catch/3

snatches errors generated during the execution of a goal.

catch(+Goal, ?CatchMask, ?RecoverGoal)

catch/3 snatches errors which are unifiable by CatchMask and generated during the execution of Goal, stops the execution of Goal and executes RecoverGoal. An error can be generated either in the program (see throw/1) or by the processor.

Arguments 

Goal                   goal
CatchMask              term
RecoverGoal            goal

Examples

X=throw(write('ok')), catch(X,Y,write('error')). Succeeds with substitution X <- throw(write(ok)), Y <- write(ok) and executes write(error).
X=write(ok), catch(X,Y,write(error)). Succeeds with substitution X <- write(ok), Y <- _735 and executes write(ok)

Standard

This predicate is part of the ISO-Prolog Standard.

See also

abort/0, break/0, call/1, fcall/1, ','(conjunction)/2, '!'(cut)/0, ';'(disjunction)/2, fail/0, true/0, halt/0/1, '->'(if-then)/2, ';'(if-then-else)/2, '\+'(not provable)/1, once/1, repeat/0, throw/1.

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