-- | Set the label to the result of applying the given function to the
-- value.
modify :: (T.Text -> T.Text) -> Label -> IO ()
modify f (C ref) = do
    !_ <- atomicModifyIORef ref $ \ i -> let i' = f i in (i', i')
    return ()
modify :: (T.Text -> T.Text) -> Label -> IO ()
modify f (C ref) = do
    !_ <- atomicModifyIORef ref $ \ i -> let i' = f i in (i', i')
    return ()
modify f (C ref) = do
    !_ <- atomicModifyIORef ref $ \ i -> let i' = f i in (i', i')
    return ()