An example of using wrap_predicate/4 to compute GCD:

:- wrap_predicate(gcd(A,B,Gcd), gcd_wrap, W, gcd_wrap(W, A, B, Gcd)).

gcd(X, Y, Gcd), X < Y => gcd(X, Y-X, Gcd).
gcd(X, Y, Gcd), X > Y => gcd(Y, X-Y, Gcd).
gcd(X, _, Gcd) => Gcd = X.

gcd_wrap(call(Closure), X, Y, Gcd) :-
  functor(Closure, ClosureBlob, 3),
  X_eval is X,
  Y_eval is Y,
  call(ClosureBlob, X_eval, Y_eval, G),
  Gcd is G.