{-# LANGUAGE DefaultSignatures #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE Rank2Types #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE TypeOperators #-}
{-# LANGUAGE NoMonomorphismRestriction #-}
{-# OPTIONS_GHC -fno-warn-orphans #-}
-- | Expression for 'Eq'.
module Language.Symantic.Expr.Eq where

import Control.Monad
import qualified Data.Eq as Eq
import Data.Proxy (Proxy(..))
import Data.Type.Equality ((:~:)(Refl))
import Prelude hiding ((==), (/=))

import Language.Symantic.Type
import Language.Symantic.Repr
import Language.Symantic.Expr.Root
import Language.Symantic.Expr.Error
import Language.Symantic.Expr.From
import Language.Symantic.Trans.Common

-- * Class 'Sym_Eq'
-- | Symantic.
class Sym_Eq repr where
	(==) :: Eq a => repr a -> repr a -> repr Bool
	(/=) :: Eq a => repr a -> repr a -> repr Bool
	
	default (==) :: (Trans t repr, Eq a) => t repr a -> t repr a -> t repr Bool
	default (/=) :: (Trans t repr, Eq a) => t repr a -> t repr a -> t repr Bool
	
	(==) = trans_map2 (==)
	(/=) = trans_map2 (/=)

infix 4 ==
infix 4 /=

instance Sym_Eq Repr_Host where
	(==) = liftM2 (Eq.==)
	(/=) = liftM2 (Eq./=)
instance Sym_Eq Repr_Text where
	(==) = repr_text_infix "==" (Precedence 4)
	(/=) = repr_text_infix "/=" (Precedence 4)
instance (Sym_Eq r1, Sym_Eq r2) => Sym_Eq (Repr_Dup r1 r2) where
	(==) = repr_dup2 sym_Eq (==)
	(/=) = repr_dup2 sym_Eq (/=)

sym_Eq :: Proxy Sym_Eq
sym_Eq = Proxy

-- * Type 'Expr_Eq'
-- | Expression.
data Expr_Eq (root:: *)
type instance Root_of_Expr      (Expr_Eq root)      = root
type instance Type_of_Expr      (Expr_Eq root)      = No_Type
type instance Sym_of_Expr       (Expr_Eq root) repr = (Sym_Eq repr)
type instance Error_of_Expr ast (Expr_Eq root)      = No_Error_Expr

-- Parse '==' or '/='.
eq_from
 :: forall root ty ast hs ret.
 ( ty ~ Type_Root_of_Expr (Expr_Eq root)
 , Type0_Lift Type_Bool (Type_of_Expr root)
 , Type0_Eq ty
 , Type0_Constraint Eq ty
 , Expr_From ast root
 , Error_Expr_Lift (Error_Expr (Error_of_Type ast ty) ty ast)
                   (Error_of_Expr ast root)
 , Root_of_Expr root ~ root
 ) => (forall repr a. (Sym_Eq repr, Eq a) => repr a -> repr a -> repr Bool)
 -> ast -> ast
 -> ExprFrom ast (Expr_Eq root) hs ret
eq_from test ast_x ast_y ex ast ctx k =
	expr_from (Proxy::Proxy root) ast_x ctx $
	 \(ty_x::ty h_x) (Forall_Repr_with_Context x) ->
	expr_from (Proxy::Proxy root) ast_y ctx $
	 \(ty_y::ty h_y) (Forall_Repr_with_Context y) ->
	check_type0_eq ex ast ty_x ty_y $ \Refl ->
	check_type0_constraint ex (Proxy::Proxy Eq) ast ty_x $ \Dict ->
	k type_bool $ Forall_Repr_with_Context $
	 \c -> x c `test` y c

-- Parse '==' or '/=', with only one argument.
eq_from1
 :: forall root ty ast hs ret.
 ( ty ~ Type_Root_of_Expr (Expr_Eq root)
 , Type0_Lift Type_Fun  (Type_of_Expr root)
 , Type0_Lift Type_Bool (Type_of_Expr root)
 , Type0_Eq ty
 , Type0_Constraint Eq ty
 , Expr_From ast root
 , Error_Expr_Lift (Error_Expr (Error_of_Type ast ty) ty ast)
                   (Error_of_Expr ast root)
 , Root_of_Expr root ~ root
 ) => (forall repr a. (Sym_Eq repr, Eq a) => repr a -> repr a -> repr Bool)
 -> ast
 -> ExprFrom ast (Expr_Eq root) hs ret
eq_from1 test ast_x ex ast ctx k =
	expr_from (Proxy::Proxy root) ast_x ctx $
	 \(ty_x::ty h_x) (Forall_Repr_with_Context x) ->
	check_type0_constraint ex (Proxy::Proxy Eq) ast ty_x $ \Dict ->
	k (type_fun ty_x type_bool) $ Forall_Repr_with_Context $
	 \c -> lam $ \y -> x c `test` y