symantic-grammar/Language/Symantic/Grammar/Error.hs

   1 {-# LANGUAGE TypeApplications #-}
   2 module Language.Symantic.Grammar.Error where
   3
   4 import Data.Proxy (Proxy)
   5
   6 -- * Class 'ErrorInj'
   7 class ErrorInj a b where
   8         errorInj :: a -> b
   9 instance ErrorInj err e => ErrorInj err (Either e a) where
  10         errorInj = Left . errorInj
  11
  12 liftError ::
  13  forall e0 err e1 a.
  14  ErrorInj e0 e1 =>
  15  ErrorInj e1 err =>
  16  Proxy e1 -> Either e0 a -> Either err a
  17 liftError _e1 (Right a) = Right a
  18 liftError _e1 (Left e)  = Left $ errorInj @e1 @err $ errorInj @e0 @e1 e