<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> <title>Porting from Spirit 1.8.x</title> <link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css"> <meta name="generator" content="DocBook XSL Stylesheets V1.75.0"> <link rel="home" href="../../index.html" title="Spirit 2.4"> <link rel="up" href="../notes.html" title="Notes"> <link rel="prev" href="../notes.html" title="Notes"> <link rel="next" href="style_guide.html" title="Style Guide"> </head> <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> <table cellpadding="2" width="100%"><tr> <td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../boost.png"></td> <td align="center"><a href="../../../../../../index.html">Home</a></td> <td align="center"><a href="../../../../../../libs/libraries.htm">Libraries</a></td> <td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> <td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> <td align="center"><a href="../../../../../../more/index.htm">More</a></td> </tr></table> <hr> <div class="spirit-nav"> <a accesskey="p" href="../notes.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../notes.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="style_guide.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> </div> <div class="section"> <div class="titlepage"><div><div><h3 class="title"> <a name="spirit.notes.porting_from_spirit_1_8_x"></a><a class="link" href="porting_from_spirit_1_8_x.html" title="Porting from Spirit 1.8.x">Porting from Spirit 1.8.x</a> </h3></div></div></div> <p> The current version of <a href="http://boost-spirit.com" target="_top">Spirit</a> is a complete rewrite of earlier versions (we refer to earlier versions as <a href="../../../../../../libs/spirit/classic/index.html" target="_top"><span class="emphasis"><em>Spirit.Classic</em></span></a>). The parser generators are now only one part of the whole library. The parser submodule of <a href="http://boost-spirit.com" target="_top">Spirit</a> is now called <span class="emphasis"><em>Spirit.Qi</em></span>. It is conceptually different and exposes a completely different interface. Generally, there is no easy (or automated) way of converting parsers written for <a href="../../../../../../libs/spirit/classic/index.html" target="_top"><span class="emphasis"><em>Spirit.Classic</em></span></a> to <span class="emphasis"><em>Spirit.Qi</em></span>. Therefore this section can give only guidelines on how to approach porting your older parsers to the current version of <a href="http://boost-spirit.com" target="_top">Spirit</a>. </p> <a name="spirit.notes.porting_from_spirit_1_8_x.include_files"></a><h5> <a name="id1253797"></a> <a class="link" href="porting_from_spirit_1_8_x.html#spirit.notes.porting_from_spirit_1_8_x.include_files">Include Files</a> </h5> <p> The overall directory structure of the <a href="http://boost-spirit.com" target="_top">Spirit</a> directories is described in the section <a class="link" href="../structure/include.html" title="Include">Include Structure</a> and the FAQ entry <a class="link" href="../faq.html#spirit.faq.i_m_very_confused_about_the_header_hell_in_my_boost_spirit_directory__what_s_all_this_about_">Header Hell</a>. This should give you a good overview on how to find the needed header files for your new parsers. Moreover, each section in the <a class="link" href="../qi/reference.html" title="Reference">Qi Reference</a> lists the required include files needed for any particular component. </p> <p> It is possible to tell from the name of a header file, what version it belongs to. While all main include files for <a href="../../../../../../libs/spirit/classic/index.html" target="_top"><span class="emphasis"><em>Spirit.Classic</em></span></a> have the string 'classic_' in their name, for instance: </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">classic_core</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> </pre> <p> we named all main include files for <span class="emphasis"><em>Spirit.Qi</em></span> to have the string 'qi_' as part of their name, for instance: </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_core</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> </pre> <p> The following table gives a rough list of corresponding header file between <a href="../../../../../../libs/spirit/classic/index.html" target="_top"><span class="emphasis"><em>Spirit.Classic</em></span></a> and <span class="emphasis"><em>Spirit.Qi</em></span>, but this can be used as a starting point only, as several components have either been moved to different submodules or might not exist in the never version anymore. We list only include files for the topmost submodules. For header files required for more lower level components please refer to the corresponding reference documentation of this component. </p> <div class="informaltable"><table class="table"> <colgroup> <col> <col> </colgroup> <thead><tr> <th> <p> Include file in <span class="emphasis"><em>Spirit.Classic</em></span> </p> </th> <th> <p> Include file in <span class="emphasis"><em>Spirit.Qi</em></span> </p> </th> </tr></thead> <tbody> <tr> <td> <p> <code class="computeroutput"><span class="identifier">classic</span><span class="special">.</span><span class="identifier">hpp</span></code> </p> </td> <td> <p> <code class="computeroutput"><span class="identifier">qi</span><span class="special">.</span><span class="identifier">hpp</span></code> </p> </td> </tr> <tr> <td> <p> <code class="computeroutput"><span class="identifier">classic_actor</span><span class="special">.</span><span class="identifier">hpp</span></code> </p> </td> <td> <p> none, use <a href="../../../../phoenix/doc/html/index.html" target="_top">Boost.Phoenix</a> for writing semantic actions </p> </td> </tr> <tr> <td> <p> <code class="computeroutput"><span class="identifier">classic_attribute</span><span class="special">.</span><span class="identifier">hpp</span></code> </p> </td> <td> <p> none, use local variables for rules instead of closures, the primitives parsers now directly support lazy parametrization </p> </td> </tr> <tr> <td> <p> <code class="computeroutput"><span class="identifier">classic_core</span><span class="special">.</span><span class="identifier">hpp</span></code> </p> </td> <td> <p> <code class="computeroutput"><span class="identifier">qi_core</span><span class="special">.</span><span class="identifier">hpp</span></code> </p> </td> </tr> <tr> <td> <p> <code class="computeroutput"><span class="identifier">classic_debug</span><span class="special">.</span><span class="identifier">hpp</span></code> </p> </td> <td> <p> <code class="computeroutput"><span class="identifier">qi_debug</span><span class="special">.</span><span class="identifier">hpp</span></code> </p> </td> </tr> <tr> <td> <p> <code class="computeroutput"><span class="identifier">classic_dynamic</span><span class="special">.</span><span class="identifier">hpp</span></code> </p> </td> <td> <p> none, use <span class="emphasis"><em>Spirit.Qi</em></span> predicates instead of if_p, while_p, for_p (included by <code class="computeroutput"><span class="identifier">qi_core</span><span class="special">.</span><span class="identifier">hpp</span></code>), the equivalent for lazy_p is now included by <code class="computeroutput"><span class="identifier">qi_auxiliary</span><span class="special">.</span><span class="identifier">hpp</span></code> </p> </td> </tr> <tr> <td> <p> <code class="computeroutput"><span class="identifier">classic_error_handling</span><span class="special">.</span><span class="identifier">hpp</span></code> </p> </td> <td> <p> none, included in <code class="computeroutput"><span class="identifier">qi_core</span><span class="special">.</span><span class="identifier">hpp</span></code> </p> </td> </tr> <tr> <td> <p> <code class="computeroutput"><span class="identifier">classic_meta</span><span class="special">.</span><span class="identifier">hpp</span></code> </p> </td> <td> <p> none </p> </td> </tr> <tr> <td> <p> <code class="computeroutput"><span class="identifier">classic_symbols</span><span class="special">.</span><span class="identifier">hpp</span></code> </p> </td> <td> <p> none, included in <code class="computeroutput"><span class="identifier">qi_core</span><span class="special">.</span><span class="identifier">hpp</span></code> </p> </td> </tr> <tr> <td> <p> <code class="computeroutput"><span class="identifier">classic_utility</span><span class="special">.</span><span class="identifier">hpp</span></code> </p> </td> <td> <p> none, not part of <span class="emphasis"><em>Spirit.Qi</em></span> anymore, these components will be added over time to the <a href="../../../../repository/doc/html/index.html" target="_top">Repository</a> </p> </td> </tr> </tbody> </table></div> <a name="spirit.notes.porting_from_spirit_1_8_x.the_free_parse_functions"></a><h5> <a name="id1254447"></a> <a class="link" href="porting_from_spirit_1_8_x.html#spirit.notes.porting_from_spirit_1_8_x.the_free_parse_functions">The Free Parse Functions</a> </h5> <p> The free parse functions (i.e. the main parser API) has been changed. This includes the names of the free functions as well as their interface. In <a href="../../../../../../libs/spirit/classic/index.html" target="_top"><span class="emphasis"><em>Spirit.Classic</em></span></a> all free functions were named <code class="computeroutput"><span class="identifier">parse</span></code>. In <span class="emphasis"><em>Spirit.Qi</em></span> they are are named either <code class="computeroutput"><span class="identifier">qi</span><span class="special">::</span><span class="identifier">parse</span></code> or <code class="computeroutput"><span class="identifier">qi</span><span class="special">::</span><span class="identifier">phrase_parse</span></code> depending on whether the parsing should be done using a skipper (<code class="computeroutput"><span class="identifier">qi</span><span class="special">::</span><span class="identifier">phrase_parse</span></code>) or not (<code class="computeroutput"><span class="identifier">qi</span><span class="special">::</span><span class="identifier">parse</span></code>). All free functions now return a simple <code class="computeroutput"><span class="keyword">bool</span></code>. A returned <code class="computeroutput"><span class="keyword">true</span></code> means success (i.e. the parser has matched) or <code class="computeroutput"><span class="keyword">false</span></code> (i.e. the parser didn't match). This is equivalent to the former old <code class="computeroutput"><span class="identifier">parse_info</span></code> member <code class="computeroutput"><span class="identifier">hit</span></code>. <span class="emphasis"><em>Spirit.Qi</em></span> doesn't support tracking of the matched input length anymore. The old <code class="computeroutput"><span class="identifier">parse_info</span></code> member <code class="computeroutput"><span class="identifier">full</span></code> can be emulated by comparing the iterators after <code class="computeroutput"><span class="identifier">qi</span><span class="special">::</span><span class="identifier">parse</span></code> returned. </p> <p> All code examples in this section assume the following include statements and using directives to be inserted. For <a href="../../../../../../libs/spirit/classic/index.html" target="_top"><span class="emphasis"><em>Spirit.Classic</em></span></a>: </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">classic</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">include</span><span class="special">/</span><span class="identifier">phoenix1</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">iostream</span><span class="special">></span> <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">string</span><span class="special">></span> </pre> <p> </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="identifier">classic</span><span class="special">;</span> </pre> <p> </p> <p> and for <span class="emphasis"><em>Spirit.Qi</em></span>: </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">include</span><span class="special">/</span><span class="identifier">phoenix_operator</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">iostream</span><span class="special">></span> <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">string</span><span class="special">></span> <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">algorithm</span><span class="special">></span> </pre> <p> </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> </pre> <p> </p> <p> The following similar examples should clearify the differences. First the base example in <a href="../../../../../../libs/spirit/classic/index.html" target="_top"><span class="emphasis"><em>Spirit.Classic</em></span></a>: </p> <p> </p> <pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">input</span><span class="special">(</span><span class="string">"1,1"</span><span class="special">);</span> <span class="identifier">parse_info</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="special">></span> <span class="identifier">pi</span> <span class="special">=</span> <span class="identifier">parse</span><span class="special">(</span><span class="identifier">input</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">input</span><span class="special">.</span><span class="identifier">end</span><span class="special">(),</span> <span class="identifier">int_p</span><span class="special">);</span> <span class="keyword">if</span> <span class="special">(</span><span class="identifier">pi</span><span class="special">.</span><span class="identifier">hit</span><span class="special">)</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"successful match!\n"</span><span class="special">;</span> <span class="keyword">if</span> <span class="special">(</span><span class="identifier">pi</span><span class="special">.</span><span class="identifier">full</span><span class="special">)</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"full match!\n"</span><span class="special">;</span> <span class="keyword">else</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"stopped at: "</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">pi</span><span class="special">.</span><span class="identifier">stop</span><span class="special">,</span> <span class="identifier">input</span><span class="special">.</span><span class="identifier">end</span><span class="special">())</span> <span class="special"><<</span> <span class="string">"\n"</span><span class="special">;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"matched length: "</span> <span class="special"><<</span> <span class="identifier">pi</span><span class="special">.</span><span class="identifier">length</span> <span class="special"><<</span> <span class="string">"\n"</span><span class="special">;</span> </pre> <p> </p> <p> And here is the equivalent piece of code using <span class="emphasis"><em>Spirit.Qi</em></span>: </p> <p> </p> <pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">input</span><span class="special">(</span><span class="string">"1,1"</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">it</span> <span class="special">=</span> <span class="identifier">input</span><span class="special">.</span><span class="identifier">begin</span><span class="special">();</span> <span class="keyword">bool</span> <span class="identifier">result</span> <span class="special">=</span> <span class="identifier">qi</span><span class="special">::</span><span class="identifier">parse</span><span class="special">(</span><span class="identifier">it</span><span class="special">,</span> <span class="identifier">input</span><span class="special">.</span><span class="identifier">end</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">if</span> <span class="special">(</span><span class="identifier">result</span><span class="special">)</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"successful match!\n"</span><span class="special">;</span> <span class="keyword">if</span> <span class="special">(</span><span class="identifier">it</span> <span class="special">==</span> <span class="identifier">input</span><span class="special">.</span><span class="identifier">end</span><span class="special">())</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"full match!\n"</span><span class="special">;</span> <span class="keyword">else</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"stopped at: "</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">it</span><span class="special">,</span> <span class="identifier">input</span><span class="special">.</span><span class="identifier">end</span><span class="special">())</span> <span class="special"><<</span> <span class="string">"\n"</span><span class="special">;</span> <span class="comment">// seldomly needed: use std::distance to calculate the length of the match </span><span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"matched length: "</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">distance</span><span class="special">(</span><span class="identifier">input</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">it</span><span class="special">)</span> <span class="special"><<</span> <span class="string">"\n"</span><span class="special">;</span> </pre> <p> </p> <p> The changes required for phrase parsing (i.e. parsing using a skipper) are similar. Here is how phrase parsing works in <a href="../../../../../../libs/spirit/classic/index.html" target="_top"><span class="emphasis"><em>Spirit.Classic</em></span></a>: </p> <p> </p> <pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">input</span><span class="special">(</span><span class="string">" 1, 1"</span><span class="special">);</span> <span class="identifier">parse_info</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="special">></span> <span class="identifier">pi</span> <span class="special">=</span> <span class="identifier">parse</span><span class="special">(</span><span class="identifier">input</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">input</span><span class="special">.</span><span class="identifier">end</span><span class="special">(),</span> <span class="identifier">int_p</span><span class="special">,</span> <span class="identifier">space_p</span><span class="special">);</span> <span class="keyword">if</span> <span class="special">(</span><span class="identifier">pi</span><span class="special">.</span><span class="identifier">hit</span><span class="special">)</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"successful match!\n"</span><span class="special">;</span> <span class="keyword">if</span> <span class="special">(</span><span class="identifier">pi</span><span class="special">.</span><span class="identifier">full</span><span class="special">)</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"full match!\n"</span><span class="special">;</span> <span class="keyword">else</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"stopped at: "</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">pi</span><span class="special">.</span><span class="identifier">stop</span><span class="special">,</span> <span class="identifier">input</span><span class="special">.</span><span class="identifier">end</span><span class="special">())</span> <span class="special"><<</span> <span class="string">"\n"</span><span class="special">;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"matched length: "</span> <span class="special"><<</span> <span class="identifier">pi</span><span class="special">.</span><span class="identifier">length</span> <span class="special"><<</span> <span class="string">"\n"</span><span class="special">;</span> </pre> <p> </p> <p> And here the equivalent example in <span class="emphasis"><em>Spirit.Qi</em></span>: </p> <p> </p> <pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">input</span><span class="special">(</span><span class="string">" 1, 1"</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">it</span> <span class="special">=</span> <span class="identifier">input</span><span class="special">.</span><span class="identifier">begin</span><span class="special">();</span> <span class="keyword">bool</span> <span class="identifier">result</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">it</span><span class="special">,</span> <span class="identifier">input</span><span class="special">.</span><span class="identifier">end</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="identifier">ascii</span><span class="special">::</span><span class="identifier">space</span><span class="special">);</span> <span class="keyword">if</span> <span class="special">(</span><span class="identifier">result</span><span class="special">)</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"successful match!\n"</span><span class="special">;</span> <span class="keyword">if</span> <span class="special">(</span><span class="identifier">it</span> <span class="special">==</span> <span class="identifier">input</span><span class="special">.</span><span class="identifier">end</span><span class="special">())</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"full match!\n"</span><span class="special">;</span> <span class="keyword">else</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"stopped at: "</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">it</span><span class="special">,</span> <span class="identifier">input</span><span class="special">.</span><span class="identifier">end</span><span class="special">())</span> <span class="special"><<</span> <span class="string">"\n"</span><span class="special">;</span> <span class="comment">// seldomly needed: use std::distance to calculate the length of the match </span><span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"matched length: "</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">distance</span><span class="special">(</span><span class="identifier">input</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">it</span><span class="special">)</span> <span class="special"><<</span> <span class="string">"\n"</span><span class="special">;</span> </pre> <p> </p> <p> Note, how character parsers are in a separate namespace (here <code class="computeroutput"><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</span></code>) as <span class="emphasis"><em>Spirit.Qi</em></span> now supports working with different character sets. See the section <a class="link" href="../qi/reference/basics.html#spirit.qi.reference.basics.character_encoding_namespace">Character Encoding Namespace</a> for more information. </p> <a name="spirit.notes.porting_from_spirit_1_8_x.naming_conventions"></a><h5> <a name="id1259217"></a> <a class="link" href="porting_from_spirit_1_8_x.html#spirit.notes.porting_from_spirit_1_8_x.naming_conventions">Naming Conventions</a> </h5> <p> In <a href="../../../../../../libs/spirit/classic/index.html" target="_top"><span class="emphasis"><em>Spirit.Classic</em></span></a> all parser primitives have suffixes appended to their names, encoding their type: <code class="computeroutput"><span class="string">"_p"</span></code> for parsers, <code class="computeroutput"><span class="string">"_a"</span></code> for lazy actions, <code class="computeroutput"><span class="string">"_d"</span></code> for directives, etc. In <span class="emphasis"><em>Spirit.Qi</em></span> we don't have anything similar. The only suffixes are single underscore letters <code class="computeroutput"><span class="string">"_"</span></code> applied where the name would otherwise conflict with a keyword or predefined name (such as <code class="computeroutput"><span class="identifier">int_</span></code> for the integer parser). Overall, most, if not all primitive parsers and directives have been renamed. Please see the <a class="link" href="../qi/quick_reference.html" title="Quick Reference">Qi Quick Reference</a> for an overview on the names for the different available parser primitives, directives and operators. </p> <a name="spirit.notes.porting_from_spirit_1_8_x.parser_attributes"></a><h5> <a name="id1259289"></a> <a class="link" href="porting_from_spirit_1_8_x.html#spirit.notes.porting_from_spirit_1_8_x.parser_attributes">Parser Attributes</a> </h5> <p> In <a href="../../../../../../libs/spirit/classic/index.html" target="_top"><span class="emphasis"><em>Spirit.Classic</em></span></a> most of the parser primitives don't expose a specific attribute type. Most parsers expose the pair of iterators pointing to the matched input sequence. As in <span class="emphasis"><em>Spirit.Qi</em></span> all parsers expose a parser specific attribute type it introduces a special directive <a class="link" href="../qi/reference/directive/raw.html" title="Transduction Parsing (raw[])"><code class="computeroutput"><span class="identifier">raw</span></code></a><code class="computeroutput"><span class="special">[]</span></code> allowing to achieve a similar effect as in <a href="../../../../../../libs/spirit/classic/index.html" target="_top"><span class="emphasis"><em>Spirit.Classic</em></span></a>. The <a class="link" href="../qi/reference/directive/raw.html" title="Transduction Parsing (raw[])"><code class="computeroutput"><span class="identifier">raw</span></code></a><code class="computeroutput"><span class="special">[]</span></code> directive exposes the pair of iterators pointing to the matching sequence of its embedded parser. Even if we very much encourage you to rewrite your parsers to take advantage of the generated parser specific attributes, sometimes it is helpful to get access to the underlying matched input sequence. </p> <a name="spirit.notes.porting_from_spirit_1_8_x.grammars_and_rules"></a><h5> <a name="id1259358"></a> <a class="link" href="porting_from_spirit_1_8_x.html#spirit.notes.porting_from_spirit_1_8_x.grammars_and_rules">Grammars and Rules</a> </h5> <p> The <code class="computeroutput"><span class="identifier">grammar</span><span class="special"><></span></code> and <code class="computeroutput"><span class="identifier">rule</span><span class="special"><></span></code> types are of equal importance to <span class="emphasis"><em>Spirit.Qi</em></span> as they are for <a href="../../../../../../libs/spirit/classic/index.html" target="_top"><span class="emphasis"><em>Spirit.Classic</em></span></a>. Their main purpose is still the same: they allow to define non-terminals and they are the main building blocks for more complex parsers. Nevertheless, both types have been redesigned and their interfaces have changed. Let's have a look at two examples first, we'll explain the differences afterwards. Here is a simple grammar and its usage in <a href="../../../../../../libs/spirit/classic/index.html" target="_top"><span class="emphasis"><em>Spirit.Classic</em></span></a>: </p> <p> </p> <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">roman</span> <span class="special">:</span> <span class="keyword">public</span> <span class="identifier">grammar</span><span class="special"><</span><span class="identifier">roman</span><span class="special">></span> <span class="special">{</span> <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">ScannerT</span><span class="special">></span> <span class="keyword">struct</span> <span class="identifier">definition</span> <span class="special">{</span> <span class="identifier">definition</span><span class="special">(</span><span class="identifier">roman</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">self</span><span class="special">)</span> <span class="special">{</span> <span class="identifier">hundreds</span><span class="special">.</span><span class="identifier">add</span> <span class="special">(</span><span class="string">"C"</span> <span class="special">,</span> <span class="number">100</span><span class="special">)(</span><span class="string">"CC"</span> <span class="special">,</span> <span class="number">200</span><span class="special">)(</span><span class="string">"CCC"</span> <span class="special">,</span> <span class="number">300</span><span class="special">)(</span><span class="string">"CD"</span> <span class="special">,</span> <span class="number">400</span><span class="special">)(</span><span class="string">"D"</span> <span class="special">,</span> <span class="number">500</span><span class="special">)</span> <span class="special">(</span><span class="string">"DC"</span> <span class="special">,</span> <span class="number">600</span><span class="special">)(</span><span class="string">"DCC"</span> <span class="special">,</span> <span class="number">700</span><span class="special">)(</span><span class="string">"DCCC"</span> <span class="special">,</span> <span class="number">800</span><span class="special">)(</span><span class="string">"CM"</span> <span class="special">,</span> <span class="number">900</span><span class="special">)</span> <span class="special">;</span> <span class="identifier">tens</span><span class="special">.</span><span class="identifier">add</span> <span class="special">(</span><span class="string">"X"</span> <span class="special">,</span> <span class="number">10</span><span class="special">)(</span><span class="string">"XX"</span> <span class="special">,</span> <span class="number">20</span><span class="special">)(</span><span class="string">"XXX"</span> <span class="special">,</span> <span class="number">30</span><span class="special">)(</span><span class="string">"XL"</span> <span class="special">,</span> <span class="number">40</span><span class="special">)(</span><span class="string">"L"</span> <span class="special">,</span> <span class="number">50</span><span class="special">)</span> <span class="special">(</span><span class="string">"LX"</span> <span class="special">,</span> <span class="number">60</span><span class="special">)(</span><span class="string">"LXX"</span> <span class="special">,</span> <span class="number">70</span><span class="special">)(</span><span class="string">"LXXX"</span> <span class="special">,</span> <span class="number">80</span><span class="special">)(</span><span class="string">"XC"</span> <span class="special">,</span> <span class="number">90</span><span class="special">)</span> <span class="special">;</span> <span class="identifier">ones</span><span class="special">.</span><span class="identifier">add</span> <span class="special">(</span><span class="string">"I"</span> <span class="special">,</span> <span class="number">1</span><span class="special">)(</span><span class="string">"II"</span> <span class="special">,</span> <span class="number">2</span><span class="special">)(</span><span class="string">"III"</span> <span class="special">,</span> <span class="number">3</span><span class="special">)(</span><span class="string">"IV"</span> <span class="special">,</span> <span class="number">4</span><span class="special">)(</span><span class="string">"V"</span> <span class="special">,</span> <span class="number">5</span><span class="special">)</span> <span class="special">(</span><span class="string">"VI"</span> <span class="special">,</span> <span class="number">6</span><span class="special">)(</span><span class="string">"VII"</span> <span class="special">,</span> <span class="number">7</span><span class="special">)(</span><span class="string">"VIII"</span> <span class="special">,</span> <span class="number">8</span><span class="special">)(</span><span class="string">"IX"</span> <span class="special">,</span> <span class="number">9</span><span class="special">)</span> <span class="special">;</span> <span class="identifier">first</span> <span class="special">=</span> <span class="identifier">eps_p</span> <span class="special">[</span><span class="identifier">phoenix</span><span class="special">::</span><span class="identifier">var</span><span class="special">(</span><span class="identifier">self</span><span class="special">.</span><span class="identifier">r</span><span class="special">)</span> <span class="special">=</span> <span class="identifier">phoenix</span><span class="special">::</span><span class="identifier">val</span><span class="special">(</span><span class="number">0</span><span class="special">)]</span> <span class="special">>></span> <span class="special">(</span> <span class="special">+</span><span class="identifier">ch_p</span><span class="special">(</span><span class="char">'M'</span><span class="special">)</span> <span class="special">[</span><span class="identifier">phoenix</span><span class="special">::</span><span class="identifier">var</span><span class="special">(</span><span class="identifier">self</span><span class="special">.</span><span class="identifier">r</span><span class="special">)</span> <span class="special">+=</span> <span class="identifier">phoenix</span><span class="special">::</span><span class="identifier">val</span><span class="special">(</span><span class="number">1000</span><span class="special">)]</span> <span class="special">||</span> <span class="identifier">hundreds</span> <span class="special">[</span><span class="identifier">phoenix</span><span class="special">::</span><span class="identifier">var</span><span class="special">(</span><span class="identifier">self</span><span class="special">.</span><span class="identifier">r</span><span class="special">)</span> <span class="special">+=</span> <span class="identifier">phoenix</span><span class="special">::</span><span class="identifier">_1</span><span class="special">]</span> <span class="special">||</span> <span class="identifier">tens</span> <span class="special">[</span><span class="identifier">phoenix</span><span class="special">::</span><span class="identifier">var</span><span class="special">(</span><span class="identifier">self</span><span class="special">.</span><span class="identifier">r</span><span class="special">)</span> <span class="special">+=</span> <span class="identifier">phoenix</span><span class="special">::</span><span class="identifier">_1</span><span class="special">]</span> <span class="special">||</span> <span class="identifier">ones</span> <span class="special">[</span><span class="identifier">phoenix</span><span class="special">::</span><span class="identifier">var</span><span class="special">(</span><span class="identifier">self</span><span class="special">.</span><span class="identifier">r</span><span class="special">)</span> <span class="special">+=</span> <span class="identifier">phoenix</span><span class="special">::</span><span class="identifier">_1</span><span class="special">]</span> <span class="special">)</span> <span class="special">;</span> <span class="special">}</span> <span class="identifier">rule</span><span class="special"><</span><span class="identifier">ScannerT</span><span class="special">></span> <span class="identifier">first</span><span class="special">;</span> <span class="identifier">symbols</span><span class="special"><</span><span class="keyword">unsigned</span><span class="special">></span> <span class="identifier">hundreds</span><span class="special">;</span> <span class="identifier">symbols</span><span class="special"><</span><span class="keyword">unsigned</span><span class="special">></span> <span class="identifier">tens</span><span class="special">;</span> <span class="identifier">symbols</span><span class="special"><</span><span class="keyword">unsigned</span><span class="special">></span> <span class="identifier">ones</span><span class="special">;</span> <span class="identifier">rule</span><span class="special"><</span><span class="identifier">ScannerT</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">start</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">first</span><span class="special">;</span> <span class="special">}</span> <span class="special">};</span> <span class="identifier">roman</span><span class="special">(</span><span class="keyword">unsigned</span><span class="special">&</span> <span class="identifier">r_</span><span class="special">)</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="special">{}</span> <span class="keyword">unsigned</span><span class="special">&</span> <span class="identifier">r</span><span class="special">;</span> <span class="special">};</span> </pre> <p> </p> <p> </p> <pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">input</span><span class="special">(</span><span class="string">"MMIX"</span><span class="special">);</span> <span class="comment">// MMIX == 2009 </span><span class="keyword">unsigned</span> <span class="identifier">value</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> <span class="identifier">roman</span> <span class="identifier">r</span><span class="special">(</span><span class="identifier">value</span><span class="special">);</span> <span class="identifier">parse_info</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="special">></span> <span class="identifier">pi</span> <span class="special">=</span> <span class="identifier">parse</span><span class="special">(</span><span class="identifier">input</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">input</span><span class="special">.</span><span class="identifier">end</span><span class="special">(),</span> <span class="identifier">r</span><span class="special">);</span> <span class="keyword">if</span> <span class="special">(</span><span class="identifier">pi</span><span class="special">.</span><span class="identifier">hit</span><span class="special">)</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"successfully matched: "</span> <span class="special"><<</span> <span class="identifier">value</span> <span class="special"><<</span> <span class="string">"\n"</span><span class="special">;</span> </pre> <p> </p> <p> And here is a similar grammar and its usage in <span class="emphasis"><em>Spirit.Qi</em></span>: </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">roman</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="keyword">unsigned</span><span class="special">()></span> <span class="special">{</span> <span class="identifier">roman</span><span class="special">()</span> <span class="special">:</span> <span class="identifier">roman</span><span class="special">::</span><span class="identifier">base_type</span><span class="special">(</span><span class="identifier">first</span><span class="special">)</span> <span class="special">{</span> <span class="identifier">hundreds</span><span class="special">.</span><span class="identifier">add</span> <span class="special">(</span><span class="string">"C"</span> <span class="special">,</span> <span class="number">100</span><span class="special">)(</span><span class="string">"CC"</span> <span class="special">,</span> <span class="number">200</span><span class="special">)(</span><span class="string">"CCC"</span> <span class="special">,</span> <span class="number">300</span><span class="special">)(</span><span class="string">"CD"</span> <span class="special">,</span> <span class="number">400</span><span class="special">)(</span><span class="string">"D"</span> <span class="special">,</span> <span class="number">500</span><span class="special">)</span> <span class="special">(</span><span class="string">"DC"</span> <span class="special">,</span> <span class="number">600</span><span class="special">)(</span><span class="string">"DCC"</span> <span class="special">,</span> <span class="number">700</span><span class="special">)(</span><span class="string">"DCCC"</span> <span class="special">,</span> <span class="number">800</span><span class="special">)(</span><span class="string">"CM"</span> <span class="special">,</span> <span class="number">900</span><span class="special">)</span> <span class="special">;</span> <span class="identifier">tens</span><span class="special">.</span><span class="identifier">add</span> <span class="special">(</span><span class="string">"X"</span> <span class="special">,</span> <span class="number">10</span><span class="special">)(</span><span class="string">"XX"</span> <span class="special">,</span> <span class="number">20</span><span class="special">)(</span><span class="string">"XXX"</span> <span class="special">,</span> <span class="number">30</span><span class="special">)(</span><span class="string">"XL"</span> <span class="special">,</span> <span class="number">40</span><span class="special">)(</span><span class="string">"L"</span> <span class="special">,</span> <span class="number">50</span><span class="special">)</span> <span class="special">(</span><span class="string">"LX"</span> <span class="special">,</span> <span class="number">60</span><span class="special">)(</span><span class="string">"LXX"</span> <span class="special">,</span> <span class="number">70</span><span class="special">)(</span><span class="string">"LXXX"</span> <span class="special">,</span> <span class="number">80</span><span class="special">)(</span><span class="string">"XC"</span> <span class="special">,</span> <span class="number">90</span><span class="special">)</span> <span class="special">;</span> <span class="identifier">ones</span><span class="special">.</span><span class="identifier">add</span> <span class="special">(</span><span class="string">"I"</span> <span class="special">,</span> <span class="number">1</span><span class="special">)(</span><span class="string">"II"</span> <span class="special">,</span> <span class="number">2</span><span class="special">)(</span><span class="string">"III"</span> <span class="special">,</span> <span class="number">3</span><span class="special">)(</span><span class="string">"IV"</span> <span class="special">,</span> <span class="number">4</span><span class="special">)(</span><span class="string">"V"</span> <span class="special">,</span> <span class="number">5</span><span class="special">)</span> <span class="special">(</span><span class="string">"VI"</span> <span class="special">,</span> <span class="number">6</span><span class="special">)(</span><span class="string">"VII"</span> <span class="special">,</span> <span class="number">7</span><span class="special">)(</span><span class="string">"VIII"</span> <span class="special">,</span> <span class="number">8</span><span class="special">)(</span><span class="string">"IX"</span> <span class="special">,</span> <span class="number">9</span><span class="special">)</span> <span class="special">;</span> <span class="comment">// qi::_val refers to the attribute of the rule on the left hand side </span> <span class="identifier">first</span> <span class="special">=</span> <span class="identifier">eps</span> <span class="special">[</span><span class="identifier">qi</span><span class="special">::</span><span class="identifier">_val</span> <span class="special">=</span> <span class="number">0</span><span class="special">]</span> <span class="special">>></span> <span class="special">(</span> <span class="special">+</span><span class="identifier">lit</span><span class="special">(</span><span class="char">'M'</span><span class="special">)</span> <span class="special">[</span><span class="identifier">qi</span><span class="special">::</span><span class="identifier">_val</span> <span class="special">+=</span> <span class="number">1000</span><span class="special">]</span> <span class="special">||</span> <span class="identifier">hundreds</span> <span class="special">[</span><span class="identifier">qi</span><span class="special">::</span><span class="identifier">_val</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="special">||</span> <span class="identifier">tens</span> <span class="special">[</span><span class="identifier">qi</span><span class="special">::</span><span class="identifier">_val</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="special">||</span> <span class="identifier">ones</span> <span class="special">[</span><span class="identifier">qi</span><span class="special">::</span><span class="identifier">_val</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="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="keyword">unsigned</span><span class="special">()></span> <span class="identifier">first</span><span class="special">;</span> <span class="identifier">qi</span><span class="special">::</span><span class="identifier">symbols</span><span class="special"><</span><span class="keyword">char</span><span class="special">,</span> <span class="keyword">unsigned</span><span class="special">></span> <span class="identifier">hundreds</span><span class="special">;</span> <span class="identifier">qi</span><span class="special">::</span><span class="identifier">symbols</span><span class="special"><</span><span class="keyword">char</span><span class="special">,</span> <span class="keyword">unsigned</span><span class="special">></span> <span class="identifier">tens</span><span class="special">;</span> <span class="identifier">qi</span><span class="special">::</span><span class="identifier">symbols</span><span class="special"><</span><span class="keyword">char</span><span class="special">,</span> <span class="keyword">unsigned</span><span class="special">></span> <span class="identifier">ones</span><span class="special">;</span> <span class="special">};</span> </pre> <p> </p> <p> </p> <pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">input</span><span class="special">(</span><span class="string">"MMIX"</span><span class="special">);</span> <span class="comment">// MMIX == 2009 </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">it</span> <span class="special">=</span> <span class="identifier">input</span><span class="special">.</span><span class="identifier">begin</span><span class="special">();</span> <span class="keyword">unsigned</span> <span class="identifier">value</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> <span class="identifier">roman</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="special">></span> <span class="identifier">r</span><span class="special">;</span> <span class="keyword">if</span> <span class="special">(</span><span class="identifier">qi</span><span class="special">::</span><span class="identifier">parse</span><span class="special">(</span><span class="identifier">it</span><span class="special">,</span> <span class="identifier">input</span><span class="special">.</span><span class="identifier">end</span><span class="special">(),</span> <span class="identifier">r</span><span class="special">,</span> <span class="identifier">value</span><span class="special">))</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"successfully matched: "</span> <span class="special"><<</span> <span class="identifier">value</span> <span class="special"><<</span> <span class="string">"\n"</span><span class="special">;</span> </pre> <p> </p> <p> Both versions look similarily enough, but we see several differences (we will cover each of those differences in more detail below): </p> <div class="itemizedlist"><ul class="itemizedlist" type="disc"> <li class="listitem"> Neither the grammars nor the rules depend on a scanner type anymore, both depend only on the underlying iterator type. That means the dreaded scanner business is no issue anymore! </li> <li class="listitem"> Grammars have no embedded class <code class="computeroutput"><span class="identifier">definition</span></code> anymore </li> <li class="listitem"> Grammars and rules may have an explicit attribute type specified in their definition </li> <li class="listitem"> Grammars do not have any explicit start rules anymore. Instead one of the contained rules is used as a start rule by default. </li> </ul></div> <p> The first two points are tightly interrelated. The scanner business (see the FAQ number one of <a href="../../../../../../libs/spirit/classic/index.html" target="_top"><span class="emphasis"><em>Spirit.Classic</em></span></a> here: <a href="../../../../../../libs/spirit/classic/doc/faq.html#scanner_business" target="_top">The Scanner Business</a>) has been a problem for a long time. The grammar and rule types have been specifically redesigned to avoid this problem in the future. This also means that we don't need any delayed instantiation of the inner definition class in a grammar anymore. So the redesign not only helped fixing a long standing design problem, it helped to simplify things considerably. </p> <p> All <span class="emphasis"><em>Spirit.Qi</em></span> parser components have well defined attribute types. Grammars and rules are no exception. But since both need to be generic enough to be usable for any parser their attribute type has to be explicitly specified. In the example above the <code class="computeroutput"><span class="identifier">roman</span></code> grammar and the rule <code class="computeroutput"><span class="identifier">first</span></code> both have an <code class="computeroutput"><span class="keyword">unsigned</span></code> attribute: </p> <pre class="programlisting"><span class="comment">// grammar definition </span><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">roman</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="keyword">unsigned</span><span class="special">()></span> <span class="special">{...};</span> <span class="comment">// rule definition </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">unsigned</span><span class="special">()></span> <span class="identifier">first</span><span class="special">;</span> </pre> <p> The used notation resembles the definition of a function type. This is very natural as you can think of the synthesized attribute of the grammar and the rule as of its 'return value'. In fact the rule and the grammar both 'return' an unsigned value - the value they matched. </p> <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 function type notation allows to specify parameters as well. These are interpreted as the types of inherited attributes the rule or grammar expect to be passed during parsing. For more information please see the section about inherited and synthesized attributes for rules and grammars (<a class="link" href="../abstracts/attributes.html" title="Attributes">Attributes</a>). </p></td></tr> </table></div> <p> If no attribute is desired none needs to be specified. The default attribute type for both, grammars and rules, is <code class="computeroutput"><span class="identifier">unused_type</span></code>, which is a special placeholder type. Generally, using <code class="computeroutput"><span class="identifier">unused_type</span></code> as the attribute of a parser is interpreted as 'this parser has no attribute'. This is mostly used for parsers applied to parts of the input not carrying any significant information, rather being delimiters or structural elements needed for correct interpretation of the input. </p> <p> The last difference might seem to be rather cosmetic and insignificant. But it turns out that not having to specify which rule in a grammar is the start rule (by returning it from the function <code class="computeroutput"><span class="identifier">start</span><span class="special">()</span></code>) also means that any rule in a grammar can be directly used as the start rule. Nevertheless, the grammar base class gets initialized with the rule it has to use as the start rule in case the grammar instance is directly used as a parser. </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"> <a accesskey="p" href="../notes.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../notes.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="style_guide.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> </div> </body> </html>