YonedaTransformations.hs

{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE MultiParamTypeClasses #-}

import           Control.Transformation
import           Data.Functor.Yoneda
import           Data.Functor.Coyoneda

instance Transformation ((->) a) g (Yoneda g a) where
  Yoneda y # a = y a

instance Functor g => Transformation ((->) a) g (Coyoneda g a) where
  Coyoneda f fb # x = fmap (x . f) fb