Universum.Bool.Guard

Documentation

guardM :: MonadPlus m => m Bool -> m ()

Monadic version of guard. Occasionally useful. Here some complex but real-life example: @ findSomePath :: IO (Maybe FilePath)

somePath :: MaybeT IO FilePath somePath = do path <- MaybeT findSomePath guardM $ liftIO $ doesDirectoryExist path return path @

ifM :: Monad m => m Bool -> m a -> m a -> m a

Monadic version of if-then-else.

>>> ifM (pure True) (putText "True text") (putText "False text")
True text

unlessM :: Monad m => m Bool -> m () -> m ()

Monadic version of unless.

>>> unlessM (pure False) $ putText "No text :("
No text :(
>>> unlessM (pure True) $ putText "Yes text :)"

whenM :: Monad m => m Bool -> m () -> m ()

Monadic version of when.

>>> whenM (pure False) $ putText "No text :("
>>> whenM (pure True)  $ putText "Yes text :)"
Yes text :)
>>> whenM (Just True) (pure ())
Just ()
>>> whenM (Just False) (pure ())
Just ()
>>> whenM Nothing (pure ())
Nothing