[Haskell-cafe] Functor instance derived from Monad

Hi cafe, 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? Can you point out some leading marks to me? Thanks FF [1] http://www.haskell.org/haskellwiki/Functor-Applicative-Monad_Proposal