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