Satisfying a Unary Prolog predicate

Question

In order to write a procedure satisfy(P,L) which returns the list L of all terms X such that the unary predicate P(X) succeeds. I have attempted the following:

satisfy(P,L):- findall(X,call(P(X)),L).

Am I on the right track or I have gone completely off?

Answer 1

You can do it using builtin predicate call/2:

satisfy(P, L):- findall(X, call(P, X), L).

Answer 2

Not quite. You're on the right track using findall/3, but you can't construct a goal to call by simply stating P(X). You need to construct the term using =../2 instead.