Compile time optimization of goals

The following code produces a choice point when calling foo(_,0).

foo(A,0):-
	( var(A) -> true ; true ).
foo(A,3):-
	true.



where as


foo(A,0):-
        true,
	( var(A) -> true ; true ).
foo(A,3):-
	true.


Correctly infers that the first clause is the only matching clause. (Note the supurflous 'true' in first clause)

Any ideas?

Andrew