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