On Thu, May 30, 2013 at 10:56 PM, Tony Morris <tmorris@tmorris.net> wrote:

class BinaryFunctor f where
bimap :: (a -> c) -> (b -> d) -> f a b -> f c d

mapFst = (`bimap id`)
mapSnd = bimap id

There's a bifunctors package with:

class Bifunctor f where

bimap :: ...

first :: a -> b -> f a c -> f b c

second :: b -> c -> f a b -> f a c