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- List Attribute - one more, with style</a>
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- <p>
- You've seen that the <code class="computeroutput"><span class="identifier">double_</span></code>
- parser has a <code class="computeroutput"><span class="keyword">double</span></code> attribute.
- All parsers have an attribute, even complex parsers. Those that are composed
- from primitives using operators, like the list parser, also have an attribute.
- It so happens that the attribute of a list parser:
- </p>
- <pre class="programlisting"><span class="identifier">p</span> <span class="special">%</span> <span class="identifier">d</span>
- </pre>
- <p>
- is a <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span></code> of the attribute of <code class="computeroutput"><span class="identifier">p</span></code>. So, for our parser:
- </p>
- <pre class="programlisting"><span class="identifier">double_</span> <span class="special">%</span> <span class="char">','</span>
- </pre>
- <p>
- we'll have an attribute of:
- </p>
- <pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="keyword">double</span><span class="special">></span>
- </pre>
- <p>
- So, what does this give us? Well, we can simply pass in a <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="keyword">double</span><span class="special">></span></code> to our number list parser and it will
- happily churn out our result in our vector. For that to happen, we'll use
- a variation of the <code class="computeroutput"><span class="identifier">phrase_parse</span></code>
- with an additional argument: the parser's attribute. With the following arguments
- passed to <code class="computeroutput"><span class="identifier">phrase_parse</span></code>
- </p>
- <div class="orderedlist"><ol class="orderedlist" type="1">
- <li class="listitem">
- An iterator pointing to the start of the input
- </li>
- <li class="listitem">
- An iterator pointing to one past the end of the input
- </li>
- <li class="listitem">
- The parser object
- </li>
- <li class="listitem">
- Another parser called the skip parser
- </li>
- <li class="listitem">
- The parser's attribute
- </li>
- </ol></div>
- <p>
- Our parser now is further simplified to:
- </p>
- <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Iterator</span><span class="special">></span>
- <span class="keyword">bool</span> <span class="identifier">parse_numbers</span><span class="special">(</span><span class="identifier">Iterator</span> <span class="identifier">first</span><span class="special">,</span> <span class="identifier">Iterator</span> <span class="identifier">last</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="keyword">double</span><span class="special">>&</span> <span class="identifier">v</span><span class="special">)</span>
- <span class="special">{</span>
- <span class="keyword">using</span> <span class="identifier">x3</span><span class="special">::</span><span class="identifier">double_</span><span class="special">;</span>
- <span class="keyword">using</span> <span class="identifier">x3</span><span class="special">::</span><span class="identifier">phrase_parse</span><span class="special">;</span>
- <span class="keyword">using</span> <span class="identifier">x3</span><span class="special">::</span><span class="identifier">_attr</span><span class="special">;</span>
- <span class="keyword">using</span> <span class="identifier">ascii</span><span class="special">::</span><span class="identifier">space</span><span class="special">;</span>
- <span class="keyword">bool</span> <span class="identifier">r</span> <span class="special">=</span> <span class="identifier">phrase_parse</span><span class="special">(</span><span class="identifier">first</span><span class="special">,</span> <span class="identifier">last</span><span class="special">,</span>
- <span class="comment">// Begin grammar</span>
- <span class="special">(</span>
- <span class="identifier">double_</span> <span class="special">%</span> <span class="char">','</span>
- <span class="special">)</span>
- <span class="special">,</span>
- <span class="comment">// End grammar</span>
- <span class="identifier">space</span><span class="special">,</span> <span class="identifier">v</span><span class="special">);</span>
- <span class="keyword">if</span> <span class="special">(</span><span class="identifier">first</span> <span class="special">!=</span> <span class="identifier">last</span><span class="special">)</span> <span class="comment">// fail if we did not get a full match</span>
- <span class="keyword">return</span> <span class="keyword">false</span><span class="special">;</span>
- <span class="keyword">return</span> <span class="identifier">r</span><span class="special">;</span>
- <span class="special">}</span>
- </pre>
- <p>
- The full cpp file for this example can be found here: <a href="../../../../../example/x3/num_list/num_list4.cpp" target="_top">num_list4.cpp</a>
- </p>
- <p>
- <span class="bold"><strong>Hey, no more actions!!!</strong></span> Now we're entering
- the realm of attribute grammars. Cool eh?
- </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 © 2001-2018 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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