merijn

{-# LANGUAGE DataKinds #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE KindSignatures #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE TypeOperators #-}
module HList where

import Prelude hiding (head, tail, zip)

merijn

{-# LANGUAGE ConstraintKinds #-}
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE TypeOperators #-}

import GHC.Prim (Constraint)

data Nat = Succ Nat | Zero

merijn

{-# LANGUAGE ConstraintKinds, DataKinds, PolyKinds, TypeFamilies, TypeOperators #-}

import GHC.Exts (Constraint)

type family Restrict (a :: k) (as :: [k]) :: Constraint where
    Restrict a (a ': as) = ("Error!" ~ "Tried to apply a restricted type!")
    Restrict x (a ': as) = Restrict x as
    Restrict x '[] = ()

foo :: Restrict a [(), Int] => a -> a