ceph/src/boost/libs/spirit/classic/doc/refactoring.html

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  26 <p><a name="refactoring_parsers"></a>There are three types of Refactoring Parsers
  27   implemented right now, which help to abstract common parser refactoring tasks.
  28   Parser refactoring means, that a concrete parser construct is replaced (refactored)
  29   by another very similar parser construct. Two of the Refactoring Parsers described
  30   here (<tt>refactor_unary_parser</tt> and <tt>refactor_action_parser</tt>) are
  31   introduced to allow a simple and more expressive notation while using <a href="confix.html">Confix
  32   Parsers</a> and <a href="list_parsers.html">List Parsers</a>. The third Refactoring
  33   Parser (<tt>attach_action_parser</tt>) is implemented to abstract some functionality
  34   required for the Grouping Parser. Nevertheless
  35   these Refactoring Parsers may help in solving other complex parsing tasks too.</p>
  36 <h3>Refactoring unary parsers</h3>
  37 <p>The <tt>refactor_unary_d</tt> parser generator, which should be used to generate
  38   a unary refactoring parser, transforms a construct of the following type</p>
  39 <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>
  40 <p>to </p>
  41 <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>
  42 <blockquote>
  43   <p>where <tt>refactor_unary_d</tt> is a predefined object of the parser generator
  44     struct <tt>refactor_unary_gen&lt;&gt;</tt></p>
  45 </blockquote>
  46 <p>The <tt>refactor_unary_d</tt> parser generator generates a new parser as shown
  47   above, only if the original construct is an auxilliary binary parser (here the
  48   difference parser) and the left operand of this binary parser is an auxilliary
  49   unary parser (here the kleene star operator). If the original parser isn't a
  50   binary parser the compilation will fail. If the left operand isn't an unary
  51   parser, no refactoring will take place.</p>
  52 <h3>Refactoring action parsers</h3>
  53 <p>The <tt>refactor_action_d</tt> parser generator, which should be used to generate
  54   an action refactoring parser, transforms a construct of the following type</p>
  55 <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>
  56 <p>to </p>
  57 <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>
  58 <blockquote>
  59   <p>where <tt>refactor_action_d</tt> is a predefined object of the parser generator
  60     struct <tt>refactor_action_gen&lt;&gt;</tt></p>
  61 </blockquote>
  62 <p>The <tt>refactor_action_d</tt> parser generator generates a new parser as shown
  63   above, only if the original construct is an auxilliary binary parser (here the
  64   difference parser) and the left operand of this binary parser is an auxilliary
  65   parser generated by an attached semantic action. If the original parser isn't
  66   a binary parser the compilation will fail. If the left operand isn't an action
  67   parser, no refactoring will take place.</p>
  68 <h3>Attach action refactoring</h3>
  69 <p>The <tt>attach_action_d</tt> parser generator, which should be used to generate
  70   an attach action refactoring parser, transforms a construct of the following
  71   type</p>
  72 <pre><code>    <span class=identifier>attach_action_d</span><span class=special>[</span><span class=identifier>(some_parser</span> <span class=special>&gt;&gt; </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>
  73 <p>to </p>
  74 <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>&gt;&gt; </span><span class=identifier>another_parser</span><span class=special>[</span><span class=identifier>some_actor</span><span class=special>]</span></code></pre>
  75 <blockquote>
  76   <p>where <tt>attach_action_d</tt> is a predefined object of the parser generator
  77     struct <tt>attach_action_gen&lt;&gt;</tt></p>
  78 </blockquote>
  79
  80 <p>The <tt>attach_action_d</tt> parser generator generates a new parser as shown
  81   above, only if the original construct is an auxilliary action parser and the
  82   parser to it this action is attached is an auxilliary binary parser (here the
  83   sequence parser). If the original parser isn't a action parser the compilation
  84   will fail. If the parser to which the action is attached isn't an binary parser,
  85   no refactoring will take place.</p>
  86 <h3>Nested refactoring</h3>
  87 <p>Sometimes it is required to nest different types of refactoring, i.e. to transform
  88   constructs like</p>
  89 <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>
  90 <p>to </p>
  91 <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>
  92 <p>To simplify the construction of such nested refactoring parsers the <tt>refactor_unary_gen&lt;&gt;</tt>
  93   and <tt>refactor_action_gen&lt;&gt;</tt> both can take another refactoring parser
  94   generator type as their respective template parameter. For instance, to construct
  95   a refactoring parser generator for the mentioned nested transformation we should
  96   write:</p>
  97 <pre><span class=special>    </span><span class=keyword>typedef </span><span class=identifier>refactor_action_gen</span><span class=special>&lt;</span><span class=identifier>refactor_unary_gen</span><span class=special>&lt;&gt; </span><span class=special>&gt; </span><span class=identifier>refactor_t</span><span class=special>;
  98     </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>
  99 <p>Now we could use it as follows to get the required result:</p>
 100 <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>
 101 <p>An empty template parameter means not to nest this particular refactoring parser.
 102   The default template parameter is <tt>non_nesting_refactoring</tt>, a predefined
 103   helper structure for inhibiting nesting. Sometimes it is required to nest a
 104   particular refactoring parser with itself. This is achieved by providing the
 105   predefined helper structure <tt>self_nested_refactoring</tt> as the template
 106   parameter to the corresponding refactoring parser generator template.</p>
 107 <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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 118 <p class="copyright">Copyright &copy; 2001-2003 Hartmut Kaiser<br>
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