Data.Functor.Contravariant.Rep

Representable contravariant endofunctors over the category of Haskell types are isomorphic to (_ -> r) and resemble mappings to a fixed range.

Representable Contravariant Functors

class Contravariant f => Representable f where

A Contravariant functor f is Representable if tabulate and index witness an isomorphism to (_ -> Rep f).

tabulate . index ≡ id
index . tabulate ≡ id

Minimal complete definition

tabulate, index

Associated Types

type Rep f :: *

Methods

tabulate :: (a -> Rep f) -> f a

contramap f (tabulate g) = tabulate (g . f)

index :: f a -> a -> Rep f

contramapWithRep :: (b -> Either a (Rep f)) -> f a -> f b

contramapWithRep f p ≡ tabulate $ either (index p) id . f

Instances

Representable Predicate

Representable (Proxy *)

Representable (Op r)

(Representable f, Representable g) => Representable (Day f g)

(Representable f, Representable g) => Representable (Product f g)

Default definitions

contramapRep :: Representable f => (a -> b) -> f b -> f a