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<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"/><title>17&nbsp;Creating Languages</title><link rel="stylesheet" type="text/css" href="../scribble.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" 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align="right">2&nbsp;</td><td><a href="to-scheme.html" class="tocviewlink" data-pltdoc="x">Racket Essentials</a></td></tr><tr><td align="right">3&nbsp;</td><td><a href="datatypes.html" class="tocviewlink" data-pltdoc="x">Built-<wbr></wbr>In Datatypes</a></td></tr><tr><td align="right">4&nbsp;</td><td><a href="scheme-forms.html" class="tocviewlink" data-pltdoc="x">Expressions and Definitions</a></td></tr><tr><td align="right">5&nbsp;</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&nbsp;</td><td><a href="modules.html" class="tocviewlink" data-pltdoc="x">Modules</a></td></tr><tr><td align="right">7&nbsp;</td><td><a href="contracts.html" class="tocviewlink" data-pltdoc="x">Contracts</a></td></tr><tr><td align="right">8&nbsp;</td><td><a href="i_o.html" class="tocviewlink" data-pltdoc="x">Input and Output</a></td></tr><tr><td align="right">9&nbsp;</td><td><a href="regexp.html" class="tocviewlink" data-pltdoc="x">Regular Expressions</a></td></tr><tr><td align="right">10&nbsp;</td><td><a href="control.html" class="tocviewlink" data-pltdoc="x">Exceptions and Control</a></td></tr><tr><td align="right">11&nbsp;</td><td><a href="for.html" class="tocviewlink" data-pltdoc="x">Iterations and Comprehensions</a></td></tr><tr><td align="right">12&nbsp;</td><td><a href="match.html" class="tocviewlink" data-pltdoc="x">Pattern Matching</a></td></tr><tr><td align="right">13&nbsp;</td><td><a href="classes.html" class="tocviewlink" data-pltdoc="x">Classes and Objects</a></td></tr><tr><td align="right">14&nbsp;</td><td><a href="units.html" class="tocviewlink" data-pltdoc="x">Units</a></td></tr><tr><td align="right">15&nbsp;</td><td><a href="reflection.html" class="tocviewlink" data-pltdoc="x">Reflection and Dynamic Evaluation</a></td></tr><tr><td align="right">16&nbsp;</td><td><a href="macros.html" class="tocviewlink" data-pltdoc="x">Macros</a></td></tr><tr><td align="right">17&nbsp;</td><td><a href="" class="tocviewselflink" data-pltdoc="x">Creating Languages</a></td></tr><tr><td align="right">18&nbsp;</td><td><a href="concurrency.html" class="tocviewlink" data-pltdoc="x">Concurrency and Synchronization</a></td></tr><tr><td align="right">19&nbsp;</td><td><a href="performance.html" class="tocviewlink" data-pltdoc="x">Performance</a></td></tr><tr><td align="right">20&nbsp;</td><td><a href="parallelism.html" class="tocviewlink" data-pltdoc="x">Parallelism</a></td></tr><tr><td align="right">21&nbsp;</td><td><a href="running.html" class="tocviewlink" data-pltdoc="x">Running and Creating Executables</a></td></tr><tr><td align="right">22&nbsp;</td><td><a href="More_Libraries.html" class="tocviewlink" data-pltdoc="x">More Libraries</a></td></tr><tr><td align="right">23&nbsp;</td><td><a href="dialects.html" class="tocviewlink" data-pltdoc="x">Dialects of Racket and Scheme</a></td></tr><tr><td align="right">24&nbsp;</td><td><a href="other-editors.html" class="tocviewlink" data-pltdoc="x">Command-<wbr></wbr>Line Tools and Your Editor of Choice</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,&quot;tocview_1&quot;);">&#9660;</a></td><td>17&nbsp;</td><td><a href="" class="tocviewselflink" data-pltdoc="x">Creating Languages</a></td></tr></table><div class="tocviewsublistbottom" style="display: block;" id="tocview_1"><table cellspacing="0" cellpadding="0"><tr><td align="right">17.1&nbsp;</td><td><a href="module-languages.html" class="tocviewlink" data-pltdoc="x">Module Languages</a></td></tr><tr><td align="right">17.2&nbsp;</td><td><a href="hash-reader.html" class="tocviewlink" data-pltdoc="x">Reader Extensions</a></td></tr><tr><td align="right">17.3&nbsp;</td><td><a href="hash-languages.html" class="tocviewlink" data-pltdoc="x">Defining new <span class="RktModLink"><span class="RktMod">#lang</span></span> Languages</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, &quot;6.7&quot;, &quot;../&quot;);" onfocus="this.style.color=&quot;black&quot;; this.style.textAlign=&quot;left&quot;; if (this.value == &quot;...search manuals...&quot;) this.value=&quot;&quot;;" onblur="if (this.value.match(/^ *$/)) { this.style.color=&quot;#888&quot;; this.style.textAlign=&quot;center&quot;; this.value=&quot;...search manuals...&quot;; }"/></form>&nbsp;&nbsp;<a href="../index.html" title="up to the documentation top" data-pltdoc="x" onclick="return GotoPLTRoot(&quot;6.7&quot;);">top</a></span><span class="navright">&nbsp;&nbsp;<a href="stx-certs.html" title="backward to &quot;16.2.7 Syntax Taints&quot;" data-pltdoc="x">&larr; prev</a>&nbsp;&nbsp;<a href="index.html" title="up to &quot;The Racket Guide&quot;" data-pltdoc="x">up</a>&nbsp;&nbsp;<a href="module-languages.html" title="forward to &quot;17.1 Module Languages&quot;" data-pltdoc="x">next &rarr;</a></span>&nbsp;</div><h3 x-source-module="(lib &quot;scribblings/guide/guide.scrbl&quot;)" x-source-pkg="racket-doc" x-part-tag="&quot;languages&quot;">17<tt>&nbsp;</tt><a name="(part._languages)"></a>Creating Languages</h3><p>The <a href="macros.html#%28tech._macro%29" class="techoutside" data-pltdoc="x"><span class="techinside">macro</span></a> facilities defined in the preceding chapter let a
programmer define syntactic extensions to a language, but a macro is
limited in two ways:</p><ul><li><p>a macro cannot restrict the syntax available in its context or
change the meaning of surrounding forms; and</p></li><li><p>a macro can extend the syntax of a language only within the
parameters of the language&rsquo;s lexical conventions, such as using
parentheses to group the macro name with its subforms and using
the core syntax of identifiers, keywords, and literals.</p></li></ul><blockquote class="refpara"><blockquote class="refcolumn"><blockquote class="refcontent"><p><span class="imageleft"><img src="finger.png" alt="+" width="24" height="24"/></span>The distinction between the <a href="Pairs__Lists__and_Racket_Syntax.html#%28tech._reader%29" class="techoutside" data-pltdoc="x"><span class="techinside">reader</span></a> and
<a href="Pairs__Lists__and_Racket_Syntax.html#%28tech._expander%29" class="techoutside" data-pltdoc="x"><span class="techinside">expander</span></a> layer is introduced in <a href="Pairs__Lists__and_Racket_Syntax.html#%28part._lists-and-syntax%29" data-pltdoc="x">Lists and Racket Syntax</a>.</p></blockquote></blockquote></blockquote><p>That is, a macro can only extend a language, and it can do so only at
the <a href="Pairs__Lists__and_Racket_Syntax.html#%28tech._expander%29" class="techoutside" data-pltdoc="x"><span class="techinside">expander</span></a> layer. Racket offers additional facilities for
defining a starting point of the <a href="Pairs__Lists__and_Racket_Syntax.html#%28tech._expander%29" class="techoutside" data-pltdoc="x"><span class="techinside">expander</span></a> layer, for extending
the <a href="Pairs__Lists__and_Racket_Syntax.html#%28tech._reader%29" class="techoutside" data-pltdoc="x"><span class="techinside">reader</span></a> layer, for defining the starting point of the
<a href="Pairs__Lists__and_Racket_Syntax.html#%28tech._reader%29" class="techoutside" data-pltdoc="x"><span class="techinside">reader</span></a> layer, and for packaging a <a href="Pairs__Lists__and_Racket_Syntax.html#%28tech._reader%29" class="techoutside" data-pltdoc="x"><span class="techinside">reader</span></a> and
<a href="Pairs__Lists__and_Racket_Syntax.html#%28tech._expander%29" class="techoutside" data-pltdoc="x"><span class="techinside">expander</span></a> starting point into a conveniently named language.</p><table cellspacing="0" cellpadding="0"><tr><td><p><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;</span><a href="module-languages.html" class="toclink" data-pltdoc="x">17.1<span class="hspace">&nbsp;</span>Module Languages</a></p></td></tr><tr><td><p><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><a href="module-languages.html#%28part._implicit-forms%29" class="toclink" data-pltdoc="x">17.1.1<span class="hspace">&nbsp;</span>Implicit Form Bindings</a></p></td></tr><tr><td><p><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><a href="module-languages.html#%28part._s-exp%29" class="toclink" data-pltdoc="x">17.1.2<span class="hspace">&nbsp;</span>Using <span class="RktModLink"><span class="RktMod">#lang</span></span><span class="stt"> </span><span class="RktModLink"><span class="RktSym">s-exp</span></span></a></p></td></tr><tr><td><p><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;</span><a href="hash-reader.html" class="toclink" data-pltdoc="x">17.2<span class="hspace">&nbsp;</span>Reader Extensions</a></p></td></tr><tr><td><p><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><a href="hash-reader.html#%28part._.Source_.Locations%29" class="toclink" data-pltdoc="x">17.2.1<span class="hspace">&nbsp;</span>Source Locations</a></p></td></tr><tr><td><p><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><a href="hash-reader.html#%28part._readtable%29" class="toclink" data-pltdoc="x">17.2.2<span class="hspace">&nbsp;</span>Readtables</a></p></td></tr><tr><td><p><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;</span><a href="hash-languages.html" class="toclink" data-pltdoc="x">17.3<span class="hspace">&nbsp;</span>Defining new <span class="RktModLink"><span class="RktMod">#lang</span></span> Languages</a></p></td></tr><tr><td><p><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><a href="hash-lang_syntax.html" class="toclink" data-pltdoc="x">17.3.1<span class="hspace">&nbsp;</span>Designating a <span class="RktModLink"><span class="RktMod">#lang</span></span> Language</a></p></td></tr><tr><td><p><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><a href="hash-lang_reader.html" class="toclink" data-pltdoc="x">17.3.2<span class="hspace">&nbsp;</span>Using <span class="RktModLink"><span class="RktMod">#lang</span></span><span class="stt"> </span><span class="RktModLink"><span class="RktSym">reader</span></span></a></p></td></tr><tr><td><p><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><a href="syntax_module-reader.html" class="toclink" data-pltdoc="x">17.3.3<span class="hspace">&nbsp;</span>Using <span class="RktModLink"><span class="RktMod">#lang</span></span><span class="stt"> </span><span class="RktModLink"><span class="RktSym">s-exp</span></span><span class="stt"> </span><span class="RktModLink"><span class="RktSym">syntax/module-reader</span></span></a></p></td></tr><tr><td><p><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><a href="language-collection.html" class="toclink" data-pltdoc="x">17.3.4<span class="hspace">&nbsp;</span>Installing a Language</a></p></td></tr><tr><td><p><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><a href="language-get-info.html" class="toclink" data-pltdoc="x">17.3.5<span class="hspace">&nbsp;</span>Source-Handling Configuration</a></p></td></tr><tr><td><p><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><a href="module-runtime-config.html" class="toclink" data-pltdoc="x">17.3.6<span class="hspace">&nbsp;</span>Module-Handling Configuration</a></p></td></tr></table><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, &quot;6.7&quot;, &quot;../&quot;);" onfocus="this.style.color=&quot;black&quot;; 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