decrement :: IORef Int -> IO Int
decrement ref = IORef.atomicModifyIORef' ref (\n -> (n-1, n))
decrement :: IORef Int -> IO Int
decrement ref = IORef.atomicModifyIORef' ref (\n -> (n-1, n))
decrement ref = IORef.atomicModifyIORef' ref (\n -> (n-1, n))