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.Type2
  19
  20 -- * Type 'Type_Fun'
  21 -- | The @->@ type.
  22 type Type_Fun lam
  23  = Type_Type2 (Proxy (Lambda lam))
  24
  25 type instance Constraint2_of (Proxy (Lambda lam))
  26  = Constraint2_Empty
  27
  28 pattern Type_Fun
  29  :: root arg -> root res
  30  -> Type_Fun lam root ((Lambda lam) arg res)
  31 pattern Type_Fun arg res
  32  = Type_Type2 Proxy arg res
  33
  34 instance -- Eq_Type
  35  Eq_Type root =>
  36  Eq_Type (Type_Type2 (Proxy (Lambda lam)) root) where
  37         eq_type
  38          (Type_Type2 _ arg1 res1)
  39          (Type_Type2 _ arg2 res2)
  40          | Just Refl <- arg1 `eq_type` arg2
  41          , Just Refl <- res1 `eq_type` res2
  42          = Just Refl
  43         eq_type _ _ = Nothing
  44 instance -- String_from_Type
  45  String_from_Type root =>
  46  String_from_Type (Type_Fun lam root) where
  47         string_from_type (Type_Type2 _ arg res) =
  48                 "(" ++ string_from_type arg ++ " -> "
  49                     ++ string_from_type res ++ ")"
  50
  51 -- ** Type 'Lambda'
  52 -- | A newtype for the host-type function (->),
  53 -- wrapping argument and result within a type constructor @lam@,
  54 -- which is used in the 'Repr_Host' instance of 'Sym_Lambda'
  55 -- to control the calling (see 'val' and 'lazy').
  56 --
  57 -- NOTE: a newtype is used instead of a type synonym
  58 -- in order to be able to use it as a type constructor: @Lambda lam arg@,
  59 -- which for instance has instances: 'Functor', 'Applicative', and 'Monad'.
  60 newtype Lambda lam arg res
  61  =      Lambda { unLambda :: (->) (lam arg) (lam res) }
  62
  63 -- | Convenient alias to include a 'Type_Fun' within a type.
  64 type_fun
  65  :: forall lam root h_arg h_res.
  66  Lift_Type_Root (Type_Fun lam) root
  67  => root h_arg -> root h_res
  68  -> root (Lambda lam h_arg h_res)
  69 type_fun arg res = lift_type_root (Type_Fun arg res
  70          ::Type_Fun lam root (Lambda lam h_arg h_res))
  71
  72 -- | Parse 'Type_Fun'.
  73 type_fun_from
  74  :: forall (lam :: * -> *) (root :: * -> *) ast ret.
  75  ( Lift_Type_Root (Type_Fun lam) root
  76  , Type_from ast root
  77  , Root_of_Type root ~ root
  78  ) => Proxy (Type_Fun lam root)
  79  -> ast -> ast
  80  -> (forall h. root h -> Either (Error_of_Type ast root) ret)
  81  -> Either (Error_of_Type ast root) ret
  82 type_fun_from _ty ast_arg ast_res k =
  83         type_from (Proxy::Proxy root) ast_arg $ \(ty_arg::root h_arg) ->
  84         type_from (Proxy::Proxy root) ast_res $ \(ty_res::root h_res) ->
  85         k (ty_arg `type_fun` ty_res
  86          :: root (Lambda lam h_arg h_res))