enumerator-0.2: hs/Data/Enumerator/Util.hs

module Data.Enumerator.Util where
import Data.Enumerator
import qualified Control.Exception as E

tryStep :: IO t
       -> (t -> IO (Step E.SomeException a IO b))
       -> IO (Step E.SomeException a IO b)
tryStep get io = do
	tried <- E.try get
	case tried of
		Right t -> io t
		Left err -> return $ Error err
{-# INLINE tryStep #-}

mapEither :: (a -> Either e b) -> [a] -> Either e [b]
mapEither f = loop [] where
	loop acc [] = Right (reverse acc)
	loop acc (a:as) = case f a of
		Left err -> Left err
		Right b -> loop (b:acc) as
{-# INLINE mapEither #-}