gistfile1.txt

{-# Language
Rank2Types,
GADTs,
DataKinds,
PolyKinds,
TypeFamilies,
DatatypeContexts,
MultiParamTypeClasses,
UndecidableInstances,
UndecidableSuperClasses
#-}

import Data.Kind
import GHC.Exts

data Stream s a = Stream (a,s)

data Linear s a = Linear (a,s) | End a

data Stack  s a = Stack  (a,s) | Empty

data Basecase s a where
 Stream' :: Stream s a -> Basecase s a
 Linear' :: Linear s a -> Basecase s a
 Stack'  :: Stack  s a -> Basecase s a

data Proxy k = Proxy

type State   s a = s -> Basecase s a

type CoState s a = Basecase s a -> s

class Get f where
 get :: CoState (f a) a

class Set f where
 set :: State (f a) a

data (Get f,Set f) => Zipper f a = Zipper [a] (f a)