dynamic predicate

[masum7]

Hello
I want to call a clause that can assert a dynamic predicate.

For example:
------------------
caller(X, Y, Z):-
        assert(X(Y, Z)).
------------------
Then if I call this:

?- caller(on(a, b))

then I wish a predicate on(a, b) will be asserted. Please help me with the idea.