*temp*.txt

{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE PolyKinds #-}
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE KindSignatures #-}
{-# LANGUAGE GADTs #-}

module KTuple where

type family Fst (xs :: (a, b)) :: a where
  Fst '(x, y) = x

type family Snd (xs :: (a, b)) :: a where
  Snd '(x, y) = y

type T = '(Int, String)

data Foo a r = Pure a (Fst r) | Foo (Foo a r)

newtype Fix f = Fix { unFix :: f '(Fix f, Fix f) }

type Foo' a b = Fix (Foo a)

foo :: () -> Snd T
foo _ = "Hello"