->/2(arrow)
Module: builtins
->/2 — if-then, and if-then-else
FORMS
Condition -> TrueGoal
Condition -> TrueGoal ; FalseGoal
DESCRIPTION
If Condition succeeds, then TrueGoal will be executed. If-then implicitly cuts the Condition. Cuts that occur within Condition or TrueGoal will cut back to the head of the parent clause. If Condition fails, then the call to ->/2 fails. The second form, results from the interaction between ;/2 and
->/2 because
Condition -> TrueGoal ; FalseGoal
is actually executed as :
( Condition -> TrueGoal) ; FalseGoal
In this case, FalseGoal will be executed instead of TrueGoal when Condition fails.
Cuts occurring in
-
Condition -
TrueGoal -
FalseGoal
cut back to the head of the parent clause.
EXAMPLES
?- true->write(a).
a
yes.
?- fail->write(a).
no.
?- fail->write(a);write(b).
b
yes.