Signature of Control.Monad when and unless

I understand why the normal signature is: when :: Monad m => Bool -> m () -> m () unless :: Monad m => Bool -> m () -> m () But why isn't there also: when_ :: Monad m => Bool -> m a -> m () unless_ :: Monad m => Bool -> m a -> m () That is, I agree that results shouldn't be discarded "by default", but it should be easy to get rid of them if they are unneeded. Thanks, Oren Ben-Kiki