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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 Syntax</title>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<link rel="stylesheet" href="../stylesheets/pyke.css" type="text/css" />
</head>
<body>
<table id="page-table">
<thead class="head">
<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">KRB Syntax</a></li>
<li>&gt;</li>
<li>Pattern</li>
</ul>
</div>
</th>
<th id="crumb-right"></th>
</tr>
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<a name="startcontent" id="startcontent"></a>
<div class="document" id="pattern-syntax">
<h1 class="title">Pattern Syntax</h1>
<div class="section">
<h2><a id="pattern" name="pattern">Pattern</a></h2>
<pre class="literal-block">
pattern ::= 'None' | 'True' | 'False'
| NUMBER | IDENTIFIER | STRING | variable
| '(' [{pattern,}] ['*' variable] ')'
</pre>
<p>IDENTIFIER acts like STRING here, meaning that it is taken as a literal
value. All variables in patterns must be preceded by a <tt class="docutils literal"><span class="pre">$</span></tt>.</p>
<p>Pyke does not currently support complex NUMBERS (for no good reason -- email
me if you need them).</p>
</div>
<div class="section">
<h2><a id="pattern-variable" name="pattern-variable">Pattern Variable</a></h2>
<p>Pattern variables are simply called <em>variable</em> in the syntax:</p>
<pre class="literal-block">
variable ::= '$'IDENTIFIER
</pre>
<p>The variable must not have a space between the <tt class="docutils literal"><span class="pre">$</span></tt> and the <tt class="docutils literal"><span class="pre">IDENTIFIER</span></tt>.</p>
</div>
<div class="section">
<h2><a id="anonymous-variable" name="anonymous-variable">Anonymous Variable</a></h2>
<p>If the pattern variable IDENTIFIER begins with an underscore (_), the variable
is an <em>anonymous</em> variable. It acts like a &quot;don't care&quot;. Technically, this
means that multiple uses of the same IDENTIFIER may stand for different
values. The name of the IDENTIFIER after the underscore is ignored and may be
used to document the use of the anonymous variable.</p>
</div>
<div class="section">
<h2><a id="rest-variable" name="rest-variable">Rest Variable</a></h2>
<p>The <tt class="docutils literal"><span class="pre">*variable</span></tt> at the end of a tuple pattern will match the rest of the
tuple. Thus, <tt class="docutils literal"><span class="pre">variable</span></tt> is always bound to a (possibly empty) tuple.</p>
<p>The syntax is taken from rest parameter syntax in python function definitions.
The difference here is that the variable needs a <tt class="docutils literal"><span class="pre">$</span></tt> on it.</p>
<p>You may use either a named variable or an anonymous variable here.</p>
</div>
</div>
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<h3>More:</h3>
<div class="right-item"><a href="fc_rule.html">Fc_rule Syntax</a><p>The syntax of a forward-chaining rule.</p>
</div>
<div class="right-item"><a href="bc_rule.html">Bc_rule Syntax</a><p>The syntax of a backward-chaining rule.</p>
</div>
<div class="right-item"><a href="pattern.html">Pattern Syntax</a><p>The syntax of a pattern used to match data values.</p>
</div>
<div class="right-item"><a href="compound_premise.html">Compound Premise Syntax</a><p>The syntax of compound premises.</p>
</div>
<div class="right-item"><a href="python_premise.html">Python Premise Syntax</a><p>The syntax of a python premise.</p>
</div>
</div>
</td>
</tr>
</tbody>
<tfoot id="foot">
<tr id="foot2">
<td id="copyright" colspan="3">
Copyright &copy; 2007 Bruce Frederiksen
</td>
</tr>
</tfoot>
</table>
<div id="last-modified">
Page last modified Tue, Jun 03 2008.
</div>
</body>
</html>