Language/Symantic/Type/Var.hs

   1 {-# LANGUAGE FlexibleContexts #-}
   2 {-# LANGUAGE GADTs #-}
   3 {-# LANGUAGE MultiParamTypeClasses #-}
   4 {-# LANGUAGE Rank2Types #-}
   5 {-# LANGUAGE ScopedTypeVariables #-}
   6 {-# LANGUAGE TypeFamilies #-}
   7 {-# LANGUAGE TypeOperators #-}
   8 {-# LANGUAGE UndecidableInstances #-}
   9 -- | Type variable.
  10 module Language.Symantic.Type.Var
  11  ( module Language.Symantic.Type.Var
  12  , module Language.Symantic.Lib.Data.Peano
  13  ) where
  14
  15 import Data.Maybe (isJust)
  16
  17 import Language.Symantic.Type.Common
  18 import Language.Symantic.Lib.Data.Peano
  19
  20 -- * Type 'Type_Var'
  21 -- | The variable type.
  22 data Type_Var (root:: * -> *) p where
  23         Type_Var :: SPeano p -> Type_Var root p
  24 type instance Root_of_Type      (Type_Var root) = root
  25 type instance Error_of_Type ast (Type_Var root) = ()
  26
  27 instance -- Type_Eq
  28  Type_Eq (Type_Var root) where
  29         type_eq (Type_Var x) (Type_Var y) = x `peano_eq` y
  30 instance -- Eq
  31  Eq (Type_Var root h) where
  32         x == y = isJust $ x `type_eq` y
  33 instance -- String_from_Type
  34  String_from_Type (Type_Var root) where
  35         string_from_type (Type_Var p) =
  36                 "t" ++ show (integral_from_peano p::Integer)
  37 instance -- Show
  38  Show (Type_Var root h) where
  39         show = string_from_type
  40 instance Type_Constraint Eq  (Type_Var root)
  41 instance Type_Constraint Ord (Type_Var root)
  42
  43 -- | Convenient alias to include a 'Type_Var' within a type.
  44 type_var :: Type_Root_Lift Type_Var root => SPeano p -> root p
  45 type_var = type_root_lift . Type_Var