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

import Data.Either (Either(..))
import Data.Function (($), (.))
import Data.Proxy (Proxy)

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

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