acme-cofunctor
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A `Cofunctor` is a structure from category theory dual to `Functor`.
We all know that 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.