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<h1 class="title">Tuple Patterns</h1>
<p>Tuple patterns only match tuples. They are written as simply a comma
separated list of patterns within parenthesis:</p>
<pre class="literal-block">
(1, $x, "buckle my shoe")
</pre>
<p>You can also write a <em>rest</em> pattern variable at the end using an asterisk
(<tt class="docutils literal">*</tt>):</p>
<pre class="literal-block">
($a, fie, $b, *$c)
</pre>
<p>This will match the rest of the items in the data value that the tuple pattern
is matched to. Note that the <em>rest</em> pattern variable is <em>always</em> bound to a
tuple.</p>
<p>Examples:</p>
<blockquote>
<ul class="simple">
<li>matching <tt class="docutils literal">(1, $x, "buckle my shoe")</tt> to <tt class="docutils literal">(1, 2, "buckle my shoe")</tt>
matches, binding <tt class="docutils literal">$x</tt> to 2.</li>
<li>matching <tt class="docutils literal">(1, $x, "buckle my shoe")</tt> to <tt class="docutils literal">(1, 2, "buckle my belt")</tt>
does not match because the third pattern within the tuple pattern fails
to match the third value in the matched tuple.</li>
<li>matching <tt class="docutils literal">($a, fie, $b, *$c)</tt> to <tt class="docutils literal">(fee, fie, foe, fum)</tt>
matches, binding <tt class="docutils literal">$a</tt> to <tt class="docutils literal">fee</tt>, <tt class="docutils literal">$b</tt> to <tt class="docutils literal">foe</tt> and <tt class="docutils literal">$c</tt> to
<tt class="docutils literal">(fum)</tt>.</li>
<li>matching <tt class="docutils literal">($a, fie, $b, *$c)</tt> to <tt class="docutils literal">(fee, fie, foe)</tt>
matches, binding <tt class="docutils literal">$a</tt> to <tt class="docutils literal">fee</tt>, <tt class="docutils literal">$b</tt> to <tt class="docutils literal">foe</tt> and <tt class="docutils literal">$c</tt> to
<tt class="docutils literal">()</tt>.</li>
<li>matching <tt class="docutils literal">($a, fie, $b, *$c)</tt> to <tt class="docutils literal">(fee, fie)</tt> does not match because
the data value has to have a length of at least three.</li>
</ul>
</blockquote>
<div class="hint">
<p class="first admonition-title">Hint</p>
<p class="last">You can use <tt class="docutils literal"><span class="pre">(*$foo)</span></tt> to only match a tuple. It will bind <tt class="docutils literal">$foo</tt> to
the entire tuple, but will fail to match any other data type.</p>
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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>
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Copyright © 2007-2009 Bruce Frederiksen
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