{-# LANGUAGE DefaultSignatures #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeFamilies #-}
{-# OPTIONS_GHC -fno-warn-orphans #-}
-- | Expression for 'Tuple'.
module Language.Symantic.Expr.Tuple where

-- import qualified Data.Tuple as Tuple
import Data.Proxy (Proxy(..))
-- import Data.Type.Equality ((:~:)(Refl))
import Prelude hiding (maybe)

import Language.Symantic.Type
import Language.Symantic.Repr.Dup
import Language.Symantic.Trans.Common
import Language.Symantic.Expr.Common
import Language.Symantic.Expr.Functor

-- * Class 'Sym_Tuple_Lam'
-- | Symantic.
class Sym_Tuple2 repr where
	tuple2 :: repr a -> repr b -> repr (a, b)
	default tuple2 :: Trans t repr => t repr a -> t repr b -> t repr (a, b)
	tuple2 = trans_map2 tuple2

instance -- Sym_Tuple2 Dup
 ( Sym_Tuple2 r1
 , Sym_Tuple2 r2
 ) => Sym_Tuple2 (Dup r1 r2) where
	tuple2 (a1 `Dup` a2) (b1 `Dup` b2) = tuple2 a1 b1 `Dup` tuple2 a2 b2

instance Constraint1_Type Functor_with_Lambda (Type_Type1 ((,) fst) root) where
	constraint1_type _c (Type_Type1 _ _) = Just Dict

-- * Type 'Expr_Tuple2'
-- | Expression.
data Expr_Tuple2 (lam:: * -> *) (root:: *)
type instance Root_of_Expr      (Expr_Tuple2 lam root)      = root
type instance Type_of_Expr      (Expr_Tuple2 lam root)      = Type_Tuple2
type instance Sym_of_Expr       (Expr_Tuple2 lam root) repr = (Sym_Tuple2 repr)
type instance Error_of_Expr ast (Expr_Tuple2 lam root)      = No_Error_Expr

-- | Parsing utility to check that the given type is a 'Type_Tuple2'
-- or raise 'Error_Expr_Type_mismatch'.
check_type_tuple2
 :: forall ast ex root ty h ret.
 ( root ~ Root_of_Expr ex
 , ty ~ Type_Root_of_Expr ex
 , Type_Lift   Type_Tuple2 (Type_of_Expr root)
 , Type_Unlift Type_Tuple2 (Type_of_Expr root)
 , Error_Expr_Lift (Error_Expr (Error_of_Type ast ty) ty ast)
                   (Error_of_Expr ast root)
 )
 => Proxy ex -> ast -> ty h
 -> (Type_Tuple2 ty h -> Either (Error_of_Expr ast root) ret)
 -> Either (Error_of_Expr ast root) ret
check_type_tuple2 ex ast ty k =
	case type_unlift $ unType_Root ty of
	 Just ty_l -> k ty_l
	 Nothing -> Left $
		error_expr ex $
		Error_Expr_Type_mismatch ast
		 (Exists_Type (type_tuple2 (type_var SZero) (type_var $ SSucc SZero)
		 :: Type_Root_of_Expr ex (Zero, Succ Zero)))
		 (Exists_Type ty)

-- | Parse 'list_cons'.
tuple2_from
 :: forall root lam ty ast hs ret.
 ( ty ~ Type_Root_of_Expr (Expr_Tuple2 lam root)
 , Eq_Type (Type_Root_of_Expr root)
 , Expr_from ast root
 , Type_Lift   Type_Tuple2 (Type_of_Expr root)
 , Type_Unlift Type_Tuple2 (Type_of_Expr root)
 , Error_Expr_Lift (Error_Expr (Error_of_Type ast ty) ty ast)
                   (Error_of_Expr ast root)
 , Root_of_Expr root ~ root
 ) => ast -> ast
 -> Expr_From ast (Expr_Tuple2 lam root) hs ret
tuple2_from ast_a ast_b _ex _ast ctx k =
	expr_from (Proxy::Proxy root) ast_a ctx $
	 \(ty_a::Type_Root_of_Expr root h_a) (Forall_Repr_with_Context a) ->
	expr_from (Proxy::Proxy root) ast_b ctx $
	 \(ty_b::Type_Root_of_Expr root h_b) (Forall_Repr_with_Context b) ->
	k (type_tuple2 ty_a ty_b) $ Forall_Repr_with_Context $
		\c -> tuple2 (a c) (b c)