Hello, I want to write a timing method to test sub steps in my program. I tested my timing method as follows: ===== time.hs ===== import Data.Time time :: String -> IO a -> IO a time str a = do start <- getCurrentTime v <- a end <- getCurrentTime let diff = diffUTCTime end start putStrLn $ str ++ showNominalDiffTime (diff) return v showNominalDiffTime :: NominalDiffTime -> String showNominalDiffTime nTime = let timeString = show nTime in take (length timeString - 1) timeString ++ " sec" fun :: IO (Int, [Int]) fun = do i <- time "product: " $ return $! product [1..10000] -- testing strictness : evaluated j <- time "product list: " $ return $! map (\_ -> product [1..10000]) [1..3] -- testing strictness : not evaluated List is in hnf return (i, j) main = fun ===== In the shell ===== $ time ./time product: 0.001813 sec product list: 0.000001 sec real 0m0.006s user 0m0.000s sys 0m0.005s Notice that the ($!) operation will reduce a term to head normal form (hnf), not normal form. In the "product list" testing, the "complicated" map evaluation is reduced to a list of redex. Therefore, the result does not reflect the time needed to get the final value. How could I improve my timing method so that it will give the time to reduce a general expression to normal form? Jiansen