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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en">
<head>
<title>Pattern Matching</title>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<link rel="stylesheet" href="../../stylesheets/pyke.css" type="text/css" />
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<tr id="header1"><th id="header" colspan="3">
&nbsp;
</th></tr>
<tr id="header2">
<th id="crumb-left"></th>
<th id="crumb-line">
<div id="nav">
<ul>
<li><a href="../../index.html">Home</a></li>
<li>&gt;</li>
<li><a href="../index.html">Logic Programming</a></li>
<li>&gt;</li>
<li>Pattern Matching</li>
</ul>
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<div class="normal-nav"><a href="../statements.html">Statements</a></div>
<div class="title-nav"><a href="index.html">Pattern Matching</a></div><div class="nav-branch">
<div class="normal-nav"><a href="literal_patterns.html">Literal Patterns</a></div>
<div class="normal-nav"><a href="pattern_variables.html">Pattern Variables</a></div>
<div class="normal-nav"><a href="tuple_patterns.html">Tuple Patterns</a></div>
<div class="normal-nav"><a href="matching_patterns.html">Matching 2 Patterns</a></div>
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<div class="document" id="pattern-matching">
<h1 class="title">Pattern Matching</h1>
<p>Pattern matching is a little strange at first, so we're going to ease into
it slowly...</p>
<p>There are two aspects to pattern matching: <em>patterns</em>, which you write, and
<em>matching</em>, which is what Pyke does with your patterns.</p>
<p>In a nutshell, patterns are made up of two fundamental building blocks:</p>
<ol class="arabic simple">
<li><a class="reference" href="literal_patterns.html">Literal patterns</a>.<ul>
<li>Theses are just data values that only match themselves.</li>
</ul>
</li>
<li><a class="reference" href="pattern_variables.html">Pattern variables</a>.<ul>
<li>These will match anything. (Including other pattern variables, as we'll
see later)!</li>
</ul>
</li>
</ol>
<p>And one compound pattern:</p>
<ol class="arabic simple">
<li><a class="reference" href="tuple_patterns.html">Tuple patterns</a>.<ul>
<li>These match -- you guessed it! -- tuples!</li>
</ul>
</li>
</ol>
<p>We'll examine all of the above looking at how Pyke matches a pattern to data.
Then we'll expand this to cover <a class="reference" href="matching_patterns.html">matching two patterns together</a>.</p>
<p>And finally, a <a class="reference" href="matching_patterns.html#pathological-question">pathological question</a> to see if you've been paying
attention.</p>
<p>Sound like fun? Good! Let's get started!</p>
<p>OK, so why do we need patterns? The simple answer is that we need patterns
to generalize <a class="reference" href="../statements.html">statements</a>. One example is to turn statements into questions.</p>
<div class="important">
<p class="first admonition-title">Important</p>
<ul class="last simple">
<li>When you want a <em>direct</em> statement, such as to state a fact, you just use
<em>data</em> for its arguments.</li>
<li>But when you want a <em>generalized</em> statement, such as to ask a question,
you use <em>patterns</em> for its arguments.</li>
</ul>
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<h3>More:</h3>
<div class="right-item"><a href="literal_patterns.html">Literal Patterns</a><p>Explanation of <em>literal patterns</em>.</p>
</div>
<div class="right-item"><a href="pattern_variables.html">Pattern Variables</a><p>Explanation of <em>pattern variables</em>.</p>
</div>
<div class="right-item"><a href="tuple_patterns.html">Tuple Patterns</a><p>Explanation of <em>tuple patterns</em>.</p>
</div>
<div class="right-item"><a href="matching_patterns.html">Matching Two Patterns</a><p>Explanation of matching two patterns together, vs matching a pattern
to data.</p>
</div>
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Copyright &copy; 2007-2009 Bruce Frederiksen
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Page last modified
Mon, Oct 27 2008.
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