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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 Context-Free Parsers</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="../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="../doc-site.js"></script><script type="text/javascript" src="file:///Users/mb/git/racket/racket/doc/local-redirect/local-redirect.js"></script><script type="text/javascript" src="file:///Users/MB/Library/Racket/6.8.0.1/doc/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">Parser Tools:<span class="mywbr"> </span> <span class="stt">lex</span> and <span class="stt">yacc</span>-<wbr></wbr>style Parsing</a></td></tr></table></div><div class="tocviewsublistonly" style="display: block;" id="tocview_0"><table cellspacing="0" cellpadding="0"><tr><td align="right">1 </td><td><a href="Lexers.html" class="tocviewlink" data-pltdoc="x">Lexers</a></td></tr><tr><td align="right">2 </td><td><a href="LALR_1__Parsers.html" class="tocviewlink" data-pltdoc="x">LALR(1) Parsers</a></td></tr><tr><td align="right">3 </td><td><a href="" class="tocviewselflink" data-pltdoc="x">Context-<wbr></wbr>Free Parsers</a></td></tr><tr><td align="right">4 </td><td><a href="Converting_yacc_or_bison_Grammars.html" class="tocviewlink" data-pltdoc="x">Converting <span class="stt">yacc</span> or <span class="stt">bison</span> Grammars</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><div class="tocsub"><div class="tocsubtitle">On this page:</div><table class="tocsublist" cellspacing="0"><tr><td><a href="#%28form._%28%28lib._br-parser-tools%2Fcfg-parser..rkt%29._cfg-parser%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">cfg-<wbr></wbr>parser</span></span></a></td></tr></table></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, "6.8.0.1", "../");" 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("6.8.0.1");">top</a></span><span class="navright"> <a href="LALR_1__Parsers.html" title="backward to "2 LALR(1) Parsers"" data-pltdoc="x">← prev</a> <a href="index.html" title="up to "Parser Tools: lex and yacc-style Parsing"" data-pltdoc="x">up</a> <a href="Converting_yacc_or_bison_Grammars.html" title="forward to "4 Converting yacc or bison Grammars"" data-pltdoc="x">next →</a></span> </div><h3 x-source-module="(lib "parser-tools/br-parser-tools.scrbl")" x-source-pkg="br-parser-tools-doc" x-part-tag=""Context-Free_Parsers"">3<tt> </tt><a name="(part._.Context-.Free_.Parsers)"></a><a name="(mod-path._br-parser-tools/cfg-parser)"></a><a name="(idx._(gentag._4._(lib._parser-tools/br-parser-tools..scrbl)))"></a>Context-Free Parsers</h3><p><div class="SIntrapara"><table cellspacing="0" cellpadding="0" class="defmodule"><tr><td align="left" colspan="2"><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/local-redirect/index.html?doc=reference&rel=require.html%23%2528form._%2528%2528lib._racket%252Fprivate%252Fbase..rkt%2529._require%2529%2529&version=6.8.0.1" class="RktStxLink Sq" data-pltdoc="x">require</a></span><span class="stt"> </span><a href="" class="RktModLink" data-pltdoc="x"><span class="RktSym">br-parser-tools/cfg-parser</span></a><span class="RktPn">)</span></td></tr><tr><td align="left"> </td><td align="right"><span class="RpackageSpec"><span class="Smaller"> package:</span> <span class="stt">br-parser-tools-lib</span></span></td></tr></table></div><div class="SIntrapara">The <a href="" class="RktModLink" data-pltdoc="x"><span class="RktSym">br-parser-tools/cfg-parser</span></a>
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library provides a parser generator that is an alternative to that of
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<a href="LALR_1__Parsers.html" class="RktModLink" data-pltdoc="x"><span class="RktSym">br-parser-tools/yacc</span></a>.</div></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._((lib._br-parser-tools/cfg-parser..rkt)._cfg-parser))"></a><span title="Provided from: br-parser-tools/cfg-parser | Package: br-parser-tools-lib"><span class="RktSym"><a href="#%28form._%28%28lib._br-parser-tools%2Fcfg-parser..rkt%29._cfg-parser%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">cfg-parser</a></span></span><span class="hspace"> </span><span class="RktVar">clause</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">clause</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"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym">grammar</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktVar">non-terminal-id</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">(</span><span class="RktVar">grammar-id</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVar">maybe-prec</span><span class="hspace"> </span><span class="RktVar">expr</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></td></tr></table></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="RktSym">tokens</span><span class="hspace"> </span><span class="RktVar">group-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="RktSym">start</span><span class="hspace"> </span><span class="RktVar">non-terminal-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="RktSym">end</span><span class="hspace"> </span><span class="RktVar">token-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="RktSym">error</span><span class="hspace"> </span><span class="RktVar">expr</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="RktSym">src-pos</span><span class="RktPn">)</span></td></tr></table></td></tr></table></blockquote></div><div class="SIntrapara">Creates a parser similar to that of <span class="RktSym"><a href="LALR_1__Parsers.html#%28form._%28%28lib._br-parser-tools%2Fyacc..rkt%29._parser%29%29" class="RktStxLink" data-pltdoc="x">parser</a></span>. Unlike <span class="RktSym"><a href="LALR_1__Parsers.html#%28form._%28%28lib._br-parser-tools%2Fyacc..rkt%29._parser%29%29" class="RktStxLink" data-pltdoc="x">parser</a></span>,
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<span class="RktSym"><a href="#%28form._%28%28lib._br-parser-tools%2Fcfg-parser..rkt%29._cfg-parser%29%29" class="RktStxLink" data-pltdoc="x">cfg-parser</a></span>, can consume arbitrary and potentially ambiguous context-free
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grammars. Its interface is a subset of <a href="LALR_1__Parsers.html" class="RktModLink" data-pltdoc="x"><span class="RktSym">br-parser-tools/yacc</span></a>, with
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the following differences:</div></p><ul><li><p><span class="RktPn">(</span><span class="RktSym">start</span><span class="stt"> </span><span class="RktVar">non-terminal-id</span><span class="RktPn">)</span></p><p>Unlike <span class="RktSym"><a href="LALR_1__Parsers.html#%28form._%28%28lib._br-parser-tools%2Fyacc..rkt%29._parser%29%29" class="RktStxLink" data-pltdoc="x">parser</a></span>, <span class="RktSym"><a href="#%28form._%28%28lib._br-parser-tools%2Fcfg-parser..rkt%29._cfg-parser%29%29" class="RktStxLink" data-pltdoc="x">cfg-parser</a></span> only allows for
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a single non-terminal-id.</p></li><li><p>The <span class="RktSym"><a href="#%28form._%28%28lib._br-parser-tools%2Fcfg-parser..rkt%29._cfg-parser%29%29" class="RktStxLink" data-pltdoc="x">cfg-parser</a></span> form does not support the <span class="RktSym">precs</span>,
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<span class="RktSym">suppress</span>, <span class="RktSym">debug</span>, or <span class="RktSym">yacc-output</span>
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options of <span class="RktSym"><a href="LALR_1__Parsers.html#%28form._%28%28lib._br-parser-tools%2Fyacc..rkt%29._parser%29%29" class="RktStxLink" data-pltdoc="x">parser</a></span>.</p></li></ul><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, "6.8.0.1", "../");" 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("6.8.0.1");">top</a></span><span class="navright"> <a href="LALR_1__Parsers.html" title="backward to "2 LALR(1) Parsers"" data-pltdoc="x">← prev</a> <a href="index.html" title="up to "Parser Tools: lex and yacc-style Parsing"" data-pltdoc="x">up</a> <a href="Converting_yacc_or_bison_Grammars.html" title="forward to "4 Converting yacc or bison Grammars"" data-pltdoc="x">next →</a></span> </div></div></div><div id="contextindicator"> </div></body></html> |