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<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE chapter SYSTEM "chapter.dtd">
<chapter>
<header>
<copyright>
<year>2003</year><year>2016</year>
<holder>Ericsson AB. All Rights Reserved.</holder>
</copyright>
<legalnotice>
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions 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><em>Examples:</em></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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