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
  15 import Language.Symantic.Type.Common
  16
  17 -- * Type 'Type_Fun'
  18 -- | The @->@ type.
  19 type Type_Fun lam
  20  = Type_Type2 Constraint2_Empty (Lambda lam)
  21 pattern Type_Fun arg res
  22  = Type_Type2 Proxy Proxy arg res
  23
  24 -- ** Type 'Lambda'
  25 -- | A newtype for the host-type function (->),
  26 -- wrapping argument and result within a type constructor @lam@,
  27 -- which is used in the 'Repr_Host' instance of 'Sym_Lambda'
  28 -- to implement 'val' and 'lazy'.
  29 --
  30 -- NOTE: a newtype is used instead of a type synonym
  31 -- in order to be able to use it as a type constructor: @Lambda lam arg@,
  32 -- which for instance has instances: 'Functor', 'Applicative', and 'Monad'.
  33 newtype Lambda lam arg res
  34  =      Lambda { unLambda :: (->) (lam arg) (lam res) }
  35
  36 instance -- String_from_Type
  37  String_from_Type root =>
  38  String_from_Type (Type_Fun lam root) where
  39         string_from_type (Type_Type2 _ _ arg res) =
  40                 "(" ++ string_from_type arg ++ " -> "
  41                     ++ string_from_type res ++ ")"
  42
  43 -- | Convenient alias to include a 'Type_Fun' within a type.
  44 type_fun
  45  :: forall lam root h_arg h_res.
  46  Lift_Type_Root (Type_Fun lam) root
  47  => root h_arg -> root h_res
  48  -> root (Lambda lam h_arg h_res)
  49 type_fun arg res = lift_type_root (Type_Fun arg res
  50          ::Type_Fun lam root (Lambda lam h_arg h_res))
  51
  52 type_fun_from
  53  :: forall (lam :: * -> *) (root :: * -> *) ast ret.
  54  ( Lift_Type_Root (Type_Fun lam) root
  55  , Type_from ast root
  56  , Root_of_Type root ~ root
  57  ) => Proxy (Type_Fun lam root)
  58  -> ast -> ast
  59  -> (forall h. root h -> Either (Error_of_Type ast root) ret)
  60  -> Either (Error_of_Type ast root) ret
  61 type_fun_from _ty ast_arg ast_res k =
  62         type_from (Proxy::Proxy root) ast_arg $ \(ty_arg::root h_arg) ->
  63         type_from (Proxy::Proxy root) ast_res $ \(ty_res::root h_res) ->
  64         k (ty_arg `type_fun` ty_res
  65          :: root (Lambda lam h_arg h_res))