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number_list_attribute___one_more__with_style.html

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  4. <title>Number List Attribute - one more, with style</title>
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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.number_list_attribute___one_more__with_style"></a><a class="link" href="number_list_attribute___one_more__with_style.html" title="Number List Attribute - one more, with style">Number
    28. 

  28.       List Attribute - one more, with style</a>
    29. 

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

  30. <p>
    31. 

  31.         You've seen that the <code class="computeroutput"><span class="identifier">double_</span></code>
    32. 

  32.         parser has a <code class="computeroutput"><span class="keyword">double</span></code> attribute.
    33. 

  33.         All parsers have an attribute, even complex parsers. Those that are composed
    34. 

  34.         from primitives using operators, like the list parser, also have an attribute.
    35. 

  35.         It so happens that the attribute of a list parser:
    36. 

  36.       </p>
    37. 

  37. <pre class="programlisting"><span class="identifier">p</span> <span class="special">%</span> <span class="identifier">d</span>
    38. 

  38. </pre>
    39. 

  39. <p>
    40. 

  40.         is a <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span></code> of the attribute of <code class="computeroutput"><span class="identifier">p</span></code>. So, for our parser:
    41. 

  41.       </p>
    42. 

  42. <pre class="programlisting"><span class="identifier">double_</span> <span class="special">%</span> <span class="char">','</span>
    43. 

  43. </pre>
    44. 

  44. <p>
    45. 

  45.         we'll have an attribute of:
    46. 

  46.       </p>
    47. 

  47. <pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="keyword">double</span><span class="special">&gt;</span>
    48. 

  48. </pre>
    49. 

  49. <p>
    50. 

  50.         So, what does this give us? Well, we can simply pass in a <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="keyword">double</span><span class="special">&gt;</span></code> to our number list parser and it will
    51. 

  51.         happily churn out our result in our vector. For that to happen, we'll use
    52. 

  52.         a variation of the <code class="computeroutput"><span class="identifier">phrase_parse</span></code>
    53. 

  53.         with an additional argument: the parser's attribute. With the following arguments
    54. 

  54.         passed to <code class="computeroutput"><span class="identifier">phrase_parse</span></code>
    55. 

  55.       </p>
    56. 

  56. <div class="orderedlist"><ol class="orderedlist" type="1">
    57. 

  57. <li class="listitem">
    58. 

  58.             An iterator pointing to the start of the input
    59. 

  59.           </li>
    60. 

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

  61.             An iterator pointing to one past the end of the input
    62. 

  62.           </li>
    63. 

  63. <li class="listitem">
    64. 

  64.             The parser object
    65. 

  65.           </li>
    66. 

  66. <li class="listitem">
    67. 

  67.             Another parser called the skip parser
    68. 

  68.           </li>
    69. 

  69. <li class="listitem">
    70. 

  70.             The parser's attribute
    71. 

  71.           </li>
    72. 

  72. </ol></div>
    73. 

  73. <p>
    74. 

  74.         Our parser now is further simplified to:
    75. 

  75.       </p>
    76. 

  76. <pre class="programlisting"><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_numbers</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">vector</span><span class="special">&lt;</span><span class="keyword">double</span><span class="special">&gt;&amp;</span> <span class="identifier">v</span><span class="special">)</span>
    78. 

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

  79.     <span class="keyword">using</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">x3</span><span class="special">::</span><span class="identifier">phrase_parse</span><span class="special">;</span>
    81. 

  81.     <span class="keyword">using</span> <span class="identifier">x3</span><span class="special">::</span><span class="identifier">_attr</span><span class="special">;</span>
    82. 

  82.     <span class="keyword">using</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">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>
    85. 

  85. 

  86.         <span class="comment">//  Begin grammar</span>
    87. 

  87.         <span class="special">(</span>
    88. 

  88.             <span class="identifier">double_</span> <span class="special">%</span> <span class="char">','</span>
    89. 

  89.         <span class="special">)</span>
    90. 

  90.         <span class="special">,</span>
    91. 

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

  92. 

  93.         <span class="identifier">space</span><span class="special">,</span> <span class="identifier">v</span><span class="special">);</span>
    94. 

  94. 

  95.     <span class="keyword">if</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>
    96. 

  96.         <span class="keyword">return</span> <span class="keyword">false</span><span class="special">;</span>
    97. 

  97.     <span class="keyword">return</span> <span class="identifier">r</span><span class="special">;</span>
    98. 

  98. <span class="special">}</span>
    99. 

  99. </pre>
    100. 

  100. <p>
    101. 

  101.         The full cpp file for this example can be found here: <a href="../../../../../example/x3/num_list/num_list4.cpp" target="_top">num_list4.cpp</a>
    102. 

  102.       </p>
    103. 

  103. <p>
    104. 

  104.         <span class="bold"><strong>Hey, no more actions!!!</strong></span> Now we're entering
    105. 

  105.         the realm of attribute grammars. Cool eh?
    106. 

  106.       </p>
    107. 

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    108. 

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    109. 

  109. <td align="left"></td>
    110. 

  110. <td align="right"><div class="copyright-footer">Copyright &#169; 2001-2018 Joel de Guzman,
    111. 

  111.       Hartmut Kaiser<p>
    112. 

  112.         Distributed under the Boost Software License, Version 1.0. (See accompanying
    113. 

  113.         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>)
    114. 

  114.       </p>
    115. 

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