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complex___our_first_complex_parser.html

complex___our_first_complex_parser.html 12 KB
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  25. <div class="section">
    26. 

  26. <div class="titlepage"><div><div><h3 class="title">
    27. 

  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. 

  28.       - Our first complex parser</a>
    29. 

  29. </h3></div></div></div>
    30. 

  30. <p>
    31. 

  31.         Well, not really a complex parser, but a parser that parses complex numbers.
    32. 

  32.       </p>
    33. 

  33. <p>
    34. 

  34.         Here's a simple parser expression for complex numbers:
    35. 

  35.       </p>
    36. 

  36. <pre class="programlisting">    <span class="char">'('</span> <span class="special">&gt;&gt;</span> <span class="identifier">double_</span> <span class="special">&gt;&gt;</span> <span class="special">-(</span><span class="char">','</span> <span class="special">&gt;&gt;</span> <span class="identifier">double_</span><span class="special">)</span> <span class="special">&gt;&gt;</span> <span class="char">')'</span>
    37. 

  37. <span class="special">|</span>   <span class="identifier">double_</span>
    38. 

  38. </pre>
    39. 

  39. <p>
    40. 

  40.         What's new? Well, we have:
    41. 

  41.       </p>
    42. 

  42. <div class="orderedlist"><ol class="orderedlist" type="1">
    43. 

  43. <li class="listitem">
    44. 

  44.             Alternates: e.g. <code class="computeroutput"><span class="identifier">a</span> <span class="special">|</span>
    45. 

  45.             <span class="identifier">b</span></code>. Try <code class="computeroutput"><span class="identifier">a</span></code>
    46. 

  46.             first. If it succeeds, good. If not, try the next alternative, <code class="computeroutput"><span class="identifier">b</span></code>.
    47. 

  47.           </li>
    48. 

  48. <li class="listitem">
    49. 

  49.             Optionals: e.g. -p. Match the parser p zero or one time.
    50. 

  50.           </li>
    51. 

  51. </ol></div>
    52. 

  52. <p>
    53. 

  53.         The complex parser presented above reads as:
    54. 

  54.       </p>
    55. 

  55. <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
    56. 

  56. <li class="listitem">
    57. 

  57.             One or two real numbers in parentheses, separated by comma (the second
    58. 

  58.             number is optional)
    59. 

  59.           </li>
    60. 

  60. <li class="listitem">
    61. 

  61.             <span class="bold"><strong>OR</strong></span> a single real number.
    62. 

  62.           </li>
    63. 

  63. </ul></div>
    64. 

  64. <p>
    65. 

  65.         This parser can parse complex numbers of the form:
    66. 

  66.       </p>
    67. 

  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. 

  68. <span class="special">(</span><span class="number">123.45</span><span class="special">)</span>
    69. 

  69. <span class="number">123.45</span>
    70. 

  70. </pre>
    71. 

  71. <p>
    72. 

  72.         Here goes, this time with actions:
    73. 

  73.       </p>
    74. 

  74. <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">client</span>
    75. 

  75. <span class="special">{</span>
    76. 

  76.     <span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">Iterator</span><span class="special">&gt;</span>
    77. 

  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">&lt;</span><span class="keyword">double</span><span class="special">&gt;&amp;</span> <span class="identifier">c</span><span class="special">)</span>
    78. 

  78.     <span class="special">{</span>
    79. 

  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. 

  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. 

  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. 

  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. 

  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. 

  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. 

  86.         <span class="keyword">auto</span> <span class="identifier">fr</span> <span class="special">=</span> <span class="special">[&amp;](</span><span class="keyword">auto</span><span class="special">&amp;</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. 

  87.         <span class="keyword">auto</span> <span class="identifier">fi</span> <span class="special">=</span> <span class="special">[&amp;](</span><span class="keyword">auto</span><span class="special">&amp;</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. 

  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. 

  90. 

  91.             <span class="comment">//  Begin grammar</span>
    92. 

  92.             <span class="special">(</span>
    93. 

  93.                     <span class="char">'('</span> <span class="special">&gt;&gt;</span> <span class="identifier">double_</span><span class="special">[</span><span class="identifier">fr</span><span class="special">]</span>
    94. 

  94.                         <span class="special">&gt;&gt;</span> <span class="special">-(</span><span class="char">','</span> <span class="special">&gt;&gt;</span> <span class="identifier">double_</span><span class="special">[</span><span class="identifier">fi</span><span class="special">])</span> <span class="special">&gt;&gt;</span> <span class="char">')'</span>
    95. 

  95.                 <span class="special">|</span>   <span class="identifier">double_</span><span class="special">[</span><span class="identifier">fr</span><span class="special">]</span>
    96. 

  96.             <span class="special">),</span>
    97. 

  97.             <span class="comment">//  End grammar</span>
    98. 

  98. 

  99.             <span class="identifier">space</span><span class="special">);</span>
    100. 

  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. 

  102.             <span class="keyword">return</span> <span class="keyword">false</span><span class="special">;</span>
    103. 

  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">&lt;</span><span class="keyword">double</span><span class="special">&gt;(</span><span class="identifier">rN</span><span class="special">,</span> <span class="identifier">iN</span><span class="special">);</span>
    104. 

  104.         <span class="keyword">return</span> <span class="identifier">r</span><span class="special">;</span>
    105. 

  105.     <span class="special">}</span>
    106. 

  106. <span class="special">}</span>
    107. 

  107. </pre>
    108. 

  108. <p>
    109. 

  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. 

  110.       </p>
    111. 

  111. <p>
    112. 

  112.         The <code class="computeroutput"><span class="identifier">double_</span></code> parser attaches
    113. 

  113.         this action:
    114. 

  114.       </p>
    115. 

  115. <pre class="programlisting"><span class="special">[&amp;](</span><span class="keyword">auto</span><span class="special">&amp;</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. 

  116. </pre>
    117. 

  117. <p>
    118. 

  118.         This assigns the parsed result (actually, the attribute of <code class="computeroutput"><span class="identifier">double_</span></code>) to n.
    119. 

  119.       </p>
    120. 

  120. </div>
    121. 

  121. <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
    122. 

  122. <td align="left"></td>
    123. 

  123. <td align="right"><div class="copyright-footer">Copyright &#169; 2001-2018 Joel de Guzman,
    124. 

  124.       Hartmut Kaiser<p>
    125. 

  125.         Distributed under the Boost Software License, Version 1.0. (See accompanying
    126. 

  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. 

  127.       </p>
    128. 

  128. </div></td>
    129. 

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    130. 

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