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<title>Qi Keyword Parser Directive</title>
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<div class="titlepage"><div><div><h4 class="title">
<a name="spirit_repository.qi_components.directives.kwd"></a><a class="link" href="kwd.html" title="Qi Keyword Parser Directive">Qi
Keyword Parser Directive </a>
</h4></div></div></div>
<a name="spirit_repository.qi_components.directives.kwd.description"></a><h6>
<a name="spirit_repository.qi_components.directives.kwd.description-heading"></a>
<a class="link" href="kwd.html#spirit_repository.qi_components.directives.kwd.description">Description</a>
</h6>
<p>
The <code class="computeroutput"><span class="identifier">kwd</span><span class="special">[]</span></code>
and <code class="computeroutput"><span class="identifier">ikwd</span><span class="special">[]</span></code>
provide a powerful and flexible mechanism for parsing keyword based input.
It works in conjuction with the / operator to create an effective keyword
parsing loop. The keyword parsing loop doesn't require the keywords to
appear in a defined order in the input but also provides the possibility
to check how many times a keyword appears in the input.
</p>
<p>
The kwd directive will parse the keywords respecting case sensitivity whereas
the ikwd direcive is case insensitive. You can mix the kwd and ikwd directives
inside a set of keywords, but be aware that this has a small overhead.
It should be prefered not to mix the kwd and ikwd directives.
</p>
<p>
The kwd directive is very similar to the repeat directive in that it enables
to enforce keyword occurence constraints but also provides very interesting
speed improvement over the pure EBNF syntax or the Nabialek-Trick.
</p>
<a name="spirit_repository.qi_components.directives.kwd.header"></a><h6>
<a name="spirit_repository.qi_components.directives.kwd.header-heading"></a>
<a class="link" href="kwd.html#spirit_repository.qi_components.directives.kwd.header">Header</a>
</h6>
<pre class="programlisting"><span class="comment">// forwards to &lt;boost/spirit/repository/home/qi/directive/kwd.hpp&gt;
</span><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">spirit</span><span class="special">/</span><span class="identifier">repository</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">qi_kwd</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
</pre>
<a name="spirit_repository.qi_components.directives.kwd.synopsis"></a><h6>
<a name="spirit_repository.qi_components.directives.kwd.synopsis-heading"></a>
<a class="link" href="kwd.html#spirit_repository.qi_components.directives.kwd.synopsis">Synopsis</a>
</h6>
<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="identifier">kwd</span><span class="special">(</span><span class="identifier">keyword</span><span class="special">)[</span><span class="identifier">subject</span><span class="special">]</span></code>
</p>
</td>
<td>
<p>
Parse ( <code class="computeroutput"><span class="string">"keyword"</span></code>
&gt; <code class="computeroutput"><span class="identifier">subject</span></code>)
zero or more times.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">kwd</span><span class="special">(</span><span class="identifier">keyword</span><span class="special">,</span><span class="identifier">n</span><span class="special">)[</span><span class="identifier">subject</span><span class="special">]</span></code>
</p>
</td>
<td>
<p>
Parse ( <code class="computeroutput"><span class="string">"keyword"</span></code>
&gt; <code class="computeroutput"><span class="identifier">subject</span></code>)
exactly <code class="computeroutput"><span class="identifier">n</span></code> times.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">kwd</span><span class="special">(</span><span class="identifier">keyword</span><span class="special">,</span><span class="identifier">min</span><span class="special">,</span>
<span class="identifier">max</span><span class="special">)[</span><span class="identifier">subject</span><span class="special">]</span></code>
</p>
</td>
<td>
<p>
Parse ( <code class="computeroutput"><span class="string">"keyword"</span></code>
&gt; <code class="computeroutput"><span class="identifier">subject</span></code>)
at least <code class="computeroutput"><span class="identifier">min</span></code>
times and at most <code class="computeroutput"><span class="identifier">max</span></code>
times.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">kwd</span><span class="special">(</span><span class="identifier">keyword</span><span class="special">,</span><span class="identifier">min</span><span class="special">,</span>
<span class="identifier">inf</span><span class="special">)[</span><span class="identifier">subject</span><span class="special">]</span></code>
</p>
</td>
<td>
<p>
Parse ( <code class="computeroutput"><span class="string">"keyword"</span></code>
&gt; <code class="computeroutput"><span class="identifier">subject</span></code>)
at least <code class="computeroutput"><span class="identifier">min</span></code>
or more.
</p>
</td>
</tr>
</tbody>
</table></div>
<p>
For non case sensitive keywords use the ikwd directive.
</p>
<a name="spirit_repository.qi_components.directives.kwd.parameters"></a><h6>
<a name="spirit_repository.qi_components.directives.kwd.parameters-heading"></a>
<a class="link" href="kwd.html#spirit_repository.qi_components.directives.kwd.parameters">Parameters</a>
</h6>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Parameter
</p>
</th>
<th>
<p>
Description
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">keyword</span></code>
</p>
</td>
<td>
<p>
The parser for the opening (the prefix).
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">subject</span></code>
</p>
</td>
<td>
<p>
The parser for the input sequence following the keyword part.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">n</span></code>
</p>
</td>
<td>
<p>
Int representing the exact number of times the keyword must be
repeated.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">min</span></code>
</p>
</td>
<td>
<p>
Int representing the minimum number of times the keyword must
be repeated.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">max</span></code>
</p>
</td>
<td>
<p>
Int representing the maximum number of times the keyword must
be repeated.
</p>
</td>
</tr>
</tbody>
</table></div>
<p>
All three parameters can be arbitrarily complex parsers themselves.
</p>
<a name="spirit_repository.qi_components.directives.kwd.attributes"></a><h6>
<a name="spirit_repository.qi_components.directives.kwd.attributes-heading"></a>
<a class="link" href="kwd.html#spirit_repository.qi_components.directives.kwd.attributes">Attributes</a>
</h6>
<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="identifier">kwd</span><span class="special">(</span><span class="identifier">k1</span><span class="special">)[</span><span class="identifier">a</span><span class="special">]</span></code>
</p>
</td>
<td>
<p>
</p>
<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="identifier">a</span><span class="special">:</span> <span class="identifier">A</span> <span class="special">--&gt;</span> <span class="identifier">kwd</span><span class="special">(</span><span class="identifier">k1</span><span class="special">)[</span><span class="identifier">a</span><span class="special">]:</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">A</span><span class="special">&gt;</span> <span class="keyword">or</span> <span class="identifier">vector</span><span class="special">&lt;</span><span class="identifier">A</span><span class="special">&gt;</span>
<span class="identifier">a</span><span class="special">:</span> <span class="identifier">Unused</span> <span class="special">--&gt;</span> <span class="identifier">kwd</span><span class="special">(</span><span class="identifier">k1</span><span class="special">)[</span><span class="identifier">a</span><span class="special">]:</span> <span class="identifier">Unused</span></pre>
<p>
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">kwd</span><span class="special">(</span><span class="identifier">k1</span><span class="special">,</span><span class="identifier">n</span><span class="special">)[</span><span class="identifier">a</span><span class="special">]</span></code>
</p>
</td>
<td>
<p>
</p>
<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="identifier">a</span><span class="special">:</span> <span class="identifier">A</span> <span class="special">--&gt;</span> <span class="identifier">kwd</span><span class="special">(</span><span class="identifier">k1</span><span class="special">,</span><span class="identifier">n</span><span class="special">)[</span><span class="identifier">a</span><span class="special">]:</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">A</span><span class="special">&gt;</span> <span class="keyword">or</span> <span class="identifier">vector</span><span class="special">&lt;</span><span class="identifier">A</span><span class="special">&gt;</span>
<span class="identifier">a</span><span class="special">:</span> <span class="identifier">Unused</span> <span class="special">--&gt;</span> <span class="identifier">kwd</span><span class="special">(</span><span class="identifier">k1</span><span class="special">,</span><span class="identifier">n</span><span class="special">)[</span><span class="identifier">a</span><span class="special">]:</span> <span class="identifier">Unused</span></pre>
<p>
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">kwd</span><span class="special">(</span><span class="identifier">k1</span><span class="special">,</span><span class="identifier">min</span><span class="special">,</span>
<span class="identifier">max</span><span class="special">)[</span><span class="identifier">a</span><span class="special">]</span></code>
</p>
</td>
<td>
<p>
</p>
<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="identifier">a</span><span class="special">:</span> <span class="identifier">A</span> <span class="special">--&gt;</span> <span class="identifier">kwd</span><span class="special">(</span><span class="identifier">k1</span><span class="special">,</span><span class="identifier">min</span><span class="special">,</span> <span class="identifier">max</span><span class="special">)[</span><span class="identifier">a</span><span class="special">]:</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">A</span><span class="special">&gt;</span> <span class="keyword">or</span> <span class="identifier">vector</span><span class="special">&lt;</span><span class="identifier">A</span><span class="special">&gt;</span>
<span class="identifier">a</span><span class="special">:</span> <span class="identifier">Unused</span> <span class="special">--&gt;</span> <span class="identifier">kwd</span><span class="special">(</span><span class="identifier">k1</span><span class="special">,</span><span class="identifier">min</span><span class="special">,</span> <span class="identifier">max</span><span class="special">)[</span><span class="identifier">a</span><span class="special">]:</span> <span class="identifier">Unused</span></pre>
<p>
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">kwd</span><span class="special">(</span><span class="identifier">k1</span><span class="special">,</span><span class="identifier">min</span><span class="special">,</span>
<span class="identifier">inf</span><span class="special">)[</span><span class="identifier">a</span><span class="special">]</span></code>
</p>
</td>
<td>
<p>
</p>
<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="identifier">a</span><span class="special">:</span> <span class="identifier">A</span> <span class="special">--&gt;</span> <span class="identifier">kwd</span><span class="special">(</span><span class="identifier">k1</span><span class="special">,</span><span class="identifier">min</span><span class="special">,</span> <span class="identifier">inf</span><span class="special">)[</span><span class="identifier">a</span><span class="special">]:</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">A</span><span class="special">&gt;</span> <span class="keyword">or</span> <span class="identifier">vector</span><span class="special">&lt;</span><span class="identifier">A</span><span class="special">&gt;</span>
<span class="identifier">a</span><span class="special">:</span> <span class="identifier">Unused</span> <span class="special">--&gt;</span> <span class="identifier">kwd</span><span class="special">(</span><span class="identifier">k1</span><span class="special">,</span><span class="identifier">min</span><span class="special">,</span> <span class="identifier">inf</span><span class="special">)[</span><span class="identifier">a</span><span class="special">]:</span> <span class="identifier">Unused</span></pre>
<p>
</p>
</td>
</tr>
</tbody>
</table></div>
<a name="spirit_repository.qi_components.directives.kwd.complexity"></a><h6>
<a name="spirit_repository.qi_components.directives.kwd.complexity-heading"></a>
<a class="link" href="kwd.html#spirit_repository.qi_components.directives.kwd.complexity">Complexity</a>
</h6>
<div class="blockquote"><blockquote class="blockquote">
<p>
The overall complexity is defined by the complexity of its subject parser.
The complexity of the keyword list construct <code class="computeroutput"><span class="identifier">kwd</span></code>
itself is O(N), where N is the number of repetitions executed.
</p>
<p>
The complexity of the keyword list itself determined by the complexity
of the internal TST contents :
</p>
<p>
O(log n+k)
</p>
<p>
Where k is the length of the string to be searched in a TST with n strings.
</p>
</blockquote></div>
<a name="spirit_repository.qi_components.directives.kwd.example"></a><h6>
<a name="spirit_repository.qi_components.directives.kwd.example-heading"></a>
<a class="link" href="kwd.html#spirit_repository.qi_components.directives.kwd.example">Example</a>
</h6>
<p>
Please refer to keyword_list.
</p>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright &#169; 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>)
</p>
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