{-# LANGUAGE KindSignatures #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE PolyKinds #-}
{-# LANGUAGE TypeOperators #-}
module Data.Vinyl.Classes where
import Control.Applicative
import Data.Functor.Identity
-- | This class is a generalized, but non-pointed version of 'Applicative'. This
-- is useful for types which range over functors rather than sets.
class Apply (arr :: k -> k -> k) (f :: k -> *) where
(<<*>>) :: f (arr a b) -> f a -> f b
-- | To accumulate effects distributed over a data type, you 'dist' it.
class Dist t where
dist :: Applicative f => t f -> f (t Identity)
-- | If a record is homogenous, you can fold over it.
class FoldRec r a where
foldRec :: (a -> b -> b) -> b -> r -> b
-- | '(~>)' is a morphism between functors.
newtype (f ~> g) x = NT { runNT :: f x -> g x }