Data.Cofunctor

Cofunctor is a structure from category theory dual to Functor

A Functor is defined by the operation fmap:

fmap :: (a -> b) -> (f a -> f b)

This means that its dual must be defined by the following operation:

cofmap :: (b -> a) -> (f b -> f a)

Since beginning his investigations, the author of this package has discovered that this pattern is at least as commonly used as Functor. In fact, many ubiquitous Haskell types (e.g. [], Maybe, ((->) a) turn out to have a Cofunctor instance.

Documentation

class Cofunctor f where

Cofunctor is a structure from category theory dual to Functor

Methods

cofmap :: (b -> a) -> f b -> f a

Instances

Cofunctor []

Cofunctor IO

Cofunctor Maybe

Cofunctor ((->) a)

Cofunctor (Either e)

Cofunctor ((,) a)