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<head><title>on -- trace a function each time it's run</title>
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<div><h1>on -- trace a function each time it's run</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>on f</tt></div>
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<li><div class="single">Inputs:<ul><li><span><tt>f</tt>, <span>a <a href="___Function.html">function</a></span></span></li>
<li><span><tt>f</tt></span></li>
<li><span> is an anonymous function (not assigned to a global variable)</span></li>
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<li><div class="single">Outputs:<ul><li><span><span>a <a href="___Function.html">function</a></span>, a new function that returns the same values that <tt>f</tt> would have returned, but has a few side effects useful for debugging: upon entry, it prints its arguments, and upon exit it prints its return values. The display includes the name of <tt>f</tt>, a sequence number in parentheses that tells how many times the function has been called, and a number in brackets that gives the nesting (recursion) depth. The sequence number allows the entry and exit reports to be connected.</span></li>
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<li><div class="single"><a href="_using_spfunctions_spwith_spoptional_spinputs.html">Optional inputs</a>:<ul><li><span><tt>CallLimit => </tt><span><span>an <a href="___Z__Z.html">integer</a></span>, <span>default value 100000</span>, the maximum number of times to permit the function f to be called</span></span></li>
<li><span><tt>Name => </tt><span><span>a <a href="___String.html">string</a></span>, <span>default value null</span>, the name to use for the function, in case </span></span></li>
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<div class="single"><h2>Description</h2>
<div><p>Ideally, this function would replace <tt>f</tt>, i.e., we would write <tt>f = on f</tt>. Unfortunately, all the pre-installed system functions are write-protected.</p>
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