# Pastebin KL6njlbt
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE PolyKinds #-}
{-# LANGUAGE TypeFamilies #-}

import Data.Kind (Type)
import Data.Map (Map)
import qualified Data.Map as Map
import Data.Set (Set)

data Pet = Cat | Dog | Horse

data PetState a where
  Cats :: Map String String -> PetState 'Cat
  Dogs :: [Int] -> PetState 'Dog
  Horses :: Set Bool -> PetState 'Horse

-- | From package "some".
data Some f where
  Some :: f a -> Some f

catState :: Some PetState
catState = Some $ Cats (Map.fromList [("meow", "meow")])

dogState :: Some PetState
dogState = Some $ Dogs [1, 2, 3]

horsesState :: Some PetState
horsesState = Some $ Horses mempty

processState :: Some PetState -> IO (Some PetState)
processState (Some st) = case st of
  Cats m -> _
  Dogs is -> _
  Horses s -> _