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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 two 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. The Refactoring Parsers described
here 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>. </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_action_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
a 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>Nested refactoring</h3>
<p>Sometimes it is required to nest both 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.</p>
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<p class="copyright">Copyright © 2001-2002 Hartmut Kaiser<br>
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