Set.hs

{-# LANGUAGE AllowAmbiguousTypes #-}
module Pandora.Paradigm.Structure.Interface.Set where

import Pandora.Core.Functor (type (>))
import Pandora.Pattern.Semigroupoid ((.))
import Pandora.Pattern.Category ((<--), (<---))
import Pandora.Pattern.Kernel (constant)
import Pandora.Pattern.Functor.Traversable (Traversable ((<<-)))
import Pandora.Pattern.Object.Setoid (Setoid ((!=)))
import Pandora.Pattern.Object.Semigroup ((+))
import Pandora.Pattern.Object.Quasiring (one)
import Pandora.Paradigm.Algebraic ()
import Pandora.Paradigm.Algebraic.Product (attached)
import Pandora.Paradigm.Algebraic.Exponential ((%))
import Pandora.Paradigm.Primary.Functor.Convergence (Convergence (Convergence))
import Pandora.Paradigm.Primary.Functor.Maybe (Maybe (Nothing))
import Pandora.Paradigm.Primary.Functor.Predicate (Predicate, equate)
import Pandora.Paradigm.Primary.Object.Boolean (Boolean)
import Pandora.Paradigm.Primary.Object.Numerator (Numerator (Zero))
import Pandora.Paradigm.Schemes.T_U (type (<:.:>))
import Pandora.Paradigm.Inventory.Ability.Modifiable (modify)
import Pandora.Paradigm.Structure.Ability.Morphable (Morphable (Morphing), Morph (Find), find)
import Pandora.Paradigm.Inventory.Some.State (State)
import Pandora.Paradigm.Controlflow.Effect ((<~~))

type Set t f a = (Traversable (->) (->) t, Setoid a, Setoid (t a), Morphable (Find f) t)

subset :: forall t f a . (Set t f a, Morphing (Find f) t ~ (Predicate <:.:> Maybe > (->))) => Convergence Boolean > t a
subset = Convergence <-- \s ss -> Nothing != ((find @f @t @Maybe % s) . equate <<- ss)

cardinality :: Traversable (->) (->) t => t a -> Numerator
cardinality s = attached <--- constant (modify @State (+ one)) <<- s <~~ Zero