module Control.Functor.Extras where
import Control.Monad
infixr 0 :~>, :~~>
type Dist f g = forall a. f (g a) -> g (f a)
type f :~> g = forall a. f a -> g a
type Natural f g = f :~> g
type f :~~> g = forall a b. f a b -> g a b
type Dinatural f g = forall a. f a a -> g a a
class PostFold m f where
postFold :: f (m (f a)) -> m (f a)
class PostUnfold w f where
postUnfold :: w (f a) -> f (w (f a))
class PreFold f m where
preFold :: f (m (f a)) -> f (m a)
class PreUnfold f w where
preUnfold :: f (w a) -> f (w (f a))
class Distributes f g where
dist :: f (g a) -> g (f a)
class Functor f => FunctorZero f where
fzero :: f a
class FunctorZero f => FunctorPlus f where
fplus :: f a -> f a -> f a
class Functor f => FunctorSplit f where
fsplit :: f a -> (f a, f a)
instance FunctorZero Maybe where
fzero = Nothing
instance FunctorPlus Maybe where
fplus = mplus
instance FunctorZero [] where
fzero = []
instance FunctorPlus [] where
fplus = (++)