# [racket] Take an element from a set

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