Language/Symantic/Type/Maybe.hs

   1 {-# LANGUAGE FlexibleContexts #-}
   2 {-# LANGUAGE FlexibleInstances #-}
   3 {-# LANGUAGE MultiParamTypeClasses #-}
   4 {-# LANGUAGE PatternSynonyms #-}
   5 {-# LANGUAGE TypeFamilies #-}
   6 {-# OPTIONS_GHC -fno-warn-orphans #-}
   7 module Language.Symantic.Type.Maybe where
   8
   9 import Data.Proxy
  10 import Data.Type.Equality ((:~:)(Refl))
  11 import Language.Symantic.Type.Root
  12 import Language.Symantic.Type.Type0
  13 import Language.Symantic.Type.Type1
  14
  15 -- * Type 'Type_Maybe'
  16 -- | The 'Maybe' type.
  17 type Type_Maybe = Type_Type1 (Proxy Maybe)
  18
  19 pattern Type_Map :: root a -> Type_Maybe root (Maybe a)
  20 pattern Type_Map a = Type_Type1 Proxy a
  21
  22 instance Constraint_Type1 Monad (Type_Maybe root) where
  23         constraint_type1 _c Type_Type1{} = Just Dict
  24 instance -- Eq_Type
  25  Eq_Type root =>
  26  Eq_Type (Type_Maybe root) where
  27         eq_type (Type_Type1 _px1 a1) (Type_Type1 _px2 a2)
  28          | Just Refl <- a1 `eq_type` a2
  29          = Just Refl
  30         eq_type _ _ = Nothing
  31 instance -- Eq_Type1
  32  Eq_Type1 (Type_Maybe root) where
  33         eq_type1 Type_Type1{} Type_Type1{}
  34          = Just Refl
  35 instance -- String_from_Type
  36  String_from_Type root =>
  37  String_from_Type (Type_Maybe root) where
  38         string_from_type (Type_Type1 _f a) =
  39                 "Maybe" ++ " (" ++ string_from_type a ++ ")"
  40
  41 -- | Inject 'Type_Maybe' within a root type.
  42 type_maybe
  43  :: Lift_Type_Root Type_Maybe root
  44  => root h_a
  45  -> root (Maybe h_a)
  46 type_maybe = lift_type_root . Type_Type1 (Proxy::Proxy Maybe)