until -package:numeric-prelude -package:util -package:hedgehog -package:faktory -package:LambdaHack -package:distribution-opensuse -package:intro package:free

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