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<title>The PolyML.Exception structure</title>
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<H2><STRONG><font face="Arial, Helvetica, sans-serif">The PolyML.Exception structure</font></STRONG></H2>
<p>The <span class="identifier">Exception</span> sub-structure contains functions
that assist in tracing exceptions.</p>
<pre class="mainsig">structure Exception :
sig
val exceptionLocation : exn -> location option
val raiseWithLocation : exn * location -> 'a
val reraise : exn -> 'a
val traceException : (unit -> 'a) * (string list * exn -> 'a) -> 'a
val exception_trace : (unit -> 'a) -> 'a
end
</pre>
<p>Exception packets in Poly/ML normally contain information about the location,
typically the file name and line number, where the exception was raised. The
<span class="identifier">exceptionLocation</span> function extracts this information
if it is available. <span class="identifier">raiseWithLocation</span> can be
used to provide an explicit location and override the default. <span class="identifier">reraise</span>
is written in terms of <span class="identifier">exceptionLocation</span> and
<span class="identifier">raiseWithLocation</span>. It is typically used where
a function needs to catch an exception and wishes to raise it again after doing
some clean-up. Using the <span class="identifier">raise</span> instruction of
ML would set the location to be the clean-up code whereas <span class="identifier">reraise</span>
will retain the original location.</p>
<p><span class="identifier">exception_trace</span> and <span class="identifier">traceException</span>
can be used to produce information about the stack when an exception is raised.
They both take an argument that is a function to be executed and if an exception
is raised within the function that is not caught they produce information from
the stack. <span class="identifier">exception_trace</span> prints this to standard-output
whereas <span class="identifier">traceException</span> uses the second argument,
a function, and calls that with the list of function names and the exception
packet. Note that if the function being traced handles any exceptions the trace
will only show the stack from that point down.</p>
<p> </p>
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