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<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"/><meta name="viewport" content="width=device-width, initial-scale=0.8"/><title>3.8 Procedure Expressions: lambda and case-lambda</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="icons.css" title="default"/><link rel="stylesheet" type="text/css" href="../manual-style.css" title="default"/><link rel="stylesheet" type="text/css" href="../manual-racket.css" title="default"/><link rel="stylesheet" type="text/css" href="../manual-racket.css" title="default"/><link rel="stylesheet" type="text/css" href="../doc-site.css" title="default"/><script type="text/javascript" src="../scribble-common.js"></script><script type="text/javascript" src="../manual-racket.js"></script><script type="text/javascript" src="../manual-racket.js"></script><script type="text/javascript" src="../doc-site.js"></script><script type="text/javascript" src="../local-redirect/local-redirect.js"></script><script type="text/javascript" src="../local-redirect/local-user-redirect.js"></script><!--[if IE 6]><style type="text/css">.SIEHidden { overflow: hidden; }</style><![endif]--></head><body id="doc-racket-lang-org"><div class="tocset"><div class="tocview"><div class="tocviewlist tocviewlisttopspace"><div class="tocviewtitle"><table cellspacing="0" cellpadding="0"><tr><td style="width: 1em;"><a href="javascript:void(0);" title="Expand/Collapse" class="tocviewtoggle" onclick="TocviewToggle(this,"tocview_0");">►</a></td><td></td><td><a href="index.html" class="tocviewlink" data-pltdoc="x">The Racket 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 </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="tocviewselflink" data-pltdoc="x">Syntactic Forms</a></td></tr><tr><td align="right">4 </td><td><a href="data.html" class="tocviewlink" data-pltdoc="x">Datatypes</a></td></tr><tr><td align="right">5 </td><td><a href="structures.html" class="tocviewlink" data-pltdoc="x">Structures</a></td></tr><tr><td align="right">6 </td><td><a href="mzlib_class.html" class="tocviewlink" data-pltdoc="x">Classes and Objects</a></td></tr><tr><td align="right">7 </td><td><a href="mzlib_unit.html" class="tocviewlink" data-pltdoc="x">Units</a></td></tr><tr><td align="right">8 </td><td><a href="contracts.html" class="tocviewlink" data-pltdoc="x">Contracts</a></td></tr><tr><td align="right">9 </td><td><a href="match.html" class="tocviewlink" data-pltdoc="x">Pattern Matching</a></td></tr><tr><td align="right">10 </td><td><a href="control.html" class="tocviewlink" data-pltdoc="x">Control Flow</a></td></tr><tr><td align="right">11 </td><td><a href="concurrency.html" class="tocviewlink" data-pltdoc="x">Concurrency and Parallelism</a></td></tr><tr><td align="right">12 </td><td><a href="Macros.html" class="tocviewlink" data-pltdoc="x">Macros</a></td></tr><tr><td align="right">13 </td><td><a href="input-and-output.html" class="tocviewlink" data-pltdoc="x">Input and Output</a></td></tr><tr><td align="right">14 </td><td><a href="security.html" class="tocviewlink" data-pltdoc="x">Reflection and Security</a></td></tr><tr><td align="right">15 </td><td><a href="os.html" class="tocviewlink" data-pltdoc="x">Operating System</a></td></tr><tr><td align="right">16 </td><td><a href="memory.html" class="tocviewlink" data-pltdoc="x">Memory Management</a></td></tr><tr><td align="right">17 </td><td><a href="unsafe.html" class="tocviewlink" data-pltdoc="x"
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arguments and which keyword arguments that the procedure accepts.</div></p><p>Considering only the first <span class="RktVar">arg</span> case, a simple
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<span class="RktVar">kw-formals</span> has one of the following three forms:</p><blockquote class="leftindent"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><span class="RktPn">(</span><span class="RktVar">id</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></td></tr></table></blockquote><p> The procedure accepts as many non-keyword
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argument values as the number of <span class="RktVar">id</span>s. Each <span class="RktVar">id</span>
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is associated with an argument value by position.</p></blockquote><blockquote class="leftindent"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><span class="RktPn">(</span><span class="RktVar">id</span><span class="hspace"> </span><span class="RktMeta">...+</span><span class="hspace"> </span><span class="RktPn">. </span><span class="RktVar">rest-id</span><span class="RktPn">)</span></td></tr></table></blockquote><p> The procedure accepts any number of
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non-keyword arguments greater or equal to the number of
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<span class="RktVar">id</span>s. When the procedure is applied, the <span class="RktVar">id</span>s
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are associated with argument values by position, and all
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leftover arguments are placed into a list that is associated to
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<span class="RktVar">rest-id</span>.</p></blockquote><blockquote class="leftindent"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><span class="RktVar">rest-id</span></td></tr></table></blockquote><p> The procedure accepts any number of non-keyword
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arguments. All arguments are placed into a list that is
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associated with <span class="RktVar">rest-id</span>.</p></blockquote><p>More generally, an <span class="RktVar">arg</span> can include a keyword and/or default
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value. Thus, the first two cases above are more completely specified
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as follows:</p><blockquote class="leftindent"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><span class="RktPn">(</span><span class="RktVar">arg</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></td></tr></table></blockquote><p> Each <span class="RktVar">arg</span> has the following
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four forms:</p><blockquote class="leftindent"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><span class="RktVar">id</span></td></tr></table></blockquote><p>Adds one to both the minimum and maximum
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number of non-keyword arguments accepted by the procedure. The
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<span class="RktVar">id</span> is associated with an actual argument by
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position.</p></blockquote><blockquote class="leftindent"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><span class="RktPn">[</span><span class="RktVar">id</span><span class="hspace"> </span><span class="RktVar">default-expr</span><span class="RktPn">]</span></td></tr></table></blockquote><p>Adds one to the maximum number
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of non-keyword arguments accepted by the procedure. The
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<span class="RktVar">id</span> is associated with an actual argument by position,
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and if no such argument is provided, the <span class="RktVar">default-expr</span>
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is evaluated to produce a value associated with <span class="RktVar">id</span>.
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No <span class="RktVar">arg</span> with a <span class="RktVar">default-expr</span> can appear
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before an <span class="RktVar">id</span> without a <span class="RktVar">default-expr</span> and
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without a <span class="RktVar">keyword</span>.</p></blockquote><blockquote class="leftindent"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><span class="RktVar">keyword</span><span class="hspace"> </span><span class="RktVar">id</span></td></tr></table></blockquote><p>The procedure requires a
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keyword-based argument using <span class="RktVar">keyword</span>. The <span class="RktVar">id</span>
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is associated with a keyword-based actual argument using
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<span class="RktVar">keyword</span>.</p></blockquote><blockquote class="leftindent"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><span class="RktVar">keyword</span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktVar">id</span><span class="hspace"> </span><span class="RktVar">default-expr</span><span class="RktPn">]</span></td></tr></table></blockquote><p>The
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procedure accepts a keyword-based argument using <span class="RktVar">keyword</span>. The
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<span class="RktVar">id</span> is associated with a keyword-based actual argument
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using <span class="RktVar">keyword</span>, if supplied in an application;
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otherwise, the <span class="RktVar">default-expr</span> is evaluated to obtain a
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value to associate with <span class="RktVar">id</span>.</p></blockquote><p>The position of a <span class="RktVar">keyword</span> <span class="RktVar">arg</span> in
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<span class="RktVar">kw-formals</span> does not matter, but each specified
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<span class="RktVar">keyword</span> must be distinct.</p></blockquote><blockquote class="leftindent"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><span class="RktPn">(</span><span class="RktVar">arg</span><span class="hspace"> </span><span class="RktMeta">...+</span><span class="hspace"> </span><span class="RktPn">. </span><span class="RktVar">rest-id</span><span class="RktPn">)</span></td></tr></table></blockquote><p> Like the previous case, but
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the procedure accepts any number of non-keyword arguments
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beyond its minimum number of arguments. When more arguments are
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provided than non-<span class="RktVar">keyword</span> arguments among the
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<span class="RktVar">arg</span>s, the extra arguments are placed into a
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list that is associated to <span class="RktVar">rest-id</span>.</p></blockquote><p><div class="SIntrapara"><blockquote class="refpara"><blockquote class="refcolumn"><blockquote class="refcontent"><p>In other words, argument bindings with
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default-value expressions are evaluated analogous to <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>.</p></blockquote></blockquote></blockquote></div><div class="SIntrapara">The <span class="RktVar">kw-formals</span> identifiers are bound in the
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<span class="RktVar">body</span>s. When the procedure is applied, a new <a href="eval-model.html#%28tech._location%29" class="techoutside" data-pltdoc="x"><span class="techinside">location</span></a>
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is created for each identifier, and the location is filled with the
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associated argument value. The <a href="eval-model.html#%28tech._location%29" class="techoutside" data-pltdoc="x"><span class="techinside">locations</span></a> are created and filled
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in order, with <span class="RktVar">default-expr</span>s evaluated as needed to fill
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locations.</div></p><p>If any identifier appears in the <span class="RktVar">body</span>s that is not one of the
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identifiers in <span class="RktVar">kw-formals</span>, then it refers to the same
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location that it would if it appeared in place of the <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>
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expression. (In other words, variable reference is lexically scoped.)</p><p>When multiple identifiers appear in a <span class="RktVar">kw-formals</span>, they must
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be distinct according to <span class="RktSym"><a href="stxcmp.html#%28def._%28%28quote._~23~25kernel%29._bound-identifier~3d~3f%29%29" class="RktValLink" data-pltdoc="x">bound-identifier=?</a></span>.</p><p>If the procedure produced by <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> is applied to fewer or
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more by-position or by-keyword arguments than it accepts, to by-keyword arguments
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that it does not accept, or without required by-keyword arguments, then
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the <span class="RktSym"><a href="exns.html#%28def._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._exn~3afail~3acontract%29%29" class="RktValLink" data-pltdoc="x">exn:fail:contract</a></span> exception is raised.</p><p>The last <span class="RktVar">body</span> expression is in tail position with respect to
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the procedure body.</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="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">x</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym">x</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVal">10</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">10</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</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">x</span><span class="hspace"> </span><span class="RktSym">y</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">y</span><span class="hspace"> </span><span class="RktSym">x</span><span class="RktPn">)</span><span class="RktPn">)</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">'(2 1)</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</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">x</span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktSym">y</span><span class="hspace"> </span><span class="RktVal">5</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">y</span><span class="hspace"> </span><span class="RktSym">x</span><span class="RktPn">)</span><span class="RktPn">)</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">'(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="let.html#%28form._%28%28lib._racket%2Fprivate%2Fletstx-scheme..rkt%29._let%29%29" class="RktStxLink" data-pltdoc="x">let</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="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">x</span><span class="hspace"> </span><span class="RktPn">#:arg</span><span class="hspace"> </span><span class="RktSym">y</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 cla
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Racket looks for a <a name="(idx._(gentag._107._(lib._scribblings/reference/reference..scrbl)))"></a><span class="RktVal">'</span><span class="RktVal">method-arity-error</span> property
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attached to the expression (see <a href="stxprops.html" data-pltdoc="x">Syntax Object Properties</a>). If it is
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present with a true value, and if no case of the procedure accepts
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zero arguments, then the procedure is marked so that an
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<span class="RktSym"><a href="exns.html#%28def._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._exn~3afail~3acontract~3aarity%29%29" class="RktValLink" data-pltdoc="x">exn:fail:contract:arity</a></span> exception involving the procedure
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will hide the first argument, if one was provided. (Hiding the first
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argument is useful when the procedure implements a method, where the
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first argument is implicit in the original source). The property
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affects only the format of <span class="RktSym"><a href="exns.html#%28def._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._exn~3afail~3acontract~3aarity%29%29" class="RktValLink" data-pltdoc="x">exn:fail:contract:arity</a></span>
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exceptions, not the result of <span class="RktSym"><a href="procedures.html#%28def._%28%28quote._~23~25kernel%29._procedure-arity%29%29" class="RktValLink" data-pltdoc="x">procedure-arity</a></span>.</p><p>When a keyword-accepting procedure is bound to an identifier in
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certain ways, and when the identifier is used in the function position
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of an application form, then the application form may be expanded in
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such a way that the original binding is obscured as the target of the
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application. To help expose the connection between the function
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application and function declaration, an identifier in the expansion
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of the function application is tagged with a <a href="stxprops.html#%28tech._syntax._property%29" class="techoutside" data-pltdoc="x"><span class="techinside">syntax property</span></a>
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accessible via <span class="RktSym"><a href="stxtrans.html#%28def._%28%28lib._racket%2Fkeyword-transform..rkt%29._syntax-procedure-alias-property%29%29" class="RktValLink" data-pltdoc="x">syntax-procedure-alias-property</a></span> if it is effectively an alias
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for the original identifier. An identifier in the expansion is tagged with a
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<a href="stxprops.html#%28tech._syntax._property%29" class="techoutside" data-pltdoc="x"><span class="techinside">syntax property</span></a> accessible via <span class="RktSym"><a href="stxtrans.html#%28def._%28%28lib._racket%2Fkeyword-transform..rkt%29._syntax-procedure-converted-arguments-property%29%29" class="RktValLink" data-pltdoc="x">syntax-procedure-converted-arguments-property</a></span> if it
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is like the original identifier except that the arguments are converted to a
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flattened form: keyword arguments, required by-position arguments,
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by-position optional arguments, and rest arguments—<wbr></wbr>all as required,
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by-position arguments; the keyword arguments are sorted by keyword
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name, each optional keyword argument is followed by a boolean to
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indicate whether a value is provided, and <span class="RktVal">#f</span> is used for an
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optional keyword argument whose value is not provided; optional
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by-position arguments include <span class="RktVal">#f</span> for each non-provided
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argument, and then the sequence of optional-argument values is
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followed by a parallel sequence of booleans to indicate whether each
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optional-argument value was provided.</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._((quote._~23~25kernel)._case-lambda))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="lambda.html#%28form._%28%28quote._~23~25kernel%29._case-lambda%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">case-lambda</a></span></span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktVar">formals</span><span class="hspace"> </span><span class="RktVar">body</span><span class="hspace"> </span><span class="RktMeta">...+</span><span class="RktPn">]</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">formals</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">id</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">id</span><span class="hspace"> </span><span class="RktMeta">...+</span><span class="hspace"> </span><span class="RktPn">. </span><span class="RktVar">rest-id</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">rest-id</span></td></tr></table></td></tr></table></blockquote></div><div class="SIntrapara">Produces a procedure. Each <span class="RktPn">[</span><span class="RktVar">formals</span><span class="stt"> </span><span class="RktVar">body</span><span class="stt"> </span><span class="RktMeta"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=syntax&rel=stxparse-patterns.html%23%2528form._%2528%2528lib._syntax%252Fparse..rkt%2529._......%252B%2529%2529&version=8.6" class="RktStxLink Sq" data-pltdoc="x">...+</a></span><span class="RktPn">]</span>
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clause is analogous to a single <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> procedure; applying
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the <span class="RktSym"><a href="lambda.html#%28form._%28%28quote._~23~25kernel%29._case-lambda%29%29" class="RktStxLink" data-pltdoc="x">case-lambda</a></span>-generated procedure is the same as applying a
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procedure that corresponds to one of the clauses—<wbr></wbr>the first procedure
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that accepts the given number of arguments. If no corresponding
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procedure accepts the given number of arguments, the
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<span class="RktSym"><a href="exns.html#%28def._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._exn~3afail~3acontract%29%29" class="RktValLink" data-pltdoc="x">exn:fail:contract</a></span> exception is raised.</div></p><p>Note that a <span class="RktSym"><a href="lambda.html#%28form._%28%28quote._~23~25kernel%29._case-lambda%29%29" class="RktStxLink" data-pltdoc="x">case-lambda</a></span> clause supports only
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<span class="RktVar">formals</span>, not the more general <span class="RktVar">kw-formals</span> of
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<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>. That is, <span class="RktSym"><a href="lambda.html#%28form._%28%28quote._~23~25kernel%29._case-lambda%29%29" class="RktStxLink" data-pltdoc="x">case-lambda</a></span> does not directly
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support keyword and optional arguments.</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="let.html#%28form._%28%28lib._racket%2Fprivate%2Fletstx-scheme..rkt%29._let%29%29" class="RktStxLink" data-pltdoc="x">let</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="RktPn">(</span><span class="RktSym"><a href="lambda.html#%28form._%28%28quote._~23~25kernel%29._case-lambda%29%29" class="RktStxLink" data-pltdoc="x">case-lambda</a></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="hspace"> </span><span class="RktVal">10</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">x</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym">x</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">x</span><span class="hspace"> </span><span class="RktSym">y</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">y</span><span class="hspace"> </span><span class="RktSym">x</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">r</span><span class="hspace"> </span><span class="RktSym">r</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="RktPn">(</span><span class="RktSym">f</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">f</span><span class="hspace"> </span><span class="RktVal">1</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">f</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="RktSym">f</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="RktPn">)</span></td></tr></table></td></tr><tr><td><p><sp
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