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<html>
<head>
<title>BOOST_PP_LIST_FOLD_LEFT_d</title>
<link rel="stylesheet" type="text/css" href="../styles.css">
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<div style="margin-left: 0px;">
The <b>BOOST_PP_LIST_FOLD_LEFT_<i>d</i></b> macro folds (or accumulates) the elements of a <i>list</i> left-to-right.
It reenters <b>BOOST_PP_WHILE</b> with maximum efficiency.
</div>
<h4>Usage</h4>
<div class="code">
<b>BOOST_PP_LIST_FOLD_LEFT_</b> ## <i>d</i>(<i>op</i>, <i>state</i>, <i>list</i>)
</div>
<h4>Arguments</h4>
<dl>
<dt>d</dt>
<dd>
The next available <b>BOOST_PP_WHILE</b> iteration.
</dd>
<dt>op</dt>
<dd>
A ternary operation of the form <i>op</i>(<i>d</i>, <i>state</i>, <i>elem</i>).
This macro is called for each element in <i>list</i>--each time returning a new <i>state</i>.
This operation is expanded by <b>BOOST_PP_LIST_FOLD_LEFT</b> with the next available <b>BOOST_PP_WHILE</b> iteration,
the current <i>state</i>, and the current element.
</dd>
<dt>state</dt>
<dd>
The initial state of the fold.
</dd>
<dt>list</dt>
<dd>
The <i>list</i> to be folded.
</dd>
</dl>
<h4>Remarks</h4>
<div>
For the <i>list</i>, (<i>0</i>, (<i>1</i>, (<i>2</i>, <b>BOOST_PP_NIL</b>))), this macro expands to:
<div>
<i>op</i>(<i>d</i>, <i>op</i>(<i>d</i>, <i>op</i>(<i>d</i>, <i>state</i>, <i>0</i>), <i>1</i>), <i>2</i>)
</div>
</div>
<h4>See Also</h4>
<ul>
<li><a href="list_fold_left.html">BOOST_PP_LIST_FOLD_LEFT</a></li>
</ul>
<h4>Requirements</h4>
<div>
<b>Header:</b> <a href="../headers/list/fold_left.html"><boost/preprocessor/list/fold_left.hpp></a>
</div>
<h4>Sample Code</h4>
<div><pre>
#include <<a href="../headers/cat.html">boost/preprocessor/cat.hpp</a>>
#include <<a href="../headers/list/fold_left.html">boost/preprocessor/list/fold_left.hpp</a>>
#define L1 (a, (b, (c, <a href="nil.html">BOOST_PP_NIL</a>)))
#define L2 (L1, (L1, (L1, <a href="nil.html">BOOST_PP_NIL</a>)))
#define OP(d, state, x) (<a href="list_fold_left_d.html">BOOST_PP_LIST_FOLD_LEFT_</a> ## d(OP_2, _, x), state)
#define OP_2(d, state, x) <a href="cat.html">BOOST_PP_CAT</a>(state, x)
<a href="list_fold_left.html">BOOST_PP_LIST_FOLD_LEFT</a>(OP, <a href="nil.html">BOOST_PP_NIL</a>, L2)
/*
expands to:
(_abc, (_abc, (_abc, <a href="nil.html">BOOST_PP_NIL</a>)))
*/
</pre></div>
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