Il 22:54, mercoledì 23 aprile 2003, hai scritto: > I conjecture that the problem would go away if you added appropriate > uses of seq or $! to your program so that the value stored in the MVar > was always fully evaluated You are right, the following code works well strictIncM x = return $! x + 1 ... forkIO (loopM (modifyMVar_ v strictIncM)) ... Thanks for your help Vincenzo