(</span><span class="RktSym">list-no-order</span><span class="stt"> </span><span class="RktVar">pat</span><span class="stt"> </span><span class="RktMeta"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span><span class="stt"> </span><span class="RktVar">lvp</span><span class="RktPn">)</span> —<wbr></wbr>
generalizes <span class="RktSym">list-no-order</span> to allow a pattern
that matches multiple list elements that are interspersed in
any order with matches for the other patterns.</p><p><div class="SIntrapara">Example:</div><div class="SIntrapara"><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="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">(</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="RktVal">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym">list-no-order</span><span class="hspace"> </span><span class="RktVal">6</span><span class="hspace"> </span><span class="RktVal">2</span><span class="hspace"> </span><span class="RktSym">y</span><span class="hspace"> </span><span class="RktMeta"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym">y</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">'(1 3 4 5)</span></p></td></tr></table></blockquote></div></p></li><li><p><span class="RktPn">(</span><span class="RktSym">vector</span><span class="stt"> </span><span class="RktVar">lvp</span><span class="stt"> </span><span class="RktMeta"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span><span class="RktPn">)</span> —<wbr></wbr> like a
<span class="RktSym">list</span> pattern, but matching a vector.</p><p><div class="SIntrapara">Example:</div><div class="SIntrapara"><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="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span><span class="hspace"> </span><span class="RktVal">#</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktVal">(</span><span class="RktVal">2</span><span class="RktVal">)</span><span class="hspace"> </span><span class="RktVal">(</span><span class="RktVal">2</span><span class="RktVal">)</span><span class="hspace"> </span><span class="RktVal">(</span><span class="RktVal">2</span><span class="RktVal">)</span><span class="hspace"> </span><span class="RktVal">5</span><span class="RktVal">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym"><a href="vectors.html#%28def._%28%28quote._~23~25kernel%29._vector%29%29" class="RktValLink" data-pltdoc="x">vector</a></span><span class="hspace"> </span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktSym">a</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym">..3</span><span class="hspace"> </span><span class="RktVal">5</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym">a</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">'(2 2 2)</span></p></td></tr></table></blockquote></div></p></li><li><p><span class="RktPn">(</span><span class="RktSym">hash-table</span><span class="stt"> </span><span class="RktPn">(</span><span class="RktVar">pat</span><span class="stt"> </span><span class="RktVar">pat</span><span class="RktPn">)</span><span class="stt"> </span><span class="RktMeta"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span><span class="RktPn">)</span> —<wbr></wbr>
similar to <span class="RktSym">list-no-order</span>, but matching against
hash table’s key–value pairs.</p><p><div class="SIntrapara">Example:</div><div class="SIntrapara"><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="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span><span class="hspace"> </span><span class="RktVal">#hash</span><span class="RktVal">(</span><span class="RktVal">(</span><span class="RktVal">"a"</span><span class="hspace"> </span><span class="RktVal">. </span><span class="RktVal">1</span><span class="RktVal">)</span><span class="hspace"> </span><span class="RktVal">(</span><span class="RktVal">"b"</span><span class="hspace"> </span><span class="RktVal">. </span><span class="RktVal">2</span><span class="RktVal">)</span><span class="RktVal">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym">hash-table</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktVal">"b"</span><span class="hspace"> </span><span class="RktSym">b</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktVal">"a"</span><span class="hspace"> </span><span class="RktSym">a</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktSym">b</span><span class="hspace"> </span><span class="RktSym">a</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">'(2 1)</span></p></td></tr></table></blockquote></div></p></li><li><p><span class="RktPn">(</span><span class="RktSym">hash-table</span><span class="stt"> </span><span class="RktPn">(</span><span class="RktVar">pat</span><span class="stt"> </span><span class="RktVar">pat</span><span class="RktPn">)</span><span class="stt"> </span><span class="RktMeta">...+</span><span class="stt"> </span><span class="RktVar">ooo</span><span class="RktPn">)</span>
—<wbr></wbr> Generalizes <span class="RktSym">hash-table</span> to support a final
repeating pattern.</p><p><div class="SIntrapara">Example:</div><div class="SIntrapara"><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="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span><span class="hspace"> </span><span class="RktVal">#hash</span><span class="RktVal">(</span><span class="RktVal">(</span><span class="RktVal">"a"</span><span class="hspace"> </span><span class="RktVal">. </span><span class="RktVal">1</span><span class="RktVal">)</span><span class="hspace"> </span><span class="RktVal">(</span><span class="RktVal">"b"</span><span class="hspace"> </span><span class="RktVal">. </span><span class="RktVal">2</span><span class="RktVal">)</span><span class="RktVal">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym">hash-table</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">key</span><span class="hspace"> </span><span class="RktSym">val</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktMeta"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym">key</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">'("b" "a")</span></p></td></tr></table></blockquote></div></p></li><li><p><span class="RktPn">(</span><span class="RktSym">cons</span><span class="stt"> </span><span class="RktVar">pat1</span><span class="stt"> </span><span class="RktVar">pat2</span><span class="RktPn">)</span> —<wbr></wbr> matches a pair value.</p><p><div class="SIntrapara">Example:</div><div class="SIntrapara"><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="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._cons%29%29" class="RktValLink" data-pltdoc="x">cons</a></span><span class="hspace"> </span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktVal">2</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._cons%29%29" class="RktValLink" data-pltdoc="x">cons</a></span><span class="hspace"> </span><span class="RktSym">a</span><span class="hspace"> </span><span class="RktSym">b</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._%2B%29%29" class="RktValLink" data-pltdoc="x">+</a></span><span class="hspace"> </span><span class="RktSym">a</span><span class="hspace"> </span><span class="RktSym">b</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">3</span></p></td></tr></table></blockquote></div></p></li><li><p><span class="RktPn">(</span><span class="RktSym">mcons</span><span class="stt"> </span><span class="RktVar">pat1</span><span class="stt"> </span><span class="RktVar">pat2</span><span class="RktPn">)</span> —<wbr></wbr> matches a mutable pair value.</p><p><div class="SIntrapara">Example:</div><div class="SIntrapara"><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="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="mpairs.html#%28def._%28%28quote._~23~25kernel%29._mcons%29%29" class="RktValLink" data-pltdoc="x">mcons</a></span><span class="hspace"> </span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktVal">2</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._cons%29%29" class="RktValLink" data-pltdoc="x">cons</a></span><span class="hspace"> </span><span class="RktSym">a</span><span class="hspace"> </span><span class="RktSym">b</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">immutable</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym"><a href="mpairs.html#%28def._%28%28quote._~23~25kernel%29._mcons%29%29" class="RktValLink" data-pltdoc="x">mcons</a></span><span class="hspace"> </span><span class="RktSym">a</span><span class="hspace"> </span><span class="RktSym">b</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">mutable</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">'mutable</span></p></td></tr></table></blockquote></div></p></li><li><p><span class="RktPn">(</span><span class="RktSym">box</span><span class="stt"> </span><span class="RktVar">pat</span><span class="RktPn">)</span> —<wbr></wbr> matches a boxed value.</p><p><div class="SIntrapara">Example:</div><div class="SIntrapara"><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="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span><span class="hspace"> </span><span class="RktVal">#&</span><span class="RktVal">1</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym"><a href="boxes.html#%28def._%28%28quote._~23~25kernel%29._box%29%29" class="RktValLink" data-pltdoc="x">box</a></span><span class="hspace"> </span><span class="RktSym">a</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym">a</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">1</span></p></td></tr></table></blockquote></div></p></li><li><p><span class="RktPn">(</span><span class="RktVar">struct-id</span><span class="stt"> </span><span class="RktVar">pat</span><span class="stt"> </span><span class="RktMeta"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span><span class="RktPn">)</span> or
<span class="RktPn">(</span><span class="RktSym">struct</span><span class="stt"> </span><span class="RktVar">struct-id</span><span class="stt"> </span><span class="RktPn">(</span><span class="RktVar">pat</span><span class="stt"> </span><span class="RktMeta"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span><span class="RktPn">)</span><span class="RktPn">)</span> —<wbr></wbr>
matches an instance of a structure type named
<span class="RktVar">struct-id</span>, where each field in the instance matches
the corresponding <span class="RktVar">pat</span>. See also <span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._struct%2A%29%29" class="RktStxLink" data-pltdoc="x">struct*</a></span>.</p><p>Usually, <span class="RktVar">struct-id</span> is defined with
<span class="RktSym"><a href="define-struct.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._struct%29%29" class="RktStxLink" data-pltdoc="x">struct</a></span>. More generally, <span class="RktVar">struct-id</span>
must be bound to expansion-time information for a structure
type (see <a href="structinfo.html" data-pltdoc="x">Structure Type Transformer Binding</a>), where the information
includes at least a predicate binding and field accessor
bindings corresponding to the number of field
<span class="RktVar">pat</span>s. In particular, a module import or a
<span class="RktSym"><a href="creatingunits.html#%28form._%28%28lib._racket%2Funit..rkt%29._unit%29%29" class="RktStxLink" data-pltdoc="x">unit</a></span> import with a signature containing a
<span class="RktSym"><a href="define-struct.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._struct%29%29" class="RktStxLink" data-pltdoc="x">struct</a></span> declaration can provide the structure type
information.</p><p><div class="SIntrapara">Examples:</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="define-struct.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._struct%29%29" class="RktStxLink" data-pltdoc="x">struct</a></span><span class="hspace"> </span><span class="RktSym">tree</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">val</span><span class="hspace"> </span><span class="RktSym">left</span><span class="hspace"> </span><span class="RktSym">right</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p> </p></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">tree</span><span class="hspace"> </span><span class="RktVal">0</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">tree</span><span class="hspace"> </span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktVal">#f</span><span class="hspace"> </span><span class="RktVal">#f</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVal">#f</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym">tree</span><span class="hspace"> </span><span class="RktSym">a</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">tree</span><span class="hspace"> </span><span class="RktSym">b</span><span class="hspace"> </span><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><span class="hspace"> </span><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><span class="RktPn">)</span><span class="hspace"> </span><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><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktSym">a</span><span class="hspace"> </span><span class="RktSym">b</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">'(0 1)</span></p></td></tr></table></blockquote></div></p></li><li><p><span class="RktPn">(</span><span class="RktSym">struct</span><span class="stt"> </span><span class="RktVar">struct-id</span><span class="stt"> </span><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><span class="RktPn">)</span> —<wbr></wbr>
matches any instance of <span class="RktVar">struct-id</span>, without regard to
contents of the fields of the instance.</p></li><li><p><span class="RktPn">(</span><span class="RktSym">regexp</span><span class="stt"> </span><span class="RktVar">rx-expr</span><span class="RktPn">)</span> —<wbr></wbr> matches a
string that matches the regexp pattern produced by
<span class="RktVar">rx-expr</span>; see <a href="regexp.html" data-pltdoc="x">Regular Expressions</a> for more information
about regexps.</p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><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="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span><span class="hspace"> </span><span class="RktVal">"apple"</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym"><a href="regexp.html#%28def._%28%28quote._~23~25kernel%29._regexp%29%29" class="RktValLink" data-pltdoc="x">regexp</a></span><span class="hspace"> </span><span class="RktVal">#rx"p+"</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">yes</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="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29.__%29%29" class="RktStxLink" data-pltdoc="x">_</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">no</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">'yes</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span><span class="hspace"> </span><span class="RktVal">"banana"</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym"><a href="regexp.html#%28def._%28%28quote._~23~25kernel%29._regexp%29%29" class="RktValLink" data-pltdoc="x">regexp</a></span><span class="hspace"> </span><span class="RktVal">#rx"p+"</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">yes</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="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29.__%29%29" class="RktStxLink" data-pltdoc="x">_</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">no</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">'no</span></p></td></tr></table></blockquote></div></p></li><li><p><span class="RktPn">(</span><span class="RktSym">regexp</span><span class="stt"> </span><span class="RktVar">rx-expr</span><span class="stt"> </span><span class="RktVar">pat</span><span class="RktPn">)</span> —<wbr></wbr> extends
the <span class="RktSym">regexp</span> form to further constrain the match
where the result of <span class="RktSym"><a href="regexp.html#%28def._%28%28quote._~23~25kernel%29._regexp-match%29%29" class="RktValLink" data-pltdoc="x">regexp-match</a></span> is matched against
<span class="RktVar">pat</span>.</p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><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="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span><span class="hspace"> </span><span class="RktVal">"apple"</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym"><a href="regexp.html#%28def._%28%28quote._~23~25kernel%29._regexp%29%29" class="RktValLink" data-pltdoc="x">regexp</a></span><span class="hspace"> </span><span class="RktVal">#rx"p+(.)"</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><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><span class="hspace"> </span><span class="RktVal">"l"</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">yes</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="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29.__%29%29" class="RktStxLink" data-pltdoc="x">_</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">no</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">'yes</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span><span class="hspace"> </span><span class="RktVal">"append"</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym"><a href="regexp.html#%28def._%28%28quote._~23~25kernel%29._regexp%29%29" class="RktValLink" data-pltdoc="x">regexp</a></span><span class="hspace"> </span><span class="RktVal">#rx"p+(.)"</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><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><span class="hspace"> </span><span class="RktVal">"l"</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">yes</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="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29.__%29%29" class="RktStxLink" data-pltdoc="x">_</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">no</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">'no</span></p></td></tr></table></blockquote></div></p></li><li><p><span class="RktPn">(</span><span class="RktSym">pregexp</span><span class="stt"> </span><span class="RktVar">rx-expr</span><span class="RktPn">)</span> or
<span class="RktPn">(</span><span class="RktSym">regexp</span><span class="stt"> </span><span class="RktVar">rx-expr</span><span class="stt"> </span><span class="RktVar">pat</span><span class="RktPn">)</span> —<wbr></wbr> like the
<span class="RktSym">regexp</span> patterns, but if <span class="RktVar">rx-expr</span>
produces a string, it is converted to a pattern using
<span class="RktSym"><a href="regexp.html#%28def._%28%28quote._~23~25kernel%29._pregexp%29%29" class="RktValLink" data-pltdoc="x">pregexp</a></span> instead of <span class="RktSym"><a href="regexp.html#%28def._%28%28quote._~23~25kernel%29._regexp%29%29" class="RktValLink" data-pltdoc="x">regexp</a></span>.</p></li><li><p><span class="RktPn">(</span><span class="RktSym">and</span><span class="stt"> </span><span class="RktVar">pat</span><span class="stt"> </span><span class="RktMeta"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span><span class="RktPn">)</span> —<wbr></wbr> matches if all
of the <span class="RktVar">pat</span>s match. This pattern is often used as
<span class="RktPn">(</span><span class="RktSym">and</span><span class="stt"> </span><span class="RktVar">id</span><span class="stt"> </span><span class="RktVar">pat</span><span class="RktPn">)</span> to bind <span class="RktVar">id</span>
to the entire value that matches <span class="RktVar">pat</span>. The <span class="RktVar">pat</span>s are
matched in the order that they appear.</p><p><div class="SIntrapara">Example:</div><div class="SIntrapara"><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="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktVal">(</span><span class="RktVal">2</span><span class="hspace"> </span><span class="RktVal">3</span><span class="RktVal">)</span><span class="hspace"> </span><span class="RktVal">4</span><span class="RktVal">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><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><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="if.html#%28form._%28%28lib._racket%2Fprivate%2Fletstx-scheme..rkt%29._and%29%29" class="RktStxLink" data-pltdoc="x">and</a></span><span class="hspace"> </span><span class="RktSym">a</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><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><span class="hspace"> </span><span class="RktMeta"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span><span class="RktPn">)</span><span class="RktPn">)</span><span class="hspace"> </span><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><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym">a</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">'(2 3)</span></p></td></tr></table></blockquote></div></p></li><li><p><span class="RktPn">(</span><span class="RktSym">or</span><span class="stt"> </span><span class="RktVar">pat</span><span class="stt"> </span><span class="RktMeta"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span><span class="RktPn">)</span> —<wbr></wbr> matches if any of
the <span class="RktVar">pat</span>s match. <span style="font-weight: bold">Beware</span>: the result expression
can be duplicated once for each <span class="RktVar">pat</span>! Identifiers in
<span class="RktVar">pat</span> are bound only in the corresponding copy of the
result expression; in a module context, if the result
expression refers to a binding, then all <span class="RktVar">pat</span>s
must include the binding.</p><p><div class="SIntrapara">Example:</div><div class="SIntrapara"><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="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktVal">2</span><span class="RktVal">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym"><a href="if.html#%28form._%28%28lib._racket%2Fprivate%2Fletstx-scheme..rkt%29._or%29%29" class="RktStxLink" data-pltdoc="x">or</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktSym">a</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"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktSym">a</span><span class="hspace"> </span><span class="RktVal">2</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym">a</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">1</span></p></td></tr></table></blockquote></div></p></li><li><p><span class="RktPn">(</span><span class="RktSym">not</span><span class="stt"> </span><span class="RktVar">pat</span><span class="stt"> </span><span class="RktMeta"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span><span class="RktPn">)</span> —<wbr></wbr> matches when
none of the <span class="RktVar">pat</span>s match, and binds no identifiers.</p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><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="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">(</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="RktVal">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._not%29%29" class="RktValLink" data-pltdoc="x">not</a></span><span class="hspace"> </span><span class="RktVal">4</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktMeta"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">yes</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="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29.__%29%29" class="RktStxLink" data-pltdoc="x">_</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">no</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">'yes</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktVal">4</span><span class="hspace"> </span><span class="RktVal">3</span><span class="RktVal">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._not%29%29" class="RktValLink" data-pltdoc="x">not</a></span><span class="hspace"> </span><span class="RktVal">4</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktMeta"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">yes</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="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29.__%29%29" class="RktStxLink" data-pltdoc="x">_</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">no</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">'no</span></p></td></tr></table></blockquote></div></p></li><li><p><span class="RktPn">(</span><span class="RktSym">app</span><span class="stt"> </span><span class="RktVar">expr</span><span class="stt"> </span><span class="RktVar">pats</span><span class="stt"> </span><span class="RktMeta"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span><span class="RktPn">)</span> —<wbr></wbr> applies
<span class="RktVar">expr</span> to the value to be matched; the result of the
application is matched against <span class="RktVar">pats</span>.</p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><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="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktVal">2</span><span class="RktVal">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym">app</span><span class="hspace"> </span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._length%29%29" class="RktValLink" data-pltdoc="x">length</a></span><span class="hspace"> </span><span class="RktVal">2</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">yes</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">'yes</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktVal">2</span><span class="RktVal">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym">app</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="lambda.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._lambda%29%29" class="RktStxLink" data-pltdoc="x">lambda</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">v</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28lib._racket%2Flist..rkt%29._split-at%29%29" class="RktValLink" data-pltdoc="x">split-at</a></span><span class="hspace"> </span><span class="RktSym">v</span><span class="hspace"> </span><span class="RktVal">1</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="RktVal">)</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">2</span><span class="RktVal">)</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">yes</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">'yes</span></p></td></tr></table></blockquote></div></p></li><li><p><span class="RktPn">(</span><span class="RktSym">?</span><span class="stt"> </span><span class="RktVar">expr</span><span class="stt"> </span><span class="RktVar">pat</span><span class="stt"> </span><span class="RktMeta"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span><span class="RktPn">)</span> —<wbr></wbr> applies
<span class="RktVar">expr</span> to the value to be matched, and checks whether
the result is a true value; the additional <span class="RktVar">pat</span>s must
also match; i.e., <span class="RktSym">?</span> combines a predicate
application and an <span class="RktSym">and</span> pattern. However,
<span class="RktSym">?</span>, unlike <span class="RktSym">and</span>, guarantees that
<span class="RktVar">expr</span> is matched before any of the <span class="RktVar">pat</span>s.</p><blockquote class="refpara"><blockquote class="refcolumn"><blockquote class="refcontent"><p>The <span class="RktVar">expr</span> procedure may be called more than once
on identical input (although this happens only rarely),
and the order in which calls to <span class="RktVar">expr</span> are
made should not be relied upon.</p></blockquote></blockquote></blockquote><p><div class="SIntrapara">Example:</div><div class="SIntrapara"><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="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktVal">3</span><span class="hspace"> </span><span class="RktVal">5</span><span class="RktVal">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">?</span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._odd~3f%29%29" class="RktValLink" data-pltdoc="x">odd?</a></span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktMeta"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">yes</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">'yes</span></p></td></tr></table></blockquote></div></p></li><li><p><span class="RktPn">(</span><span class="RktSym">quasiquote</span><span class="stt"> </span><span class="RktVar">qp</span><span class="RktPn">)</span> —<wbr></wbr> introduces a
quasipattern, in which identifiers match symbols. Like the
<span class="RktSym"><a href="quasiquote.html#%28form._%28%28lib._racket%2Fprivate%2Fletstx-scheme..rkt%29._quasiquote%29%29" class="RktStxLink" data-pltdoc="x">quasiquote</a></span> expression form, <span class="RktSym">unquote</span>
and <span class="RktSym">unquote-splicing</span> escape back to normal
patterns.</p><p><div class="SIntrapara">Example:</div><div class="SIntrapara"><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="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">(</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="RktVal">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktVal">`</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktRdr">,</span><span class="RktSym">a</span><span class="hspace"> </span><span class="RktRdr">,</span><span class="RktPn">(</span><span class="RktSym">?</span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._odd~3f%29%29" class="RktValLink" data-pltdoc="x">odd?</a></span><span class="hspace"> </span><span class="RktSym">b</span><span class="RktPn">)</span><span class="RktVal">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktSym">a</span><span class="hspace"> </span><span class="RktSym">b</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">'(2 3)</span></p></td></tr></table></blockquote></div></p></li><li><p><span class="RktVar">derived-pattern</span> —<wbr></wbr> matches a pattern defined by a
macro extension via <span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._define-match-expander%29%29" class="RktStxLink" data-pltdoc="x">define-match-expander</a></span>.</p></li></ul><p>Note that the matching process may destructure the input multiple times, and
may evaluate expressions embedded in patterns such as <span class="RktPn">(</span><span class="RktSym">app</span><span class="stt"> </span><span class="RktSym">expr</span><span class="stt"> </span><span class="RktVar">pat</span><span class="RktPn">)</span> in arbitrary order, or multiple times. Therefore, such
expressions must be safe to call multiple times, or in an order other than they
appear in the original program.</p><h4 x-source-module="(lib "scribblings/reference/reference.scrbl")" x-source-pkg="racket-doc" x-part-tag=""Additional_Matching_Forms"">9.1<tt> </tt><a name="(part._.Additional_.Matching_.Forms)"></a>Additional Matching Forms</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"><span class="RktPn">(</span><a name="(form._((lib._racket/match..rkt)._match*))"></a><span title="Provided from: racket/match, racket | Package: base"><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%2A%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">match*</a></span></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktVar">val-expr</span><span class="hspace"> </span><span class="RktMeta">...+</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVar">clause*</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr><tr><td><span class="stt"> </span></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="specgrammar"><tr><td align="right" valign="baseline"><span class="RktVar">clause*</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="RktPn">(</span><span class="RktVar">pat</span><span class="hspace"> </span><span class="RktMeta">...+</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVar">body</span><span class="hspace"> </span><span class="RktMeta">...+</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="RktPn">(</span><span class="RktVar">pat</span><span class="hspace"> </span><span class="RktMeta">...+</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktVar">=></span><span class="hspace"> </span><span class="RktVar">id</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVar">body</span><span class="hspace"> </span><span class="RktMeta">...+</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="RktPn">(</span><span class="RktVar">pat</span><span class="hspace"> </span><span class="RktMeta">...+</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">#:when</span><span class="hspace"> </span><span class="RktVar">cond-expr</span><span class="hspace"> </span><span class="RktVar">body</span><span class="hspace"> </span><span class="RktMeta">...+</span><span class="RktPn">]</span></td></tr></table></td></tr></table></blockquote></div><div class="SIntrapara">Matches a sequence of values against each clause in order, matching
only when all patterns in a clause match. Each clause must have the
same number of patterns as the number of <span class="RktVar">val-expr</span>s.</div></p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><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="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%2A%29%29" class="RktStxLink" data-pltdoc="x">match*</a></span><span class="hspace"> </span><span class="RktPn">(</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></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><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><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">?</span><span class="hspace"> </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><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym">x</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._add1%29%29" class="RktValLink" data-pltdoc="x">add1</a></span><span class="hspace"> </span><span class="RktSym">x</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">4</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%2A%29%29" class="RktStxLink" data-pltdoc="x">match*</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktVal">15</span><span class="hspace"> </span><span class="RktVal">17</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktPn">(</span><span class="RktSym">?</span><span class="hspace"> </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><span class="hspace"> </span><span class="RktSym">a</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">?</span><span class="hspace"> </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><span class="hspace"> </span><span class="RktSym">b</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">#:when</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._~3d%29%29" class="RktValLink" data-pltdoc="x">=</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._%2B%29%29" class="RktValLink" data-pltdoc="x">+</a></span><span class="hspace"> </span><span class="RktSym">a</span><span class="hspace"> </span><span class="RktVal">2</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym">b</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">diff-by-two</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">'diff-by-two</span></p></td></tr></table></blockquote></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>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/match..rkt)._match/values))"></a><span title="Provided from: racket/match, racket | Package: base"><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%2Fvalues%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">match/values</a></span></span><span class="hspace"> </span><span class="RktVar">expr</span><span class="hspace"> </span><span class="RktVar">clause</span><span class="hspace"> </span><span class="RktVar">clause</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">If <span class="RktVar">expr</span> evaluates to <span class="RktSym">n</span> values, then match all <span class="RktSym">n</span>
values against the patterns in <span class="RktVar">clause</span><span class="stt"> </span><span class="RktMeta"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span>. Each clause must contain
exactly <span class="RktSym">n</span> patterns. At least one clause is required to determine how
many values to expect from <span class="RktVar">expr</span>.</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>syntax</p></div></div><table cellspacing="0" cellpadding="0" class="RktBlk RForeground"><tr><td><span class="RktPn">(</span><a name="(form._((lib._racket/match..rkt)._define/match))"></a><span title="Provided from: racket/match, racket | Package: base"><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._define%2Fmatch%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">define/match</a></span></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktVar">head</span><span class="hspace"> </span><span class="RktVar">args</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">match*-clause</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></td></tr></table></blockquote></td></tr><tr><td><span class="stt"> </span></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="specgrammar"><tr><td align="right" valign="baseline"><span class="RktVar">head</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">id</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">head</span><span class="hspace"> </span><span class="RktVar">args</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="RktVar">args</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">arg</span><span class="hspace"> </span><span class="RktMeta">...</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">arg</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="hspace"> </span><span class="RktPn">.</span><span class="hspace"> </span><span class="RktVar">rest-id</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="RktVar">arg</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">arg-id</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">arg-id</span><span class="hspace"> </span><span class="RktVar">default-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="RktVar">keyword</span><span class="hspace"> </span><span class="RktVar">arg-id</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">keyword</span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktVar">arg-id</span><span class="hspace"> </span><span class="RktVar">default-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="RktVar">match*-clause</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="RktPn">(</span><span class="RktVar">pat</span><span class="hspace"> </span><span class="RktMeta">...+</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVar">body</span><span class="hspace"> </span><span class="RktMeta">...+</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="RktPn">(</span><span class="RktVar">pat</span><span class="hspace"> </span><span class="RktMeta">...+</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktVar">=></span><span class="hspace"> </span><span class="RktVar">id</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVar">body</span><span class="hspace"> </span><span class="RktMeta">...+</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="RktPn">(</span><span class="RktVar">pat</span><span class="hspace"> </span><span class="RktMeta">...+</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">#:when</span><span class="hspace"> </span><span class="RktVar">cond-expr</span><span class="hspace"> </span><span class="RktVar">body</span><span class="hspace"> </span><span class="RktMeta">...+</span><span class="RktPn">]</span></td></tr></table></td></tr></table></blockquote></div><div class="SIntrapara">Binds <span class="RktVar">id</span> to a procedure that is defined by pattern matching
clauses using <span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%2A%29%29" class="RktStxLink" data-pltdoc="x">match*</a></span>. Each clause takes a sequence of
patterns that correspond to the arguments in the function header.
The arguments are ordered as they appear in the function header for
matching purposes.</div></p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._define%2Fmatch%29%29" class="RktStxLink" data-pltdoc="x">define/match</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">fact</span><span class="hspace"> </span><span class="RktSym">n</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktVal">0</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVal">1</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym">n</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._%2A%29%29" class="RktValLink" data-pltdoc="x">*</a></span><span class="hspace"> </span><span class="RktSym">n</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">fact</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._sub1%29%29" class="RktValLink" data-pltdoc="x">sub1</a></span><span class="hspace"> </span><span class="RktSym">n</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p> </p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">fact</span><span class="hspace"> </span><span class="RktVal">5</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">120</span></p></td></tr></table></blockquote></div></p><p>The function header may also contain optional or keyword arguments,
may have curried arguments, and may also contain a rest argument.</p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._define%2Fmatch%29%29" class="RktStxLink" data-pltdoc="x">define/match</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">(</span><span class="RktSym">f</span><span class="hspace"> </span><span class="RktSym">x</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">#:y</span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktSym">y</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">(</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="RktVal">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktPn">(</span><span class="RktSym"><a href="regexp.html#%28def._%28%28quote._~23~25kernel%29._regexp%29%29" class="RktValLink" data-pltdoc="x">regexp</a></span><span class="hspace"> </span><span class="RktVal">#rx"p+"</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVal">`</span><span class="RktVal">(</span><span class="RktRdr">,</span><span class="RktSym">a</span><span class="hspace"> </span><span class="RktVal">2</span><span class="hspace"> </span><span class="RktVal">3</span><span class="RktVal">)</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym">a</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><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><span class="hspace"> </span><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><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVal">#f</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p> </p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktPn">(</span><span class="RktSym">f</span><span class="hspace"> </span><span class="RktVal">"ape"</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">#:y</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">5</span><span class="hspace"> </span><span class="RktVal">2</span><span class="hspace"> </span><span class="RktVal">3</span><span class="RktVal">)</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="RktPn">(</span><span class="RktSym">f</span><span class="hspace"> </span><span class="RktVal">"dog"</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#f</span></p></td></tr><tr><td><p> </p></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._racket%2Fmatch..rkt%29._define%2Fmatch%29%29" class="RktStxLink" data-pltdoc="x">define/match</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">g</span><span class="hspace"> </span><span class="RktSym">x</span><span class="hspace"> </span><span class="RktSym">y</span><span class="hspace"> </span><span class="RktPn">. </span><span class="RktSym">rst</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktVal">0</span><span class="hspace"> </span><span class="RktVal">0</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">)</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVal">#t</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktVal">5</span><span class="hspace"> </span><span class="RktVal">5</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">5</span><span class="hspace"> </span><span class="RktVal">5</span><span class="RktVal">)</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVal">#t</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><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><span class="hspace"> </span><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><span class="hspace"> </span><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><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVal">#f</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p> </p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">g</span><span class="hspace"> </span><span class="RktVal">0</span><span class="hspace"> </span><span class="RktVal">0</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#t</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">g</span><span class="hspace"> </span><span class="RktVal">5</span><span class="hspace"> </span><span class="RktVal">5</span><span class="hspace"> </span><span class="RktVal">5</span><span class="hspace"> </span><span class="RktVal">5</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#t</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">g</span><span class="hspace"> </span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktVal">2</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#f</span></p></td></tr></table></blockquote></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>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/match..rkt)._match-lambda))"></a><span title="Provided from: racket/match, racket | Package: base"><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match-lambda%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">match-lambda</a></span></span><span class="hspace"> </span><span class="RktVar">clause</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Equivalent to <span class="RktPn">(</span><span class="RktSym"><a href="lambda.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._lambda%29%29" class="RktStxLink" data-pltdoc="x">lambda</a></span><span class="stt"> </span><span class="RktPn">(</span><span class="RktSym">id</span><span class="RktPn">)</span><span class="stt"> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span><span class="stt"> </span><span class="RktSym">id</span><span class="stt"> </span><span class="RktVar">clause</span><span class="stt"> </span><span class="RktMeta"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span><span class="RktPn">)</span><span class="RktPn">)</span>.</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>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/match..rkt)._match-lambda*))"></a><span title="Provided from: racket/match, racket | Package: base"><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match-lambda%2A%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">match-lambda*</a></span></span><span class="hspace"> </span><span class="RktVar">clause</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Equivalent to <span class="RktPn">(</span><span class="RktSym"><a href="lambda.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._lambda%29%29" class="RktStxLink" data-pltdoc="x">lambda</a></span><span class="stt"> </span><span class="RktSym">lst</span><span class="stt"> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span><span class="stt"> </span><span class="RktSym">lst</span><span class="stt"> </span><span class="RktVar">clause</span><span class="stt"> </span><span class="RktMeta"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span><span class="RktPn">)</span><span class="RktPn">)</span>.</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>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/match..rkt)._match-lambda**))"></a><span title="Provided from: racket/match, racket | Package: base"><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match-lambda%2A%2A%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">match-lambda**</a></span></span><span class="hspace"> </span><span class="RktVar">clause*</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Equivalent to <span class="RktPn">(</span><span class="RktSym"><a href="lambda.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._lambda%29%29" class="RktStxLink" data-pltdoc="x">lambda</a></span><span class="stt"> </span><span class="RktPn">(</span><span class="RktSym">args</span><span class="stt"> </span><span class="RktMeta"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span><span class="RktPn">)</span><span class="stt"> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%2A%29%29" class="RktStxLink" data-pltdoc="x">match*</a></span><span class="stt"> </span><span class="RktPn">(</span><span class="RktSym">args</span><span class="stt"> </span><span class="RktMeta"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span><span class="RktPn">)</span><span class="stt"> </span><span class="RktVar">clause*</span><span class="stt"> </span><span class="RktMeta"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span><span class="RktPn">)</span><span class="RktPn">)</span>,
where the number of <span class="RktSym">args</span><span class="stt"> </span><span class="RktMeta"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span> is computed from the number of patterns
appearing in each of the <span class="RktVar">clause*</span>.</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>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/match..rkt)._match-let))"></a><span title="Provided from: racket/match, racket | Package: base"><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match-let%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">match-let</a></span></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktVar">pat</span><span class="hspace"> </span><span class="RktVar">expr</span><span class="RktPn">]</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVar">body</span><span class="hspace"> </span><span class="RktMeta">...+</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Generalizes <span class="RktSym"><a href="let.html#%28form._%28%28lib._racket%2Fprivate%2Fletstx-scheme..rkt%29._let%29%29" class="RktStxLink" data-pltdoc="x">let</a></span> to support pattern bindings. Each
<span class="RktVar">expr</span> is matched against its corresponding <span class="RktVar">pat</span> (the
match must succeed), and the bindings that <span class="RktVar">pat</span> introduces are
visible in the <span class="RktVar">body</span>s.</div></p><p><div class="SIntrapara">Example:</div><div class="SIntrapara"><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="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match-let%29%29" class="RktStxLink" data-pltdoc="x">match-let</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktSym">a</span><span class="hspace"> </span><span class="RktSym">b</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktVal">2</span><span class="RktVal">)</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym"><a href="vectors.html#%28def._%28%28quote._~23~25kernel%29._vector%29%29" class="RktValLink" data-pltdoc="x">vector</a></span><span class="hspace"> </span><span class="RktSym">x</span><span class="hspace"> </span><span class="RktMeta"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVal">#</span><span class="RktVal">(</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="RktVal">)</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="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktSym">b</span><span class="hspace"> </span><span class="RktSym">a</span><span class="hspace"> </span><span class="RktSym">x</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">'(2 1 (1 2 3 4))</span></p></td></tr></table></blockquote></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>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/match..rkt)._match-let*))"></a><span title="Provided from: racket/match, racket | Package: base"><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match-let%2A%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">match-let*</a></span></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktVar">pat</span><span class="hspace"> </span><span class="RktVar">expr</span><span class="RktPn">]</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVar">body</span><span class="hspace"> </span><span class="RktMeta">...+</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Like <span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match-let%29%29" class="RktStxLink" data-pltdoc="x">match-let</a></span>, but generalizes <span class="RktSym"><a href="let.html#%28form._%28%28lib._racket%2Fprivate%2Fletstx-scheme..rkt%29._let%2A%29%29" class="RktStxLink" data-pltdoc="x">let*</a></span>, so that the
bindings of each <span class="RktVar">pat</span> are available in each subsequent
<span class="RktVar">expr</span>.</div></p><p><div class="SIntrapara">Example:</div><div class="SIntrapara"><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="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match-let%2A%29%29" class="RktStxLink" data-pltdoc="x">match-let*</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktSym">a</span><span class="hspace"> </span><span class="RktSym">b</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">#</span><span class="RktVal">(</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="RktVal">)</span><span class="hspace"> </span><span class="RktVal">2</span><span class="RktVal">)</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym"><a href="vectors.html#%28def._%28%28quote._~23~25kernel%29._vector%29%29" class="RktValLink" data-pltdoc="x">vector</a></span><span class="hspace"> </span><span class="RktSym">x</span><span class="hspace"> </span><span class="RktMeta"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym">a</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktSym">x</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">'(1 2 3 4)</span></p></td></tr></table></blockquote></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>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/match..rkt)._match-let-values))"></a><span title="Provided from: racket/match, racket | Package: base"><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match-let-values%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">match-let-values</a></span></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktVar">pat</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVar">expr</span><span class="RktPn">]</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVar">body</span><span class="hspace"> </span><span class="RktMeta">...+</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Like <span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match-let%29%29" class="RktStxLink" data-pltdoc="x">match-let</a></span>, but generalizes <span class="RktSym"><a href="let.html#%28form._%28%28quote._~23~25kernel%29._let-values%29%29" class="RktStxLink" data-pltdoc="x">let-values</a></span>.</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>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/match..rkt)._match-let*-values))"></a><span title="Provided from: racket/match, racket | Package: base"><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match-let%2A-values%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">match-let*-values</a></span></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktVar">pat</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVar">expr</span><span class="RktPn">]</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVar">body</span><span class="hspace"> </span><span class="RktMeta">...+</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Like <span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match-let%2A%29%29" class="RktStxLink" data-pltdoc="x">match-let*</a></span>, but generalizes <span class="RktSym"><a href="let.html#%28form._%28%28lib._racket%2Fprivate%2Fletstx-scheme..rkt%29._let%2A-values%29%29" class="RktStxLink" data-pltdoc="x">let*-values</a></span>.</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>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/match..rkt)._match-letrec))"></a><span title="Provided from: racket/match, racket | Package: base"><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match-letrec%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">match-letrec</a></span></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktVar">pat</span><span class="hspace"> </span><span class="RktVar">expr</span><span class="RktPn">]</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVar">body</span><span class="hspace"> </span><span class="RktMeta">...+</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Like <span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match-let%29%29" class="RktStxLink" data-pltdoc="x">match-let</a></span>, but generalizes <span class="RktSym"><a href="let.html#%28form._%28%28lib._racket%2Fprivate%2Fletstx-scheme..rkt%29._letrec%29%29" class="RktStxLink" data-pltdoc="x">letrec</a></span>.</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>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/match..rkt)._match-letrec-values))"></a><span title="Provided from: racket/match, racket | Package: base"><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match-letrec-values%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">match-letrec-values</a></span></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktVar">pat</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVar">expr</span><span class="RktPn">]</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVar">body</span><span class="hspace"> </span><span class="RktMeta">...+</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Like <span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match-let%29%29" class="RktStxLink" data-pltdoc="x">match-let</a></span>, but generalizes <span class="RktSym"><a href="let.html#%28form._%28%28quote._~23~25kernel%29._letrec-values%29%29" class="RktStxLink" data-pltdoc="x">letrec-values</a></span>.</div></p><p class="SHistory">Added in version 6.1.1.8 of package <span class="stt">base</span>.</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._racket/match..rkt)._match-define))"></a><span title="Provided from: racket/match, racket | Package: base"><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match-define%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">match-define</a></span></span><span class="hspace"> </span><span class="RktVar">pat</span><span class="hspace"> </span><span class="RktVar">expr</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Defines the names bound by <span class="RktVar">pat</span> to the values produced by
matching against the result of <span class="RktVar">expr</span>.</div></p><p><div class="SIntrapara">Examples:</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"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match-define%29%29" class="RktStxLink" data-pltdoc="x">match-define</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktSym">a</span><span class="hspace"> </span><span class="RktSym">b</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktVal">2</span><span class="RktVal">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="stt">> </span><span class="RktSym">b</span></td></tr><tr><td><p><span class="RktRes">2</span></p></td></tr></table></blockquote></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>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/match..rkt)._match-define-values))"></a><span title="Provided from: racket/match, racket | Package: base"><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match-define-values%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">match-define-values</a></span></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktVar">pat</span><span class="hspace"> </span><span class="RktVar">pats</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVar">expr</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Like <span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match-define%29%29" class="RktStxLink" data-pltdoc="x">match-define</a></span> but for when expr produces multiple values.
Like match/values, it requires at least one pattern to determine the
number of values to expect.</div></p><p><div class="SIntrapara">Examples:</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"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match-define-values%29%29" class="RktStxLink" data-pltdoc="x">match-define-values</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">a</span><span class="hspace"> </span><span class="RktSym">b</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="values.html#%28def._%28%28quote._~23~25kernel%29._values%29%29" class="RktValLink" data-pltdoc="x">values</a></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><span class="stt">> </span><span class="RktSym">b</span></td></tr><tr><td><p><span class="RktRes">2</span></p></td></tr></table></blockquote></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._racket/match..rkt)._exn~3amisc~3amatch~3f))"></a><span title="Provided from: racket/match, racket | Package: base"><span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fmatch..rkt%29._exn~3amisc~3amatch~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">exn:misc:match?</a></span></span><span class="hspace"> </span><span class="RktVar">v</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._boolean~3f%29%29" class="RktValLink" data-pltdoc="x">boolean?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">v</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span></td></tr></table></blockquote></div><div class="SIntrapara">A predicate for the exception raised in the case of a match failure.</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>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/match..rkt)._failure-cont))"></a><span title="Provided from: racket/match, racket | Package: base"><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._failure-cont%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">failure-cont</a></span></span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Continues matching as if the current pattern failed. Note that unlike
use of the <span class="RktSym"><a href="if.html#%28form._%28%28lib._racket%2Fprivate%2Fletstx-scheme..rkt%29._~3d~3e%29%29" class="RktStxLink" data-pltdoc="x">=></a></span> form, this does <span style="font-style: italic">not</span> escape the current
context, and thus should only be used in tail position with respect to
the <span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span> form.</div></p><h4 x-source-module="(lib "scribblings/reference/reference.scrbl")" x-source-pkg="racket-doc" x-part-tag=""Extending_match"">9.2<tt> </tt><a name="(part._.Extending_match)"></a>Extending <span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span></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"><span class="RktPn">(</span><a name="(form._((lib._racket/match..rkt)._define-match-expander))"></a><span title="Provided from: racket/match, racket | Package: base"><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._define-match-expander%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">define-match-expander</a></span></span><span class="hspace"> </span><span class="RktVar">id</span><span class="hspace"> </span><span class="RktVar">proc-expr</span><span class="RktPn">)</span></p></blockquote></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._define-match-expander%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">define-match-expander</a></span><span class="hspace"> </span><span class="RktVar">id</span><span class="hspace"> </span><span class="RktVar">proc-expr</span><span class="hspace"> </span><span class="RktVar">proc-expr</span><span class="RktPn">)</span></td></tr></table></blockquote></div><div class="SIntrapara">Binds <span class="RktVar">id</span> to a <a name="(tech._match._expander)"></a><span style="font-style: italic">match expander</span>.</div></p><p>The first <span class="RktVar">proc-expr</span> sub-expression must evaluate to a
transformer that produces a <span class="RktVar">pat</span> for <span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span>.
Whenever <span class="RktVar">id</span> appears as the beginning of a pattern, this
transformer is given, at expansion time, a syntax object
corresponding to the entire pattern (including <span class="RktVar">id</span>). The
pattern is replaced with the result of the transformer.</p><p>A transformer produced by a second <span class="RktVar">proc-expr</span> sub-expression is
used when <span class="RktVar">id</span> is used in an expression context. Using the
second <span class="RktVar">proc-expr</span>, <span class="RktVar">id</span> can be given meaning both
inside and outside patterns.</p><p>Match expanders are not invoked unless <span class="RktVar">id</span> appears in the first
position in a sequence. Instead, identifiers bound by <span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._define-match-expander%29%29" class="RktStxLink" data-pltdoc="x">define-match-expander</a></span>
are used as binding identifiers (like any other identifier) when they appear
anywhere except the first position in a sequence.</p><p><div class="SIntrapara">For example, to extend the pattern matcher and destructure syntax lists,
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="define.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">syntax-list?</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="if.html#%28form._%28%28lib._racket%2Fprivate%2Fletstx-scheme..rkt%29._and%29%29" class="RktStxLink" data-pltdoc="x">and</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="stxops.html#%28def._%28%28quote._~23~25kernel%29._syntax~3f%29%29" class="RktValLink" data-pltdoc="x">syntax?</a></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="pairs.html#%28def._%28%28quote._~23~25kernel%29._list~3f%29%29" class="RktValLink" data-pltdoc="x">list?</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="stxops.html#%28def._%28%28quote._~23~25kernel%29._syntax-~3elist%29%29" class="RktValLink" data-pltdoc="x">syntax->list</a></span><span class="hspace"> </span><span class="RktSym">x</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._define-match-expander%29%29" class="RktStxLink" data-pltdoc="x">define-match-expander</a></span><span class="hspace"> </span><span class="RktSym">syntax-list</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="lambda.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._lambda%29%29" class="RktStxLink" data-pltdoc="x">lambda</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">stx</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._syntax-case%29%29" class="RktStxLink" data-pltdoc="x">syntax-case</a></span><span class="hspace"> </span><span class="RktSym">stx</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><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><span class="hspace"> </span><span class="RktSym">elts</span><span class="hspace"> </span><span class="RktMeta"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktRdr">#'</span><span class="RktPn">(</span><span class="RktSym">?</span><span class="hspace"> </span><span class="RktSym">syntax-list?</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">app</span><span class="hspace"> </span><span class="RktSym"><a href="stxops.html#%28def._%28%28quote._~23~25kernel%29._syntax-~3elist%29%29" class="RktValLink" data-pltdoc="x">syntax->list</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktSym">elts</span><span class="hspace"> </span><span class="RktMeta"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></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><span class="RktPn">)</span></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="define.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">make-keyword-predicate</span><span class="hspace"> </span><span class="RktSym">keyword</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="lambda.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._lambda%29%29" class="RktStxLink" data-pltdoc="x">lambda</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">stx</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="if.html#%28form._%28%28lib._racket%2Fprivate%2Fletstx-scheme..rkt%29._and%29%29" class="RktStxLink" data-pltdoc="x">and</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="stxops.html#%28def._%28%28lib._racket%2Fprivate%2Fstx..rkt%29._identifier~3f%29%29" class="RktValLink" data-pltdoc="x">identifier?</a></span><span class="hspace"> </span><span class="RktSym">stx</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="stxcmp.html#%28def._%28%28quote._~23~25kernel%29._free-identifier~3d~3f%29%29" class="RktValLink" data-pltdoc="x">free-identifier=?</a></span><span class="hspace"> </span><span class="RktSym">stx</span><span class="hspace"> </span><span class="RktSym">keyword</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="define.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktSym">or-keyword?</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">make-keyword-predicate</span><span class="hspace"> </span><span class="RktRdr">#'</span><span class="RktSym"><a href="if.html#%28form._%28%28lib._racket%2Fprivate%2Fletstx-scheme..rkt%29._or%29%29" class="RktStxLink" data-pltdoc="x">or</a></span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="define.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktSym">and-keyword?</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">make-keyword-predicate</span><span class="hspace"> </span><span class="RktRdr">#'</span><span class="RktSym"><a href="if.html#%28form._%28%28lib._racket%2Fprivate%2Fletstx-scheme..rkt%29._and%29%29" class="RktStxLink" data-pltdoc="x">and</a></span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p> </p></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span><span class="hspace"> </span><span class="RktRdr">#'</span><span class="RktPn">(</span><span class="RktSym"><a href="if.html#%28form._%28%28lib._racket%2Fprivate%2Fletstx-scheme..rkt%29._or%29%29" class="RktStxLink" data-pltdoc="x">or</a></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><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym">syntax-list</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">?</span><span class="hspace"> </span><span class="RktSym">or-keyword?</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym">b</span><span class="hspace"> </span><span class="RktSym">c</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="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktVal">"OOORRR!"</span><span class="hspace"> </span><span class="RktSym">b</span><span class="hspace"> </span><span class="RktSym">c</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="RktPn">(</span><span class="RktSym">syntax-list</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">?</span><span class="hspace"> </span><span class="RktSym">and-keyword?</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym">b</span><span class="hspace"> </span><span class="RktSym">c</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="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktVal">"AAANND!"</span><span class="hspace"> </span><span class="RktSym">b</span><span class="hspace"> </span><span class="RktSym">c</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">'("OOORRR!" #<syntax:59:0 3> #<syntax:59:0 4>)</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span><span class="hspace"> </span><span class="RktRdr">#'</span><span class="RktPn">(</span><span class="RktSym"><a href="if.html#%28form._%28%28lib._racket%2Fprivate%2Fletstx-scheme..rkt%29._and%29%29" class="RktStxLink" data-pltdoc="x">and</a></span><span class="hspace"> </span><span class="RktVal">5</span><span class="hspace"> </span><span class="RktVal">6</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym">syntax-list</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">?</span><span class="hspace"> </span><span class="RktSym">or-keyword?</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym">b</span><span class="hspace"> </span><span class="RktSym">c</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="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktVal">"OOORRR!"</span><span class="hspace"> </span><span class="RktSym">b</span><span class="hspace"> </span><span class="RktSym">c</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="RktPn">(</span><span class="RktSym">syntax-list</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">?</span><span class="hspace"> </span><span class="RktSym">and-keyword?</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym">b</span><span class="hspace"> </span><span class="RktSym">c</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="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktVal">"AAANND!"</span><span class="hspace"> </span><span class="RktSym">b</span><span class="hspace"> </span><span class="RktSym">c</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">'("AAANND!" #<syntax:60:0 5> #<syntax:60:0 6>)</span></p></td></tr></table></blockquote></div></p><p><div class="SIntrapara">And here is an example showing how
<span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._define-match-expander%29%29" class="RktStxLink" data-pltdoc="x">define-match-expander</a></span>-bound identifiers are
not treated specially unless they appear
in the first position of pattern sequence.
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._define-match-expander%29%29" class="RktStxLink" data-pltdoc="x">define-match-expander</a></span><span class="hspace"> </span><span class="RktSym">nil</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="lambda.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._~ce~bb%29%29" class="RktStxLink" data-pltdoc="x">λ</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">stx</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktRdr">#'</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="lambda.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._~ce~bb%29%29" class="RktStxLink" data-pltdoc="x">λ</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">stx</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktRdr">#'</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="define.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">len</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="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span><span class="hspace"> </span><span class="RktSym">l</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">[</span><span class="RktSym">nil</span><span class="hspace"> </span><span class="RktVal">0</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._cons%29%29" class="RktValLink" data-pltdoc="x">cons</a></span><span class="hspace"> </span><span class="RktSym">hd</span><span class="hspace"> </span><span class="RktSym">tl</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._%2B%29%29" class="RktValLink" data-pltdoc="x">+</a></span><span class="hspace"> </span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">len</span><span class="hspace"> </span><span class="RktSym">tl</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p> </p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">len</span><span class="hspace"> </span><span class="RktSym">nil</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">len</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._cons%29%29" class="RktValLink" data-pltdoc="x">cons</a></span><span class="hspace"> </span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktSym">nil</span><span class="RktPn">)</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">len</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._cons%29%29" class="RktValLink" data-pltdoc="x">cons</a></span><span class="hspace"> </span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._cons%29%29" class="RktValLink" data-pltdoc="x">cons</a></span><span class="hspace"> </span><span class="RktVal">2</span><span class="hspace"> </span><span class="RktSym">nil</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">0</span></p></td></tr></table></blockquote></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>value</p></div></div><p class="RForeground"><a name="(def._((lib._racket/match..rkt)._prop~3amatch-expander))"></a><span title="Provided from: racket/match, racket | Package: base"><span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fmatch..rkt%29._prop~3amatch-expander%29%29" class="RktValDef RktValLink" data-pltdoc="x">prop:match-expander</a></span></span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="structprops.html#%28def._%28%28quote._~23~25kernel%29._struct-type-property~3f%29%29" class="RktValLink" data-pltdoc="x">struct-type-property?</a></span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">A <a href="structprops.html#%28tech._structure._type._property%29" class="techoutside" data-pltdoc="x"><span class="techinside">structure type property</span></a> to identify structure types that act
as <a href="#%28tech._match._expander%29" class="techoutside" data-pltdoc="x"><span class="techinside">match expanders</span></a> like the ones created by
<span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._define-match-expander%29%29" class="RktStxLink" data-pltdoc="x">define-match-expander</a></span>.</div></p><p>The property value must be an exact non-negative integer or a
procedure of one or two arguments. In the former case, the integer
designates a field within the structure that should contain a
procedure; the integer must be between <span class="RktVal">0</span> (inclusive) and the
number of non-automatic fields in the structure type (exclusive, not
counting supertype fields), and the designated field must also be
specified as immutable.</p><p>If the property value is a procedure of one argument, then the
procedure serves as the transformer for match expansion. If the property value is a procedure of two
arguments, then the first argument is the structure whose type has
<span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fmatch..rkt%29._prop~3amatch-expander%29%29" class="RktValLink" data-pltdoc="x">prop:match-expander</a></span> property, and the second argument is a
syntax object as for a <a href="#%28tech._match._expander%29" class="techoutside" data-pltdoc="x"><span class="techinside">match expander</span></a>..</p><p>If the property value is a <a href="syntax-model.html#%28tech._assignment._transformer%29" class="techoutside" data-pltdoc="x"><span class="techinside">assignment transformer</span></a>, then the wrapped
procedure is extracted with
<span class="RktSym"><a href="stxtrans.html#%28def._%28%28quote._~23~25kernel%29._set%21-transformer-procedure%29%29" class="RktValLink" data-pltdoc="x">set!-transformer-procedure</a></span> before it is called.</p><p>This binding is provided <span class="RktSym"><a href="require.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for-syntax%29%29" class="RktStxLink" data-pltdoc="x">for-syntax</a></span>.</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>value</p></div></div><p class="RForeground"><a name="(def._((lib._racket/match..rkt)._prop~3alegacy-match-expander))"></a><span title="Provided from: racket/match, racket | Package: base"><span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fmatch..rkt%29._prop~3alegacy-match-expander%29%29" class="RktValDef RktValLink" data-pltdoc="x">prop:legacy-match-expander</a></span></span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="structprops.html#%28def._%28%28quote._~23~25kernel%29._struct-type-property~3f%29%29" class="RktValLink" data-pltdoc="x">struct-type-property?</a></span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Like <span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fmatch..rkt%29._prop~3amatch-expander%29%29" class="RktValLink" data-pltdoc="x">prop:match-expander</a></span>, but for the legacy match syntax.</div></p><p>This binding is provided <span class="RktSym"><a href="require.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for-syntax%29%29" class="RktStxLink" data-pltdoc="x">for-syntax</a></span>.</p><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>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/match..rkt)._match-expander~3f))"></a><span title="Provided from: racket/match, racket | Package: base"><span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fmatch..rkt%29._match-expander~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">match-expander?</a></span></span><span class="hspace"> </span><span class="RktVar">v</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._boolean~3f%29%29" class="RktValLink" data-pltdoc="x">boolean?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">v</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span></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>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/match..rkt)._legacy-match-expander~3f))"></a><span title="Provided from: racket/match, racket | Package: base"><span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fmatch..rkt%29._legacy-match-expander~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">legacy-match-expander?</a></span></span><span class="hspace"> </span><span class="RktVar">v</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._boolean~3f%29%29" class="RktValLink" data-pltdoc="x">boolean?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">v</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span></td></tr></table></td></tr></table></blockquote></div><div class="SIntrapara">Predicates for values which implement the appropriate match expander
properties.</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._racket/match..rkt)._syntax-local-match-introduce))"></a><span title="Provided from: racket/match, racket | Package: base"><span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fmatch..rkt%29._syntax-local-match-introduce%29%29" class="RktValDef RktValLink" data-pltdoc="x">syntax-local-match-introduce</a></span></span><span class="hspace"> </span><span class="RktVar">stx</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="stxops.html#%28def._%28%28quote._~23~25kernel%29._syntax~3f%29%29" class="RktValLink" data-pltdoc="x">syntax?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">stx</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="stxops.html#%28def._%28%28quote._~23~25kernel%29._syntax~3f%29%29" class="RktValLink" data-pltdoc="x">syntax?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Like <span class="RktSym"><a href="stxtrans.html#%28def._%28%28quote._~23~25kernel%29._syntax-local-introduce%29%29" class="RktValLink" data-pltdoc="x">syntax-local-introduce</a></span>, but for match expanders.</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>parameter</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/match..rkt)._match-equality-test))"></a><span title="Provided from: racket/match, racket | Package: base"><span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fmatch..rkt%29._match-equality-test%29%29" class="RktValDef RktValLink" data-pltdoc="x">match-equality-test</a></span></span><span class="RktPn"></span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span><span class="hspace"> </span><span class="RktPn">. </span><span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="RktPn"> .</span><span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%29%29" class="RktStxLink" data-pltdoc="x">any</a></span><span class="RktPn">)</span></p></blockquote></td></tr><tr><td><span class="RktPn">(</span><span title="Provided from: racket/match, racket | Package: base"><span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fmatch..rkt%29._match-equality-test%29%29" class="RktValDef RktValLink" data-pltdoc="x">match-equality-test</a></span></span><span class="hspace"> </span><span class="RktVar">comp-proc</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="void.html#%28def._%28%28quote._~23~25kernel%29._void~3f%29%29" class="RktValLink" data-pltdoc="x">void?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">comp-proc</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span><span class="hspace"> </span><span class="RktPn">. </span><span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="RktPn"> .</span><span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%29%29" class="RktStxLink" data-pltdoc="x">any</a></span><span class="RktPn">)</span></td></tr></table></blockquote></div><div class="SIntrapara">A <a href="eval-model.html#%28tech._parameter%29" class="techoutside" data-pltdoc="x"><span class="techinside">parameter</span></a> that determines the comparison procedure used to check
whether multiple uses of an identifier match the “same” value. The
default is <span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._equal~3f%29%29" class="RktValLink" data-pltdoc="x">equal?</a></span>.</div></p><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="RktPn">(</span><a name="(form._((lib._racket/match..rkt)._match/derived))"></a><span title="Provided from: racket/match, racket | Package: base"><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%2Fderived%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">match/derived</a></span></span><span class="hspace"> </span><span class="RktVar">val-expr</span><span class="hspace"> </span><span class="RktVar">original-datum</span><span class="hspace"> </span><span class="RktVar">clause</span><span class="hspace"> </span><span class="RktMeta">...</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><a name="(form._((lib._racket/match..rkt)._match*/derived))"></a><span title="Provided from: racket/match, racket | Package: base"><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%2A%2Fderived%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">match*/derived</a></span></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktVar">val-expr</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVar">original-datum</span><span class="hspace"> </span><span class="RktVar">clause*</span><span class="hspace"> </span><span class="RktMeta">...</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._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span> and <span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%2A%29%29" class="RktStxLink" data-pltdoc="x">match*</a></span> respectively, but includes a
sub-expression to be used as the source for all syntax errors within the form.
For example, <span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match-lambda%29%29" class="RktStxLink" data-pltdoc="x">match-lambda</a></span> expands to <span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%2Fderived%29%29" class="RktStxLink" data-pltdoc="x">match/derived</a></span> so that
errors in the body of the form are reported in terms of <span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match-lambda%29%29" class="RktStxLink" data-pltdoc="x">match-lambda</a></span>
instead of <span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span>.</div></p><h4 x-source-module="(lib "scribblings/reference/reference.scrbl")" x-source-pkg="racket-doc" x-part-tag=""Library_Extensions"">9.3<tt> </tt><a name="(part._.Library_.Extensions)"></a>Library Extensions</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"><span class="RktPn">(</span><a name="(form._((lib._racket/match..rkt)._~3d~3d))"></a><span title="Provided from: racket/match, racket | Package: base"><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._~3d~3d%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">==</a></span></span><span class="hspace"> </span><span class="RktVar">val</span><span class="hspace"> </span><span class="RktVar">comparator</span><span class="RktPn">)</span></p></blockquote></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._~3d~3d%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">==</a></span><span class="hspace"> </span><span class="RktVar">val</span><span class="RktPn">)</span></td></tr></table></blockquote></div><div class="SIntrapara">A <a href="#%28tech._match._expander%29" class="techoutside" data-pltdoc="x"><span class="techinside">match expander</span></a>
which checks if the matched value is the same as <span class="RktVar">val</span> when
compared by <span class="RktVar">comparator</span>. If <span class="RktVar">comparator</span> is
not provided, it defaults to <span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._equal~3f%29%29" class="RktValLink" data-pltdoc="x">equal?</a></span>.</div></p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><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="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></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></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._~3d~3d%29%29" class="RktStxLink" data-pltdoc="x">==</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></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="RktVal">'</span><span class="RktVal">yes</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="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29.__%29%29" class="RktStxLink" data-pltdoc="x">_</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">no</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">'yes</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></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></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._~3d~3d%29%29" class="RktStxLink" data-pltdoc="x">==</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></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="hspace"> </span><span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._eq~3f%29%29" class="RktValLink" data-pltdoc="x">eq?</a></span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">yes</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="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29.__%29%29" class="RktStxLink" data-pltdoc="x">_</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">no</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">'no</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></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></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></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="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._~3d~3d%29%29" class="RktStxLink" data-pltdoc="x">==</a></span><span class="hspace"> </span><span class="RktVal">3</span><span class="hspace"> </span><span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._~3d%29%29" class="RktValLink" data-pltdoc="x">=</a></span><span class="RktPn">)</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">yes</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="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29.__%29%29" class="RktStxLink" data-pltdoc="x">_</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">no</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">'yes</span></p></td></tr></table></blockquote></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>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/match..rkt)._struct*))"></a><span title="Provided from: racket/match, racket | Package: base"><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._struct%2A%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">struct*</a></span></span><span class="hspace"> </span><span class="RktVar">struct-id</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktVar">field</span><span class="hspace"> </span><span class="RktVar">pat</span><span class="RktPn">]</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">A <span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span> pattern form that matches an instance of a structure
type named <span class="RktVar">struct-id</span>, where the field <span class="RktVar">field</span> in the
instance matches the corresponding <span class="RktVar">pat</span>.</div></p><p>Any field of <span class="RktVar">struct-id</span> may be omitted, and such fields can
occur in any order.</p><p><div class="SIntrapara">Examples:</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="define-struct.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._struct%29%29" class="RktStxLink" data-pltdoc="x">struct</a></span><span class="hspace"> </span><span class="RktSym">tree</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">val</span><span class="hspace"> </span><span class="RktSym">left</span><span class="hspace"> </span><span class="RktSym">right</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p> </p></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._match%29%29" class="RktStxLink" data-pltdoc="x">match</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">tree</span><span class="hspace"> </span><span class="RktVal">0</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">tree</span><span class="hspace"> </span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktVal">#f</span><span class="hspace"> </span><span class="RktVal">#f</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVal">#f</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._struct%2A%29%29" class="RktStxLink" data-pltdoc="x">struct*</a></span><span class="hspace"> </span><span class="RktSym">tree</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">val</span><span class="hspace"> </span><span class="RktSym">a</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktSym">left</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28form._%28%28lib._racket%2Fmatch..rkt%29._struct%2A%29%29" class="RktStxLink" data-pltdoc="x">struct*</a></span><span class="hspace"> </span><span class="RktSym">tree</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">right</span><span class="hspace"> </span><span class="RktVal">#f</span><span class="RktPn">]</span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktSym">val</span><span class="hspace"> </span><span class="RktSym">b</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><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktSym">a</span><span class="hspace"> </span><span class="RktSym">b</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">'(0 1)</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, "6.7", "../");" 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="Random_generation.html" title="backward to "8.11 Random generation"" data-pltdoc="x">← prev</a> <a href="index.html" title="up to "The Racket Reference"" data-pltdoc="x">up</a> <a href="control.html" title="forward to "10 Control Flow"" data-pltdoc="x">next →</a></span> </div></div></div><div id="contextindicator"> </div></body></html>
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