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<head><title>break -- break from a loop</title>
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<div><h1>break -- break from a loop</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>break x</tt></div>
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<li><div class="single">Consequences:<ul><li>this interrupts execution of a loop controlled by <a href="_for.html" title="for loops">for</a>, <a href="_while.html" title="while loops">while</a>, <a href="_apply.html" title="apply a function to each element">apply</a>, or <a href="_scan.html" title="apply a function to each element">scan</a>, returning <tt>x</tt> as the value of the loop currently being evaluated.</li>
<li>Alternatively, as a top level command in the debugger, it leaves the debugger, returning the user to top level.</li>
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<div class="single"><h2>Description</h2>
<div><p>Omitting <tt>x</tt>, and executing <tt>break</tt>, interrupts execution of a loop as above, returning <a href="_null.html" title="the unique member of the empty class">null</a> as the value of the function currently being evaluated, except, in the case of a <a href="_for.html" title="for loops">for</a> loop or a <a href="_while.html" title="while loops">while</a> loop with a list clause, the list accumulated so far is returned as the value.</p>
<table class="examples"><tr><td><pre>i1 : for i from 1 to 10 do if i == 7 then break hi
o1 = hi
o1 : Symbol</pre>
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<p>Warning: trying to break from a loop controlled by <a href="_table.html" title="make a table (nested list)">table</a> will probably not do what you expect, since <a href="_table.html" title="make a table (nested list)">table</a> is implemented by two nested loops controlled by <a href="_apply.html" title="apply a function to each element">apply</a>, and only the inner one will stop, as in the following example.</p>
<table class="examples"><tr><td><pre>i2 : table(3,3,(i,j) -> if i == 1 then break 3 else hi)
o2 = {{hi, hi, hi}, 3, {hi, hi, hi}}
o2 : List</pre>
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<tr><td><pre>i3 : table(3,3,(i,j) -> if j == 1 then break 3 else hi)
o3 = {3, 3, 3}
o3 : List</pre>
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<p>Here is an example as a debugger command.</p>
<table class="examples"><tr><td><pre>i4 : load "Macaulay2Doc/demo1.m2"</pre>
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<tr><td><pre>i5 : g 2
/builddir/build/BUILD/Macaulay2-1.3.1-r10737/Macaulay2/packages/Macaulay2Doc/demo1.m2:8:12:(3):[2]: error: division by zero
/builddir/build/BUILD/Macaulay2-1.3.1-r10737/Macaulay2/packages/Macaulay2Doc/demo1.m2:8:12:(3):[2]: --entering debugger (type help to see debugger commands)
/builddir/build/BUILD/Macaulay2-1.3.1-r10737/Macaulay2/packages/Macaulay2Doc/demo1.m2:8:11-8:13: --source code:
b := 1/x;</pre>
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<tr><td><pre>ii6 : x
oo6 = 0</pre>
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<tr><td><pre>ii7 : break</pre>
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<tr><td><pre>i8 : g 3
7
o8 = -
2
o8 : QQ</pre>
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<div class="single"><h2>See also</h2>
<ul><li><span><a href="_apply.html" title="apply a function to each element">apply</a> -- apply a function to each element</span></li>
<li><span><a href="_scan.html" title="apply a function to each element">scan</a> -- apply a function to each element</span></li>
<li><span><a href="_while.html" title="while loops">while</a> -- while loops</span></li>
<li><span><a href="_for.html" title="for loops">for</a> -- for loops</span></li>
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<div class="waystouse"><h2>For the programmer</h2>
<p>The object <a href="_break.html" title="break from a loop">break</a> is <span>a <a href="___Keyword.html">keyword</a></span>.</p>
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