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<td width="85%"> <font size="6" face="Verdana, Arial, Helvetica, sans-serif"><b>Refactoring Parsers</b></font></td>
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<p><a name="refactoring_parsers"></a>There are three types of Refactoring Parsers
implemented right now, which help to abstract common parser refactoring tasks.
Parser refactoring means, that a concrete parser construct is replaced (refactored)
by another very similar parser construct. Two of the Refactoring Parsers described
here (<tt>refactor_unary_parser</tt> and <tt>refactor_action_parser</tt>) are
introduced to allow a simple and more expressive notation while using <a href="confix.html">Confix
Parsers</a> and <a href="list_parsers.html">List Parsers</a>. The third Refactoring
Parser (<tt>attach_action_parser</tt>) is implemented to abstract some functionality
required for the Grouping Parser. Nevertheless
these Refactoring Parsers may help in solving other complex parsing tasks too.</p>
<h3>Refactoring unary parsers</h3>
<p>The <tt>refactor_unary_d</tt> parser generator, which should be used to generate
a unary refactoring parser, transforms a construct of the following type</p>
<pre><code> <span class=identifier>refactor_unary_d</span><span class=special>[*</span><span class=identifier>some_parser </span><span class=special>- </span><span class=identifier>another_parser</span><span class=special>]</span></code></pre>
<p>to </p>
<pre><code> <span class=special>*(</span><span class=identifier>some_parser</span> <span class=special>- </span><span class=identifier>another_parser</span><span class=special>)</span></code></pre>
<blockquote>
<p>where <tt>refactor_unary_d</tt> is a predefined object of the parser generator
struct <tt>refactor_unary_gen<></tt></p>
</blockquote>
<p>The <tt>refactor_unary_d</tt> parser generator generates a new parser as shown
above, only if the original construct is an auxilliary binary parser (here the
difference parser) and the left operand of this binary parser is an auxilliary
unary parser (here the kleene star operator). If the original parser isn't a
binary parser the compilation will fail. If the left operand isn't an unary
parser, no refactoring will take place.</p>
<h3>Refactoring action parsers</h3>
<p>The <tt>refactor_action_d</tt> parser generator, which should be used to generate
an action refactoring parser, transforms a construct of the following type</p>
<pre><code> <span class=identifier>refactor_action_d</span><span class=special>[</span><span class=identifier>some_parser</span><span class=special>[</span><span class=identifier>some_actor</span><span class=special>] </span><span class=special>- </span><span class=identifier>another_parser</span><span class=special>]</span></code></pre>
<p>to </p>
<pre><code> <span class=special>(</span><span class=identifier>some_parser </span><span class=special>- </span><span class=identifier>another_parser</span><span class=special>)[</span><span class=identifier>some_actor</span><span class=special>]</span></code></pre>
<blockquote>
<p>where <tt>refactor_action_d</tt> is a predefined object of the parser generator
struct <tt>refactor_action_gen<></tt></p>
</blockquote>
<p>The <tt>refactor_action_d</tt> parser generator generates a new parser as shown
above, only if the original construct is an auxilliary binary parser (here the
difference parser) and the left operand of this binary parser is an auxilliary
parser generated by an attached semantic action. If the original parser isn't
a binary parser the compilation will fail. If the left operand isn't an action
parser, no refactoring will take place.</p>
<h3>Attach action refactoring</h3>
<p>The <tt>attach_action_d</tt> parser generator, which should be used to generate
an attach action refactoring parser, transforms a construct of the following
type</p>
<pre><code> <span class=identifier>attach_action_d</span><span class=special>[</span><span class=identifier>(some_parser</span> <span class=special>>> </span><span class=identifier>another_parser</span>)<span class=special>[</span><span class=identifier>some_actor</span><span class=special>]</span><span class=special>]</span></code></pre>
<p>to </p>
<pre><code> <span class=identifier>some_parser</span><span class=special>[</span><span class=identifier>some_actor</span><span class=special>]</span><span class=identifier> </span><span class=special>>> </span><span class=identifier>another_parser</span><span class=special>[</span><span class=identifier>some_actor</span><span class=special>]</span></code></pre>
<blockquote>
<p>where <tt>attach_action_d</tt> is a predefined object of the parser generator
struct <tt>attach_action_gen<></tt></p>
</blockquote>
<p>The <tt>attach_action_d</tt> parser generator generates a new parser as shown
above, only if the original construct is an auxilliary action parser and the
parser to it this action is attached is an auxilliary binary parser (here the
sequence parser). If the original parser isn't a action parser the compilation
will fail. If the parser to which the action is attached isn't an binary parser,
no refactoring will take place.</p>
<h3>Nested refactoring</h3>
<p>Sometimes it is required to nest different types of refactoring, i.e. to transform
constructs like</p>
<pre><code> <span class=special>(*</span><span class=identifier>some_parser</span><span class=special>)[</span><span class=identifier>some_actor</span><span class=special>] </span><span class=special>- </span><span class=identifier>another_parser</span></code></pre>
<p>to </p>
<pre><code> <span class=special>(*(</span><span class=identifier>some_parser </span><span class=special>- </span><span class=identifier>another_parser</span><span class=special>))[</span><span class=identifier>some_actor</span><span class=special>]</span></code></pre>
<p>To simplify the construction of such nested refactoring parsers the <tt>refactor_unary_gen<></tt>
and <tt>refactor_action_gen<></tt> both can take another refactoring parser
generator type as their respective template parameter. For instance, to construct
a refactoring parser generator for the mentioned nested transformation we should
write:</p>
<pre><span class=special> </span><span class=keyword>typedef </span><span class=identifier>refactor_action_gen</span><span class=special><</span><span class=identifier>refactor_unary_gen</span><span class=special><> </span><span class=special>> </span><span class=identifier>refactor_t</span><span class=special>;
</span><span class=keyword>const </span><span class=identifier>refactor_t </span><span class=identifier>refactor_nested_d </span><span class=special>= </span><span class=identifier>refactor_t</span><span class=special>(</span><span class=identifier>refactor_unary_d</span><span class=special>);</span></pre>
<p>Now we could use it as follows to get the required result:</p>
<pre><code><font color="#0000FF"> </font><span class=identifier>refactor_nested_d</span><span class=special>[(*</span><span class=identifier>some_parser</span><span class=special>)[</span><span class=identifier>some_actor</span><span class=special>] </span><span class=special>- </span><span class=identifier>another_parser</span><span class=special>]</span></code></pre>
<p>An empty template parameter means not to nest this particular refactoring parser.
The default template parameter is <tt>non_nesting_refactoring</tt>, a predefined
helper structure for inhibiting nesting. Sometimes it is required to nest a
particular refactoring parser with itself. This is achieved by providing the
predefined helper structure <tt>self_nested_refactoring</tt> as the template
parameter to the corresponding refactoring parser generator template.</p>
<p><img src="theme/lens.gif" width="15" height="16"> See <a href="../example/fundamental/refactoring.cpp">refactoring.cpp</a> for a compilable example. This is part of the Spirit distribution. </p>
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<p class="copyright">Copyright © 2001-2003 Hartmut Kaiser<br>
<br>
<font size="2">Use, modification and distribution is subject to the Boost Software
License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
http://www.boost.org/LICENSE_1_0.txt)</font></p>
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