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[SVN r16152]
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Paul Mensonides
2002-11-08 02:12:35 +00:00
parent 91eba2f11b
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<html>
<head>
<title>BOOST_PP_SEQ_FOLD_LEFT_s</title>
<link rel="stylesheet" type="text/css" href="../styles.css">
</head>
<body>
<div style="margin-left: 0px;">
The <b>BOOST_PP_SEQ_FOLD_LEFT_<i>s</i></b> macro folds (or accumulates) the
elements of a <i>seq</i> left-to-right.&nbsp; It reenters <b>BOOST_PP_SEQ_FOLD_LEFT</b>
with maximum efficiency.
</div>
<h4>
Usage
</h4>
<div class="code">
<b>BOOST_PP_SEQ_FOLD_LEFT_</b> ## <i>s</i>(<i>op</i>, <i>state</i>, <i>seq</i>)
</div>
<h4>
Arguments
</h4>
<dl>
<dt>s</dt>
<dd>
The next available <b>BOOST_PP_SEQ_FOLD_LEFT</b> fold step.
</dd>
<dt>op</dt>
<dd>
A ternary operation of the form <i>op</i>(<i>s</i>, <i>state</i>, <i>elem</i>).&nbsp;
This macro is called for each element in <i>seq</i>--each time returning a new <i>state</i>.&nbsp;
This operation is expanded by <b>BOOST_PP_SEQ_FOLD_LEFT</b> with the next
available fold step, the current <i>state</i>, and the current element.
</dd>
<dt>state</dt>
<dd>
The initial state of the fold.
</dd>
<dt>seq</dt>
<dd>
The <i>seq</i> to be folded.
</dd>
</dl>
<h4>
Remarks
</h4>
<div>
For the <i>seq</i>, (<i>0</i>)(<i>1</i>)(<i>2</i>), this macro expands to:
<div>
<i>op</i>(<i>s</i>, <i>op</i>(<i>s</i>, <i>op</i>(<i>s</i>, <i>state</i>, <i>0</i>),
<i>1</i>), <i>2</i>)
</div>
</div>
<h4>
See Also
</h4>
<ul>
<li>
<a href="seq_fold_left.html">BOOST_PP_SEQ_FOLD_LEFT</a></li>
</ul>
<h4>
Requirements
</h4>
<div>
<b>Header:</b> &nbsp;<a href="../headers/seq/fold_left.hpp.html">&lt;boost/preprocessor/seq/fold_left.hpp&gt;</a>
</div>
<h4>
Sample Code
</h4>
<div>
<pre>
#include &lt;<a href="../headers/cat.hpp.html">boost/preprocessor/cat.hpp</a>&gt;
#include &lt;<a href="../headers/seq/fold_left.hpp.html">boost/preprocessor/seq/fold_left.hpp</a>&gt;
#include &lt;<a href="../headers/seq/seq.hpp.html">boost/preprocessor/seq/seq.hpp</a>&gt;
#define S1 (a)(b)(c)
#define S2 (S1)(S1)(S1)
#define OP(s, state, x) state (<a href="seq_fold_left_s.html">BOOST_PP_SEQ_FOLD_LEFT_</a> ## s(OP_2, _, x))
#define OP_2(s, state, x) <a href="cat.html">BOOST_PP_CAT</a>(state, x)
<a href="seq_fold_left.html">BOOST_PP_SEQ_FOLD_LEFT</a>(OP, <a href="seq_nil.html">BOOST_PP_SEQ_NIL</a>, S2)
// expands to (_abc)(_abc)(_abc)
</pre>
</div>
</body>
</html>