Module

Data.Functor.Contravariant

#Contravariant 

class Contravariant f  where

A Contravariant functor can be seen as a way of changing the input type of a consumer of input, in contrast to the standard covariant Functor that can be seen as a way of changing the output type of a producer of output.

Contravariant instances should satisfy the following laws:

  • Identity cmap id = id
  • Composition cmap f <<< cmap g = cmap (g <<< f)

Members

  • cmap :: forall a b. (b -> a) -> f a -> f b

Instances

#(>$<)

Operator alias for Data.Functor.Contravariant.cmap (left-associative / precedence 4)

#cmapFlipped 

cmapFlipped :: forall a b f. Contravariant f => f a -> (b -> a) -> f b

cmapFlipped is cmap with its arguments reversed.

#(>#<)

Operator alias for Data.Functor.Contravariant.cmapFlipped (left-associative / precedence 4)

#coerce 

coerce :: forall f a b. Contravariant f => Functor f => f a -> f b

#imapC 

imapC :: forall f a b. Contravariant f => (a -> b) -> (b -> a) -> f a -> f b

As all Contravariant functors are also trivially Invariant, this function can be used as the imap implementation for any types that have an existing Contravariant instance.

Modules