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30 <dt><span class=
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31 <dt><span class=
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32 <dt><span class=
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34 Statement
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36 Statement
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40 catch_ Statement
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44 <span class=
"bold"><strong><span class=
"emphasis"><em>Lazy statements...
</em></span></strong></span>
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:
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>):
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>
63 Huh? Is that valid C++? Read on...
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
72 <div class=
"note"><table border=
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"Note">
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75 <th align=
"left">Note
</th>
77 <tr><td align=
"left" valign=
"top">
79 <span class=
"bold"><strong>C++ in C++?
</strong></span>
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++!!!
87 <div class=
"note"><table border=
"0" summary=
"Note">
89 <td rowspan=
"2" align=
"center" valign=
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"../../../../../../doc/src/images/note.png"></td>
90 <th align=
"left">Note
</th>
92 <tr><td align=
"left" valign=
"top"><p>
93 Unlike lazy functions and lazy operators, lazy statements always return
98 Here are more examples with annotations. The code almost speaks for itself.
101 <table xmlns:
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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>)
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