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<html>
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<title>Not-Predicate Parser (!a)</title>
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<div class="section">
<div class="titlepage"><div><div><h5 class="title">
<a name="spirit.qi.reference.operator.not_predicate"></a><a class="link" href="not_predicate.html" title="Not-Predicate Parser (!a)">Not-Predicate
Parser (<code class="computeroutput"><span class="special">!</span><span class="identifier">a</span></code>)</a>
</h5></div></div></div>
<h6>
<a name="spirit.qi.reference.operator.not_predicate.h0"></a>
<span><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>
</h6>
<p>
Syntactic predicates assert a certain conditional syntax to be satisfied
before evaluating another production. Similar to semantic predicates,
<a class="link" href="../auxiliary/eps.html" title="Epsilon Parser (eps)"><code class="computeroutput"><span class="identifier">eps</span></code></a>,
syntactic predicates do not consume any input. The <span class="emphasis"><em>not-predicate</em></span>,
<code class="computeroutput"><span class="special">!</span><span class="identifier">a</span></code>,
is a negative syntactic predicate that returns a zero length match only
if its predicate fails to match.
</p>
<h6>
<a name="spirit.qi.reference.operator.not_predicate.h1"></a>
<span><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>
</h6>
<pre class="programlisting"><span class="comment">// forwards to <boost/spirit/home/qi/operator/not_predicate.hpp></span>
<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>
</pre>
<p>
Also, see <a class="link" href="../../../structure/include.html" title="Include">Include Structure</a>.
</p>
<h6>
<a name="spirit.qi.reference.operator.not_predicate.h2"></a>
<span><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>
</h6>
<div class="blockquote"><blockquote class="blockquote"><p>
<a class="link" href="../parser_concepts/unaryparser.html" title="UnaryParser"><code class="computeroutput"><span class="identifier">UnaryParser</span></code></a>
</p></blockquote></div>
<div class="variablelist">
<p class="title"><b>Notation</b></p>
<dl>
<dt><span class="term"><code class="computeroutput"><span class="identifier">a</span></code></span></dt>
<dd><p>
A <a class="link" href="../parser_concepts/parser.html" title="Parser"><code class="computeroutput"><span class="identifier">Parser</span></code></a>
</p></dd>
</dl>
</div>
<h6>
<a name="spirit.qi.reference.operator.not_predicate.h3"></a>
<span><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
Semantics</a>
</h6>
<p>
Semantics of an expression is defined only where it differs from, or
is not defined in <a class="link" href="../parser_concepts/unaryparser.html" title="UnaryParser"><code class="computeroutput"><span class="identifier">UnaryParser</span></code></a>.
</p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Expression
</p>
</th>
<th>
<p>
Semantics
</p>
</th>
</tr></thead>
<tbody><tr>
<td>
<p>
<code class="computeroutput"><span class="special">!</span><span class="identifier">a</span></code>
</p>
</td>
<td>
<p>
If the predicate <code class="computeroutput"><span class="identifier">a</span></code>
matches, fail. Otherwise, return a zero length match.
</p>
</td>
</tr></tbody>
</table></div>
<h6>
<a name="spirit.qi.reference.operator.not_predicate.h4"></a>
<span><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>
</h6>
<p>
See <a class="link" href="../../quick_reference/compound_attribute_rules.html#spirit.qi.quick_reference.compound_attribute_rules.notation">Compound
Attribute Notation</a>.
</p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Expression
</p>
</th>
<th>
<p>
Attribute
</p>
</th>
</tr></thead>
<tbody><tr>
<td>
<p>
<code class="computeroutput"><span class="special">!</span><span class="identifier">a</span></code>
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">unused_type</span></code>
</p>
</td>
</tr></tbody>
</table></div>
<h6>
<a name="spirit.qi.reference.operator.not_predicate.h5"></a>
<span><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>
</h6>
<div class="blockquote"><blockquote class="blockquote"><p>
The complexity is defined by the complexity of the predicate, <code class="computeroutput"><span class="identifier">a</span></code>
</p></blockquote></div>
<h6>
<a name="spirit.qi.reference.operator.not_predicate.h6"></a>
<span><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>
</h6>
<div class="note"><table border="0" summary="Note">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../images/note.png"></td>
<th align="left">Note</th>
</tr>
<tr><td align="left" valign="top"><p>
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>
section.
</p></td></tr>
</table></div>
<p>
Some using declarations:
</p>
<p>
</p>
<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>
<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>
<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>
<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>
</pre>
<p>
</p>
<p>
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>
idiom using the not-predicate instead. This parses a list of characters
terminated by a ';':
</p>
<p>
</p>
<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>
</pre>
<p>
</p>
<p>
The following parser ensures that we match distinct keywords (stored
in a symbol table). To do this, we make sure that the keyword does not
follow an alpha or an underscore:
</p>
<p>
</p>
<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>
<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>
<span class="comment">// This should fail:</span>
<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>
<span class="comment">// This is ok:</span>
<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>
<span class="comment">// This is ok:</span>
<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>
</pre>
<p>
</p>
</div>
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<td align="right"><div class="copyright-footer">Copyright © 2001-2011 Joel de Guzman, Hartmut Kaiser<p>
Distributed under the Boost Software License, Version 1.0. (See accompanying
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>)
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