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| <div class="section"> |
| <div class="titlepage"><div><div><h5 class="title"> |
| <a name="spirit.qi.reference.nonterminal.rule"></a><a class="link" href="rule.html" title="Rule">Rule</a> |
| </h5></div></div></div> |
| <a name="spirit.qi.reference.nonterminal.rule.description"></a><h6> |
| <a name="id899151"></a> |
| <a class="link" href="rule.html#spirit.qi.reference.nonterminal.rule.description">Description</a> |
| </h6> |
| <p> |
| The rule is a polymorphic parser that acts as a named placeholder capturing |
| the behavior of a <a class="link" href="../../../abstracts/parsing_expression_grammar.html" title="Parsing Expression Grammar">Parsing |
| Expression Grammar</a> expression assigned to it. Naming a <a class="link" href="../../../abstracts/parsing_expression_grammar.html" title="Parsing Expression Grammar">Parsing |
| Expression Grammar</a> expression allows it to be referenced later |
| and makes it possible for the rule to call itself. This is one of the |
| most important mechanisms and the reason behind the word "recursive" |
| in recursive descent parsing. |
| </p> |
| <a name="spirit.qi.reference.nonterminal.rule.header"></a><h6> |
| <a name="id899177"></a> |
| <a class="link" href="rule.html#spirit.qi.reference.nonterminal.rule.header">Header</a> |
| </h6> |
| <pre class="programlisting"><span class="comment">// forwards to <boost/spirit/home/qi/nonterminal/rule.hpp> |
| </span><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">spirit</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">qi_rule</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| </pre> |
| <p> |
| Also, see <a class="link" href="../../../structure/include.html" title="Include">Include Structure</a>. |
| </p> |
| <a name="spirit.qi.reference.nonterminal.rule.namespace"></a><h6> |
| <a name="id899251"></a> |
| <a class="link" href="rule.html#spirit.qi.reference.nonterminal.rule.namespace">Namespace</a> |
| </h6> |
| <div class="informaltable"><table class="table"> |
| <colgroup><col></colgroup> |
| <thead><tr><th> |
| <p> |
| Name |
| </p> |
| </th></tr></thead> |
| <tbody><tr><td> |
| <p> |
| <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">qi</span><span class="special">::</span><span class="identifier">rule</span></code> |
| </p> |
| </td></tr></tbody> |
| </table></div> |
| <a name="spirit.qi.reference.nonterminal.rule.synopsis"></a><h6> |
| <a name="id899332"></a> |
| <a class="link" href="rule.html#spirit.qi.reference.nonterminal.rule.synopsis">Synopsis</a> |
| </h6> |
| <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Iterator</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">A1</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">A2</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">A3</span><span class="special">></span> |
| <span class="keyword">struct</span> <span class="identifier">rule</span><span class="special">;</span> |
| </pre> |
| <a name="spirit.qi.reference.nonterminal.rule.template_parameters"></a><h6> |
| <a name="id899425"></a> |
| <a class="link" href="rule.html#spirit.qi.reference.nonterminal.rule.template_parameters">Template |
| parameters</a> |
| </h6> |
| <div class="informaltable"><table class="table"> |
| <colgroup> |
| <col> |
| <col> |
| <col> |
| </colgroup> |
| <thead><tr> |
| <th> |
| <p> |
| Parameter |
| </p> |
| </th> |
| <th> |
| <p> |
| Description |
| </p> |
| </th> |
| <th> |
| <p> |
| Default |
| </p> |
| </th> |
| </tr></thead> |
| <tbody> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">Iterator</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| The underlying iterator type that the rule is expected to work |
| on. |
| </p> |
| </td> |
| <td> |
| <p> |
| none |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">A1</span></code>, <code class="computeroutput"><span class="identifier">A2</span></code>, <code class="computeroutput"><span class="identifier">A3</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| Either <code class="computeroutput"><span class="identifier">Signature</span></code>, |
| <code class="computeroutput"><span class="identifier">Skipper</span></code> or |
| <code class="computeroutput"><span class="identifier">Locals</span></code> in any |
| order. See table below. |
| </p> |
| </td> |
| <td> |
| <p> |
| See table below. |
| </p> |
| </td> |
| </tr> |
| </tbody> |
| </table></div> |
| <p> |
| Here is more information about the template parameters: |
| </p> |
| <div class="informaltable"><table class="table"> |
| <colgroup> |
| <col> |
| <col> |
| <col> |
| </colgroup> |
| <thead><tr> |
| <th> |
| <p> |
| Parameter |
| </p> |
| </th> |
| <th> |
| <p> |
| Description |
| </p> |
| </th> |
| <th> |
| <p> |
| Default |
| </p> |
| </th> |
| </tr></thead> |
| <tbody> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">Signature</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| Specifies the rule's synthesized (return value) and inherited |
| attributes (arguments). More on this here: <a class="link" href="../parser_concepts/nonterminal.html" title="Nonterminal"><code class="computeroutput"><span class="identifier">Nonterminal</span></code></a>. |
| </p> |
| </td> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">unused_type</span></code>. |
| When <code class="computeroutput"><span class="identifier">Signature</span></code> |
| defaults to <code class="computeroutput"><span class="identifier">unused_type</span></code>, |
| the effect is the same as specifying a signature of <code class="computeroutput"><span class="keyword">void</span><span class="special">()</span></code> |
| which is also equivalent to <code class="computeroutput"><span class="identifier">unused_type</span><span class="special">()</span></code> |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">Skipper</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| Specifies the rule's skipper parser. Specify this if you want |
| the rule to skip white spaces. If this is not specified, the |
| rule is an "implicit lexeme" and will not skip spaces. |
| "implicit lexeme" rules can still be called with |
| a skipper. In such a case, the rule does a pre-skip just as |
| all lexemes and primitives do. |
| </p> |
| </td> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">unused_type</span></code> |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">Locals</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| Specifies the rule's local variables. See <a class="link" href="../parser_concepts/nonterminal.html" title="Nonterminal"><code class="computeroutput"><span class="identifier">Nonterminal</span></code></a>. |
| </p> |
| </td> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">unused_type</span></code> |
| </p> |
| </td> |
| </tr> |
| </tbody> |
| </table></div> |
| <a name="spirit.qi.reference.nonterminal.rule.model_of"></a><h6> |
| <a name="id899805"></a> |
| <a class="link" href="rule.html#spirit.qi.reference.nonterminal.rule.model_of">Model of</a> |
| </h6> |
| <div class="blockquote"><blockquote class="blockquote"><p> |
| <a class="link" href="../parser_concepts/nonterminal.html" title="Nonterminal"><code class="computeroutput"><span class="identifier">Nonterminal</span></code></a> |
| </p></blockquote></div> |
| <div class="variablelist"> |
| <p class="title"><b>Notation</b></p> |
| <dl> |
| <dt><span class="term"><code class="computeroutput"><span class="identifier">r</span><span class="special">,</span> |
| <span class="identifier">r2</span></code></span></dt> |
| <dd><p> |
| Rules |
| </p></dd> |
| <dt><span class="term"><code class="computeroutput"><span class="identifier">p</span></code></span></dt> |
| <dd><p> |
| A parser expression |
| </p></dd> |
| <dt><span class="term"><code class="computeroutput"><span class="identifier">Iterator</span></code></span></dt> |
| <dd><p> |
| The underlying iterator type that the rule is expected to work |
| on. |
| </p></dd> |
| <dt><span class="term"><code class="computeroutput"><span class="identifier">A1</span></code>, <code class="computeroutput"><span class="identifier">A2</span></code>, <code class="computeroutput"><span class="identifier">A3</span></code></span></dt> |
| <dd><p> |
| Either <code class="computeroutput"><span class="identifier">Signature</span></code>, |
| <code class="computeroutput"><span class="identifier">Skipper</span></code> or <code class="computeroutput"><span class="identifier">Locals</span></code> in any order. |
| </p></dd> |
| </dl> |
| </div> |
| <a name="spirit.qi.reference.nonterminal.rule.expression_semantics"></a><h6> |
| <a name="id899965"></a> |
| <a class="link" href="rule.html#spirit.qi.reference.nonterminal.rule.expression_semantics">Expression |
| Semantics</a> |
| </h6> |
| <p> |
| Semantics of an expression is defined only where it differs from, or |
| is not defined in <a class="link" href="../parser_concepts/nonterminal.html" title="Nonterminal"><code class="computeroutput"><span class="identifier">Nonterminal</span></code></a>. |
| </p> |
| <div class="informaltable"><table class="table"> |
| <colgroup> |
| <col> |
| <col> |
| </colgroup> |
| <thead><tr> |
| <th> |
| <p> |
| Expression |
| </p> |
| </th> |
| <th> |
| <p> |
| Description |
| </p> |
| </th> |
| </tr></thead> |
| <tbody> |
| <tr> |
| <td> |
| <p> |
| |
| </p> |
| <pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="identifier">rule</span><span class="special"><</span><span class="identifier">Iterator</span><span class="special">,</span> <span class="identifier">A1</span><span class="special">,</span> <span class="identifier">A2</span><span class="special">,</span> <span class="identifier">A3</span><span class="special">></span> |
| <span class="identifier">r</span><span class="special">(</span><span class="identifier">name</span><span class="special">);</span></pre> |
| <p> |
| </p> |
| </td> |
| <td> |
| <p> |
| Rule declaration. <code class="computeroutput"><span class="identifier">Iterator</span></code> |
| is required. <code class="computeroutput"><span class="identifier">A1</span><span class="special">,</span> <span class="identifier">A2</span><span class="special">,</span> <span class="identifier">A3</span></code> |
| are optional and can be specified in any order. <code class="computeroutput"><span class="identifier">name</span></code> is an optional string |
| that gives the rule its name, useful for debugging and error |
| handling. |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| |
| </p> |
| <pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="identifier">rule</span><span class="special"><</span><span class="identifier">Iterator</span><span class="special">,</span> <span class="identifier">A1</span><span class="special">,</span> <span class="identifier">A2</span><span class="special">,</span> <span class="identifier">A3</span><span class="special">></span> |
| <span class="identifier">r</span><span class="special">(</span><span class="identifier">r2</span><span class="special">);</span></pre> |
| <p> |
| </p> |
| </td> |
| <td> |
| <p> |
| Copy construct rule <code class="computeroutput"><span class="identifier">r</span></code> |
| from rule <code class="computeroutput"><span class="identifier">r2</span></code>. |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">r</span> <span class="special">=</span> |
| <span class="identifier">r2</span><span class="special">;</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| Assign rule <code class="computeroutput"><span class="identifier">r2</span></code> |
| to <code class="computeroutput"><span class="identifier">r</span></code>. |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">r</span><span class="special">.</span><span class="identifier">alias</span><span class="special">()</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| return an alias of <code class="computeroutput"><span class="identifier">r</span></code>. |
| The alias is a parser that holds a reference to <code class="computeroutput"><span class="identifier">r</span></code>. |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">r</span><span class="special">.</span><span class="identifier">copy</span><span class="special">()</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| Get a copy of <code class="computeroutput"><span class="identifier">r</span></code>. |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">r</span> <span class="special">=</span> |
| <span class="identifier">p</span><span class="special">;</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| Rule definition. This is equivalent to <code class="computeroutput"><span class="identifier">r</span> |
| <span class="special">%=</span> <span class="identifier">p</span></code> |
| (see below) if there are no semantic actions attached anywhere |
| in <code class="computeroutput"><span class="identifier">p</span></code>. |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">r</span> <span class="special">%=</span> |
| <span class="identifier">p</span><span class="special">;</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| Auto-rule definition. The attribute of <code class="computeroutput"><span class="identifier">p</span></code> |
| should be compatible with the synthesized attribute of <code class="computeroutput"><span class="identifier">r</span></code>. When <code class="computeroutput"><span class="identifier">p</span></code> |
| is successful, its attribute is automatically propagated to |
| <code class="computeroutput"><span class="identifier">r</span></code>'s synthesized |
| attribute. |
| </p> |
| </td> |
| </tr> |
| </tbody> |
| </table></div> |
| <a name="spirit.qi.reference.nonterminal.rule.attributes"></a><h6> |
| <a name="id900514"></a> |
| <a class="link" href="rule.html#spirit.qi.reference.nonterminal.rule.attributes">Attributes</a> |
| </h6> |
| <div class="blockquote"><blockquote class="blockquote"><p> |
| The parser attribute of the rule is <code class="computeroutput"><span class="identifier">T</span></code>, |
| its synthesized attribute. See <a class="link" href="../parser_concepts/nonterminal.html#spirit.qi.reference.parser_concepts.nonterminal.attributes"><code class="computeroutput"><span class="identifier">Attribute</span></code></a> |
| </p></blockquote></div> |
| <a name="spirit.qi.reference.nonterminal.rule.complexity"></a><h6> |
| <a name="id900553"></a> |
| <a class="link" href="rule.html#spirit.qi.reference.nonterminal.rule.complexity">Complexity</a> |
| </h6> |
| <div class="blockquote"><blockquote class="blockquote"><p> |
| The complexity is defined by the complexity of the RHS parser, <code class="computeroutput"><span class="identifier">p</span></code> |
| </p></blockquote></div> |
| <a name="spirit.qi.reference.nonterminal.rule.example"></a><h6> |
| <a name="id900581"></a> |
| <a class="link" href="rule.html#spirit.qi.reference.nonterminal.rule.example">Example</a> |
| </h6> |
| <div class="note"><table border="0" summary="Note"> |
| <tr> |
| <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../images/note.png"></td> |
| <th align="left">Note</th> |
| </tr> |
| <tr><td align="left" valign="top"><p> |
| The test harness for the example(s) below is presented in the <a class="link" href="../basics.html#spirit.qi.reference.basics.examples">Basics Examples</a> |
| section. |
| </p></td></tr> |
| </table></div> |
| <p> |
| Some using declarations: |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">qi</span><span class="special">::</span><span class="identifier">rule</span><span class="special">;</span> |
| <span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">qi</span><span class="special">::</span><span class="identifier">int_</span><span class="special">;</span> |
| <span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">qi</span><span class="special">::</span><span class="identifier">locals</span><span class="special">;</span> |
| <span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">qi</span><span class="special">::</span><span class="identifier">_1</span><span class="special">;</span> |
| <span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">qi</span><span class="special">::</span><span class="identifier">_a</span><span class="special">;</span> |
| <span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">ascii</span><span class="special">::</span><span class="identifier">alpha</span><span class="special">;</span> |
| <span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">ascii</span><span class="special">::</span><span class="identifier">char_</span><span class="special">;</span> |
| <span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">ascii</span><span class="special">::</span><span class="identifier">space_type</span><span class="special">;</span></pre> |
| <p> |
| </p> |
| <p> |
| Basic rule: |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="identifier">rule</span><span class="special"><</span><span class="keyword">char</span> <span class="keyword">const</span><span class="special">*></span> <span class="identifier">r</span><span class="special">;</span> |
| <span class="identifier">r</span> <span class="special">=</span> <span class="identifier">int_</span><span class="special">;</span> |
| <span class="identifier">test_parser</span><span class="special">(</span><span class="string">"123"</span><span class="special">,</span> <span class="identifier">r</span><span class="special">);</span></pre> |
| <p> |
| </p> |
| <p> |
| Rule with synthesized attribute: |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="identifier">rule</span><span class="special"><</span><span class="keyword">char</span> <span class="keyword">const</span><span class="special">*,</span> <span class="keyword">int</span><span class="special">()></span> <span class="identifier">ra</span><span class="special">;</span> |
| <span class="identifier">ra</span> <span class="special">=</span> <span class="identifier">int_</span><span class="special">;</span> |
| <span class="keyword">int</span> <span class="identifier">i</span><span class="special">;</span> |
| <span class="identifier">test_parser_attr</span><span class="special">(</span><span class="string">"123"</span><span class="special">,</span> <span class="identifier">ra</span><span class="special">,</span> <span class="identifier">i</span><span class="special">);</span> |
| <span class="identifier">assert</span><span class="special">(</span><span class="identifier">i</span> <span class="special">==</span> <span class="number">123</span><span class="special">);</span></pre> |
| <p> |
| </p> |
| <p> |
| Rule with skipper and synthesized attribute: |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="identifier">rule</span><span class="special"><</span><span class="keyword">char</span> <span class="keyword">const</span><span class="special">*,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="keyword">int</span><span class="special">>(),</span> <span class="identifier">space_type</span><span class="special">></span> <span class="identifier">rs</span><span class="special">;</span> |
| <span class="identifier">rs</span> <span class="special">=</span> <span class="special">*</span><span class="identifier">int_</span><span class="special">;</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">v</span><span class="special">;</span> |
| <span class="identifier">test_phrase_parser_attr</span><span class="special">(</span><span class="string">"123 456 789"</span><span class="special">,</span> <span class="identifier">rs</span><span class="special">,</span> <span class="identifier">v</span><span class="special">);</span> |
| <span class="identifier">assert</span><span class="special">(</span><span class="identifier">v</span><span class="special">[</span><span class="number">0</span><span class="special">]</span> <span class="special">==</span> <span class="number">123</span><span class="special">);</span> |
| <span class="identifier">assert</span><span class="special">(</span><span class="identifier">v</span><span class="special">[</span><span class="number">1</span><span class="special">]</span> <span class="special">==</span> <span class="number">456</span><span class="special">);</span> |
| <span class="identifier">assert</span><span class="special">(</span><span class="identifier">v</span><span class="special">[</span><span class="number">2</span><span class="special">]</span> <span class="special">==</span> <span class="number">789</span><span class="special">);</span></pre> |
| <p> |
| </p> |
| <p> |
| Rule with one local variable: |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="identifier">rule</span><span class="special"><</span><span class="keyword">char</span> <span class="keyword">const</span><span class="special">*,</span> <span class="identifier">locals</span><span class="special"><</span><span class="keyword">char</span><span class="special">></span> <span class="special">></span> <span class="identifier">rl</span><span class="special">;</span> |
| <span class="identifier">rl</span> <span class="special">=</span> <span class="identifier">alpha</span><span class="special">[</span><span class="identifier">_a</span> <span class="special">=</span> <span class="identifier">_1</span><span class="special">]</span> <span class="special">>></span> <span class="identifier">char_</span><span class="special">(</span><span class="identifier">_a</span><span class="special">);</span> <span class="comment">// get two identical characters |
| </span><span class="identifier">test_parser</span><span class="special">(</span><span class="string">"aa"</span><span class="special">,</span> <span class="identifier">rl</span><span class="special">);</span> <span class="comment">// pass |
| </span><span class="identifier">test_parser</span><span class="special">(</span><span class="string">"ax"</span><span class="special">,</span> <span class="identifier">rl</span><span class="special">);</span> <span class="comment">// fail |
| </span></pre> |
| <p> |
| </p> |
| </div> |
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| <td align="right"><div class="copyright-footer">Copyright © 2001-2010 Joel de Guzman, Hartmut Kaiser<p> |
| Distributed under the Boost Software License, Version 1.0. (See accompanying |
| file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) |
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