when reading the Functor-Applicative-Monad proposal [1] on Haskell
wiki I remembered that I have seen instance similar to

    instance (Monad m) => Functor m where
        fmap f a = a >>= \x -> return $ f x

with FlexibleInstances and UndecidableInstances language extensions.
But I cannot remember where it was nor can I find any useful reference.
Is there some library in Hackage with this and similar instances?