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documment alarm/3 a bit better

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vsc 2001-09-19 19:15:04 +00:00
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docs/yap.tex
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@ -5405,6 +5405,25 @@ In this case after @code{10} seconds our @code{loop} is interrupted,
@code{ball} is thrown, and the handler writes @code{Quota exhausted}.
Execution then continues from the handler.
Note that in this case @code{loop/0} always executes until the alarm is
sent. Often, the code you are executing succeeds or fails before the
alarm is actually delivered. In this case, you probably want to disable
the alarm when you leave the procedure. The next procedure does exactly so:
@example
once_with_alarm(Time,Goal,DoOnAlarm) :-
catch(execute_once_with_alarm(Time, Goal), alarm, DoOnAlarm).
execute_once_with_alarm(Time, Goal) :-
alarm(Time, alarm, _),
( call(Goal) -> alarm(0, alarm, _) ; alarm(0, alarm, _)).
@end example
The procedure has three arguments: the @var{Time} before the alarm is
sent; the @var{Goal} to execute; and the goal @var{DoOnAlarm} to execute
if the alarm is sent. It uses @code{catch/3} to handle the case the
@code{alarm} is sent. Then it starts the alarm, calls the goal
@var{Goal}, and disables the alarm on success or failure.
@end table
@node Term Modification, Profiling, OS, Top