{-# LANGUAGE TypeApplications #-}
module Language.Symantic.Grammar.Error where

import Data.Proxy (Proxy)

-- * Class 'Inj_Error'
class Inj_Error a b where
	inj_Error :: a -> b
instance Inj_Error err e => Inj_Error err (Either e a) where
	inj_Error = Left . inj_Error

liftError ::
 forall e0 err e1 a.
 Inj_Error e0 e1 =>
 Inj_Error e1 err =>
 Proxy e1 -> Either e0 a -> Either err a
liftError _e1 (Right a) = Right a
liftError _e1 (Left e)  = Left $ inj_Error @e1 @err $ inj_Error @e0 @e1 e