1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Not-Predicate Parser (!a)</title> 5<link rel="stylesheet" href="../../../../../../../../doc/src/boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../../../../index.html" title="Spirit 2.5.8"> 8<link rel="up" href="../operator.html" title="Parser Operators"> 9<link rel="prev" href="list.html" title="List Parser (a % b)"> 10<link rel="next" href="optional.html" title="Optional Parser (-a)"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr> 14<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../../boost.png"></td> 15<td align="center"><a href="../../../../../../../../index.html">Home</a></td> 16<td align="center"><a href="../../../../../../../../libs/libraries.htm">Libraries</a></td> 17<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 18<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 19<td align="center"><a href="../../../../../../../../more/index.htm">More</a></td> 20</tr></table> 21<hr> 22<div class="spirit-nav"> 23<a accesskey="p" href="list.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../operator.html"><img src="../../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../../index.html"><img src="../../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="optional.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h5 class="title"> 27<a name="spirit.qi.reference.operator.not_predicate"></a><a class="link" href="not_predicate.html" title="Not-Predicate Parser (!a)">Not-Predicate 28 Parser (<code class="computeroutput"><span class="special">!</span><span class="identifier">a</span></code>)</a> 29</h5></div></div></div> 30<h6> 31<a name="spirit.qi.reference.operator.not_predicate.h0"></a> 32 <span class="phrase"><a name="spirit.qi.reference.operator.not_predicate.description"></a></span><a class="link" href="not_predicate.html#spirit.qi.reference.operator.not_predicate.description">Description</a> 33 </h6> 34<p> 35 Syntactic predicates assert a certain conditional syntax to be satisfied 36 before evaluating another production. Similar to semantic predicates, 37 <a class="link" href="../auxiliary/eps.html" title="Epsilon Parser (eps)"><code class="computeroutput"><span class="identifier">eps</span></code></a>, 38 syntactic predicates do not consume any input. The <span class="emphasis"><em>not-predicate</em></span>, 39 <code class="computeroutput"><span class="special">!</span><span class="identifier">a</span></code>, 40 is a negative syntactic predicate that returns a zero length match only 41 if its predicate fails to match. 42 </p> 43<h6> 44<a name="spirit.qi.reference.operator.not_predicate.h1"></a> 45 <span class="phrase"><a name="spirit.qi.reference.operator.not_predicate.header"></a></span><a class="link" href="not_predicate.html#spirit.qi.reference.operator.not_predicate.header">Header</a> 46 </h6> 47<pre class="programlisting"><span class="comment">// forwards to <boost/spirit/home/qi/operator/not_predicate.hpp></span> 48<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">spirit</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">qi_not_predicate</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 49</pre> 50<p> 51 Also, see <a class="link" href="../../../structure/include.html" title="Include">Include Structure</a>. 52 </p> 53<h6> 54<a name="spirit.qi.reference.operator.not_predicate.h2"></a> 55 <span class="phrase"><a name="spirit.qi.reference.operator.not_predicate.model_of"></a></span><a class="link" href="not_predicate.html#spirit.qi.reference.operator.not_predicate.model_of">Model of</a> 56 </h6> 57<div class="blockquote"><blockquote class="blockquote"><p> 58 <a class="link" href="../parser_concepts/unaryparser.html" title="UnaryParser"><code class="computeroutput"><span class="identifier">UnaryParser</span></code></a> 59 </p></blockquote></div> 60<div class="variablelist"> 61<p class="title"><b>Notation</b></p> 62<dl class="variablelist"> 63<dt><span class="term"><code class="computeroutput"><span class="identifier">a</span></code></span></dt> 64<dd><p> 65 A <a class="link" href="../parser_concepts/parser.html" title="Parser"><code class="computeroutput"><span class="identifier">Parser</span></code></a> 66 </p></dd> 67</dl> 68</div> 69<h6> 70<a name="spirit.qi.reference.operator.not_predicate.h3"></a> 71 <span class="phrase"><a name="spirit.qi.reference.operator.not_predicate.expression_semantics"></a></span><a class="link" href="not_predicate.html#spirit.qi.reference.operator.not_predicate.expression_semantics">Expression 72 Semantics</a> 73 </h6> 74<p> 75 Semantics of an expression is defined only where it differs from, or 76 is not defined in <a class="link" href="../parser_concepts/unaryparser.html" title="UnaryParser"><code class="computeroutput"><span class="identifier">UnaryParser</span></code></a>. 77 </p> 78<div class="informaltable"><table class="table"> 79<colgroup> 80<col> 81<col> 82</colgroup> 83<thead><tr> 84<th> 85 <p> 86 Expression 87 </p> 88 </th> 89<th> 90 <p> 91 Semantics 92 </p> 93 </th> 94</tr></thead> 95<tbody><tr> 96<td> 97 <p> 98 <code class="computeroutput"><span class="special">!</span><span class="identifier">a</span></code> 99 </p> 100 </td> 101<td> 102 <p> 103 If the predicate <code class="computeroutput"><span class="identifier">a</span></code> 104 matches, fail. Otherwise, return a zero length match. 105 </p> 106 </td> 107</tr></tbody> 108</table></div> 109<h6> 110<a name="spirit.qi.reference.operator.not_predicate.h4"></a> 111 <span class="phrase"><a name="spirit.qi.reference.operator.not_predicate.attributes"></a></span><a class="link" href="not_predicate.html#spirit.qi.reference.operator.not_predicate.attributes">Attributes</a> 112 </h6> 113<p> 114 See <a class="link" href="../../quick_reference/compound_attribute_rules.html#spirit.qi.quick_reference.compound_attribute_rules.notation">Compound 115 Attribute Notation</a>. 116 </p> 117<div class="informaltable"><table class="table"> 118<colgroup> 119<col> 120<col> 121</colgroup> 122<thead><tr> 123<th> 124 <p> 125 Expression 126 </p> 127 </th> 128<th> 129 <p> 130 Attribute 131 </p> 132 </th> 133</tr></thead> 134<tbody><tr> 135<td> 136 <p> 137 <code class="computeroutput"><span class="special">!</span><span class="identifier">a</span></code> 138 </p> 139 </td> 140<td> 141 <p> 142 <code class="computeroutput"><span class="identifier">unused_type</span></code> 143 </p> 144 </td> 145</tr></tbody> 146</table></div> 147<h6> 148<a name="spirit.qi.reference.operator.not_predicate.h5"></a> 149 <span class="phrase"><a name="spirit.qi.reference.operator.not_predicate.complexity"></a></span><a class="link" href="not_predicate.html#spirit.qi.reference.operator.not_predicate.complexity">Complexity</a> 150 </h6> 151<div class="blockquote"><blockquote class="blockquote"><p> 152 The complexity is defined by the complexity of the predicate, <code class="computeroutput"><span class="identifier">a</span></code> 153 </p></blockquote></div> 154<h6> 155<a name="spirit.qi.reference.operator.not_predicate.h6"></a> 156 <span class="phrase"><a name="spirit.qi.reference.operator.not_predicate.example"></a></span><a class="link" href="not_predicate.html#spirit.qi.reference.operator.not_predicate.example">Example</a> 157 </h6> 158<div class="note"><table border="0" summary="Note"> 159<tr> 160<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../images/note.png"></td> 161<th align="left">Note</th> 162</tr> 163<tr><td align="left" valign="top"><p> 164 The test harness for the example(s) below is presented in the <a class="link" href="../basics.html#spirit.qi.reference.basics.examples">Basics Examples</a> 165 section. 166 </p></td></tr> 167</table></div> 168<p> 169 Some using declarations: 170 </p> 171<p> 172</p> 173<pre class="programlisting"><span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">ascii</span><span class="special">::</span><span class="identifier">char_</span><span class="special">;</span> 174<span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">ascii</span><span class="special">::</span><span class="identifier">alpha</span><span class="special">;</span> 175<span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">qi</span><span class="special">::</span><span class="identifier">lit</span><span class="special">;</span> 176<span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">qi</span><span class="special">::</span><span class="identifier">symbols</span><span class="special">;</span> 177</pre> 178<p> 179 </p> 180<p> 181 Here's an alternative to the <code class="computeroutput"><span class="special">*(</span><span class="identifier">r</span> <span class="special">-</span> <span class="identifier">x</span><span class="special">)</span> <span class="special">>></span> <span class="identifier">x</span></code> 182 idiom using the not-predicate instead. This parses a list of characters 183 terminated by a ';': 184 </p> 185<p> 186</p> 187<pre class="programlisting"><span class="identifier">test_parser</span><span class="special">(</span><span class="string">"abcdef;"</span><span class="special">,</span> <span class="special">*(!</span><span class="identifier">lit</span><span class="special">(</span><span class="char">';'</span><span class="special">)</span> <span class="special">>></span> <span class="identifier">char_</span><span class="special">)</span> <span class="special">>></span> <span class="char">';'</span><span class="special">);</span> 188</pre> 189<p> 190 </p> 191<p> 192 The following parser ensures that we match distinct keywords (stored 193 in a symbol table). To do this, we make sure that the keyword does not 194 follow an alpha or an underscore: 195 </p> 196<p> 197</p> 198<pre class="programlisting"><span class="identifier">symbols</span><span class="special"><</span><span class="keyword">char</span><span class="special">,</span> <span class="keyword">int</span><span class="special">></span> <span class="identifier">keywords</span><span class="special">;</span> 199<span class="identifier">keywords</span> <span class="special">=</span> <span class="string">"begin"</span><span class="special">,</span> <span class="string">"end"</span><span class="special">,</span> <span class="string">"for"</span><span class="special">;</span> 200 201<span class="comment">// This should fail:</span> 202<span class="identifier">test_parser</span><span class="special">(</span><span class="string">"beginner"</span><span class="special">,</span> <span class="identifier">keywords</span> <span class="special">>></span> <span class="special">!(</span><span class="identifier">alpha</span> <span class="special">|</span> <span class="char">'_'</span><span class="special">));</span> 203 204<span class="comment">// This is ok:</span> 205<span class="identifier">test_parser</span><span class="special">(</span><span class="string">"end "</span><span class="special">,</span> <span class="identifier">keywords</span> <span class="special">>></span> <span class="special">!(</span><span class="identifier">alpha</span> <span class="special">|</span> <span class="char">'_'</span><span class="special">),</span> <span class="keyword">false</span><span class="special">);</span> 206 207<span class="comment">// This is ok:</span> 208<span class="identifier">test_parser</span><span class="special">(</span><span class="string">"for()"</span><span class="special">,</span> <span class="identifier">keywords</span> <span class="special">>></span> <span class="special">!(</span><span class="identifier">alpha</span> <span class="special">|</span> <span class="char">'_'</span><span class="special">),</span> <span class="keyword">false</span><span class="special">);</span> 209</pre> 210<p> 211 </p> 212</div> 213<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 214<td align="left"></td> 215<td align="right"><div class="copyright-footer">Copyright © 2001-2011 Joel de Guzman, Hartmut Kaiser<p> 216 Distributed under the Boost Software License, Version 1.0. (See accompanying 217 file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) 218 </p> 219</div></td> 220</tr></table> 221<hr> 222<div class="spirit-nav"> 223<a accesskey="p" href="list.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../operator.html"><img src="../../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../../index.html"><img src="../../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="optional.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a> 224</div> 225</body> 226</html> 227
