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| <div class="section"> |
| <div class="titlepage"><div><div><h4 class="title"> |
| <a name="spirit.qi.tutorials.mini_xml___asts_"></a><a class="link" href="mini_xml___asts_.html" title="Mini XML - ASTs!">Mini XML - ASTs!</a> |
| </h4></div></div></div> |
| <p> |
| Stop and think about it... We've come very close to generating an AST (abstract |
| syntax tree) in our last example. We parsed a single structure and generated |
| an in-memory representation of it in the form of a struct: the <code class="computeroutput"><span class="keyword">struct</span> <span class="identifier">employee</span></code>. |
| If we changed the implementation to parse one or more employees, the result |
| would be a <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="identifier">employee</span><span class="special">></span></code>. |
| We can go on and add more hierarchy: teams, departments, corporations. |
| Then we'll have an AST representation of it all. |
| </p> |
| <p> |
| In this example (actually two examples), we'll now explore how to create |
| ASTs. We will parse a minimalistic XML-like language and compile the results |
| into our data structures in the form of a tree. |
| </p> |
| <p> |
| Along the way, we'll see new features: |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" type="disc"> |
| <li class="listitem"> |
| Inherited attributes |
| </li> |
| <li class="listitem"> |
| Variant attributes |
| </li> |
| <li class="listitem"> |
| Local Variables |
| </li> |
| <li class="listitem"> |
| Not Predicate |
| </li> |
| <li class="listitem"> |
| Lazy Lit |
| </li> |
| </ul></div> |
| <p> |
| The full cpp files for these examples can be found here: <a href="../../../../../example/qi/mini_xml1.cpp" target="_top">../../example/qi/mini_xml1.cpp</a> |
| and here: <a href="../../../../../example/qi/mini_xml2.cpp" target="_top">../../example/qi/mini_xml2.cpp</a> |
| </p> |
| <p> |
| There are a couple of sample toy-xml files in the mini_xml_samples subdirectory: |
| <a href="../../../../../example/qi/mini_xml_samples/1.toyxml" target="_top">../../example/qi/mini_xml_samples/1.toyxml</a>, |
| <a href="../../../../../example/qi/mini_xml_samples/2.toyxml" target="_top">../../example/qi/mini_xml_samples/2.toyxml</a>, |
| and <a href="../../../../../example/qi/mini_xml_samples/3.toyxml" target="_top">../../example/qi/mini_xml_samples/3.toyxml</a> |
| for testing purposes. The example <a href="../../../../../example/qi/mini_xml_samples/4.toyxml" target="_top">../../example/qi/mini_xml_samples/4.toyxml</a> |
| has an error in it. |
| </p> |
| <a name="spirit.qi.tutorials.mini_xml___asts_.first_cut"></a><h6> |
| <a name="id813740"></a> |
| <a class="link" href="mini_xml___asts_.html#spirit.qi.tutorials.mini_xml___asts_.first_cut">First Cut</a> |
| </h6> |
| <p> |
| Without further delay, here's the first version of the XML grammar: |
| </p> |
| <p> |
| |
| </p> |
| <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">struct</span> <span class="identifier">mini_xml_grammar</span> <span class="special">:</span> <span class="identifier">qi</span><span class="special">::</span><span class="identifier">grammar</span><span class="special"><</span><span class="identifier">Iterator</span><span class="special">,</span> <span class="identifier">mini_xml</span><span class="special">(),</span> <span class="identifier">ascii</span><span class="special">::</span><span class="identifier">space_type</span><span class="special">></span> |
| <span class="special">{</span> |
| <span class="identifier">mini_xml_grammar</span><span class="special">()</span> <span class="special">:</span> <span class="identifier">mini_xml_grammar</span><span class="special">::</span><span class="identifier">base_type</span><span class="special">(</span><span class="identifier">xml</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="keyword">using</span> <span class="identifier">qi</span><span class="special">::</span><span class="identifier">lit</span><span class="special">;</span> |
| <span class="keyword">using</span> <span class="identifier">qi</span><span class="special">::</span><span class="identifier">lexeme</span><span class="special">;</span> |
| <span class="keyword">using</span> <span class="identifier">qi</span><span class="special">::</span><span class="identifier">raw</span><span class="special">;</span> |
| <span class="keyword">using</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">ascii</span><span class="special">::</span><span class="identifier">string</span><span class="special">;</span> |
| <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">qi</span><span class="special">::</span><span class="identifier">labels</span><span class="special">;</span> |
| |
| <span class="keyword">using</span> <span class="identifier">phoenix</span><span class="special">::</span><span class="identifier">at_c</span><span class="special">;</span> |
| <span class="keyword">using</span> <span class="identifier">phoenix</span><span class="special">::</span><span class="identifier">push_back</span><span class="special">;</span> |
| |
| <span class="identifier">text</span> <span class="special">%=</span> <span class="identifier">lexeme</span><span class="special">[+(</span><span class="identifier">char_</span> <span class="special">-</span> <span class="char">'<'</span><span class="special">)</span> <span class="special">]</span> <span class="special">;</span> <span class="comment">// [_val = phoenix::construct<std::string>(begin(_1),end(_1))]; |
| </span> <span class="identifier">node</span> <span class="special">=</span> <span class="special">(</span><span class="identifier">xml</span> <span class="special">|</span> <span class="identifier">text</span><span class="special">)</span> <span class="special">[</span><span class="identifier">_val</span> <span class="special">=</span> <span class="identifier">_1</span><span class="special">];</span> |
| |
| <span class="identifier">start_tag</span> <span class="special">%=</span> |
| <span class="char">'<'</span> |
| <span class="special">>></span> <span class="special">!</span><span class="identifier">lit</span><span class="special">(</span><span class="char">'/'</span><span class="special">)</span> |
| <span class="special">>></span> <span class="identifier">raw</span><span class="special">[</span><span class="identifier">lexeme</span><span class="special">[+(</span><span class="identifier">char_</span> <span class="special">-</span> <span class="char">'>'</span><span class="special">)]]</span> |
| <span class="special">>></span> <span class="char">'>'</span> |
| <span class="special">;</span> |
| |
| <span class="identifier">end_tag</span> <span class="special">=</span> |
| <span class="string">"</"</span> |
| <span class="special">>></span> <span class="identifier">string</span><span class="special">(</span><span class="identifier">_r1</span><span class="special">)</span> |
| <span class="special">>></span> <span class="char">'>'</span> |
| <span class="special">;</span> |
| |
| <span class="identifier">xml</span> <span class="special">=</span> |
| <span class="identifier">start_tag</span> <span class="special">[</span><span class="identifier">at_c</span><span class="special"><</span><span class="number">0</span><span class="special">>(</span><span class="identifier">_val</span><span class="special">)</span> <span class="special">=</span> <span class="identifier">_1</span><span class="special">]</span> |
| <span class="special">>></span> <span class="special">*</span><span class="identifier">node</span> <span class="special">[</span><span class="identifier">push_back</span><span class="special">(</span><span class="identifier">at_c</span><span class="special"><</span><span class="number">1</span><span class="special">>(</span><span class="identifier">_val</span><span class="special">),</span> <span class="identifier">_1</span><span class="special">)]</span> |
| <span class="special">>></span> <span class="identifier">end_tag</span><span class="special">(</span><span class="identifier">at_c</span><span class="special"><</span><span class="number">0</span><span class="special">>(</span><span class="identifier">_val</span><span class="special">))</span> |
| <span class="special">;</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="identifier">Iterator</span><span class="special">,</span> <span class="identifier">mini_xml</span><span class="special">(),</span> <span class="identifier">ascii</span><span class="special">::</span><span class="identifier">space_type</span><span class="special">></span> <span class="identifier">xml</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="identifier">Iterator</span><span class="special">,</span> <span class="identifier">mini_xml_node</span><span class="special">(),</span> <span class="identifier">ascii</span><span class="special">::</span><span class="identifier">space_type</span><span class="special">></span> <span class="identifier">node</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="identifier">Iterator</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">ascii</span><span class="special">::</span><span class="identifier">space_type</span><span class="special">></span> <span class="identifier">text</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="identifier">Iterator</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">ascii</span><span class="special">::</span><span class="identifier">space_type</span><span class="special">></span> <span class="identifier">start_tag</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="identifier">Iterator</span><span class="special">,</span> <span class="keyword">void</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">ascii</span><span class="special">::</span><span class="identifier">space_type</span><span class="special">></span> <span class="identifier">end_tag</span><span class="special">;</span> |
| <span class="special">};</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| Going bottom up, let's examine the <code class="computeroutput"><span class="identifier">text</span></code> |
| rule: |
| </p> |
| <pre class="programlisting"><span class="identifier">rule</span><span class="special"><</span><span class="identifier">Iterator</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">space_type</span><span class="special">></span> <span class="identifier">text</span><span class="special">;</span> |
| </pre> |
| <p> |
| and its definition: |
| </p> |
| <pre class="programlisting"><span class="identifier">text</span> <span class="special">=</span> <span class="identifier">lexeme</span><span class="special">[+(</span><span class="identifier">char_</span> <span class="special">-</span> <span class="char">'<'</span><span class="special">)</span> <span class="special">[</span><span class="identifier">_val</span> <span class="special">+=</span> <span class="identifier">_1</span><span class="special">]];</span> |
| </pre> |
| <p> |
| The semantic action collects the chars and appends them (via +=) to the |
| <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span></code> attribute of the rule (represented |
| by the placeholder <code class="computeroutput"><span class="identifier">_val</span></code>). |
| </p> |
| <a name="spirit.qi.tutorials.mini_xml___asts_.alternates"></a><h6> |
| <a name="id814916"></a> |
| <a class="link" href="mini_xml___asts_.html#spirit.qi.tutorials.mini_xml___asts_.alternates">Alternates</a> |
| </h6> |
| <pre class="programlisting"><span class="identifier">rule</span><span class="special"><</span><span class="identifier">Iterator</span><span class="special">,</span> <span class="identifier">mini_xml_node</span><span class="special">(),</span> <span class="identifier">space_type</span><span class="special">></span> <span class="identifier">node</span><span class="special">;</span> |
| </pre> |
| <p> |
| and its definition: |
| </p> |
| <pre class="programlisting"><span class="identifier">node</span> <span class="special">=</span> <span class="special">(</span><span class="identifier">xml</span> <span class="special">|</span> <span class="identifier">text</span><span class="special">)</span> <span class="special">[</span><span class="identifier">_val</span> <span class="special">=</span> <span class="identifier">_1</span><span class="special">];</span> |
| </pre> |
| <p> |
| We'll see a <code class="computeroutput"><span class="identifier">mini_xml_node</span></code> |
| structure later. Looking at the rule definition, we see some alternation |
| going on here. An xml <code class="computeroutput"><span class="identifier">node</span></code> |
| is either an <code class="computeroutput"><span class="identifier">xml</span></code> OR <code class="computeroutput"><span class="identifier">text</span></code>. Hmmm... hold on to that thought... |
| </p> |
| <pre class="programlisting"><span class="identifier">rule</span><span class="special"><</span><span class="identifier">Iterator</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">space_type</span><span class="special">></span> <span class="identifier">start_tag</span><span class="special">;</span> |
| </pre> |
| <p> |
| Again, with an attribute of <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span></code>. |
| Then, it's definition: |
| </p> |
| <pre class="programlisting"><span class="identifier">start_tag</span> <span class="special">=</span> |
| <span class="char">'<'</span> |
| <span class="special">>></span> <span class="special">!</span><span class="identifier">char_</span><span class="special">(</span><span class="char">'/'</span><span class="special">)</span> |
| <span class="special">>></span> <span class="identifier">lexeme</span><span class="special">[+(</span><span class="identifier">char_</span> <span class="special">-</span> <span class="char">'>'</span><span class="special">)</span> <span class="special">[</span><span class="identifier">_val</span> <span class="special">+=</span> <span class="identifier">_1</span><span class="special">]]</span> |
| <span class="special">>></span> <span class="char">'>'</span> |
| <span class="special">;</span> |
| </pre> |
| <a name="spirit.qi.tutorials.mini_xml___asts_.not_predicate"></a><h6> |
| <a name="id815790"></a> |
| <a class="link" href="mini_xml___asts_.html#spirit.qi.tutorials.mini_xml___asts_.not_predicate">Not |
| Predicate</a> |
| </h6> |
| <p> |
| <code class="computeroutput"><span class="identifier">start_tag</span></code> is similar to |
| the <code class="computeroutput"><span class="identifier">text</span></code> rule apart from |
| the added <code class="computeroutput"><span class="char">'<'</span></code> and <code class="computeroutput"><span class="char">'>'</span></code>. But wait, to make sure that the <code class="computeroutput"><span class="identifier">start_tag</span></code> does not parse <code class="computeroutput"><span class="identifier">end_tag</span></code>s too, we add: <code class="computeroutput"><span class="special">!</span><span class="identifier">char_</span><span class="special">(</span><span class="char">'/'</span><span class="special">)</span></code>. This |
| is a "Not Predicate": |
| </p> |
| <pre class="programlisting"><span class="special">!</span><span class="identifier">p</span> |
| </pre> |
| <p> |
| It will try the parser, <code class="computeroutput"><span class="identifier">p</span></code>. |
| If it is successful, fail; otherwise, pass. In other words, it negates |
| the result of <code class="computeroutput"><span class="identifier">p</span></code>. Like the |
| <code class="computeroutput"><span class="identifier">eps</span></code>, it does not consume |
| any input though. It will always rewind the iterator position to where |
| it was upon entry. So, the expression: |
| </p> |
| <pre class="programlisting"><span class="special">!</span><span class="identifier">char_</span><span class="special">(</span><span class="char">'/'</span><span class="special">)</span> |
| </pre> |
| <p> |
| basically says: we should not have a <code class="computeroutput"><span class="char">'/'</span></code> |
| at this point. |
| </p> |
| <a name="spirit.qi.tutorials.mini_xml___asts_.inherited_attribute"></a><h6> |
| <a name="id815945"></a> |
| <a class="link" href="mini_xml___asts_.html#spirit.qi.tutorials.mini_xml___asts_.inherited_attribute">Inherited |
| Attribute</a> |
| </h6> |
| <p> |
| The <code class="computeroutput"><span class="identifier">end_tag</span></code>: |
| </p> |
| <pre class="programlisting"><span class="identifier">rule</span><span class="special"><</span><span class="identifier">Iterator</span><span class="special">,</span> <span class="keyword">void</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">space_type</span><span class="special">></span> <span class="identifier">end_tag</span><span class="special">;</span> |
| </pre> |
| <p> |
| Ohh! Now we see an inherited attribute there: <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span></code>. |
| The <code class="computeroutput"><span class="identifier">end_tag</span></code> does not have |
| a synthesized attribute. Let's see its definition: |
| </p> |
| <pre class="programlisting"><span class="identifier">end_tag</span> <span class="special">=</span> |
| <span class="string">"</"</span> |
| <span class="special">>></span> <span class="identifier">lit</span><span class="special">(</span><span class="identifier">_r1</span><span class="special">)</span> |
| <span class="special">>></span> <span class="char">'>'</span> |
| <span class="special">;</span> |
| </pre> |
| <p> |
| <code class="computeroutput"><span class="identifier">_r1</span></code> is yet another <a href="../../../../../phoenix/doc/html/index.html" target="_top">Phoenix</a> placeholder for |
| the first inherited attribute (we have only one, use <code class="computeroutput"><span class="identifier">_r2</span></code>, |
| <code class="computeroutput"><span class="identifier">_r3</span></code>, etc. if you have more). |
| </p> |
| <a name="spirit.qi.tutorials.mini_xml___asts_.a_lazy_lit"></a><h6> |
| <a name="id816140"></a> |
| <a class="link" href="mini_xml___asts_.html#spirit.qi.tutorials.mini_xml___asts_.a_lazy_lit">A Lazy |
| Lit</a> |
| </h6> |
| <p> |
| Check out how we used <code class="computeroutput"><span class="identifier">lit</span></code> |
| here, this time, not with a literal string, but with the value of the first |
| inherited attribute, which is specified as <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span></code> |
| in our rule declaration. |
| </p> |
| <p> |
| Finally, our <code class="computeroutput"><span class="identifier">xml</span></code> rule: |
| </p> |
| <pre class="programlisting"><span class="identifier">rule</span><span class="special"><</span><span class="identifier">Iterator</span><span class="special">,</span> <span class="identifier">mini_xml</span><span class="special">(),</span> <span class="identifier">space_type</span><span class="special">></span> <span class="identifier">xml</span><span class="special">;</span> |
| </pre> |
| <p> |
| <code class="computeroutput"><span class="identifier">mini_xml</span></code> is our attribute |
| here. We'll see later what it is. Let's see its definition: |
| </p> |
| <pre class="programlisting"><span class="identifier">xml</span> <span class="special">=</span> |
| <span class="identifier">start_tag</span> <span class="special">[</span><span class="identifier">at_c</span><span class="special"><</span><span class="number">0</span><span class="special">>(</span><span class="identifier">_val</span><span class="special">)</span> <span class="special">=</span> <span class="identifier">_1</span><span class="special">]</span> |
| <span class="special">>></span> <span class="special">*</span><span class="identifier">node</span> <span class="special">[</span><span class="identifier">push_back</span><span class="special">(</span><span class="identifier">at_c</span><span class="special"><</span><span class="number">1</span><span class="special">>(</span><span class="identifier">_val</span><span class="special">),</span> <span class="identifier">_1</span><span class="special">)]</span> |
| <span class="special">>></span> <span class="identifier">end_tag</span><span class="special">(</span><span class="identifier">at_c</span><span class="special"><</span><span class="number">0</span><span class="special">>(</span><span class="identifier">_val</span><span class="special">))</span> |
| <span class="special">;</span> |
| </pre> |
| <p> |
| Those who know <a href="../../../../../../../libs/fusion/doc/html/index.html" target="_top">Boost.Fusion</a> |
| now will notice <code class="computeroutput"><span class="identifier">at_c</span><span class="special"><</span><span class="number">0</span><span class="special">></span></code> and |
| <code class="computeroutput"><span class="identifier">at_c</span><span class="special"><</span><span class="number">1</span><span class="special">></span></code>. This |
| gives us a hint that <code class="computeroutput"><span class="identifier">mini_xml</span></code> |
| is a sort of a tuple - a fusion sequence. <code class="computeroutput"><span class="identifier">at_c</span><span class="special"><</span><span class="identifier">N</span><span class="special">></span></code> here is a lazy version of the tuple |
| accessors, provided by <a href="../../../../../phoenix/doc/html/index.html" target="_top">Phoenix</a>. |
| </p> |
| <a name="spirit.qi.tutorials.mini_xml___asts_.how_it_all_works"></a><h6> |
| <a name="id816471"></a> |
| <a class="link" href="mini_xml___asts_.html#spirit.qi.tutorials.mini_xml___asts_.how_it_all_works">How |
| it all works</a> |
| </h6> |
| <p> |
| So, what's happening? |
| </p> |
| <div class="orderedlist"><ol class="orderedlist" type="1"> |
| <li class="listitem"> |
| Upon parsing <code class="computeroutput"><span class="identifier">start_tag</span></code>, |
| the parsed start-tag string is placed in <code class="computeroutput"><span class="identifier">at_c</span><span class="special"><</span><span class="number">0</span><span class="special">>(</span><span class="identifier">_val</span><span class="special">)</span></code>. |
| </li> |
| <li class="listitem"> |
| Then we parse zero or more <code class="computeroutput"><span class="identifier">node</span></code>s. |
| At each step, we <code class="computeroutput"><span class="identifier">push_back</span></code> |
| the result into <code class="computeroutput"><span class="identifier">at_c</span><span class="special"><</span><span class="number">1</span><span class="special">>(</span><span class="identifier">_val</span><span class="special">)</span></code>. |
| </li> |
| <li class="listitem"> |
| Finally, we parse the <code class="computeroutput"><span class="identifier">end_tag</span></code> |
| giving it an inherited attribute: <code class="computeroutput"><span class="identifier">at_c</span><span class="special"><</span><span class="number">0</span><span class="special">>(</span><span class="identifier">_val</span><span class="special">)</span></code>. This is the string we obtained from |
| the <code class="computeroutput"><span class="identifier">start_tag</span></code>. Investigate |
| <code class="computeroutput"><span class="identifier">end_tag</span></code> above. It will |
| fail to parse if it gets something different from what we got from |
| the <code class="computeroutput"><span class="identifier">start_tag</span></code>. This |
| ensures that our tags are balanced. |
| </li> |
| </ol></div> |
| <p> |
| To give the last item some more light, what happens is this: |
| </p> |
| <pre class="programlisting"><span class="identifier">end_tag</span><span class="special">(</span><span class="identifier">at_c</span><span class="special"><</span><span class="number">0</span><span class="special">>(</span><span class="identifier">_val</span><span class="special">))</span> |
| </pre> |
| <p> |
| calls: |
| </p> |
| <pre class="programlisting"><span class="identifier">end_tag</span> <span class="special">=</span> |
| <span class="string">"</"</span> |
| <span class="special">>></span> <span class="identifier">lit</span><span class="special">(</span><span class="identifier">_r1</span><span class="special">)</span> |
| <span class="special">>></span> <span class="char">'>'</span> |
| <span class="special">;</span> |
| </pre> |
| <p> |
| passing in <code class="computeroutput"><span class="identifier">at_c</span><span class="special"><</span><span class="number">0</span><span class="special">>(</span><span class="identifier">_val</span><span class="special">)</span></code>, the string from start tag. This is referred |
| to in the <code class="computeroutput"><span class="identifier">end_tag</span></code> body |
| as <code class="computeroutput"><span class="identifier">_r1</span></code>. |
| </p> |
| <a name="spirit.qi.tutorials.mini_xml___asts_.the_structures"></a><h6> |
| <a name="id816780"></a> |
| <a class="link" href="mini_xml___asts_.html#spirit.qi.tutorials.mini_xml___asts_.the_structures">The |
| Structures</a> |
| </h6> |
| <p> |
| Let's see our structures. It will definitely be hierarchical: xml is hierarchical. |
| It will also be recursive: xml is recursive. |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">mini_xml</span><span class="special">;</span> |
| |
| <span class="keyword">typedef</span> |
| <span class="identifier">boost</span><span class="special">::</span><span class="identifier">variant</span><span class="special"><</span> |
| <span class="identifier">boost</span><span class="special">::</span><span class="identifier">recursive_wrapper</span><span class="special"><</span><span class="identifier">mini_xml</span><span class="special">></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">mini_xml_node</span><span class="special">;</span> |
| |
| <span class="keyword">struct</span> <span class="identifier">mini_xml</span> |
| <span class="special">{</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">name</span><span class="special">;</span> <span class="comment">// tag name |
| </span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="identifier">mini_xml_node</span><span class="special">></span> <span class="identifier">children</span><span class="special">;</span> <span class="comment">// children |
| </span><span class="special">};</span> |
| </pre> |
| <p> |
| </p> |
| <a name="spirit.qi.tutorials.mini_xml___asts_.of_alternates_and_variants"></a><h6> |
| <a name="id816972"></a> |
| <a class="link" href="mini_xml___asts_.html#spirit.qi.tutorials.mini_xml___asts_.of_alternates_and_variants">Of |
| Alternates and Variants</a> |
| </h6> |
| <p> |
| So that's what a <code class="computeroutput"><span class="identifier">mini_xml_node</span></code> |
| looks like. We had a hint that it is either a <code class="computeroutput"><span class="identifier">string</span></code> |
| or a <code class="computeroutput"><span class="identifier">mini_xml</span></code>. For this, |
| we use <a href="http://www.boost.org/doc/html/variant.html" target="_top">Boost.Variant</a>. |
| <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">recursive_wrapper</span></code> wraps <code class="computeroutput"><span class="identifier">mini_xml</span></code>, making it a recursive data |
| structure. |
| </p> |
| <p> |
| Yep, you got that right: the attribute of an alternate: |
| </p> |
| <pre class="programlisting"><span class="identifier">a</span> <span class="special">|</span> <span class="identifier">b</span> |
| </pre> |
| <p> |
| is a |
| </p> |
| <pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">variant</span><span class="special"><</span><span class="identifier">A</span><span class="special">,</span> <span class="identifier">B</span><span class="special">></span> |
| </pre> |
| <p> |
| where <code class="computeroutput"><span class="identifier">A</span></code> is the attribute |
| of <code class="computeroutput"><span class="identifier">a</span></code> and <code class="computeroutput"><span class="identifier">B</span></code> is the attribute of <code class="computeroutput"><span class="identifier">b</span></code>. |
| </p> |
| <a name="spirit.qi.tutorials.mini_xml___asts_.adapting_structs_again"></a><h6> |
| <a name="id817137"></a> |
| <a class="link" href="mini_xml___asts_.html#spirit.qi.tutorials.mini_xml___asts_.adapting_structs_again">Adapting |
| structs again</a> |
| </h6> |
| <p> |
| <code class="computeroutput"><span class="identifier">mini_xml</span></code> is no brainier. |
| It is a plain ol' struct. But as we've seen in our employee example, we |
| can adapt that to be a <a href="../../../../../../../libs/fusion/doc/html/index.html" target="_top">Boost.Fusion</a> |
| sequence: |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="identifier">BOOST_FUSION_ADAPT_STRUCT</span><span class="special">(</span> |
| <span class="identifier">client</span><span class="special">::</span><span class="identifier">mini_xml</span><span class="special">,</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">name</span><span class="special">)</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="identifier">client</span><span class="special">::</span><span class="identifier">mini_xml_node</span><span class="special">>,</span> <span class="identifier">children</span><span class="special">)</span> |
| <span class="special">)</span> |
| </pre> |
| <p> |
| </p> |
| <a name="spirit.qi.tutorials.mini_xml___asts_.one_more_take"></a><h6> |
| <a name="id817274"></a> |
| <a class="link" href="mini_xml___asts_.html#spirit.qi.tutorials.mini_xml___asts_.one_more_take">One |
| More Take</a> |
| </h6> |
| <p> |
| Here's another version. The AST structure remains the same, but this time, |
| you'll see that we make use of auto-rules making the grammar semantic-action-less. |
| Here it is: |
| </p> |
| <p> |
| |
| </p> |
| <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">struct</span> <span class="identifier">mini_xml_grammar</span> |
| <span class="special">:</span> <span class="identifier">qi</span><span class="special">::</span><span class="identifier">grammar</span><span class="special"><</span><span class="identifier">Iterator</span><span class="special">,</span> <span class="identifier">mini_xml</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="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">>,</span> <span class="identifier">ascii</span><span class="special">::</span><span class="identifier">space_type</span><span class="special">></span> |
| <span class="special">{</span> |
| <span class="identifier">mini_xml_grammar</span><span class="special">()</span> |
| <span class="special">:</span> <span class="identifier">mini_xml_grammar</span><span class="special">::</span><span class="identifier">base_type</span><span class="special">(</span><span class="identifier">xml</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="keyword">using</span> <span class="identifier">qi</span><span class="special">::</span><span class="identifier">lit</span><span class="special">;</span> |
| <span class="keyword">using</span> <span class="identifier">qi</span><span class="special">::</span><span class="identifier">lexeme</span><span class="special">;</span> |
| <span class="keyword">using</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">ascii</span><span class="special">::</span><span class="identifier">string</span><span class="special">;</span> |
| <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">qi</span><span class="special">::</span><span class="identifier">labels</span><span class="special">;</span> |
| |
| <span class="identifier">text</span> <span class="special">%=</span> <span class="identifier">lexeme</span><span class="special">[+(</span><span class="identifier">char_</span> <span class="special">-</span> <span class="char">'<'</span><span class="special">)];</span> |
| <span class="identifier">node</span> <span class="special">%=</span> <span class="identifier">xml</span> <span class="special">|</span> <span class="identifier">text</span><span class="special">;</span> |
| |
| <span class="identifier">start_tag</span> <span class="special">%=</span> |
| <span class="char">'<'</span> |
| <span class="special">>></span> <span class="special">!</span><span class="identifier">lit</span><span class="special">(</span><span class="char">'/'</span><span class="special">)</span> |
| <span class="special">>></span> <span class="identifier">lexeme</span><span class="special">[+(</span><span class="identifier">char_</span> <span class="special">-</span> <span class="char">'>'</span><span class="special">)]</span> |
| <span class="special">>></span> <span class="char">'>'</span> |
| <span class="special">;</span> |
| |
| <span class="identifier">end_tag</span> <span class="special">=</span> |
| <span class="string">"</"</span> |
| <span class="special">>></span> <span class="identifier">string</span><span class="special">(</span><span class="identifier">_r1</span><span class="special">)</span> |
| <span class="special">>></span> <span class="char">'>'</span> |
| <span class="special">;</span> |
| |
| <span class="identifier">xml</span> <span class="special">%=</span> |
| <span class="identifier">start_tag</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="special">*</span><span class="identifier">node</span> |
| <span class="special">>></span> <span class="identifier">end_tag</span><span class="special">(</span><span class="identifier">_a</span><span class="special">)</span> |
| <span class="special">;</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="identifier">Iterator</span><span class="special">,</span> <span class="identifier">mini_xml</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="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">>,</span> <span class="identifier">ascii</span><span class="special">::</span><span class="identifier">space_type</span><span class="special">></span> <span class="identifier">xml</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="identifier">Iterator</span><span class="special">,</span> <span class="identifier">mini_xml_node</span><span class="special">(),</span> <span class="identifier">ascii</span><span class="special">::</span><span class="identifier">space_type</span><span class="special">></span> <span class="identifier">node</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="identifier">Iterator</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">ascii</span><span class="special">::</span><span class="identifier">space_type</span><span class="special">></span> <span class="identifier">text</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="identifier">Iterator</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">ascii</span><span class="special">::</span><span class="identifier">space_type</span><span class="special">></span> <span class="identifier">start_tag</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="identifier">Iterator</span><span class="special">,</span> <span class="keyword">void</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">ascii</span><span class="special">::</span><span class="identifier">space_type</span><span class="special">></span> <span class="identifier">end_tag</span><span class="special">;</span> |
| <span class="special">};</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| This one shouldn't be any more difficult to understand after going through |
| the first xml parser example. The rules are almost the same, except that, |
| we got rid of semantic actions and used auto-rules (see the employee example |
| if you missed that). There is some new stuff though. It's all in the <code class="computeroutput"><span class="identifier">xml</span></code> rule: |
| </p> |
| <a name="spirit.qi.tutorials.mini_xml___asts_.local_variables"></a><h6> |
| <a name="id819347"></a> |
| <a class="link" href="mini_xml___asts_.html#spirit.qi.tutorials.mini_xml___asts_.local_variables">Local |
| Variables</a> |
| </h6> |
| <pre class="programlisting"><span class="identifier">rule</span><span class="special"><</span><span class="identifier">Iterator</span><span class="special">,</span> <span class="identifier">mini_xml</span><span class="special">(),</span> <span class="identifier">locals</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">space_type</span><span class="special">></span> <span class="identifier">xml</span><span class="special">;</span> |
| </pre> |
| <p> |
| Wow, we have four template parameters now. What's that <code class="computeroutput"><span class="identifier">locals</span></code> |
| guy doing there? Well, it declares that the rule <code class="computeroutput"><span class="identifier">xml</span></code> |
| will have one local variable: a <code class="computeroutput"><span class="identifier">string</span></code>. |
| Let's see how this is used in action: |
| </p> |
| <pre class="programlisting"><span class="identifier">xml</span> <span class="special">%=</span> |
| <span class="identifier">start_tag</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="special">*</span><span class="identifier">node</span> |
| <span class="special">>></span> <span class="identifier">end_tag</span><span class="special">(</span><span class="identifier">_a</span><span class="special">)</span> |
| <span class="special">;</span> |
| </pre> |
| <div class="orderedlist"><ol class="orderedlist" type="1"> |
| <li class="listitem"> |
| Upon parsing <code class="computeroutput"><span class="identifier">start_tag</span></code>, |
| the parsed start-tag string is placed in the local variable specified |
| by (yet another) <a href="../../../../../phoenix/doc/html/index.html" target="_top">Phoenix</a> |
| placeholder: <code class="computeroutput"><span class="identifier">_a</span></code>. We |
| have only one local variable. If we had more, these are designated |
| by <code class="computeroutput"><span class="identifier">_b</span></code>..<code class="computeroutput"><span class="identifier">_z</span></code>. |
| </li> |
| <li class="listitem"> |
| Then we parse zero or more <code class="computeroutput"><span class="identifier">node</span></code>s. |
| </li> |
| <li class="listitem"> |
| Finally, we parse the <code class="computeroutput"><span class="identifier">end_tag</span></code> |
| giving it an inherited attribute: <code class="computeroutput"><span class="identifier">_a</span></code>, |
| our local variable. |
| </li> |
| </ol></div> |
| <p> |
| There are no actions involved in stuffing data into our <code class="computeroutput"><span class="identifier">xml</span></code> |
| attribute. It's all taken care of thanks to the auto-rule. |
| </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 © 2001-2010 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>) |
| </p> |
| </div></td> |
| </tr></table> |
| <hr> |
| <div class="spirit-nav"> |
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