Given values x and y return rule name if it is true

问题

This is my prolog file.

male(bob).
male(john).

female(betty).
female(dana).

father(bob, john).
father(bob, dana).
mother(betty, john).
mother(betty, dana).

husband(X, Y) :- male(X), mother(Y, Z), father(X, Z).
wife(X, Y) :- female(X), father(Y, Z), mother(X, Z).
son(X, Y) :- male(X), mother(Y, X);female(X), father(Y, X).
daughter(X, Y) :- female(X), mother(Y, X);female(X), father(Y, X).
sister(X, Y) :- female(X), mother(Z, X), mother(Z, Y), X \= Y.
brother(X, Y) :- male(X), mother(Z, X), mother(Z, Y), X \= Y.

I want a name of rule if it returns true for any value x or y. Let's say x = betty and y = john.

mother(betty, john). <- this will meet so my rule should return 'mother'. Similarly if any other rule or fact meets true for some value x, y it should return that rule name.

How can I achieve something like that?

回答1:

could be easy as

query_family(P1, P2, P) :-
    % current_predicate(P/2),
    member(P, [father, mother, husband, wife, son, daughter, sister, brother]),
    call(P, P1, P2).

that gives

?- query_family(betty, john, R).
R = mother ;
false.

?- query_family(betty, X, R).
X = john,
R = mother ;
X = dana,
R = mother ;
X = bob,
R = wife ;
X = bob,
R = wife ;
false.

the semicolon after the answer means 'gimme next'

回答2:

$ swipl
?- ['facts'].
?- setof( Functor,
          Term^(member(Functor, [father, mother, husband, wife, son, daughter, sister, brother]),
           Term =.. [Functor, betty, john],
           once(Term)),
          Answer).

Answer = [mother].
?-

If you want to avoid having to specify the list of functors of interest, you could use current_predicate(F/2).

来源：https://stackoverflow.com/questions/32770849/given-values-x-and-y-return-rule-name-if-it-is-true

标签

prolog