11.3.247 when/2

Synopsis

when(+Condition,+Goal)

Blocks Goal until the Condition is true.

Arguments

Condition

callable, must be nonvar and one of:

nonvar(X)

False until X is nonvar.

ground(X)

False until X is ground.

?=(X,Y)

False while dif(X,Y) would block.

Condition,Condition

True if both conditions are true.

Condition;Condition

True if at least one condition is true.

:Goal

callable, must be nonvar

Backtracking

Depends on Goal.

Examples

     | ?- when(((nonvar(X);?=(X,Y)),ground(T)), process(X,Y,T)).

Exceptions

Call errors (see ref-sem-exc).

See Also

ref-sem-sec.