{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE UndecidableInstances #-}
module Language.LOL.Symantic.Type.Unit where

import Data.Maybe (isJust)
import Data.Type.Equality ((:~:)(Refl))

import Language.LOL.Symantic.Type.Common

-- * Type 'Type_Unit'
-- | The unit type.
data Type_Unit (root:: * -> *) h where
	Type_Unit :: Type_Unit root ()
type instance Root_of_Type      (Type_Unit root) = root
type instance Error_of_Type ast (Type_Unit root) = ()

instance -- Type_Eq
 Type_Eq (Type_Unit root) where
	type_eq Type_Unit Type_Unit = Just Refl
instance -- Eq
 Eq (Type_Unit root h) where
	x == y = isJust $ x `type_eq` y
instance -- String_from_Type
 String_from_Type (Type_Unit root) where
	string_from_type Type_Unit = "Unit"
instance -- Show
 Show (Type_Unit root h) where
	show = string_from_type
instance Type_Constraint Eq (Type_Unit root) where
	type_constraint _c Type_Unit = Just Dict
instance Type_Constraint Ord (Type_Unit root) where
	type_constraint _c Type_Unit = Just Dict

-- | Convenient alias to include a 'Type_Unit' within a type.
type_unit :: Type_Root_Lift Type_Unit root => root ()
type_unit = type_root_lift Type_Unit