until -package:numeric-prelude -package:streaming -package:util -package:snap-core -package:basic-prelude package:free -is:exact -is:exact

Repeatedly run a computation until it produces a Just value. This can be useful when paired with a monad that has side effects. For example, we may have genId :: IO (Maybe Id) that uses a random number generator to allocate ids, but fails if it finds a collision. We can repeatedly run this with
retract (untilJust genId) :: IO Id