1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Complex - Our first complex parser</title> 5<link rel="stylesheet" href="../../../../../../../doc/src/boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../../index.html" title="Spirit X3 3.0.4"> 8<link rel="up" href="../tutorials.html" title="Tutorials"> 9<link rel="prev" href="semantic_actions.html" title="Parser Semantic Actions"> 10<link rel="next" href="sum___adding_numbers.html" title="Sum - adding numbers"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr> 14<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../boost.png"></td> 15<td align="center"><a href="../../../../../../../index.html">Home</a></td> 16<td align="center"><a href="../../../../../../../libs/libraries.htm">Libraries</a></td> 17<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 18<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 19<td align="center"><a href="../../../../../../../more/index.htm">More</a></td> 20</tr></table> 21<hr> 22<div class="spirit-nav"> 23<a accesskey="p" href="semantic_actions.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../tutorials.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="sum___adding_numbers.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h3 class="title"> 27<a name="spirit_x3.tutorials.complex___our_first_complex_parser"></a><a class="link" href="complex___our_first_complex_parser.html" title="Complex - Our first complex parser">Complex 28 - Our first complex parser</a> 29</h3></div></div></div> 30<p> 31 Well, not really a complex parser, but a parser that parses complex numbers. 32 </p> 33<p> 34 Here's a simple parser expression for complex numbers: 35 </p> 36<pre class="programlisting"> <span class="char">'('</span> <span class="special">>></span> <span class="identifier">double_</span> <span class="special">>></span> <span class="special">-(</span><span class="char">','</span> <span class="special">>></span> <span class="identifier">double_</span><span class="special">)</span> <span class="special">>></span> <span class="char">')'</span> 37<span class="special">|</span> <span class="identifier">double_</span> 38</pre> 39<p> 40 What's new? Well, we have: 41 </p> 42<div class="orderedlist"><ol class="orderedlist" type="1"> 43<li class="listitem"> 44 Alternates: e.g. <code class="computeroutput"><span class="identifier">a</span> <span class="special">|</span> 45 <span class="identifier">b</span></code>. Try <code class="computeroutput"><span class="identifier">a</span></code> 46 first. If it succeeds, good. If not, try the next alternative, <code class="computeroutput"><span class="identifier">b</span></code>. 47 </li> 48<li class="listitem"> 49 Optionals: e.g. -p. Match the parser p zero or one time. 50 </li> 51</ol></div> 52<p> 53 The complex parser presented above reads as: 54 </p> 55<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 56<li class="listitem"> 57 One or two real numbers in parentheses, separated by comma (the second 58 number is optional) 59 </li> 60<li class="listitem"> 61 <span class="bold"><strong>OR</strong></span> a single real number. 62 </li> 63</ul></div> 64<p> 65 This parser can parse complex numbers of the form: 66 </p> 67<pre class="programlisting"><span class="special">(</span><span class="number">123.45</span><span class="special">,</span> <span class="number">987.65</span><span class="special">)</span> 68<span class="special">(</span><span class="number">123.45</span><span class="special">)</span> 69<span class="number">123.45</span> 70</pre> 71<p> 72 Here goes, this time with actions: 73 </p> 74<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">client</span> 75<span class="special">{</span> 76 <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Iterator</span><span class="special">></span> 77 <span class="keyword">bool</span> <span class="identifier">parse_complex</span><span class="special">(</span><span class="identifier">Iterator</span> <span class="identifier">first</span><span class="special">,</span> <span class="identifier">Iterator</span> <span class="identifier">last</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">complex</span><span class="special"><</span><span class="keyword">double</span><span class="special">>&</span> <span class="identifier">c</span><span class="special">)</span> 78 <span class="special">{</span> 79 <span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">x3</span><span class="special">::</span><span class="identifier">double_</span><span class="special">;</span> 80 <span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">x3</span><span class="special">::</span><span class="identifier">_attr</span><span class="special">;</span> 81 <span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">x3</span><span class="special">::</span><span class="identifier">phrase_parse</span><span class="special">;</span> 82 <span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">x3</span><span class="special">::</span><span class="identifier">ascii</span><span class="special">::</span><span class="identifier">space</span><span class="special">;</span> 83 84 <span class="keyword">double</span> <span class="identifier">rN</span> <span class="special">=</span> <span class="number">0.0</span><span class="special">;</span> 85 <span class="keyword">double</span> <span class="identifier">iN</span> <span class="special">=</span> <span class="number">0.0</span><span class="special">;</span> 86 <span class="keyword">auto</span> <span class="identifier">fr</span> <span class="special">=</span> <span class="special">[&](</span><span class="keyword">auto</span><span class="special">&</span> <span class="identifier">ctx</span><span class="special">){</span> <span class="identifier">rN</span> <span class="special">=</span> <span class="identifier">_attr</span><span class="special">(</span><span class="identifier">ctx</span><span class="special">);</span> <span class="special">};</span> 87 <span class="keyword">auto</span> <span class="identifier">fi</span> <span class="special">=</span> <span class="special">[&](</span><span class="keyword">auto</span><span class="special">&</span> <span class="identifier">ctx</span><span class="special">){</span> <span class="identifier">iN</span> <span class="special">=</span> <span class="identifier">_attr</span><span class="special">(</span><span class="identifier">ctx</span><span class="special">);</span> <span class="special">};</span> 88 89 <span class="keyword">bool</span> <span class="identifier">r</span> <span class="special">=</span> <span class="identifier">phrase_parse</span><span class="special">(</span><span class="identifier">first</span><span class="special">,</span> <span class="identifier">last</span><span class="special">,</span> 90 91 <span class="comment">// Begin grammar</span> 92 <span class="special">(</span> 93 <span class="char">'('</span> <span class="special">>></span> <span class="identifier">double_</span><span class="special">[</span><span class="identifier">fr</span><span class="special">]</span> 94 <span class="special">>></span> <span class="special">-(</span><span class="char">','</span> <span class="special">>></span> <span class="identifier">double_</span><span class="special">[</span><span class="identifier">fi</span><span class="special">])</span> <span class="special">>></span> <span class="char">')'</span> 95 <span class="special">|</span> <span class="identifier">double_</span><span class="special">[</span><span class="identifier">fr</span><span class="special">]</span> 96 <span class="special">),</span> 97 <span class="comment">// End grammar</span> 98 99 <span class="identifier">space</span><span class="special">);</span> 100 101 <span class="keyword">if</span> <span class="special">(!</span><span class="identifier">r</span> <span class="special">||</span> <span class="identifier">first</span> <span class="special">!=</span> <span class="identifier">last</span><span class="special">)</span> <span class="comment">// fail if we did not get a full match</span> 102 <span class="keyword">return</span> <span class="keyword">false</span><span class="special">;</span> 103 <span class="identifier">c</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">complex</span><span class="special"><</span><span class="keyword">double</span><span class="special">>(</span><span class="identifier">rN</span><span class="special">,</span> <span class="identifier">iN</span><span class="special">);</span> 104 <span class="keyword">return</span> <span class="identifier">r</span><span class="special">;</span> 105 <span class="special">}</span> 106<span class="special">}</span> 107</pre> 108<p> 109 The full cpp file for this example can be found here: <a href="../../../../../example/x3/complex_number.cpp" target="_top">complex_number.cpp</a> 110 </p> 111<p> 112 The <code class="computeroutput"><span class="identifier">double_</span></code> parser attaches 113 this action: 114 </p> 115<pre class="programlisting"><span class="special">[&](</span><span class="keyword">auto</span><span class="special">&</span> <span class="identifier">ctx</span><span class="special">){</span> <span class="identifier">n</span> <span class="special">=</span> <span class="identifier">_attr</span><span class="special">(</span><span class="identifier">ctx</span><span class="special">);</span> <span class="special">}</span> 116</pre> 117<p> 118 This assigns the parsed result (actually, the attribute of <code class="computeroutput"><span class="identifier">double_</span></code>) to n. 119 </p> 120</div> 121<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 122<td align="left"></td> 123<td align="right"><div class="copyright-footer">Copyright © 2001-2018 Joel de Guzman, 124 Hartmut Kaiser<p> 125 Distributed under the Boost Software License, Version 1.0. (See accompanying 126 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>) 127 </p> 128</div></td> 129</tr></table> 130<hr> 131<div class="spirit-nav"> 132<a accesskey="p" href="semantic_actions.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../tutorials.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="sum___adding_numbers.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a> 133</div> 134</body> 135</html> 136
