Language/LOL/Symantic/Type/Maybe.hs

   1 {-# LANGUAGE FlexibleContexts #-}
   2 {-# LANGUAGE GADTs #-}
   3 {-# LANGUAGE MultiParamTypeClasses #-}
   4 {-# LANGUAGE OverloadedStrings #-}
   5 {-# LANGUAGE ScopedTypeVariables #-}
   6 {-# LANGUAGE TypeFamilies #-}
   7 {-# LANGUAGE UndecidableInstances #-}
   8 module Language.LOL.Symantic.Type.Maybe where
   9
  10 import Data.Maybe (isJust)
  11 import Data.Type.Equality ((:~:)(Refl))
  12
  13 import Language.LOL.Symantic.Type.Common
  14 import Language.LOL.Symantic.Type.Fun
  15 import Language.LOL.Symantic.Type.Bool
  16 import Language.LOL.Symantic.Type.Var
  17
  18 -- * Type 'Type_Maybe'
  19 -- | The 'Maybe' type.
  20 data Type_Maybe root h where
  21         Type_Maybe :: root h_a
  22                    -> Type_Maybe root (Maybe h_a)
  23
  24 type instance Root_of_Type      (Type_Maybe root) = root
  25 type instance Error_of_Type ast (Type_Maybe root) = ()
  26
  27 instance -- Type_Eq
  28  Type_Eq root =>
  29  Type_Eq (Type_Maybe root) where
  30         type_eq (Type_Maybe a1) (Type_Maybe a2)
  31          | Just Refl <- a1 `type_eq` a2
  32          = Just Refl
  33         type_eq _ _ = Nothing
  34 instance -- Eq
  35  Type_Eq root =>
  36  Eq (Type_Maybe root h) where
  37         x == y = isJust $ type_eq x y
  38 instance -- String_from_Type
  39  String_from_Type root =>
  40  String_from_Type (Type_Maybe root) where
  41         string_from_type (Type_Maybe a) =
  42                 "Maybe (" ++ string_from_type a ++ ")"
  43 instance -- Show
  44  String_from_Type root =>
  45  Show (Type_Maybe root h) where
  46         show = string_from_type
  47
  48 -- | Convenient alias to include a 'Type_Maybe' within a type.
  49 type_maybe
  50  :: Type_Root_Lift Type_Maybe root
  51  => root h_a
  52  -> root (Maybe h_a)
  53 type_maybe a = type_root_lift (Type_Maybe a)
  54
  55 -- * Type 'Type_Fun_Bool_Maybe'
  56 -- | Convenient alias.
  57 type Type_Fun_Bool_Maybe lam
  58  = Type_Root (Type_Alt Type_Var
  59              (Type_Alt (Type_Fun lam)
  60              (Type_Alt Type_Bool
  61                        Type_Maybe)))