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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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