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