[Haskell-cafe] Functor instance derived from Monad

Frantisek Farka frantisek at farka.eu
Wed Feb 19 22:25:30 UTC 2014

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?




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