Accumulator.hs

{-# OPTIONS_GHC -fno-warn-orphans #-}

module Pandora.Paradigm.Inventory.Accumulator (Accumulator (..), Accumulated, gather) where

import Pandora.Pattern.Morphism.Straight (Straight (Straight))
import Pandora.Pattern.Semigroupoid ((.))
import Pandora.Pattern.Category (($), (#))
import Pandora.Pattern.Functor.Covariant (Covariant ((<$>)))
import Pandora.Pattern.Functor.Semimonoidal (Semimonoidal (mult))
import Pandora.Pattern.Functor.Bindable (Bindable ((=<<)))
import Pandora.Pattern.Functor.Monad (Monad)
import Pandora.Pattern.Object.Monoid (Monoid)
import Pandora.Pattern.Object.Semigroup (Semigroup ((+)))
import Pandora.Paradigm.Primary.Algebraic.Exponential (type (-->))
import Pandora.Paradigm.Primary.Algebraic.Product ((:*:) ((:*:)))
import Pandora.Paradigm.Primary.Algebraic (point)
import Pandora.Paradigm.Controlflow.Effect.Interpreted (Schematic, Interpreted (Primary, run, unite))
import Pandora.Paradigm.Controlflow.Effect.Transformer.Monadic (Monadic (wrap), (:>) (TM))
import Pandora.Paradigm.Controlflow.Effect.Adaptable (Adaptable (adapt))
import Pandora.Paradigm.Schemes.UT (UT (UT), type (<.:>))

newtype Accumulator e a = Accumulator (e :*: a)

instance Covariant (->) (->) (Accumulator e) where
	f <$> Accumulator x = Accumulator $ f <$> x

instance Semigroup e => Semimonoidal (-->) (:*:) (:*:) (Accumulator e) where
	mult = Straight $ \(x :*: y) -> Accumulator $ k # run x # run y where
		k ~(ex :*: x') ~(ey :*: y') = ex + ey :*: x' :*: y'

instance Semigroup e => Bindable (->) (Accumulator e) where
	f =<< Accumulator (e :*: x) = let e' :*: b = run $ f x in
		Accumulator $ e + e':*: b

type instance Schematic Monad (Accumulator e) = (<.:>) ((:*:) e)

instance Interpreted (->) (Accumulator e) where
	type Primary (Accumulator e) a = e :*: a
	run ~(Accumulator x) = x
	unite = Accumulator

instance Monoid e => Monadic (Accumulator e) where
	wrap = TM . UT . point . run

type Accumulated e t = Adaptable (Accumulator e) t

gather :: Accumulated e t => e -> t ()
gather x = adapt . Accumulator $ x :*: ()