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compare_instances(-Relationship, ?Term1, ?Term2)
Succeeds if Relationship is an atom describing the instance relationship
between Term1 and Term2.
- Relationship
- Variable or one of the atoms '<', '>', '='
- Term1
- An arbitrary term.
- Term2
- An arbitrary term.
Description
Succeeds if Relationship is unified with one of the three term
relationship symbols indicated by '<', '>', '=' where:
'<': Term1 is an instance of Term2.
'>': Term2 is an instance of Term1.
'=': Term1 is variant of Term2.
For the definition of instance and variant refer to instance/2 and
variant/2, respectively.
Modes and Determinism
- compare_instances(-, ?, ?) is det
Fail Conditions
Fails if none of the terms is an instance of the other
Examples
Success:
compare_instances(Rel,X,Y), Rel == '='.
compare_instances(=, [a,X], [a,Y]).
compare_instances(<, [a,b], [X,Y]).
compare_instances(<, [X], [X|Y]).
compare_instances(>, X, f(1,1)).
compare_instances(<, f(1,1), X).
Fail:
compare_instances(Rel, f(X), 1).
compare_instances(Rel, 1, f(X)).
compare_instances(<, X, a).
See Also
instance / 2, variant / 2