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Predicate setup_call_catcher_cleanup/4
Availability:built-in
Sourcesetup_call_catcher_cleanup(:Setup, :Goal, +Catcher, :Cleanup)
Similar to setup_call_cleanup(Setup, Goal, Cleanup) with additional information on the reason for calling Cleanup. Prior to calling Cleanup, Catcher unifies with the termination code (see below). If this unification fails, Cleanup is not called.
exit
Goal succeeded without leaving any choice points.
fail
Goal failed.
!
Goal succeeded with choice points and these are now discarded by the execution of a cut (or other pruning of the search tree such as if-then-else).
exception(Exception)
Goal raised the given Exception.
external_exception(Exception)
Goal succeeded with choice points and these are now discarded due to an exception. For example: 
?- setup_call_catcher_cleanup(true, (X=1;X=2),
                              Catcher, writeln(Catcher)),
   throw(ball).
external_exception(ball)
ERROR: Unhandled exception: Unknown message: ball

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Anne Ogborn said (2017-06-11T02:08:30):1 upvotes 1 0 downvotes
Picture of user Anne Ogborn.

I found the external_exception confusing at first.

What's going on - cleanup gets called only when Goal is 'done' - has exited with no more choice points, or in some other way is 'over' and will not be backtracked into.

?- setup_call_catcher_cleanup(true, ((X=1;X=2), writeln(X)), C, writeln(C)).
1
X = 1 ;  <waits for user>
2
exit
X = 2,
C = exit.