Conclusion.hs

module Pandora.Paradigm.Basis.Conclusion (Conclusion (..), conclusion, fail) where

import Pandora.Core.Morphism ((.), ($))
import Pandora.Paradigm.Junction.Transformer (T (T, t), type (:!:))
import Pandora.Pattern.Functor.Covariant (Covariant ((<$>)))
import Pandora.Pattern.Functor.Pointable (Pointable (point))
import Pandora.Pattern.Functor.Alternative (Alternative ((<+>)))
import Pandora.Pattern.Functor.Applicative (Applicative ((<*>)))
import Pandora.Pattern.Functor.Traversable (Traversable ((->>)))
import Pandora.Pattern.Functor.Bindable (Bindable ((>>=)))
import Pandora.Pattern.Functor.Monad (Monad)
import Pandora.Pattern.Object.Setoid (Setoid ((==)), Boolean (False))
import Pandora.Pattern.Object.Chain (Chain ((<=>)), Ordering (Less, Greater))
import Pandora.Pattern.Object.Semigroup (Semigroup ((+)))

data Conclusion e a = Failure e | Success a

instance Covariant (Conclusion e) where
	f <$> Success x = Success $ f x
	_ <$> Failure y = Failure y

instance Pointable (Conclusion e) where
	point = Success

instance Applicative (Conclusion e) where
	Success f <*> x = f <$> x
	Failure y <*> _ = Failure y

instance Alternative (Conclusion e) where
	Failure _ <+> x = x
	Success x <+> _ = Success x

instance Traversable (Conclusion e) where
	Failure y ->> _ = point $ Failure y
	Success x ->> f = Success <$> f x

instance Bindable (Conclusion e) where
	Success x >>= f = f x
	Failure y >>= _ = Failure y

instance Monad (Conclusion e) where

instance (Pointable t, Bindable t) => Bindable (Conclusion e :!: t) where
	T x >>= f = T $ x >>= conclusion (point . Failure) (t . f)

instance Monad t => Monad (Conclusion e :!: t) where

instance (Setoid e, Setoid a) => Setoid (Conclusion e a) where
	Success x == Success y = x == y
	Failure x == Failure y = x == y
	_ == _ = False

instance (Chain e, Chain a) => Chain (Conclusion e a) where
	Success x <=> Success y = x <=> y
	Failure x <=> Failure y = x <=> y
	Failure _ <=> Success _ = Less
	Success _ <=> Failure _ = Greater

instance (Semigroup e, Semigroup a) => Semigroup (Conclusion e a) where
	Success x + Success y = Success $ x + y
	Failure x + Failure y = Failure $ x + y
	Failure _ + Success y = Success y
	Success x + Failure _ = Success x

conclusion :: (e -> r) -> (a -> r) -> Conclusion e a -> r
conclusion f _ (Failure x) = f x
conclusion _ s (Success x) = s x

fail :: (e -> r) -> Conclusion e a -> Conclusion r a
fail f (Failure x) = Failure $ f x
fail _ (Success y) = Success y