1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Statement</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="Chapter 1. Phoenix 3.2.0"> 8<link rel="up" href="../modules.html" title="Modules"> 9<link rel="prev" href="operator.html" title="Operator"> 10<link rel="next" href="statement/block_statement.html" title="Block Statement"> 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="operator.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../modules.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="statement/block_statement.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="phoenix.modules.statement"></a><a class="link" href="statement.html" title="Statement">Statement</a> 28</h3></div></div></div> 29<div class="toc"><dl class="toc"> 30<dt><span class="section"><a href="statement/block_statement.html">Block Statement</a></span></dt> 31<dt><span class="section"><a href="statement/if__statement.html">if_ Statement</a></span></dt> 32<dt><span class="section"><a href="statement/___if_else_____statement.html">if_else_ Statement</a></span></dt> 33<dt><span class="section"><a href="statement/switch__statement.html">switch_ 34 Statement</a></span></dt> 35<dt><span class="section"><a href="statement/while__statement.html">while_ 36 Statement</a></span></dt> 37<dt><span class="section"><a href="statement/___do_while_____statement.html">do_while_ Statement</a></span></dt> 38<dt><span class="section"><a href="statement/for_statement.html">for_ Statement</a></span></dt> 39<dt><span class="section"><a href="statement/try__catch__statement.html">try_ 40 catch_ Statement</a></span></dt> 41<dt><span class="section"><a href="statement/throw_.html">throw_</a></span></dt> 42</dl></div> 43<p> 44 <span class="bold"><strong><span class="emphasis"><em>Lazy statements...</em></span></strong></span> 45 </p> 46<p> 47 The expressions presented so far are sufficiently powerful to construct quite 48 elaborate structures. We have presented lazy-functions and lazy-operators. 49 How about lazy-statements? First, an appetizer: 50 </p> 51<p> 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 (<a href="../../../../example/all_odds.cpp" target="_top">all_odds.cpp</a>): 54 </p> 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 <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 <span class="special">[</span> 58 <span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">arg1</span> <span class="special"><<</span> <span class="char">' '</span> 59 <span class="special">]</span> 60<span class="special">);</span> 61</pre> 62<p> 63 Huh? Is that valid C++? Read on... 64 </p> 65<p> 66 Yes, it is valid C++. The sample code above is as close as you can get to 67 the syntax of C++. This stylized C++ syntax differs from actual C++ code. 68 First, the <code class="computeroutput"><span class="keyword">if</span></code> has a trailing 69 underscore. Second, the block uses square brackets instead of the familiar 70 curly braces {}. 71 </p> 72<div class="note"><table border="0" summary="Note"> 73<tr> 74<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../doc/src/images/note.png"></td> 75<th align="left">Note</th> 76</tr> 77<tr><td align="left" valign="top"> 78<p> 79 <span class="bold"><strong>C++ in C++?</strong></span> 80 </p> 81<p> 82 In as much as <a href="http://spirit.sourceforge.net" target="_top">Spirit</a> 83 attempts to mimic EBNF in C++, Phoenix attempts to mimic C++ in C++!!! 84 </p> 85</td></tr> 86</table></div> 87<div class="note"><table border="0" summary="Note"> 88<tr> 89<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../doc/src/images/note.png"></td> 90<th align="left">Note</th> 91</tr> 92<tr><td align="left" valign="top"><p> 93 Unlike lazy functions and lazy operators, lazy statements always return 94 void. 95 </p></td></tr> 96</table></div> 97<p> 98 Here are more examples with annotations. The code almost speaks for itself. 99 </p> 100</div> 101<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 102<td align="left"></td> 103<td align="right"><div class="copyright-footer">Copyright © 2002-2005, 2010, 2014, 2015 Joel de Guzman, Dan Marsden, Thomas 104 Heller, John Fletcher<p> 105 Distributed under the Boost Software License, Version 1.0. (See accompanying 106 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>) 107 </p> 108</div></td> 109</tr></table> 110<hr> 111<div class="spirit-nav"> 112<a accesskey="p" href="operator.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../modules.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="statement/block_statement.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> 113</div> 114</body> 115</html> 116
