module Pandora.Paradigm.Primary.Functor.Delta where

import Pandora.Pattern.Category ((.))
import Pandora.Pattern.Functor.Covariant (Covariant ((<$>)))
import Pandora.Pattern.Functor.Pointable (Pointable (point))
import Pandora.Pattern.Functor.Applicative (Applicative ((<*>)))
import Pandora.Pattern.Functor.Distributive (Distributive ((>>-)))
import Pandora.Pattern.Functor.Traversable (Traversable ((->>)))
import Pandora.Pattern.Functor.Representable (Representable (Representation, (<#>), tabulate))
import Pandora.Pattern.Object.Setoid (Setoid ((==)))
import Pandora.Pattern.Object.Semigroup (Semigroup ((+)))
import Pandora.Pattern.Object.Ringoid (Ringoid ((*)))
import Pandora.Paradigm.Primary.Object.Boolean (Boolean (True, False))

infixr 1 :^:

data Delta a = a :^: a

instance Covariant Delta where
	f <$> (x :^: y) = f x :^: f y

instance Pointable Delta where
	point x = x :^: x

instance Applicative Delta where
	(f :^: g) <*> (x :^: y) = f x :^: g y

instance Distributive Delta where
	t >>- f = (True <#>) . f <$> t :^: (False <#>) . f <$> t

instance Traversable Delta where
	(x :^: y) ->> f = (:^:) <$> f x <*> f y

instance Representable Delta where
	type Representation Delta = Boolean
	True <#> (x :^: _) = x
	False <#> (_ :^: y) = y
	tabulate f = f True :^: f False

instance Setoid a => Setoid (Delta a) where
	(x :^: y) == (x' :^: y') = (x == x') * (y == y')

instance Semigroup a => Semigroup (Delta a) where
	(x :^: y) + (x' :^: y') = (x + x') :^: (y + y')

instance Ringoid a => Ringoid (Delta a) where
	(x :^: y) * (x' :^: y') = (x * x') :^: (y * y')