+-- | Atomically update the reference. Does not force the evaluation of the
+-- new variable contents. For strict update, use 'atomicUpdMutVar''.
+atomicUpdMutVar :: IORef a -> (a -> (a, b)) -> IOEnv env b
+atomicUpdMutVar var upd = liftIO (atomicModifyIORef var upd)
+
+-- | Strict variant of 'atomicUpdMutVar'.
+atomicUpdMutVar' :: IORef a -> (a -> (a, b)) -> IOEnv env b
+atomicUpdMutVar' var upd = do
+ r <- atomicUpdMutVar var upd
+ _ <- liftIO . evaluate =<< readMutVar var
+ return r