In opposition of Functor as super-class of Monad

Isaac Dupree ml at
Wed Jan 5 19:58:16 CET 2011

Tony, you're missing the point... Alexey isn't making a complete patch 
to GHC/base libraries, just a hacky-looking demonstration.  Alexey is 
saying that in a class hierarchy (such as if Functor => Monad were a 
hierarchy, or for that matter "XFunctor"=>"XMonad" or Eq => Ord), it is 
still possible to define the superclass functions (fmap) in terms of the 
subclass functions (return and >>=) (such as writing a functor instance 
in which "fmap f m = m >>= (return . f)").  This has always been true in 
Haskell, it just might not have been obvious.

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