This looks like a reasonable way to get an element, but thinking ahead, you will probably want something both like "first" (which you have) and a corresponding "rest".
The problem is that which element you get from the "first" operation is nondetermistic in a set. Therefore, you have to either - pass the returned first element to the rest operation, or - accept that (set-union (set (set-item S)) (set-rest S)) is not the same as S A better design would be to use a different signature: get-one/rest : (forall (A) (Set A) -> (values A (Set A))) This performs the split "atomically", so it can ensure that the combination of "one" and "rest" is the same as the original set. Shriram _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/users
