Thank you, Marcin. Your reply seems to imply that the structure of the program I posted was basically OK? A slightly related point, I was having difficulties with TimeDiff values - I got negative tdPicosecs sometimes, and some functions (show) even dumped core. Are such problems known (I am using a binary ghc-4.08)? For the moment, I switched to Posix.EpochTime. I found TimeDiff and ClockTime quite restrictive: they are not instances of Num, I can't add/subtract/negate TimeDiffs; and I cannot generate a zero ClockTime. (In my application, I need to simulate two clocks, where always one is running, the other one is stopped - as used in tournament Chess.) -- -- Johannes Waldmann ---- http://www.informatik.uni-leipzig.de/~joe/ -- -- joe@informatik.uni-leipzig.de -- phone/fax (+49) 341 9732 204/252 --