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<?xml version="1.0" encoding="latin1" ?>
<!DOCTYPE chapter SYSTEM "chapter.dtd">
<chapter>
<header>
<copyright>
<year>2003</year><year>2009</year>
<holder>Ericsson AB. All Rights Reserved.</holder>
</copyright>
<legalnotice>
The contents of this file are subject to the Erlang Public License,
Version 1.1, (the "License"); you may not use this file except in
compliance with the License. You should have received a copy of the
Erlang Public License along with this software. If not, it can be
retrieved online at http://www.erlang.org/.
Software distributed under the License is distributed on an "AS IS"
basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
the License for the specific language governing rights and limitations
under the License.
</legalnotice>
<title>Pattern Matching</title>
<prepared></prepared>
<docno></docno>
<date></date>
<rev></rev>
<file>patterns.xml</file>
</header>
<section>
<title>Pattern Matching</title>
<p>Variables are bound to values through the <em>pattern matching</em> mechanism. Pattern matching occurs when
evaluating a function call, <c>case</c>- <c>receive</c>-
<c>try</c>- expressions and match operator (=) expressions.</p>
<p>In a pattern matching, a left-hand side
<seealso marker="expressions#pattern">pattern</seealso> is matched
against a right-hand side
<seealso marker="expressions#term">term</seealso>. If
the matching succeeds, any unbound variables in the pattern
become bound. If the matching fails, a run-time error occurs.</p>
<p>Examples:</p>
<pre>
1> <input>X.</input>
** 1: variable 'X' is unbound **
2> <input>X = 2.</input>
2
3> <input>X + 1.</input>
3
4> <input>{X, Y} = {1, 2}.</input>
** exception error: no match of right hand side value {1,2}
5> <input>{X, Y} = {2, 3}.</input>
{2,3}
6> <input>Y.</input>
3</pre>
</section>
</chapter>
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