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<html>
<head>
<title>sequences.html</title>
<link rel="stylesheet" type="text/css" href="../styles.css">
</head>
<body>
<h4>
Sequences
</h4>
<div>
A <i>sequence</i> (abbreviated to <i>seq</i>) is a group of adjacent parenthesized elements. For example,
</div>
<div class="code">
(<i>a</i>)(<i>b</i>)(<i>c</i>)
</div>
<div>
...is a <i>seq</i> of <i>3</i> elements--<i>a</i>, <i>b</i>, and <i>c</i>.
</div>
<div>
<i>Sequences</i> are data structures that merge the properties of both <i>lists</i> and
<i>tuples</i> with the exception that a <i>seq</i> cannot be empty.
Therefore, an "empty" <i>seq</i> is considered a special case scenario that
must be handled separately in C++.
</div>
<div class="code">
<pre>
#define SEQ (x)(y)(z)
#define REVERSE(s, state, elem) (elem) state
// append to head ^
BOOST_PP_SEQ_FOLD_LEFT(REVERSE, BOOST_PP_EMPTY, SEQ)()
// #1 #2
// 1) placeholder for "empty" seq
// 2) remove placeholder
#define SEQ_B (1)(2)(3)
#define INC(s, state, elem) state (BOOST_PP_INC(elem))
// append to tail ^
BOOST_PP_SEQ_FOLD_RIGHT(INC, BOOST_PP_SEQ_NIL, SEQ)
// ^
// special placeholder that will be "eaten"
// by appending to the tail
</pre>
</div>
<div>
<i>Sequences</i> are extremely efficient. Element access speed approaches
random access--even with <i>seqs</i> of up to <i>256</i> elements. This
is because element access (among other things) is implemented iteratively
rather than recursively. Therefore, elements can be accessed at extremely
high indices even on preprocessors with low maximum expansion depths.
</div>
<div>
Elements of a <i>seq</i> can be extracted with <b>BOOST_PP_SEQ_ELEM</b>.
</div>
<h4>
Primitives
</h4>
<ul>
<li>
<a href="../ref/seq_elem.html">BOOST_PP_SEQ_ELEM</a></li>
</ul>
<hr size="1">
<div style="margin-left: 0px;">
<i> Copyright <a href="http://www.housemarque.com" target="_top">Housemarque Oy</a> 2002</i>
</br><i> Copyright Paul Mensonides 2002</i>
</div>
<div style="margin-left: 0px;">
<p><small>Distributed under the Boost Software License, Version 1.0. (See
accompanying file <a href="../../../../LICENSE_1_0.txt">LICENSE_1_0.txt</a> or
copy at <a href=
"http://www.boost.org/LICENSE_1_0.txt">www.boost.org/LICENSE_1_0.txt</a>)</small></p>
</div>
</body>
</html>
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