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<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"/><title>16.2.1 Syntax Objects</title><link rel="stylesheet" type="text/css" href="../scribble.css" title="default"/><link rel="stylesheet" type="text/css" href="../racket.css" title="default"/><link rel="stylesheet" type="text/css" href="../manual-style.css" title="default"/><link rel="stylesheet" type="text/css" href="../manual-racket.css" title="default"/><link rel="stylesheet" type="text/css" href="../manual-racket.css" title="default"/><link rel="stylesheet" type="text/css" href="../doc-site.css" title="default"/><script type="text/javascript" src="../scribble-common.js"></script><script type="text/javascript" src="../manual-racket.js"></script><script type="text/javascript" src="../manual-racket.js"></script><script type="text/javascript" src="../doc-site.js"></script><script type="text/javascript" src="../local-redirect/local-redirect.js"></script><script type="text/javascript" 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Essentials</a></td></tr><tr><td align="right">3 </td><td><a href="datatypes.html" class="tocviewlink" data-pltdoc="x">Built-<wbr></wbr>In Datatypes</a></td></tr><tr><td align="right">4 </td><td><a href="scheme-forms.html" class="tocviewlink" data-pltdoc="x">Expressions and Definitions</a></td></tr><tr><td align="right">5 </td><td><a href="define-struct.html" class="tocviewlink" data-pltdoc="x">Programmer-<wbr></wbr>Defined Datatypes</a></td></tr><tr><td align="right">6 </td><td><a href="modules.html" class="tocviewlink" data-pltdoc="x">Modules</a></td></tr><tr><td align="right">7 </td><td><a href="contracts.html" class="tocviewlink" data-pltdoc="x">Contracts</a></td></tr><tr><td align="right">8 </td><td><a href="i_o.html" class="tocviewlink" data-pltdoc="x">Input and Output</a></td></tr><tr><td align="right">9 </td><td><a href="regexp.html" class="tocviewlink" data-pltdoc="x">Regular Expressions</a></td></tr><tr><td align="right">10 </td><td><a href="control.html" class="tocviewlink" 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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>16 </td><td><a href="macros.html" class="tocviewlink" data-pltdoc="x">Macros</a></td></tr></table><div class="tocviewsublist" style="display: none;" id="tocview_1"><table cellspacing="0" cellpadding="0"><tr><td align="right">16.1 </td><td><a href="pattern-macros.html" class="tocviewlink" data-pltdoc="x">Pattern-<wbr></wbr>Based Macros</a></td></tr><tr><td align="right">16.2 </td><td><a href="proc-macros.html" class="tocviewselflink" data-pltdoc="x">General Macro Transformers</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_2");">▼</a></td><td>16.2 </td><td><a href="proc-macros.html" class="tocviewlink" data-pltdoc="x">General Macro Transformers</a></td></tr></table><div class="tocviewsublistbottom" style="display: block;" id="tocview_2"><table cellspacing="0" cellpadding="0"><tr><td align="right">16.2.1 </td><td><a href="" class="tocviewselflink" data-pltdoc="x">Syntax Objects</a></td></tr><tr><td align="right">16.2.2 </td><td><a href="macro-transformers.html" class="tocviewlink" data-pltdoc="x">Macro Transformer Procedures</a></td></tr><tr><td align="right">16.2.3 </td><td><a href="syntax-case.html" class="tocviewlink" data-pltdoc="x">Mixing Patterns and Expressions:<span class="mywbr"> </span> <span class="RktSym"><span class="RktStxLink">syntax-<wbr></wbr>case</span></span></a></td></tr><tr><td align="right">16.2.4 </td><td><a href="with-syntax.html" class="tocviewlink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">with-<wbr></wbr>syntax</span></span> and <span class="RktSym"><span class="RktValLink">generate-<wbr></wbr>temporaries</span></span></a></td></tr><tr><td align="right">16.2.5 </td><td><a href="stx-phases.html" class="tocviewlink" data-pltdoc="x">Compile and Run-<wbr></wbr>Time Phases</a></td></tr><tr><td align="right">16.2.6 </td><td><a href="phases.html" class="tocviewlink" data-pltdoc="x">General Phase Levels</a></td></tr><tr><td align="right">16.2.7 </td><td><a href="stx-certs.html" class="tocviewlink" data-pltdoc="x">Syntax Taints</a></td></tr></table></div></div></div></div><div class="maincolumn"><div class="main"><div class="navsettop"><span class="navleft"><form class="searchform"><input class="searchbox" style="color: #888;" type="text" value="...search manuals..." title="Enter a search string to search the manuals" onkeypress="return DoSearchKey(event, this, "6.1", "../");" 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("6.1");">top</a></span><span class="navright"> <a href="proc-macros.html" title="backward to "16.2 General Macro Transformers"" data-pltdoc="x">← prev</a> <a href="proc-macros.html" title="up to "16.2 General Macro Transformers"" data-pltdoc="x">up</a> <a href="macro-transformers.html" title="forward to "16.2.2 Macro Transformer Procedures"" data-pltdoc="x">next →</a></span> </div><h5 x-source-module="(lib "scribblings/guide/guide.scrbl")" x-part-tag=""stx-obj"">16.2.1<tt> </tt><a name="(part._stx-obj)"></a>Syntax Objects</h5><p>The input and output of a macro transformer (i.e., source and
replacement forms) are represented as <a name="(tech._syntax._object)"></a><span style="font-style: italic">syntax objects</span>. A
syntax object contains symbols, lists, and constant values (such as
numbers) that essentially correspond to the <span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=quote.html%23%2528form._%2528%2528quote._%7E23%7E25kernel%2529._quote%2529%2529&version=6.1" class="RktStxLink Sq" data-pltdoc="x">quote</a></span>d form of
the expression. For example, a representation of the expression
<span class="RktPn">(</span><span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=generic-numbers.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._%252B%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">+</a></span><span class="stt"> </span><span class="RktVal">1</span><span class="stt"> </span><span class="RktVal">2</span><span class="RktPn">)</span> contains the symbol <span class="RktVal">'</span><span class="RktVal">+</span> and the numbers
<span class="RktVal">1</span> and <span class="RktVal">2</span>, all in a list. In addition to this quoted
content, a syntax object associates source-location and
lexical-binding information with each part of the form. The
source-location information is used when reporting syntax errors (for
example), and the lexical-binding information allows the macro system
to maintain lexical scope. To accommodate this extra information, the
represention of the expression <span class="RktPn">(</span><span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=generic-numbers.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._%252B%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">+</a></span><span class="stt"> </span><span class="RktVal">1</span><span class="stt"> </span><span class="RktVal">2</span><span class="RktPn">)</span> is not merely
<span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">+</span><span class="stt"> </span><span class="RktVal">1</span><span class="stt"> </span><span class="RktVal">2</span><span class="RktVal">)</span>, but a packaging of <span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">+</span><span class="stt"> </span><span class="RktVal">1</span><span class="stt"> </span><span class="RktVal">2</span><span class="RktVal">)</span> into a syntax
object.</p><p>To create a literal syntax object, use the <span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=stx-patterns.html%23%2528form._%2528%2528lib._racket%252Fprivate%252Fstxcase-scheme..rkt%2529._syntax%2529%2529&version=6.1" class="RktStxLink Sq" data-pltdoc="x">syntax</a></span> form:</p><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="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=stx-patterns.html%23%2528form._%2528%2528lib._racket%252Fprivate%252Fstxcase-scheme..rkt%2529._syntax%2529%2529&version=6.1" class="RktStxLink Sq" data-pltdoc="x">syntax</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=generic-numbers.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._%252B%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">+</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><p><span class="RktRes">#<syntax:1:0 (+ 1 2)></span></p></td></tr></table></blockquote><p>In the same way that <span class="RktInBG"><span class="hspace"></span><span class="RktIn">'</span><span class="hspace"></span></span> abbreviates <span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=quote.html%23%2528form._%2528%2528quote._%7E23%7E25kernel%2529._quote%2529%2529&version=6.1" class="RktStxLink Sq" data-pltdoc="x">quote</a></span>,
<span class="RktInBG"><span class="hspace"></span><span class="RktIn">#'</span><span class="hspace"></span></span> abbreviates <span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=stx-patterns.html%23%2528form._%2528%2528lib._racket%252Fprivate%252Fstxcase-scheme..rkt%2529._syntax%2529%2529&version=6.1" class="RktStxLink Sq" data-pltdoc="x">syntax</a></span>:</p><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktRdr">#'</span><span class="RktPn">(</span><span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=generic-numbers.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._%252B%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">+</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><p><span class="RktRes">#<syntax:1:0 (+ 1 2)></span></p></td></tr></table></blockquote><p>A syntax object that contains just a symbol is an <a name="(tech._identifier._syntax._object)"></a><span style="font-style: italic">identifier
syntax object</span>. Racket provides some additional operations specific to
identifier syntax objects, including the <span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=stxops.html%23%2528def._%2528%2528lib._racket%252Fprivate%252Fstx..rkt%2529._identifier%7E3f%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">identifier?</a></span>
operation to detect identifiers. Most notably,
<span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=stxcmp.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._free-identifier%7E3d%7E3f%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">free-identifier=?</a></span> determines whether two identifiers refer
to the same binding:</p><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="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=stxops.html%23%2528def._%2528%2528lib._racket%252Fprivate%252Fstx..rkt%2529._identifier%7E3f%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">identifier?</a></span><span class="hspace"> </span><span class="RktRdr">#'</span><span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=pairs.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._car%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">car</a></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"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=stxops.html%23%2528def._%2528%2528lib._racket%252Fprivate%252Fstx..rkt%2529._identifier%7E3f%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">identifier?</a></span><span class="hspace"> </span><span class="RktRdr">#'</span><span class="RktPn">(</span><span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=generic-numbers.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._%252B%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">+</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><p><span class="RktRes">#f</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=stxcmp.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._free-identifier%7E3d%7E3f%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">free-identifier=?</a></span><span class="hspace"> </span><span class="RktRdr">#'</span><span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=pairs.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._car%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">car</a></span><span class="hspace"> </span><span class="RktRdr">#'</span><span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=pairs.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._cdr%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">cdr</a></span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#f</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=stxcmp.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._free-identifier%7E3d%7E3f%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">free-identifier=?</a></span><span class="hspace"> </span><span class="RktRdr">#'</span><span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=pairs.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._car%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">car</a></span><span class="hspace"> </span><span class="RktRdr">#'</span><span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=pairs.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._car%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">car</a></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"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=require.html%23%2528form._%2528%2528lib._racket%252Fprivate%252Fbase..rkt%2529._require%2529%2529&version=6.1" class="RktStxLink Sq" data-pltdoc="x">require</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=require.html%23%2528form._%2528%2528lib._racket%252Fprivate%252Fbase..rkt%2529._only-in%2529%2529&version=6.1" class="RktStxLink Sq" data-pltdoc="x">only-in</a></span><span class="hspace"> </span><span class="RktSym">racket/base</span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=pairs.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._car%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">car</a></span><span class="hspace"> </span><span class="RktSym">also-car</span><span class="RktPn">]</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><table cellspacing="0" cellpadding="0"><tr><td></td></tr></table></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=stxcmp.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._free-identifier%7E3d%7E3f%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">free-identifier=?</a></span><span class="hspace"> </span><span class="RktRdr">#'</span><span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=pairs.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._car%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">car</a></span><span class="hspace"> </span><span class="RktRdr">#'</span><span class="RktSym">also-car</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#t</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="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=stxcmp.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._free-identifier%7E3d%7E3f%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">free-identifier=?</a></span><span class="hspace"> </span><span class="RktRdr">#'</span><span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=pairs.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._car%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">car</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=let.html%23%2528form._%2528%2528lib._racket%252Fprivate%252Fletstx-scheme..rkt%2529._let%2529%2529&version=6.1" class="RktStxLink Sq" data-pltdoc="x">let</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=pairs.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._car%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">car</a></span><span class="hspace"> </span><span class="RktVal">8</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktRdr">#'</span><span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=pairs.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._car%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">car</a></span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">#f</span></p></td></tr></table></blockquote><p>The last example above, in particular, illustrates how syntax objects
preserve lexical-context information.</p><p>To see the lists, symbols, numbers, etc<span class="Sendabbrev">.</span> within a syntax object, use
<span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=stxops.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._syntax-%7E3edatum%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">syntax->datum</a></span>:</p><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="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=stxops.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._syntax-%7E3edatum%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">syntax->datum</a></span><span class="hspace"> </span><span class="RktRdr">#'</span><span class="RktPn">(</span><span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=generic-numbers.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._%252B%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">+</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><p><span class="RktRes">'(+ 1 2)</span></p></td></tr></table></blockquote><p>The <span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=stxops.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._syntax-e%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">syntax-e</a></span> function is similar to <span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=stxops.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._syntax-%7E3edatum%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">syntax->datum</a></span>,
but it unwraps a single layer of source-location and lexical-context
information, leaving sub-forms that have their own information wrapped
as syntax objects:</p><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="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=stxops.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._syntax-e%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">syntax-e</a></span><span class="hspace"> </span><span class="RktRdr">#'</span><span class="RktPn">(</span><span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=generic-numbers.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._%252B%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">+</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><p><span class="RktRes">'(#<syntax:1:0 +> #<syntax:1:0 1> #<syntax:1:0 2>)</span></p></td></tr></table></blockquote><p>The <span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=stxops.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._syntax-e%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">syntax-e</a></span> function always leaves syntax-object wrappers
around sub-forms that are represented via symbols, numbers, and other
literal values. The only time it unwraps extra sub-forms is when
unwrapping a pair, in which case the <span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=pairs.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._cdr%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">cdr</a></span> of the pair may be
recursively unwrapped, depending on how the syntax object was
constructed.</p><p>The opposite of <span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=stxops.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._syntax-%7E3edatum%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">syntax->datum</a></span> is, of course,
<span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=stxops.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._datum-%7E3esyntax%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">datum->syntax</a></span>. In addition to a datum like <span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">+</span><span class="stt"> </span><span class="RktVal">1</span><span class="stt"> </span><span class="RktVal">2</span><span class="RktVal">)</span>, <span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=stxops.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._datum-%7E3esyntax%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">datum->syntax</a></span> needs an existing syntax object to donate
its lexical context, and optionally another syntax object to donate
its source location:</p><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="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=stxops.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._datum-%7E3esyntax%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">datum->syntax</a></span><span class="hspace"> </span><span class="RktRdr">#'</span><span class="RktSym">lex</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">+</span><span class="hspace"> </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="RktRdr">#'</span><span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=exns.html%23%2528def._%2528%2528lib._racket%252Fprivate%252Fbase..rkt%2529._srcloc%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">srcloc</a></span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">#<syntax:1:0 (+ 1 2)></span></p></td></tr></table></blockquote><p>In the above example, the lexical context of <span class="RktRdr">#'</span><span class="RktSym">lex</span> is used
for the new syntax object, while the source location of
<span class="RktRdr">#'</span><span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=exns.html%23%2528def._%2528%2528lib._racket%252Fprivate%252Fbase..rkt%2529._srcloc%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">srcloc</a></span> is used.</p><p>When the second (i.e., the “datum”) argument to
<span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=stxops.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._datum-%7E3esyntax%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">datum->syntax</a></span> includes syntax objects, those syntax objects
are preserved intact in the result. That is, deconstructing the result
with <span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=stxops.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._syntax-e%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">syntax-e</a></span> eventually produces the syntax objects that
were given to <span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=stxops.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._datum-%7E3esyntax%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">datum->syntax</a></span>.</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, "6.1", "../");" 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("6.1");">top</a></span><span class="navright"> <a href="proc-macros.html" title="backward to "16.2 General Macro Transformers"" data-pltdoc="x">← prev</a> <a href="proc-macros.html" title="up to "16.2 General Macro Transformers"" data-pltdoc="x">up</a> <a href="macro-transformers.html" title="forward to "16.2.2 Macro Transformer Procedures"" data-pltdoc="x">next →</a></span> </div></div></div><div id="contextindicator"> </div></body></html>
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