marcuskammer/emacs.d
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions
emacs.d/clones/scheme/docs.racket-lang.org/reference/case.html

14 lines
34 KiB
HTML
Raw Normal View History

Add racket guides
2022-09-30 11:00:09 +02:00
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"/><meta name="viewport" content="width=device-width, initial-scale=0.8"/><title>3.13&nbsp;Dispatch: case</title><link rel="stylesheet" type="text/css" href="../scribble.css" title="default"/><link rel="stylesheet" type="text/css" href="extras.css" title="default"/><link rel="stylesheet" type="text/css" href="../racket.css" title="default"/><link rel="stylesheet" type="text/css" href="../manual-style.css" title="default"/><link rel="stylesheet" type="text/css" href="../manual-racket.css" title="default"/><link rel="stylesheet" type="text/css" href="../manual-racket.css" title="default"/><link rel="stylesheet" type="text/css" href="../doc-site.css" title="default"/><script type="text/javascript" src="../scribble-common.js"></script><script type="text/javascript" src="../manual-racket.js"></script><script type="text/javascript" src="../manual-racket.js"></script><script type="text/javascript" src="../doc-site.js"></script><script type="text/javascript" src="../local-redirect/local-redirect.js"></script><script type="text/javascript" src="../local-redirect/local-user-redirect.js"></script><!--[if IE 6]><style type="text/css">.SIEHidden { overflow: hidden; }</style><![endif]--></head><body id="doc-racket-lang-org"><div class="tocset"><div class="tocview"><div class="tocviewlist tocviewlisttopspace"><div class="tocviewtitle"><table cellspacing="0" cellpadding="0"><tr><td style="width: 1em;"><a href="javascript:void(0);" title="Expand/Collapse" class="tocviewtoggle" onclick="TocviewToggle(this,&quot;tocview_0&quot;);">&#9658;</a></td><td></td><td><a href="index.html" class="tocviewlink" data-pltdoc="x">The Racket Reference</a></td></tr></table></div><div class="tocviewsublisttop" style="display: none;" id="tocview_0"><table cellspacing="0" cellpadding="0"><tr><td align="right">1&nbsp;</td><td><a href="model.html" class="tocviewlink" data-pltdoc="x">Language Model</a></td></tr><tr><td align="right">2&nbsp;</td><td><a href="notation.html" class="tocviewlink" data-pltdoc="x">Notation for Documentation</a></td></tr><tr><td align="right">3&nbsp;</td><td><a href="syntax.html" class="tocviewselflink" data-pltdoc="x">Syntactic Forms</a></td></tr><tr><td align="right">4&nbsp;</td><td><a href="data.html" class="tocviewlink" data-pltdoc="x">Datatypes</a></td></tr><tr><td align="right">5&nbsp;</td><td><a href="structures.html" class="tocviewlink" data-pltdoc="x">Structures</a></td></tr><tr><td align="right">6&nbsp;</td><td><a href="mzlib_class.html" class="tocviewlink" data-pltdoc="x">Classes and Objects</a></td></tr><tr><td align="right">7&nbsp;</td><td><a href="mzlib_unit.html" class="tocviewlink" data-pltdoc="x">Units</a></td></tr><tr><td align="right">8&nbsp;</td><td><a href="contracts.html" class="tocviewlink" data-pltdoc="x">Contracts</a></td></tr><tr><td align="right">9&nbsp;</td><td><a href="match.html" class="tocviewlink" data-pltdoc="x">Pattern Matching</a></td></tr><tr><td align="right">10&nbsp;</td><td><a href="control.html" class="tocviewlink" data-pltdoc="x">Control Flow</a></td></tr><tr><td align="right">11&nbsp;</td><td><a href="concurrency.html" class="tocviewlink" data-pltdoc="x">Concurrency and Parallelism</a></td></tr><tr><td align="right">12&nbsp;</td><td><a href="Macros.html" class="tocviewlink" data-pltdoc="x">Macros</a></td></tr><tr><td align="right">13&nbsp;</td><td><a href="input-and-output.html" class="tocviewlink" data-pltdoc="x">Input and Output</a></td></tr><tr><td align="right">14&nbsp;</td><td><a href="security.html" class="tocviewlink" data-pltdoc="x">Reflection and Security</a></td></tr><tr><td align="right">15&nbsp;</td><td><a href="os.html" class="tocviewlink" data-pltdoc="x">Operating System</a></td></tr><tr><td align="right">16&nbsp;</td><td><a href="memory.html" class="tocviewlink" data-pltdoc="x">Memory Management</a></td></tr><tr><td align="right">17&nbsp;</td><td><a href="unsafe.html" class="tocviewlink" data-pltdoc="x">Unsafe Operations</a></td></tr><tr><td align="right">18&nbsp;</td><td><a href="running.html" class="to
<span class="RktVar">case-clause</span>. The selected clause is the first one with a
<span class="RktVar">datum</span> whose <span class="RktSym"><a href="quote.html#%28form._%28%28quote._~23~25kernel%29._quote%29%29" class="RktStxLink" data-pltdoc="x">quote</a></span>d form is <span class="RktSym"><a href="Equality.html#%28def._%28%28quote._~23~25kernel%29._equal~3f%29%29" class="RktValLink" data-pltdoc="x">equal?</a></span> to the
result of <span class="RktVar">val-expr</span>. If no such <span class="RktVar">datum</span> is present, the
<span class="RktSym"><a href="if.html#%28form._%28%28lib._racket%2Fprivate%2Fletstx-scheme..rkt%29._else%29%29" class="RktStxLink" data-pltdoc="x">else</a></span> <span class="RktVar">case-clause</span> is selected; if no <span class="RktSym"><a href="if.html#%28form._%28%28lib._racket%2Fprivate%2Fletstx-scheme..rkt%29._else%29%29" class="RktStxLink" data-pltdoc="x">else</a></span>
<span class="RktVar">case-clause</span> is present, either, then the result of the
<span class="RktSym"><a href="case.html#%28form._%28%28lib._racket%2Fprivate%2Fmore-scheme..rkt%29._case%29%29" class="RktStxLink" data-pltdoc="x">case</a></span> form is <a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=guide&amp;rel=void_undefined.html&amp;version=8.6" class="RktModLink Sq" data-pltdoc="x"><span class="nobreak"><span class="RktRes">#&lt;void&gt;</span></span></a>.</div><div class="SIntrapara"><blockquote class="refpara"><blockquote class="refcolumn"><blockquote class="refcontent"><p>The <span class="RktSym"><a href="case.html#%28form._%28%28lib._racket%2Fprivate%2Fmore-scheme..rkt%29._case%29%29" class="RktStxLink" data-pltdoc="x">case</a></span>
form of <a href="index.html" class="RktModLink" data-pltdoc="x"><span class="RktSym">racket</span></a> differs from that of <a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=r6rs&amp;rel=index.html&amp;version=8.6" class="Sq" data-pltdoc="x">R6RS: Scheme</a> or <a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=r5rs&amp;rel=index.html&amp;version=8.6" class="Sq" data-pltdoc="x">R5RS: Legacy Scheme</a> by being based on <span class="RktSym"><a href="Equality.html#%28def._%28%28quote._~23~25kernel%29._equal~3f%29%29" class="RktValLink" data-pltdoc="x">equal?</a></span> instead of
<span class="RktSym"><a href="Equality.html#%28def._%28%28quote._~23~25kernel%29._eqv~3f%29%29" class="RktValLink" data-pltdoc="x">eqv?</a></span> (in addition to allowing internal definitions).</p></blockquote></blockquote></blockquote></div></p><p>For the selected <span class="RktVar">case-clause</span>, the results of the last
<span class="RktVar">then-body</span>, which is in tail position with respect to the
<span class="RktSym"><a href="case.html#%28form._%28%28lib._racket%2Fprivate%2Fmore-scheme..rkt%29._case%29%29" class="RktStxLink" data-pltdoc="x">case</a></span> form, are the results for the whole <span class="RktSym"><a href="case.html#%28form._%28%28lib._racket%2Fprivate%2Fmore-scheme..rkt%29._case%29%29" class="RktStxLink" data-pltdoc="x">case</a></span> form.</p><p>A <span class="RktVar">case-clause</span> that starts with <span class="RktSym"><a href="if.html#%28form._%28%28lib._racket%2Fprivate%2Fletstx-scheme..rkt%29._else%29%29" class="RktStxLink" data-pltdoc="x">else</a></span> must be the last
<span class="RktVar">case-clause</span>.</p><p>The <span class="RktSym"><a href="case.html#%28form._%28%28lib._racket%2Fprivate%2Fmore-scheme..rkt%29._case%29%29" class="RktStxLink" data-pltdoc="x">case</a></span> form can dispatch to a matching <span class="RktVar">case-clause</span>
in <span style="font-style: italic">O</span>(<span style="font-style: italic">log N</span>)<span style="font-style: italic"></span> time for <span style="font-style: italic">N</span> <span class="RktVar">datum</span>s.</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">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="case.html#%28form._%28%28lib._racket%2Fprivate%2Fmore-scheme..rkt%29._case%29%29" class="RktStxLink" data-pltdoc="x">case</a></span><span class="hspace">&nbsp;</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">&nbsp;</span><span class="RktVal">7</span><span class="hspace">&nbsp;</span><span class="RktVal">5</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;</span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktVal">1</span><span class="hspace">&nbsp;</span><span class="RktVal">2</span><span class="hspace">&nbsp;</span><span class="RktVal">3</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">small</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;</span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktVal">10</span><span class="hspace">&nbsp;</span><span class="RktVal">11</span><span class="hspace">&nbsp;</span><span class="RktVal">12</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">big</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">'big</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="case.html#%28form._%28%28lib._racket%2Fprivate%2Fmore-scheme..rkt%29._case%29%29" class="RktStxLink" data-pltdoc="x">case</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._-%29%29" class="RktValLink" data-pltdoc="x"><span class="nobreak">-</span></a></span><span class="hspace">&nbsp;</span><span class="RktVal">7</span><span class="hspace">&nbsp;</span><span class="RktVal">5</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;</span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktVal">1</span><span class="hspace">&nbsp;</span><span class="RktVal">2</span><span class="hspace">&nbsp;</span><span class="RktVal">3</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">small</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;</span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktVal">10</span><span class="hspace">&nbsp;</span><span class="RktVal">11</span><span class="hspace">&nbsp;</span><span class="RktVal">12</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">big</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">'small</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="case.html#%28form._%28%28lib._racket%2Fprivate%2Fmore-scheme..rkt%29._case%29%29" class="RktStxLink" data-pltdoc="x">case</a></span><span class="hspace">&nbsp;</span><span class="Rkt
Reference in a new issue Copy permalink