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<head><title>try -- catch an error</title>
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<div><a href="index.html" title="">Macaulay2Doc</a> > <a href="___The_sp__Macaulay2_splanguage.html" title="">The Macaulay2 language</a> > <a href="_error_sphandling.html" title="signalling and trapping errors">error handling</a> > <a href="_try.html" title="catch an error">try</a></div>
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<div><h1>try -- catch an error</h1>
<div class="single"><h2>Synopsis</h2>
<ul><li><div class="list"><dl class="element"><dt class="heading">Usage: </dt><dd class="value"><div><tt>try x then y else z</tt></div>
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<li><div class="single">Inputs:<ul><li><span><tt>x</tt>, code</span></li>
<li><span><tt>y</tt>, code</span></li>
<li><span><tt>z</tt>, code</span></li>
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<li><div class="single">Consequences:<ul><li>the code <tt>x</tt> is run; if no error or <a href="_alarm.html" title="set an alarm">alarm</a> occurs, then the code <tt>y</tt> is run; otherwise, the code <tt>z</tt> is run</li>
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<div class="single"><h2>Description</h2>
<div>The return value is the value returned by <tt>y</tt> or <tt>z</tt>, as the case may be.<p/>
The clause '<tt>then y</tt>' may be omitted, in which case the return value is the value returned by <tt>x</tt>, if there is no error or alarm.<p/>
The clauses '<tt>then y else z</tt>' may both be omitted, in which case the return value is the value returned by <tt>x</tt>, unless an error or alarm occurs, in which case <a href="_null.html" title="the unique member of the empty class">null</a> is returned.<p/>
The behavior of interrupts (other than alarms) is unaffected.<table class="examples"><tr><td><pre>i1 : apply(-3..3,i->try 1/i else infinity)
1 1 1 1
o1 = (- -, - -, -1, infinity, 1, -, -)
3 2 2 3
o1 : Sequence</pre>
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<div class="single"><h2>Caveat</h2>
<div>We will change the behavior of this function soon so that it will be possible to catch errors of a particular type. Meanwhile, users are recommended to use this function sparingly, if at all.</div>
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<div class="waystouse"><h2>For the programmer</h2>
<p>The object <a href="_try.html" title="catch an error">try</a> is <span>a <a href="___Keyword.html">keyword</a></span>.</p>
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