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instance(?Instance, ?Term)
Succeeds if Instance is an instance of Term.
- Instance
- An arbitrary term.
- Term
- An arbitrary term.
Description
Succeeds if it is possible to find an instantiation of free variables in
Term such that Term and Instance are equal. The result is undefined if
Term and Instance share variables. Note that no unification actually
occurs.
Attributed variables are handled via the attribute's compare_instances
handler. In particular, domain variables should be handled correctly.
Modes and Determinism
- instance(?, ?) is semidet
Fail Conditions
Fails if Instance is not an instance of Term.
Examples
Success:
instance(atom,X).
instance(f(a,b),X).
instance(f(a,b),f(X,Y)).
instance(f(a,X),f(Y,X)).
instance(f(a,X),f(X,Y)).
instance(f(X,Y),f(Y,X)).
instance([a,b,c],[A,B,C]).
instance([a,f(1,b,X),Y|Z],T).
X::1..5, instance(3,X).
X::2..4, Y::1..5, instance(X,Y).
Fail:
instance(f(a,b),f(X,X)).
instance(X,a).
X::2..4, Y::1..5, instance(Y,X).
See Also
compare_instances / 3, prune_instances / 2, variant / 2