126 lines
9.5 KiB
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126 lines
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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
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implemented right now, which help to abstract common parser refactoring tasks.
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Parser refactoring means, that a concrete parser construct is replaced (refactored)
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by another very similar parser construct. Two of the Refactoring Parsers described
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here (<tt>refactor_unary_parser</tt> and <tt>refactor_action_parser</tt>) are
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introduced to allow a simple and more expressive notation while using <a href="confix.html">Confix
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Parsers</a> and <a href="list_parsers.html">List Parsers</a>. The third Refactoring
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Parser (<tt>attach_action_parser</tt>) is implemented to abstract some functionality
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required for the Grouping Parser. Nevertheless
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these Refactoring Parsers may help in solving other complex parsing tasks too.</p>
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<h3>Refactoring unary parsers</h3>
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<p>The <tt>refactor_unary_d</tt> parser generator, which should be used to generate
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a unary refactoring parser, transforms a construct of the following type</p>
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<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>
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<p>to </p>
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<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>
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<blockquote>
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<p>where <tt>refactor_unary_d</tt> is a predefined object of the parser generator
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struct <tt>refactor_unary_gen<></tt></p>
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</blockquote>
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<p>The <tt>refactor_unary_d</tt> parser generator generates a new parser as shown
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above, only if the original construct is an auxilliary binary parser (here the
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difference parser) and the left operand of this binary parser is an auxilliary
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unary parser (here the kleene star operator). If the original parser isn't a
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binary parser the compilation will fail. If the left operand isn't an unary
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parser, no refactoring will take place.</p>
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<h3>Refactoring action parsers</h3>
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<p>The <tt>refactor_action_d</tt> parser generator, which should be used to generate
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an action refactoring parser, transforms a construct of the following type</p>
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<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>
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<p>to </p>
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<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>
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<blockquote>
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<p>where <tt>refactor_action_d</tt> is a predefined object of the parser generator
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struct <tt>refactor_action_gen<></tt></p>
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</blockquote>
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<p>The <tt>refactor_action_d</tt> parser generator generates a new parser as shown
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above, only if the original construct is an auxilliary binary parser (here the
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difference parser) and the left operand of this binary parser is an auxilliary
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parser generated by an attached semantic action. If the original parser isn't
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a binary parser the compilation will fail. If the left operand isn't an action
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parser, no refactoring will take place.</p>
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<h3>Attach action refactoring</h3>
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<p>The <tt>attach_action_d</tt> parser generator, which should be used to generate
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an attach action refactoring parser, transforms a construct of the following
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type</p>
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<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>
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<p>to </p>
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<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>
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<blockquote>
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<p>where <tt>attach_action_d</tt> is a predefined object of the parser generator
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struct <tt>attach_action_gen<></tt></p>
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</blockquote>
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<p>The <tt>attach_action_d</tt> parser generator generates a new parser as shown
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above, only if the original construct is an auxilliary action parser and the
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parser to it this action is attached is an auxilliary binary parser (here the
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sequence parser). If the original parser isn't a action parser the compilation
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will fail. If the parser to which the action is attached isn't an binary parser,
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no refactoring will take place.</p>
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<h3>Nested refactoring</h3>
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<p>Sometimes it is required to nest different types of refactoring, i.e. to transform
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constructs like</p>
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<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>
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<p>to </p>
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<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>
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<p>To simplify the construction of such nested refactoring parsers the <tt>refactor_unary_gen<></tt>
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and <tt>refactor_action_gen<></tt> both can take another refactoring parser
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generator type as their respective template parameter. For instance, to construct
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a refactoring parser generator for the mentioned nested transformation we should
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write:</p>
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<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>;
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</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>
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<p>Now we could use it as follows to get the required result:</p>
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<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>
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<p>An empty template parameter means not to nest this particular refactoring parser.
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The default template parameter is <tt>non_nesting_refactoring</tt>, a predefined
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helper structure for inhibiting nesting. Sometimes it is required to nest a
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particular refactoring parser with itself. This is achieved by providing the
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predefined helper structure <tt>self_nested_refactoring</tt> as the template
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parameter to the corresponding refactoring parser generator template.</p>
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<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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</tr>
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<br>
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<hr size="1">
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<p class="copyright">Copyright © 2001-2003 Hartmut Kaiser<br>
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<br>
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<font size="2">Use, modification and distribution is subject to the Boost Software
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License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
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http://www.boost.org/LICENSE_1_0.txt)</font></p>
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<p> </p>
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