[Haskell-cafe] General Functor and Traversable

M Farkas-Dyck strake888 at gmail.com
Tue Aug 25 03:18:52 UTC 2015

Consider this:

class (Category c, Category d) => Functor c d f where
    map :: c a b -> d (f a) (f b)

Clearly mapM of Traversable is simply map :: Kleisli m a b -> Kleisli m (f a) (f b). But what is traverse? can it be so defined? I am thinking no, as Kleisli composition is not defined in general, but I know very little category theory so I may easily be wrong.

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