higher-order-open-union-0.1.0.0: src/Data/TypeElem.hs

{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE DataKinds, PolyKinds #-}
{-# LANGUAGE TypeOperators #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE FlexibleInstances #-}
{-# OPTIONS_GHC -Wall -fno-warn-tabs #-}

module Data.TypeElem (P, unP, Member, elemNo, Base, elemNoBase) where

newtype P t ts = P { unP :: Word } deriving Show

class Member (t :: k) (ts :: [k]) where elemNo :: P t ts

instance Member t (t ': ts) where elemNo = P 0

instance {-# OVERLAPPABLE #-} Member t ts => Member t (_t' ': ts) where
	elemNo = P $ 1 + unP (elemNo :: P t ts)

class Base (t :: k) (ts :: [k]) where elemNoBase :: P t ts

instance Base t '[t] where elemNoBase = P 0

instance {-# OVERLAPPABLE #-} Base t ts => Base t (_t' ': ts) where
	elemNoBase = P $ 1 + unP (elemNoBase :: P t ts)