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<html>
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<head>
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<title>sequences.html</title>
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<link rel="stylesheet" type="text/css" href="../styles.css">
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</head>
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<body>
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<h4>
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Sequences
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</h4>
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<div>
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2002-11-08 02:12:35 +00:00
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A <i>sequence</i> (abbreviated to <i>seq</i>) is a group of adjacent parenthesized elements. For example,
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</div>
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<div class="code">
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(<i>a</i>)(<i>b</i>)(<i>c</i>)
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</div>
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<div>
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...is a <i>seq</i> of <i>3</i> elements--<i>a</i>, <i>b</i>, and <i>c</i>.
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</div>
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<div>
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<i>Sequences</i> are data structures that merge the properties of both <i>lists</i> and
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<i>tuples</i> with the exception that a <i>seq</i> cannot be empty.
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Therefore, an "empty" <i>seq</i> is considered a special case scenario that
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must be handled separately in C++.
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</div>
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<div class="code">
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<pre>
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#define SEQ (x)(y)(z)
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#define REVERSE(s, state, elem) (elem) state
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// append to head ^
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BOOST_PP_SEQ_FOLD_LEFT(REVERSE, BOOST_PP_EMPTY, SEQ)()
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// #1 #2
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// 1) placeholder for "empty" seq
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// 2) remove placeholder
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#define SEQ_B (1)(2)(3)
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#define INC(s, state, elem) state (BOOST_PP_INC(elem))
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// append to tail ^
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BOOST_PP_SEQ_FOLD_RIGHT(INC, BOOST_PP_SEQ_NIL, SEQ)
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// ^
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// special placeholder that will be "eaten"
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// by appending to the tail
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</pre>
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</div>
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<div>
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<i>Sequences</i> are extremely efficient. Element access speed approaches
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random access--even with <i>seqs</i> of up to <i>256</i> elements. This
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is because element access (among other things) is implemented iteratively
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rather than recursively. Therefore, elements can be accessed at extremely
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high indices even on preprocessors with low maximum expansion depths.
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</div>
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<div>
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Elements of a <i>seq</i> can be extracted with <b>BOOST_PP_SEQ_ELEM</b>.
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</div>
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<h4>
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Primitives
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</h4>
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<ul>
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<li>
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<a href="../ref/seq_elem.html">BOOST_PP_SEQ_ELEM</a></li>
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</ul>
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</body>
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2002-10-13 05:47:23 +00:00
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</html>
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