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- <div class="titlepage"><div><div><h4 class="title">
- <a name="spirit_repository.qi_components.directives.distinct"></a><a class="link" href="distinct.html" title="Qi Distinct Parser Directive">Qi
- Distinct Parser Directive</a>
- </h4></div></div></div>
- <h6>
- <a name="spirit_repository.qi_components.directives.distinct.h0"></a>
- <span class="phrase"><a name="spirit_repository.qi_components.directives.distinct.description"></a></span><a class="link" href="distinct.html#spirit_repository.qi_components.directives.distinct.description">Description</a>
- </h6>
- <p>
- The <span class="emphasis"><em>Spirit.Qi</em></span> <code class="computeroutput"><span class="identifier">distinct</span></code>
- parser is a directive component allowing to avoid partial matches while
- parsing using a skipper. A simple example is the common task of matching
- a C keyword. Consider:
- </p>
- <pre class="programlisting"><span class="string">"description"</span> <span class="special">>></span> <span class="special">-</span><span class="identifier">lit</span><span class="special">(</span><span class="string">":"</span><span class="special">)</span> <span class="special">>></span> <span class="special">*(</span><span class="identifier">char_</span> <span class="special">-</span> <span class="identifier">eol</span><span class="special">)</span>
- </pre>
- <p>
- intended to match a line in a configuration file. Let's assume further,
- that this rule is used with a <code class="computeroutput"><span class="identifier">space</span></code>
- skipper and that we have the following strings in the input:
- </p>
- <pre class="programlisting"><span class="string">"description: ident\n"</span>
- <span class="string">"description ident\n"</span>
- <span class="string">"descriptionident\n"</span>
- </pre>
- <p>
- It might seem unexpected, but the parser above matches all three inputs
- just fine, even if the third input should not match at all! In order to
- avoid the unwanted match we are forced to make our rule more complicated:
- </p>
- <pre class="programlisting"><span class="identifier">lexeme</span><span class="special">[</span><span class="string">"description"</span> <span class="special">>></span> <span class="special">!</span><span class="identifier">char_</span><span class="special">(</span><span class="string">"a-zA-Z_0-9"</span><span class="special">)]</span> <span class="special">>></span> <span class="special">-</span><span class="identifier">lit</span><span class="special">(</span><span class="string">":"</span><span class="special">)</span> <span class="special">>></span> <span class="special">*(</span><span class="identifier">char_</span> <span class="special">-</span> <span class="identifier">eol</span><span class="special">)</span>
- </pre>
- <p>
- (the rule reads as: match <code class="computeroutput"><span class="string">"description"</span></code>
- as long as it's not <span class="emphasis"><em>directly</em></span> followed by a valid identifier).
- </p>
- <p>
- The <code class="computeroutput"><span class="identifier">distinct</span><span class="special">[]</span></code>
- directive is meant to simplify the rule above:
- </p>
- <pre class="programlisting"><span class="identifier">distinct</span><span class="special">(</span><span class="identifier">char_</span><span class="special">(</span><span class="string">"a-zA-Z_0-9"</span><span class="special">))[</span><span class="string">"description"</span><span class="special">]</span> <span class="special">>></span> <span class="special">-</span><span class="identifier">lit</span><span class="special">(</span><span class="string">":"</span><span class="special">)</span> <span class="special">>></span> <span class="special">*(</span><span class="identifier">char_</span> <span class="special">-</span> <span class="identifier">eol</span><span class="special">)</span>
- </pre>
- <p>
- Using the <code class="computeroutput"><span class="identifier">distinct</span><span class="special">[]</span></code>
- component instead of the explicit sequence has the advantage of being able
- to encapsulate the tail (i.e the <code class="computeroutput"><span class="identifier">char_</span><span class="special">(</span><span class="string">"a-zA-Z_0-9"</span><span class="special">)</span></code>) as a separate parser construct. The following
- code snippet illustrates the idea (for the full code of this example please
- see <a href="../../../../../test/qi/distinct.cpp" target="_top">distinct.cpp</a>):
- </p>
- <p>
- </p>
- <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">spirit</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="keyword">namespace</span> <span class="identifier">ascii</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">ascii</span><span class="special">;</span>
- <span class="keyword">namespace</span> <span class="identifier">repo</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">repository</span><span class="special">;</span>
- <span class="comment">// Define metafunctions allowing to compute the type of the distinct()</span>
- <span class="comment">// and ascii::char_() constructs</span>
- <span class="keyword">namespace</span> <span class="identifier">traits</span>
- <span class="special">{</span>
- <span class="comment">// Metafunction allowing to get the type of any repository::distinct(...) </span>
- <span class="comment">// construct</span>
- <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Tail</span><span class="special">></span>
- <span class="keyword">struct</span> <span class="identifier">distinct_spec</span>
- <span class="special">:</span> <span class="identifier">spirit</span><span class="special">::</span><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">terminal</span><span class="special"><</span><span class="identifier">repo</span><span class="special">::</span><span class="identifier">tag</span><span class="special">::</span><span class="identifier">distinct</span><span class="special">(</span><span class="identifier">Tail</span><span class="special">)></span>
- <span class="special">{};</span>
- <span class="comment">// Metafunction allowing to get the type of any ascii::char_(...) construct</span>
- <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">String</span><span class="special">></span>
- <span class="keyword">struct</span> <span class="identifier">char_spec</span>
- <span class="special">:</span> <span class="identifier">spirit</span><span class="special">::</span><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">terminal</span><span class="special"><</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">tag</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="identifier">String</span><span class="special">)></span>
- <span class="special">{};</span>
- <span class="special">}</span>
- <span class="comment">// Define a helper function allowing to create a distinct() construct from </span>
- <span class="comment">// an arbitrary tail parser</span>
- <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Tail</span><span class="special">></span>
- <span class="keyword">inline</span> <span class="keyword">typename</span> <span class="identifier">traits</span><span class="special">::</span><span class="identifier">distinct_spec</span><span class="special"><</span><span class="identifier">Tail</span><span class="special">>::</span><span class="identifier">type</span>
- <span class="identifier">distinct_spec</span><span class="special">(</span><span class="identifier">Tail</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">tail</span><span class="special">)</span>
- <span class="special">{</span>
- <span class="keyword">return</span> <span class="identifier">repo</span><span class="special">::</span><span class="identifier">distinct</span><span class="special">(</span><span class="identifier">tail</span><span class="special">);</span>
- <span class="special">}</span>
- <span class="comment">// Define a helper function allowing to create a ascii::char_() construct </span>
- <span class="comment">// from an arbitrary string representation</span>
- <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">String</span><span class="special">></span>
- <span class="keyword">inline</span> <span class="keyword">typename</span> <span class="identifier">traits</span><span class="special">::</span><span class="identifier">char_spec</span><span class="special"><</span><span class="identifier">String</span><span class="special">>::</span><span class="identifier">type</span>
- <span class="identifier">char_spec</span><span class="special">(</span><span class="identifier">String</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">str</span><span class="special">)</span>
- <span class="special">{</span>
- <span class="keyword">return</span> <span class="identifier">ascii</span><span class="special">::</span><span class="identifier">char_</span><span class="special">(</span><span class="identifier">str</span><span class="special">);</span>
- <span class="special">}</span>
- <span class="comment">// the following constructs the type of a distinct_spec holding a</span>
- <span class="comment">// charset("0-9a-zA-Z_") as its tail parser</span>
- <span class="keyword">typedef</span> <span class="identifier">traits</span><span class="special">::</span><span class="identifier">char_spec</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">>::</span><span class="identifier">type</span> <span class="identifier">charset_tag_type</span><span class="special">;</span>
- <span class="keyword">typedef</span> <span class="identifier">traits</span><span class="special">::</span><span class="identifier">distinct_spec</span><span class="special"><</span><span class="identifier">charset_tag_type</span><span class="special">>::</span><span class="identifier">type</span> <span class="identifier">keyword_tag_type</span><span class="special">;</span>
- <span class="comment">// Define a new Qi 'keyword' directive usable as a shortcut for a</span>
- <span class="comment">// repository::distinct(char_(std::string("0-9a-zA-Z_")))</span>
- <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="keyword">const</span> <span class="identifier">keyword_spec</span><span class="special">(</span><span class="string">"0-9a-zA-Z_"</span><span class="special">);</span>
- <span class="identifier">keyword_tag_type</span> <span class="keyword">const</span> <span class="identifier">keyword</span> <span class="special">=</span> <span class="identifier">distinct_spec</span><span class="special">(</span><span class="identifier">char_spec</span><span class="special">(</span><span class="identifier">keyword_spec</span><span class="special">));</span>
- </pre>
- <p>
- </p>
- <p>
- These definitions define a new Qi parser recognizing keywords! This allows
- to rewrite our declaration parser expression as:
- </p>
- <pre class="programlisting"><span class="identifier">keyword</span><span class="special">[</span><span class="string">"description"</span><span class="special">]</span> <span class="special">>></span> <span class="special">-</span><span class="identifier">lit</span><span class="special">(</span><span class="string">":"</span><span class="special">)</span> <span class="special">>></span> <span class="special">*(</span><span class="identifier">char_</span> <span class="special">-</span> <span class="identifier">eol</span><span class="special">)</span>
- </pre>
- <p>
- which is much more readable and concise if compared to the original parser
- expression. In addition the new <code class="computeroutput"><span class="identifier">keyword</span><span class="special">[]</span></code> directive has the advantage to be usable
- for wrapping any parser expression, not only strings as in the example
- above.
- </p>
- <h6>
- <a name="spirit_repository.qi_components.directives.distinct.h1"></a>
- <span class="phrase"><a name="spirit_repository.qi_components.directives.distinct.header"></a></span><a class="link" href="distinct.html#spirit_repository.qi_components.directives.distinct.header">Header</a>
- </h6>
- <pre class="programlisting"><span class="comment">// forwards to <boost/spirit/repository/home/qi/directive/distinct.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">repository</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">qi_distinct</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
- </pre>
- <h6>
- <a name="spirit_repository.qi_components.directives.distinct.h2"></a>
- <span class="phrase"><a name="spirit_repository.qi_components.directives.distinct.synopsis"></a></span><a class="link" href="distinct.html#spirit_repository.qi_components.directives.distinct.synopsis">Synopsis</a>
- </h6>
- <pre class="programlisting"><span class="identifier">distinct</span><span class="special">(</span><span class="identifier">tail</span><span class="special">)[</span><span class="identifier">subject</span><span class="special">]</span>
- </pre>
- <h6>
- <a name="spirit_repository.qi_components.directives.distinct.h3"></a>
- <span class="phrase"><a name="spirit_repository.qi_components.directives.distinct.parameters"></a></span><a class="link" href="distinct.html#spirit_repository.qi_components.directives.distinct.parameters">Parameters</a>
- </h6>
- <div class="informaltable"><table class="table">
- <colgroup>
- <col>
- <col>
- </colgroup>
- <thead><tr>
- <th>
- <p>
- Parameter
- </p>
- </th>
- <th>
- <p>
- Description
- </p>
- </th>
- </tr></thead>
- <tbody>
- <tr>
- <td>
- <p>
- <code class="computeroutput"><span class="identifier">tail</span></code>
- </p>
- </td>
- <td>
- <p>
- The parser construct specifying what whould not follow the subject
- in order to match the overall expression.
- </p>
- </td>
- </tr>
- <tr>
- <td>
- <p>
- <code class="computeroutput"><span class="identifier">subject</span></code>
- </p>
- </td>
- <td>
- <p>
- The parser construct to use to match the current input. The distinct
- directive makes sure that no unexpected partial matches occur.
- </p>
- </td>
- </tr>
- </tbody>
- </table></div>
- <p>
- All two parameters can be arbitrary complex parsers themselves.
- </p>
- <h6>
- <a name="spirit_repository.qi_components.directives.distinct.h4"></a>
- <span class="phrase"><a name="spirit_repository.qi_components.directives.distinct.attribute"></a></span><a class="link" href="distinct.html#spirit_repository.qi_components.directives.distinct.attribute">Attribute</a>
- </h6>
- <p>
- The <code class="computeroutput"><span class="identifier">distinct</span></code> component
- exposes the attribute type of its subject as its own attribute type. If
- the <code class="computeroutput"><span class="identifier">subject</span></code> does not expose
- any attribute (the type is <code class="computeroutput"><span class="identifier">unused_type</span></code>),
- then the <code class="computeroutput"><span class="identifier">distinct</span></code> does
- not expose any attribute either.
- </p>
- <pre class="programlisting"><span class="identifier">a</span><span class="special">:</span> <span class="identifier">A</span><span class="special">,</span> <span class="identifier">b</span><span class="special">:</span> <span class="identifier">B</span> <span class="special">--></span> <span class="identifier">distinct</span><span class="special">(</span><span class="identifier">b</span><span class="special">)[</span><span class="identifier">a</span><span class="special">]:</span> <span class="identifier">A</span>
- </pre>
- <h6>
- <a name="spirit_repository.qi_components.directives.distinct.h5"></a>
- <span class="phrase"><a name="spirit_repository.qi_components.directives.distinct.example"></a></span><a class="link" href="distinct.html#spirit_repository.qi_components.directives.distinct.example">Example</a>
- </h6>
- <p>
- The following example shows simple use cases of the <code class="computeroutput"><span class="identifier">distinct</span></code>
- parser. <a href="../../../../../example/qi/distinct.cpp" target="_top">distinct.cpp</a>)
- </p>
- <h6>
- <a name="spirit_repository.qi_components.directives.distinct.h6"></a>
- <span class="phrase"><a name="spirit_repository.qi_components.directives.distinct.prerequisites"></a></span><a class="link" href="distinct.html#spirit_repository.qi_components.directives.distinct.prerequisites">Prerequisites</a>
- </h6>
- <p>
- In addition to the main header file needed to include the core components
- implemented in <span class="emphasis"><em>Spirit.Qi</em></span> we add the header file needed
- for the new <code class="computeroutput"><span class="identifier">distinct</span></code> generator.
- </p>
- <p>
- </p>
- <pre class="programlisting"><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</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></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">repository</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">qi_distinct</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
- </pre>
- <p>
- </p>
- <p>
- To make all the code below more readable we introduce the following namespaces.
- </p>
- <p>
- </p>
- <pre class="programlisting"><span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">;</span>
- <span class="keyword">using</span> <span class="keyword">namespace</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="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">repository</span><span class="special">::</span><span class="identifier">distinct</span><span class="special">;</span>
- </pre>
- <p>
- </p>
- <h6>
- <a name="spirit_repository.qi_components.directives.distinct.h7"></a>
- <span class="phrase"><a name="spirit_repository.qi_components.directives.distinct.using_the_distinct_directive_to_match_keywords"></a></span><a class="link" href="distinct.html#spirit_repository.qi_components.directives.distinct.using_the_distinct_directive_to_match_keywords">Using
- The Distinct Directive to Match keywords</a>
- </h6>
- <p>
- We show several examples of how the <code class="computeroutput"><span class="identifier">distinct</span><span class="special">[]</span></code> directive can be used to force correct
- behavior while matching keywords. The first two code snippets show the
- correct matching of the <code class="computeroutput"><span class="identifier">description</span></code>
- keyword (in this hypothetical example we allow keywords to be directly
- followed by an optional <code class="computeroutput"><span class="string">"--"</span></code>):
- </p>
- <p>
- </p>
- <pre class="programlisting"><span class="special">{</span>
- <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">str</span><span class="special">(</span><span class="string">"description ident"</span><span class="special">);</span>
- <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">::</span><span class="identifier">iterator</span> <span class="identifier">first</span><span class="special">(</span><span class="identifier">str</span><span class="special">.</span><span class="identifier">begin</span><span class="special">());</span>
- <span class="keyword">bool</span> <span class="identifier">r</span> <span class="special">=</span> <span class="identifier">qi</span><span class="special">::</span><span class="identifier">phrase_parse</span><span class="special">(</span><span class="identifier">first</span><span class="special">,</span> <span class="identifier">str</span><span class="special">.</span><span class="identifier">end</span><span class="special">()</span>
- <span class="special">,</span> <span class="identifier">distinct</span><span class="special">(</span><span class="identifier">alnum</span> <span class="special">|</span> <span class="char">'_'</span><span class="special">)[</span><span class="string">"description"</span><span class="special">]</span> <span class="special">>></span> <span class="special">-</span><span class="identifier">lit</span><span class="special">(</span><span class="string">"--"</span><span class="special">)</span> <span class="special">>></span> <span class="special">+(</span><span class="identifier">alnum</span> <span class="special">|</span> <span class="char">'_'</span><span class="special">)</span>
- <span class="special">,</span> <span class="identifier">space</span><span class="special">);</span>
- <span class="identifier">BOOST_ASSERT</span><span class="special">(</span><span class="identifier">r</span> <span class="special">&&</span> <span class="identifier">first</span> <span class="special">==</span> <span class="identifier">str</span><span class="special">.</span><span class="identifier">end</span><span class="special">());</span>
- <span class="special">}</span>
- </pre>
- <p>
- </p>
- <p>
- </p>
- <pre class="programlisting"><span class="special">{</span>
- <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">str</span><span class="special">(</span><span class="string">"description--ident"</span><span class="special">);</span>
- <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">::</span><span class="identifier">iterator</span> <span class="identifier">first</span><span class="special">(</span><span class="identifier">str</span><span class="special">.</span><span class="identifier">begin</span><span class="special">());</span>
- <span class="keyword">bool</span> <span class="identifier">r</span> <span class="special">=</span> <span class="identifier">qi</span><span class="special">::</span><span class="identifier">phrase_parse</span><span class="special">(</span><span class="identifier">first</span><span class="special">,</span> <span class="identifier">str</span><span class="special">.</span><span class="identifier">end</span><span class="special">()</span>
- <span class="special">,</span> <span class="identifier">distinct</span><span class="special">(</span><span class="identifier">alnum</span> <span class="special">|</span> <span class="char">'_'</span><span class="special">)[</span><span class="string">"description"</span><span class="special">]</span> <span class="special">>></span> <span class="special">-</span><span class="identifier">lit</span><span class="special">(</span><span class="string">"--"</span><span class="special">)</span> <span class="special">>></span> <span class="special">+(</span><span class="identifier">alnum</span> <span class="special">|</span> <span class="char">'_'</span><span class="special">)</span>
- <span class="special">,</span> <span class="identifier">space</span><span class="special">);</span>
- <span class="identifier">BOOST_ASSERT</span><span class="special">(</span><span class="identifier">r</span> <span class="special">&&</span> <span class="identifier">first</span> <span class="special">==</span> <span class="identifier">str</span><span class="special">.</span><span class="identifier">end</span><span class="special">());</span>
- <span class="special">}</span>
- </pre>
- <p>
- </p>
- <p>
- The last example shows that the <code class="computeroutput"><span class="identifier">distinct</span><span class="special">[]</span></code> parser component correctly refuses to
- match "description-ident":
- </p>
- <p>
- </p>
- <pre class="programlisting"><span class="special">{</span>
- <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">str</span><span class="special">(</span><span class="string">"description-ident"</span><span class="special">);</span>
- <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">::</span><span class="identifier">iterator</span> <span class="identifier">first</span><span class="special">(</span><span class="identifier">str</span><span class="special">.</span><span class="identifier">begin</span><span class="special">());</span>
- <span class="keyword">bool</span> <span class="identifier">r</span> <span class="special">=</span> <span class="identifier">qi</span><span class="special">::</span><span class="identifier">phrase_parse</span><span class="special">(</span><span class="identifier">first</span><span class="special">,</span> <span class="identifier">str</span><span class="special">.</span><span class="identifier">end</span><span class="special">()</span>
- <span class="special">,</span> <span class="identifier">distinct</span><span class="special">(</span><span class="identifier">alnum</span> <span class="special">|</span> <span class="char">'_'</span><span class="special">)[</span><span class="string">"description"</span><span class="special">]</span> <span class="special">>></span> <span class="special">-</span><span class="identifier">lit</span><span class="special">(</span><span class="string">"--"</span><span class="special">)</span> <span class="special">>></span> <span class="special">+(</span><span class="identifier">alnum</span> <span class="special">|</span> <span class="char">'_'</span><span class="special">)</span>
- <span class="special">,</span> <span class="identifier">space</span><span class="special">);</span>
- <span class="identifier">BOOST_ASSERT</span><span class="special">(!</span><span class="identifier">r</span> <span class="special">&&</span> <span class="identifier">first</span> <span class="special">==</span> <span class="identifier">str</span><span class="special">.</span><span class="identifier">begin</span><span class="special">());</span>
- <span class="special">}</span>
- </pre>
- <p>
- </p>
- </div>
- <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
- <td align="left"></td>
- <td align="right"><div class="copyright-footer">Copyright © 2001-2011 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>)
- </p>
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