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  26. <div class="titlepage"><div><div><h3 class="title">
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  29. <div class="toc"><dl>
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  30. <dt><span class="section"><a href="statement/block_statement.html">Block Statement</a></span></dt>
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  31. <dt><span class="section"><a href="statement/if__statement.html">if_ Statement</a></span></dt>
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  32. <dt><span class="section"><a href="statement/___if_else_____statement.html">if_else_ Statement</a></span></dt>
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  33. <dt><span class="section"><a href="statement/switch__statement.html">switch_
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  34.         Statement</a></span></dt>
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  35. <dt><span class="section"><a href="statement/while__statement.html">while_
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  36.         Statement</a></span></dt>
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  37. <dt><span class="section"><a href="statement/___do_while_____statement.html">do_while_ Statement</a></span></dt>
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  38. <dt><span class="section"><a href="statement/for_statement.html">for_ Statement</a></span></dt>
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  39. <dt><span class="section"><a href="statement/try__catch__statement.html">try_
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  40.         catch_ Statement</a></span></dt>
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  41. <dt><span class="section"><a href="statement/throw_.html">throw_</a></span></dt>
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  43. <p>
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  44.         <span class="bold"><strong><span class="emphasis"><em>Lazy statements...</em></span></strong></span>
    45. 

  45.       </p>
    46. 

  46. <p>
    47. 

  47.         The expressions presented so far are sufficiently powerful to construct quite
    48. 

  48.         elaborate structures. We have presented lazy-functions and lazy-operators.
    49. 

  49.         How about lazy-statements? First, an appetizer:
    50. 

  50.       </p>
    51. 

  51. <p>
    52. 

  52.         Print all odd-numbered contents of an STL container using <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">for_each</span></code>
    53. 

  53.         (<a href="../../../../example/all_odds.cpp" target="_top">all_odds.cpp</a>):
    54. 

  54.       </p>
    55. 

  55. <pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">for_each</span><span class="special">(</span><span class="identifier">c</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">c</span><span class="special">.</span><span class="identifier">end</span><span class="special">(),</span>
    56. 

  56.     <span class="identifier">if_</span><span class="special">(</span><span class="identifier">arg1</span> <span class="special">%</span> <span class="number">2</span> <span class="special">==</span> <span class="number">1</span><span class="special">)</span>
    57. 

  57.     <span class="special">[</span>
    58. 

  58.         <span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="identifier">arg1</span> <span class="special">&lt;&lt;</span> <span class="char">' '</span>
    59. 

  59.     <span class="special">]</span>
    60. 

  60. <span class="special">);</span>
    61. 

  61. </pre>
    62. 

  62. <p>
    63. 

  63.         Huh? Is that valid C++? Read on...
    64. 

  64.       </p>
    65. 

  65. <p>
    66. 

  66.         Yes, it is valid C++. The sample code above is as close as you can get to
    67. 

  67.         the syntax of C++. This stylized C++ syntax differs from actual C++ code.
    68. 

  68.         First, the <code class="computeroutput"><span class="keyword">if</span></code> has a trailing
    69. 

  69.         underscore. Second, the block uses square brackets instead of the familiar
    70. 

  70.         curly braces {}.
    71. 

  71.       </p>
    72. 

  72. <div class="note"><table border="0" summary="Note">
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  73. <tr>
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  74. <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../doc/src/images/note.png"></td>
    75. 

  75. <th align="left">Note</th>
    76. 

  76. </tr>
    77. 

  77. <tr><td align="left" valign="top">
    78. 

  78. <p>
    79. 

  79.           <span class="bold"><strong>C++ in C++?</strong></span>
    80. 

  80.         </p>
    81. 

  81. <p>
    82. 

  82.           In as much as <a href="http://spirit.sourceforge.net" target="_top">Spirit</a>
    83. 

  83.           attempts to mimic EBNF in C++, Phoenix attempts to mimic C++ in C++!!!
    84. 

  84.         </p>
    85. 

  85. </td></tr>
    86. 

  86. </table></div>
    87. 

  87. <div class="note"><table border="0" summary="Note">
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    89. 

  89. <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../doc/src/images/note.png"></td>
    90. 

  90. <th align="left">Note</th>
    91. 

  91. </tr>
    92. 

  92. <tr><td align="left" valign="top"><p>
    93. 

  93.           Unlike lazy functions and lazy operators, lazy statements always return
    94. 

  94.           void.
    95. 

  95.         </p></td></tr>
    96. 

  96. </table></div>
    97. 

  97. <p>
    98. 

  98.         Here are more examples with annotations. The code almost speaks for itself.
    99. 

  99.       </p>
    100. 

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  102. <td align="left"></td>
    103. 

  103. <td align="right"><div class="copyright-footer">Copyright &#169; 2002-2005, 2010 Joel de Guzman, Dan Marsden, Thomas Heller<p>
    104. 

  104.         Distributed under the Boost Software License, Version 1.0. (See accompanying
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  105.         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>)
    106. 

  106.       </p>
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