';'(If-then-else)/2

causes that one goal implicates alternative goals.

+IfGoal -> +ThenGoal; +ElseGoal
;((IfGoal-> +ThenGoal), +ElseGoal)

If IfGoal succeeds then ThenGoal will be executed.
If IfGoal fails ElseGoal will be executed.
'->'/2 succeeds if either ThenGoal or ElseGoal succeeds.

There are two significant differences to ','/2:

';'/2 is a predefined infix-operator with priority 1100 which is right-associative,

'->'/2 is a predefined infix-operator with priority 1050 which is right-associative (see also current_op/3).

Arguments 

IfGoal                 goal
ThenGoal               goal
ElseGoal               goal

Examples

Day=sunny -> Weather=sunshine; Weather=raining. Succeeds.
X=b, X=a -> write(a); write(b). Succeeds with substitution X <- b
and outputs to the current outputstream 'b'.

Standard

This predicate is part of the ISO-Prolog Standard.

See also

abort/0, break/0, call/1, fcall/1, catch/3, ','(conjunction)/2, '!'(cut)/0, ';'(disjunction)/2, fail/0, true/0, halt/0/1, '->'(if-then)/2, '\+'(not provable)/1, once/1, repeat/0, throw/1.

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