alternate-catcherror.hs

catchError' :: Monad m =>
               Iteratee a m b
            -> (SomeException -> Iteratee a m b)
            -> Iteratee a m b
catchError' iter h = do
    step <- lift $ runIteratee iter
    go step

  where
    go step = 
      case step of
        (Error e)    -> h e
        (Yield x r)  -> yield x r
        (Continue k) -> do
            mbX <- head
            maybe (k EOF)
                  (\x -> do
                      step' <- lift $ runIteratee $ k (Chunks [x])
                      go step')
                  mbX