Language/Symantic/Type/Unit.hs

   1 {-# LANGUAGE FlexibleContexts #-}
   2 {-# LANGUAGE GADTs #-}
   3 {-# LANGUAGE MultiParamTypeClasses #-}
   4 {-# LANGUAGE TypeFamilies #-}
   5 {-# OPTIONS_GHC -fno-warn-missing-methods #-}
   6 module Language.Symantic.Type.Unit where
   7
   8 import Data.Maybe (isJust)
   9 import Data.Type.Equality ((:~:)(Refl))
  10
  11 import Language.Symantic.Type.Common
  12
  13 -- * Type 'Type_Unit'
  14 -- | The unit type.
  15 data Type_Unit (root:: * -> *) h where
  16         Type_Unit :: Type_Unit root ()
  17 type instance Root_of_Type      (Type_Unit root) = root
  18 type instance Error_of_Type ast (Type_Unit root) = No_Error_Type
  19
  20 instance -- Eq_Type
  21  Eq_Type (Type_Unit root) where
  22         eq_type Type_Unit Type_Unit = Just Refl
  23 instance -- Eq
  24  Eq (Type_Unit root h) where
  25         x == y = isJust $ x `eq_type` y
  26 instance -- String_from_Type
  27  String_from_Type (Type_Unit root) where
  28         string_from_type Type_Unit = "Unit"
  29 instance -- Show
  30  Show (Type_Unit root h) where
  31         show = string_from_type
  32 instance Constraint_Type Eq (Type_Unit root) where
  33         constraint_type _c Type_Unit = Just Dict
  34 instance Constraint_Type Ord (Type_Unit root) where
  35         constraint_type _c Type_Unit = Just Dict
  36 instance Unlift_Type1 Type_Unit
  37 instance Eq_Type1 (Type_Unit root)
  38
  39 -- | Convenient alias to include a 'Type_Unit' within a type.
  40 type_unit :: Type_Root_Lift Type_Unit root => root ()
  41 type_unit = type_root_lift Type_Unit