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<link type="text/css" rel="stylesheet" href="http://pasterack.org/scribble.css"/><link type="text/css" rel="stylesheet" href="http://pasterack.org/racket.css"/><link type="text/css" rel="stylesheet" href="http://fonts.googleapis.com/css?family=Droid+Sans+Mono"/><div style="font-family:'Droid Sans Mono',monospace;background-color:transparent"><ol start="0" style="font-size:70%;color:#A0A0A0"><li><span style="font-family:'Droid Sans Mono',monospace;font-size:125%"><a class="RktModLink" data-pltdoc="x" href="http://docs.racket-lang.org/guide/Module_Syntax.html#%28part._hash-lang%29"><span class="RktMod">#lang</span></a><span class="RktMeta"></span><span class="hspace"> </span><span class="RktMeta"></span><a class="RktModLink" data-pltdoc="x" href="http://docs.racket-lang.org/reference/index.html"><span class="RktSym">racket</span></a><span class="RktMeta"></span></span></li><li><span style="font-family:'Droid Sans Mono',monospace;font-size:125%"><span class="RktMeta"> </span></span></li><li><span style="font-family:'Droid Sans Mono',monospace;font-size:125%"><span class="RktMeta"></span><span class="RktPn">(</span><span class="RktSym"><a class="RktStxLink" data-pltdoc="x" href="http://docs.racket-lang.org/reference/require.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._require%29%29">require</a></span><span class="RktMeta"></span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktSym">syntax/parse/define</span><span class="RktPn">)</span><span class="RktMeta"></span></span></li><li><span style="font-family:'Droid Sans Mono',monospace;font-size:125%"><span class="RktMeta"> </span></span></li><li><span style="font-family:'Droid Sans Mono',monospace;font-size:125%"><span class="RktMeta"></span><span class="RktPn">(</span><span class="RktSym"><a class="RktStxLink" data-pltdoc="x" href="http://docs.racket-lang.org/syntax/Defining_Simple_Macros.html#%28form._%28%28lib._syntax%2Fparse%2Fdefine..rkt%29._define-simple-macro%29%29">define-simple-macro</a></span><span class="RktMeta"></span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktPn">(</span><span class="RktSym">opt</span><span class="RktMeta"></span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktPn">{</span><span class="RktSym">~optional</span><span class="RktMeta"></span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktSym">x</span><span class="RktMeta"></span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktPn">#:defaults</span><span class="RktMeta"></span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">x</span><span class="RktMeta"></span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktSym"><a class="RktStxLink" data-pltdoc="x" href="http://docs.racket-lang.org/reference/stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._syntax%29%29">#'</a></span><span class="RktVal">#f</span><span class="RktPn">]</span><span class="RktPn">)</span><span class="RktPn">}</span><span class="RktPn">)</span><span class="RktMeta"></span></span></li><li><span style="font-family:'Droid Sans Mono',monospace;font-size:125%"><span class="RktMeta"></span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktSym">x</span><span class="RktPn">)</span><span class="RktMeta"></span></span></li><li><span style="font-family:'Droid Sans Mono',monospace;font-size:125%"><span class="RktMeta"> </span></span></li><li><span style="font-family:'Droid Sans Mono',monospace;font-size:125%"><span class="RktMeta"></span><span class="RktPn">(</span><span class="RktSym">opt</span><span class="RktPn">)</span><span class="RktMeta"></span></span></li><li><span style="font-family:'Droid Sans Mono',monospace;font-size:125%"><span class="RktMeta"></span><span class="RktPn">(</span><span class="RktSym">opt</span><span class="RktMeta"></span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktVal">42</span><span class="RktPn">)</span><span class="RktMeta"></span></span></li></ol><p>=></p><blockquote><table style="font-size:90%;table-layout:fixed;width:100%;word-wrap:break-word"><tr><td><p><span class="RktRes">#f</span></p></td></tr><tr><td><p><span class="RktRes">42</span></p></td></tr></table></blockquote></div>
#lang
racket
(
require
syntax/parse/define
)
(
define-simple-macro
(
opt
{
~optional
x
#:defaults
(
[
x
#'
#f
]
)
}
)
x
)
(
opt
)
(
opt
42
)
=>
#f
42