mirror of
https://github.com/idris-lang/Idris2.git
synced 2024-12-22 19:21:39 +03:00
51 lines
1.5 KiB
Idris
51 lines
1.5 KiB
Idris
module Data.Contravariant
|
|
|
|
%default total
|
|
|
|
infixl 4 >$, >$<, >&<, $<
|
|
|
|
||| Contravariant functors
|
|
public export
|
|
interface Contravariant (0 f : Type -> Type) where
|
|
contramap : (a -> b) -> f b -> f a
|
|
|
|
(>$) : b -> f b -> f a
|
|
v >$ fb = contramap (const v) fb
|
|
|
|
||| If `f` is both `Functor` and `Contravariant` then by the time you factor in the
|
|
||| laws of each of those classes, it can't actually use its argument in any
|
|
||| meaningful capacity.
|
|
public export %inline
|
|
phantom : Contravariant f => Functor f => f a -> f b
|
|
phantom fa = () >$ (fa $> ())
|
|
|
|
||| This is an infix alias for `contramap`.
|
|
public export %inline
|
|
(>$<) : Contravariant f => (a -> b) -> f b -> f a
|
|
(>$<) = contramap
|
|
|
|
||| This is an infix version of `contramap` with the arguments flipped.
|
|
public export %inline
|
|
(>&<) : Contravariant f => f b -> (a -> b) -> f a
|
|
(>&<) = flip contramap
|
|
|
|
||| This is `>$` with its arguments flipped.
|
|
public export %inline
|
|
($<) : Contravariant f => f b -> b -> f a
|
|
($<) = flip (>$)
|
|
|
|
||| Composition of `Contravariant` is a `Functor`.
|
|
public export
|
|
[Compose] (Contravariant f, Contravariant g) => Functor (f . g) where
|
|
map = contramap . contramap
|
|
|
|
||| Composition of a `Functor` and a `Contravariant` is a `Contravariant`.
|
|
public export
|
|
[ComposeFC] (Functor f, Contravariant g) => Contravariant (f . g) where
|
|
contramap = map . contramap
|
|
|
|
||| Composition of a `Contravariant` and a `Functor` is a `Contravariant`.
|
|
public export
|
|
[ComposeCF] (Contravariant f, Functor g) => Contravariant (f . g) where
|
|
contramap = contramap . map
|