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.Common
  16
  17 -- * Type 'Type_Fun'
  18 -- | The @->@ type.
  19 type Type_Fun lam
  20  = Type_Type2 (Proxy (Lambda lam))
  21
  22 type instance Constraint2_of (Proxy (Lambda lam))
  23  = Constraint2_Empty
  24
  25 pattern Type_Fun
  26  :: root arg -> root res
  27  -> Type_Fun lam root ((Lambda lam) arg res)
  28 pattern Type_Fun arg res
  29  = Type_Type2 Proxy arg res
  30
  31 instance -- Eq_Type
  32  Eq_Type root =>
  33  Eq_Type (Type_Type2 (Proxy (Lambda lam)) root) where
  34         eq_type
  35          (Type_Type2 _ arg1 res1)
  36          (Type_Type2 _ arg2 res2)
  37          | Just Refl <- arg1 `eq_type` arg2
  38          , Just Refl <- res1 `eq_type` res2
  39          = Just Refl
  40         eq_type _ _ = Nothing
  41 instance -- String_from_Type
  42  String_from_Type root =>
  43  String_from_Type (Type_Fun lam root) where
  44         string_from_type (Type_Type2 _ arg res) =
  45                 "(" ++ string_from_type arg ++ " -> "
  46                     ++ string_from_type res ++ ")"
  47
  48 -- ** Type 'Lambda'
  49 -- | A newtype for the host-type function (->),
  50 -- wrapping argument and result within a type constructor @lam@,
  51 -- which is used in the 'Repr_Host' instance of 'Sym_Lambda'
  52 -- to implement 'val' and 'lazy'.
  53 --
  54 -- NOTE: a newtype is used instead of a type synonym
  55 -- in order to be able to use it as a type constructor: @Lambda lam arg@,
  56 -- which for instance has instances: 'Functor', 'Applicative', and 'Monad'.
  57 newtype Lambda lam arg res
  58  =      Lambda { unLambda :: (->) (lam arg) (lam res) }
  59
  60 -- | Convenient alias to include a 'Type_Fun' within a type.
  61 type_fun
  62  :: forall lam root h_arg h_res.
  63  Lift_Type_Root (Type_Fun lam) root
  64  => root h_arg -> root h_res
  65  -> root (Lambda lam h_arg h_res)
  66 type_fun arg res = lift_type_root (Type_Fun arg res
  67          ::Type_Fun lam root (Lambda lam h_arg h_res))
  68
  69 -- | Parse 'Type_Fun'.
  70 type_fun_from
  71  :: forall (lam :: * -> *) (root :: * -> *) ast ret.
  72  ( Lift_Type_Root (Type_Fun lam) root
  73  , Type_from ast root
  74  , Root_of_Type root ~ root
  75  ) => Proxy (Type_Fun lam root)
  76  -> ast -> ast
  77  -> (forall h. root h -> Either (Error_of_Type ast root) ret)
  78  -> Either (Error_of_Type ast root) ret
  79 type_fun_from _ty ast_arg ast_res k =
  80         type_from (Proxy::Proxy root) ast_arg $ \(ty_arg::root h_arg) ->
  81         type_from (Proxy::Proxy root) ast_res $ \(ty_res::root h_res) ->
  82         k (ty_arg `type_fun` ty_res
  83          :: root (Lambda lam h_arg h_res))