Language/Symantic/Type/Fun.hs

   1 {-# LANGUAGE FlexibleContexts #-}
   2 {-# LANGUAGE FlexibleInstances #-}
   3 {-# LANGUAGE GADTs #-}
   4 {-# LANGUAGE MultiParamTypeClasses #-}
   5 {-# LANGUAGE OverloadedStrings #-}
   6 {-# LANGUAGE PatternSynonyms #-}
   7 {-# LANGUAGE Rank2Types #-}
   8 {-# LANGUAGE ScopedTypeVariables #-}
   9 {-# LANGUAGE TypeFamilies #-}
  10 {-# OPTIONS_GHC -fno-warn-missing-methods #-}
  11 module Language.Symantic.Type.Fun where
  12
  13 import Data.Proxy
  14 import Data.Type.Equality ((:~:)(Refl))
  15 import Language.Symantic.Type.Root
  16 import Language.Symantic.Type.Error
  17 import Language.Symantic.Type.Type0
  18 import Language.Symantic.Type.Type1
  19 import Language.Symantic.Type.Type2
  20
  21 -- * Type 'Type_Fun'
  22 -- | The @->@ type.
  23 type Type_Fun lam
  24  = Type_Type2 (Proxy (Lambda lam))
  25
  26 type instance Constraint2_of (Proxy (Lambda lam))
  27  = Constraint2_Empty
  28 instance Unlift_Type1 (Type_Type2 (Proxy (Lambda lam))) where
  29         unlift_type1 (Type_Type2 px a b) k =
  30                 k ( Type_Type1 (Proxy::Proxy (Lambda lam a)) b
  31                   , Lift_Type1 (\(Type_Type1 _ b') -> Type_Type2 px a b')
  32                   )
  33 instance Constraint_Type1 Applicative (Type_Fun lam root)
  34
  35 pattern Type_Fun
  36  :: root arg -> root res
  37  -> Type_Fun lam root ((Lambda lam) arg res)
  38 pattern Type_Fun arg res
  39  = Type_Type2 Proxy arg res
  40
  41 instance -- Eq_Type
  42  Eq_Type root =>
  43  Eq_Type (Type_Type2 (Proxy (Lambda lam)) root) where
  44         eq_type
  45          (Type_Type2 _ arg1 res1)
  46          (Type_Type2 _ arg2 res2)
  47          | Just Refl <- arg1 `eq_type` arg2
  48          , Just Refl <- res1 `eq_type` res2
  49          = Just Refl
  50         eq_type _ _ = Nothing
  51 instance -- String_from_Type
  52  String_from_Type root =>
  53  String_from_Type (Type_Fun lam root) where
  54         string_from_type (Type_Type2 _ arg res) =
  55                 "(" ++ string_from_type arg ++ " -> "
  56                     ++ string_from_type res ++ ")"
  57
  58 -- ** Type 'Lambda'
  59 -- | A newtype for the host-type function (->),
  60 -- wrapping argument and result within a type constructor @lam@,
  61 -- which is used in the 'Repr_Host' instance of 'Sym_Lambda'
  62 -- to control the calling (see 'val' and 'lazy').
  63 --
  64 -- NOTE: a newtype is used instead of a type synonym
  65 -- in order to be able to use it as a type constructor: @Lambda lam arg@,
  66 -- which for instance has instances: 'Functor', 'Applicative', and 'Monad'.
  67 newtype Lambda lam arg res
  68  =      Lambda { unLambda :: (->) (lam arg) (lam res) }
  69
  70 -- | Convenient alias to include a 'Type_Fun' within a type.
  71 type_fun
  72  :: forall lam root h_arg h_res.
  73  Lift_Type_Root (Type_Fun lam) root
  74  => root h_arg -> root h_res
  75  -> root (Lambda lam h_arg h_res)
  76 type_fun arg res = lift_type_root (Type_Fun arg res
  77          ::Type_Fun lam root (Lambda lam h_arg h_res))
  78
  79 -- | Parse 'Type_Fun'.
  80 type_fun_from
  81  :: forall (lam :: * -> *) (root :: * -> *) ast ret.
  82  ( Lift_Type_Root (Type_Fun lam) root
  83  , Type_from ast root
  84  , Root_of_Type root ~ root
  85  ) => Proxy (Type_Fun lam root)
  86  -> ast -> ast
  87  -> (forall h. root h -> Either (Error_of_Type ast root) ret)
  88  -> Either (Error_of_Type ast root) ret
  89 type_fun_from _ty ast_arg ast_res k =
  90         type_from (Proxy::Proxy root) ast_arg $ \(ty_arg::root h_arg) ->
  91         type_from (Proxy::Proxy root) ast_res $ \(ty_res::root h_res) ->
  92         k (ty_arg `type_fun` ty_res
  93          :: root (Lambda lam h_arg h_res))