{-# LANGUAGE StandaloneDeriving #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE PatternSynonyms #-}
{-# LANGUAGE ConstraintKinds #-}
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE UndecidableInstances #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE LambdaCase #-}
{-# LANGUAGE TypeOperators #-}
{-# LANGUAGE KindSignatures #-}
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE PolyKinds #-}
{-# LANGUAGE GADTs #-}
-----------------------------------------------------------------------------
-- |
-- Module : Data.Type.Sym
-- Copyright : Copyright (C) 2015 Kyle Carter
-- License : BSD3
--
-- Maintainer : Kyle Carter <kylcarte@indiana.edu>
-- Stability : experimental
-- Portability : RankNTypes
--
-- A @singleton@-esque type for representing type-level Symbols.
--
-----------------------------------------------------------------------------
module Data.Type.Sym where
import Data.Type.Boolean
import Type.Class.Higher
import Type.Class.Known
import Type.Class.Witness
import Type.Family.Constraint
import Type.Family.Symbol
import Data.Proxy
data Sym :: Symbol -> * where
Sym :: KnownSymbol x => Sym x
deriving instance Eq (Sym x)
deriving instance Ord (Sym x)
instance Show (Sym x) where
showsPrec d x = showParen (d > 0)
$ showString "Sym "
. shows (symbol x)
instance Eq1 Sym
instance Ord1 Sym
instance Show1 Sym
instance TestEquality Sym where
testEquality Sym Sym = sameSymbol Proxy Proxy
instance BoolEquality Sym where
type BoolEqC Sym a b = Known Boolean (a == b)
Sym .== Sym = known
instance KnownSymbol x => Known Sym x where
type KnownC Sym x = KnownSymbol x
known = Sym
instance Witness ØC (KnownSymbol x) (Sym x) where
r \\ Sym = r
symbol :: Sym x -> String
symbol x = symbolVal x \\ x