decr :: IORef Int -> IO Int
decr ioref = do
 atomicModifyIORef' ioref (\a -> (a-1,a-1))
decr :: IORef Int -> IO Int
decr ioref = do
 atomicModifyIORef' ioref (\a -> (a-1,a-1))
decr ioref = do
 atomicModifyIORef' ioref (\a -> (a-1,a-1))