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1 {-# LANGUAGE FlexibleContexts #-}
2 {-# LANGUAGE FlexibleInstances #-}
3 {-# LANGUAGE PatternSynonyms #-}
4 {-# LANGUAGE TypeFamilies #-}
5 {-# OPTIONS_GHC -fno-warn-orphans #-}
6 module Language.Symantic.Type.Maybe where
7
8 import Data.Proxy
9 import Data.Type.Equality ((:~:)(Refl))
10 import Language.Symantic.Type.Root
11 import Language.Symantic.Type.Type0
12 import Language.Symantic.Type.Type1
13
14 -- * Type 'Type_Maybe'
15 -- | The 'Maybe' type.
16 type Type_Maybe = Type_Type1 (Proxy Maybe)
17
18 pattern Type_Map :: root a -> Type_Maybe root (Maybe a)
19 pattern Type_Map a = Type_Type1 Proxy a
20
21 instance -- Eq_Type
22 Eq_Type root =>
23 Eq_Type (Type_Type1 (Proxy Maybe) root) where
24 eq_type (Type_Type1 _px1 a1) (Type_Type1 _px2 a2)
25 | Just Refl <- a1 `eq_type` a2
26 = Just Refl
27 eq_type _ _ = Nothing
28 instance -- Eq_Type1
29 Eq_Type1 (Type_Type1 (Proxy Maybe) root) where
30 eq_type1 Type_Type1{} Type_Type1{}
31 = Just Refl
32 instance -- String_from_Type
33 String_from_Type root =>
34 String_from_Type (Type_Maybe root) where
35 string_from_type (Type_Type1 _f a) =
36 "Maybe" ++ " (" ++ string_from_type a ++ ")"
37
38 -- | Inject 'Type_Maybe' within a root type.
39 type_maybe
40 :: Lift_Type_Root Type_Maybe root
41 => root h_a
42 -> root (Maybe h_a)
43 type_maybe = lift_type_root . Type_Type1 (Proxy::Proxy Maybe)