On Wed, Feb 19, 2014 at 5:25 PM, Frantisek Farka wrote:

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?

There is not, because the need for UndecidableInstances there is warning you that this is perilous. I thought some of the discussion behind the AMP touched on why this was not considered as a solution? -- brandon s allbery kf8nh sine nomine associates allbery.b@gmail.com ballbery@sinenomine.net unix, openafs, kerberos, infrastructure, xmonad http://sinenomine.net