until -package:numeric-prelude -package:streaming -package:foundation -package:hosc -package:protolude -package:hledger-web 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