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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>2 LALR(1) 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="" class="tocviewselflink" data-pltdoc="x">LALR(1) Parsers</a></td></tr><tr><td align="right">3 </td><td><a href="Context-Free_Parsers.html" class="tocviewlink" 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%2Fyacc..rkt%29._parser%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">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="Lexers.html" title="backward to "1 Lexers"" 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="Context-Free_Parsers.html" title="forward to "3 Context-Free Parsers"" 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=""LALR_1__Parsers"">2<tt> </tt><a name="(part._.L.A.L.R_1__.Parsers)"></a><a name="(mod-path._br-parser-tools/yacc)"></a><a name="(idx._(gentag._3._(lib._parser-tools/br-parser-tools..scrbl)))"></a>LALR(1) Parsers</h3><p><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/yacc</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></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/yacc..rkt)._parser))"></a><span title="Provided from: br-parser-tools/yacc | Package: br-parser-tools-lib"><span class="RktSym"><a href="#%28form._%28%28lib._br-parser-tools%2Fyacc..rkt%29._parser%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">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">precs</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktVar">assoc</span><span class="hspace"> </span><span class="RktVar">token-id</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></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><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">suppress</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">debug</span><span class="hspace"> </span><span class="RktVar">filename</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">yacc-output</span><span class="hspace"> </span><span class="RktVar">filename</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"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td></tr><tr><td align="right" valign="baseline"><span class="RktVar">maybe-prec</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></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">prec</span><span class="hspace"> </span><span class="RktVar">token-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"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td></tr><tr><td align="right" valign="baseline"><span class="RktVar">assoc</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">left</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">right</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">nonassoc</span></td></tr></table></td></tr></table></blockquote></div><div class="SIntrapara">Creates a parser. The clauses may be in any order, as long as there
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are no duplicates and all non-<span style="font-style: italic">OPTIONAL</span> declarations are
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present:</div></p><ul><li><p><table cellspacing="0" cellpadding="0" class="RktBlk" style="display: inline-table; vertical-align: text-top; margin-top: 0;"><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"><a href="http://docs.racket-lang.org/local-redirect/index.html?doc=reference&rel=stx-patterns.html%23%2528form._%2528%2528lib._racket%252Fprivate%252Fstxcase-scheme..rkt%2529._......%2529%2529&version=6.8.0.1" class="RktStxLink Sq" data-pltdoc="x">...</a></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"><a href="http://docs.racket-lang.org/local-redirect/index.html?doc=reference&rel=stx-patterns.html%23%2528form._%2528%2528lib._racket%252Fprivate%252Fstxcase-scheme..rkt%2529._......%2529%2529&version=6.8.0.1" class="RktStxLink Sq" data-pltdoc="x">...</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktMeta"><a href="http://docs.racket-lang.org/local-redirect/index.html?doc=reference&rel=stx-patterns.html%23%2528form._%2528%2528lib._racket%252Fprivate%252Fstxcase-scheme..rkt%2529._......%2529%2529&version=6.8.0.1" class="RktStxLink Sq" data-pltdoc="x">...</a></span><span class="RktPn">)</span></td></tr></table></p><p>Declares the grammar to be parsed. Each <span class="RktVar">grammar-id</span> can
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be a <span class="RktVar">token-id</span> from a <span class="RktVar">group-id</span> named in a
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<span class="RktSym">tokens</span> declaration, or it can be a
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<span class="RktVar">non-terminal-id</span> declared in the <span class="RktSym">grammar</span>
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declaration. The optional <span class="RktSym">prec</span> declaration works with
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the <span class="RktSym">precs</span> declaration. The <span class="RktVar">expr</span> is a
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“semantic action,” which is evaluated when the input is found
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to match its corresponding production.</p><p>Each action is Racket code that has the same scope as its
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parser’s definition, except that the variables <span class="RktSym">$1</span>, ...,
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<span class="RktSym">$</span><span style="font-style: italic">i</span> are bound, where <span style="font-style: italic">i</span> is the number
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of <span class="RktVar">grammar-id</span>s in the corresponding production. Each
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<span class="RktSym">$</span><span style="font-style: italic">k</span> is bound to the result of the action
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for the <span style="font-style: italic">k</span><span style="vertical-align: super; font-size: 80%">th</span> grammar symbol on the right of
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the production, if that grammar symbol is a non-terminal, or the
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value stored in the token if the grammar symbol is a terminal.
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If the <span class="RktSym">src-pos</span> option is present in the parser, then
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variables <span class="RktSym">$1-start-pos</span>, ...,
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<span class="RktSym">$</span><span style="font-style: italic">i</span><span class="RktSym">-start-pos</span> and
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<span class="RktSym">$1-end-pos</span>, ...,
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<span class="RktSym">$</span><span style="font-style: italic">i</span><span class="RktSym">-end-pos</span> and are also
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available, and they refer to the position structures
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corresponding to the start and end of the corresponding
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<span class="RktSym">grammar-symbol</span>. Grammar symbols defined as empty-tokens
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have no <span class="RktSym">$</span><span style="font-style: italic">k</span> associated, but do have
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<span class="RktSym">$</span><span style="font-style: italic">k</span><span class="RktSym">-start-pos</span> and
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<span class="RktSym">$</span><span style="font-style: italic">k</span><span class="RktSym">-end-pos</span>.
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Also <span class="RktSym">$n-start-pos</span> and <span class="RktSym">$n-end-pos</span>
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are bound to the largest start and end positions, (i.e.,
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<span class="RktSym">$</span><span style="font-style: italic">i</span><span class="RktSym">-start-pos</span> and
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<span class="RktSym">$</span><span style="font-style: italic">i</span><span class="RktSym">-end-pos</span>).</p><p>An <a name="(tech._error._production)"></a><span style="font-style: italic">error production</span> can be defined by providing
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a production of the form <span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/local-redirect/index.html?doc=reference&rel=exns.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._error%2529%2529&version=6.8.0.1" class="RktValLink Sq" data-pltdoc="x">error</a></span><span class="stt"> </span><span class="RktSym">α</span><span class="RktPn">)</span>, where α is a
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string of grammar symbols, possibly empty.</p><p>All of the productions for a given non-terminal must be grouped
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with it. That is, no <span class="RktVar">non-terminal-id</span> may appear twice
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on the left hand side in a parser.</p></li><li><p><span class="RktPn">(</span><span class="RktSym">tokens</span><span class="stt"> </span><span class="RktVar">group-id</span><span class="stt"> </span><span class="RktMeta"><a href="http://docs.racket-lang.org/local-redirect/index.html?doc=reference&rel=stx-patterns.html%23%2528form._%2528%2528lib._racket%252Fprivate%252Fstxcase-scheme..rkt%2529._......%2529%2529&version=6.8.0.1" class="RktStxLink Sq" data-pltdoc="x">...</a></span><span class="RktPn">)</span></p><p>Declares that all of the tokens defined in each
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<span class="RktVar">group-id</span>—<wbr></wbr>as bound by <span class="RktSym"><a href="Lexers.html#%28form._%28%28lib._br-parser-tools%2Flex..rkt%29._define-tokens%29%29" class="RktStxLink" data-pltdoc="x">define-tokens</a></span> or
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<span class="RktSym"><a href="Lexers.html#%28form._%28%28lib._br-parser-tools%2Flex..rkt%29._define-empty-tokens%29%29" class="RktStxLink" data-pltdoc="x">define-empty-tokens</a></span>—<wbr></wbr>can be used by the parser in the
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<span class="RktSym">grammar</span> declaration.</p></li><li><p><span class="RktPn">(</span><span class="RktSym">start</span><span class="stt"> </span><span class="RktVar">non-terminal-id</span><span class="stt"> </span><span class="RktMeta"><a href="http://docs.racket-lang.org/local-redirect/index.html?doc=reference&rel=stx-patterns.html%23%2528form._%2528%2528lib._racket%252Fprivate%252Fstxcase-scheme..rkt%2529._......%2529%2529&version=6.8.0.1" class="RktStxLink Sq" data-pltdoc="x">...</a></span><span class="RktPn">)</span></p><p>Declares a list of starting non-terminals for the grammar.</p></li><li><p><span class="RktPn">(</span><span class="RktSym">end</span><span class="stt"> </span><span class="RktVar">token-id</span><span class="stt"> </span><span class="RktMeta"><a href="http://docs.racket-lang.org/local-redirect/index.html?doc=reference&rel=stx-patterns.html%23%2528form._%2528%2528lib._racket%252Fprivate%252Fstxcase-scheme..rkt%2529._......%2529%2529&version=6.8.0.1" class="RktStxLink Sq" data-pltdoc="x">...</a></span><span class="RktPn">)</span></p><p>Specifies a set of tokens from which some member must follow any
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valid parse. For example, an EOF token would be specified for a
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parser that parses entire files and a newline token for a parser
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that parses entire lines individually.</p></li><li><p><span class="RktPn">(</span><span class="RktSym">error</span><span class="stt"> </span><span class="RktVar">expr</span><span class="RktPn">)</span></p><p>The <span class="RktVar">expr</span> should evaluate to a function which will be
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executed for its side-effect whenever the parser encounters an
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error.</p><p>If the <span class="RktSym">src-pos</span> declaration is present, the function
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should accept 5 arguments,:</p><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/local-redirect/index.html?doc=reference&rel=lambda.html%23%2528form._%2528%2528lib._racket%252Fprivate%252Fbase..rkt%2529._lambda%2529%2529&version=6.8.0.1" class="RktStxLink Sq" data-pltdoc="x">lambda</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">tok-ok?</span><span class="hspace"> </span><span class="RktSym">tok-name</span><span class="hspace"> </span><span class="RktSym">tok-value</span><span class="hspace"> </span><span class="RktVar">start-pos</span><span class="hspace"> </span><span class="RktVar">end-pos</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktSym">....</span><span class="RktPn">)</span></td></tr></table></blockquote><p>Otherwise it should accept 3:</p><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/local-redirect/index.html?doc=reference&rel=lambda.html%23%2528form._%2528%2528lib._racket%252Fprivate%252Fbase..rkt%2529._lambda%2529%2529&version=6.8.0.1" class="RktStxLink Sq" data-pltdoc="x">lambda</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">tok-ok?</span><span class="hspace"> </span><span class="RktSym">tok-name</span><span class="hspace"> </span><span class="RktSym">tok-value</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktSym">....</span><span class="RktPn">)</span></td></tr></table></blockquote><p>The first argument will be <span class="RktVal">#f</span> if and only if the error
|
|
is that an invalid token was received. The second and third
|
|
arguments will be the name and the value of the token at which
|
|
the error was detected. The fourth and fifth arguments, if
|
|
present, provide the source positions of that token.</p></li><li><p><span class="RktPn">(</span><span class="RktSym">precs</span><span class="stt"> </span><span class="RktPn">(</span><span class="RktVar">assoc</span><span class="stt"> </span><span class="RktVar">token-id</span><span class="stt"> </span><span class="RktMeta"><a href="http://docs.racket-lang.org/local-redirect/index.html?doc=reference&rel=stx-patterns.html%23%2528form._%2528%2528lib._racket%252Fprivate%252Fstxcase-scheme..rkt%2529._......%2529%2529&version=6.8.0.1" class="RktStxLink Sq" data-pltdoc="x">...</a></span><span class="RktPn">)</span><span class="stt"> </span><span class="RktMeta"><a href="http://docs.racket-lang.org/local-redirect/index.html?doc=reference&rel=stx-patterns.html%23%2528form._%2528%2528lib._racket%252Fprivate%252Fstxcase-scheme..rkt%2529._......%2529%2529&version=6.8.0.1" class="RktStxLink Sq" data-pltdoc="x">...</a></span><span class="RktPn">)</span>
|
|
<span style="font-style: italic">OPTIONAL</span></p><p>Precedence declarations to resolve shift/reduce and
|
|
reduce/reduce conflicts as in <span class="stt">yacc</span>/<span class="stt">bison</span>. An
|
|
<span class="RktVar">assoc</span> must be one of <span class="RktVar">left</span>, <span class="RktVar">right</span> or
|
|
<span class="RktVar">nonassoc</span>. States with multiple shift/reduce or
|
|
reduce/reduce conflicts (or some combination thereof) are not
|
|
resolved with precedence.</p></li><li><p><span class="RktPn">(</span><span class="RktSym">src-pos</span><span class="RktPn">)</span> <span style="font-style: italic">OPTIONAL</span></p><p>Causes the generated parser to expect input in the form
|
|
<span class="RktPn">(</span><span class="RktSym"><a href="Lexers.html#%28def._%28%28lib._br-parser-tools%2Flex..rkt%29._make-position-token%29%29" class="RktValLink" data-pltdoc="x">make-position-token</a></span><span class="stt"> </span><span class="RktVar">token</span><span class="stt"> </span><span class="RktVar">start-pos</span><span class="stt"> </span><span class="RktVar">end-pos</span><span class="RktPn">)</span> instead
|
|
of simply <span class="RktVar">token</span>. Include this option when using the
|
|
parser with a lexer generated with <span class="RktSym"><a href="Lexers.html#%28form._%28%28lib._br-parser-tools%2Flex..rkt%29._lexer-src-pos%29%29" class="RktStxLink" data-pltdoc="x">lexer-src-pos</a></span>.</p></li><li><p><span class="RktPn">(</span><span class="RktSym">debug</span><span class="stt"> </span><span class="RktVar">filename</span><span class="RktPn">)</span> <span style="font-style: italic">OPTIONAL</span></p><p>Causes the parser generator to write the LALR table to the file
|
|
named <span class="RktVar">filename</span> (unless the file exists), where
|
|
<span class="RktVar">filename</span> is a literal string. Additionally, if a debug
|
|
file is specified, when a running generated parser encounters a
|
|
parse error on some input file, after the user specified error
|
|
expression returns, the complete parse stack is printed to
|
|
assist in debugging the grammar of that particular parser. The
|
|
numbers in the stack printout correspond to the state numbers in
|
|
the LALR table file.</p></li><li><p><span class="RktPn">(</span><span class="RktSym">yacc-output</span><span class="stt"> </span><span class="RktVar">filename</span><span class="RktPn">)</span> <span style="font-style: italic">OPTIONAL</span></p><p>Causes the parser generator to write a grammar file in
|
|
approximately the syntax of <span class="stt">yacc</span>/<span class="stt">bison</span>. The file
|
|
might not be a valid <span class="stt">yacc</span> file, because the Racket
|
|
grammar can use symbols that are invalid in C.</p></li><li><p><span class="RktPn">(</span><span class="RktSym">suppress</span><span class="RktPn">)</span> <span style="font-style: italic">OPTIONAL</span></p><p>Causes the parser generator not to report shift/reduce or
|
|
reduce/reduce conflicts.</p></li></ul><p>The result of a <span class="RktSym"><a href="#%28form._%28%28lib._br-parser-tools%2Fyacc..rkt%29._parser%29%29" class="RktStxLink" data-pltdoc="x">parser</a></span> expression with one <span class="RktSym">start</span>
|
|
non-terminal is a function, <span class="RktVar">parse</span>, that takes one
|
|
argument. This argument must be a zero argument function,
|
|
<span class="RktVar">gen</span>, that produces successive tokens of the input each
|
|
time it is called. If desired, the <span class="RktVar">gen</span> may return
|
|
symbols instead of tokens, and the parser will treat symbols as
|
|
tokens of the corresponding name (with <span class="RktVal">#f</span> as a value, so
|
|
it is usual to return symbols only in the case of empty tokens).
|
|
The <span class="RktVar">parse</span> function returns the value associated with the
|
|
parse tree by the semantic actions. If the parser encounters an
|
|
error, after invoking the supplied error function, it will try to
|
|
use <a href="#%28tech._error._production%29" class="techoutside" data-pltdoc="x"><span class="techinside">error production</span></a>s to continue parsing. If it cannot, it
|
|
raises <span class="RktSym"><a href="http://docs.racket-lang.org/local-redirect/index.html?doc=reference&rel=exns.html%23%2528def._%2528%2528lib._racket%252Fprivate%252Fbase..rkt%2529._exn%7E3afail%7E3aread%2529%2529&version=6.8.0.1" class="RktValLink Sq" data-pltdoc="x">exn:fail:read</a></span>.</p><p>If multiple non-terminals are provided in <span class="RktSym">start</span>, the
|
|
<span class="RktSym"><a href="#%28form._%28%28lib._br-parser-tools%2Fyacc..rkt%29._parser%29%29" class="RktStxLink" data-pltdoc="x">parser</a></span> expression produces a list of parsing functions,
|
|
one for each non-terminal in the same order. Each parsing function
|
|
is like the result of a parser expression with only one
|
|
<span class="RktSym">start</span> non-terminal,</p><p>Each time the Racket code for a <span class="RktSym"><a href="#%28form._%28%28lib._br-parser-tools%2Fyacc..rkt%29._parser%29%29" class="RktStxLink" data-pltdoc="x">parser</a></span> is compiled
|
|
(e.g. when a <span class="stt">".rkt"</span> file containing a <span class="RktSym"><a href="#%28form._%28%28lib._br-parser-tools%2Fyacc..rkt%29._parser%29%29" class="RktStxLink" data-pltdoc="x">parser</a></span> form
|
|
is loaded), the parser generator is run. To avoid this overhead
|
|
place the parser into a module and compile the module to a
|
|
<span class="stt">".zo"</span> bytecode file.</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, "6.8.0.1", "../");" 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="Lexers.html" title="backward to "1 Lexers"" 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="Context-Free_Parsers.html" title="forward to "3 Context-Free Parsers"" data-pltdoc="x">next →</a></span> </div></div></div><div id="contextindicator"> </div></body></html> |