unless package:relude

unless :: Applicative f => Bool -> f () -> f ()

The reverse of when.

>>> do x <- getLine
unless (x == "hi") (putStrLn "hi!")
comingupwithexamplesisdifficult
hi!

>>> unless (pi > exp 1) Nothing
Just ()

Monadic version of unless. Reverse of whenM. Conditionally don't execute the provided action.

>>> unlessM (pure False) $ putTextLn "No text :("
No text :(

>>> unlessM (pure True) $ putTextLn "Yes text :)"