Hi, I tried the first example from "A tutorial on Parallel and Concurrent programming in Haskell" but I cant seem to get sparks to get converted to OS threads. Below is the program I am using. I did ghc --make -threaded program.hs then ./program +RTS -N2 I don't see any speed gain compared to N1. Am I missing something? import System.Time import Control.Parallel fib :: Int -> Int fib 0 = 0 fib 1 = 1 fib n = fib (n-1) + fib (n-2) mkList :: Int -> [Int] mkList n = [1..n-1] relPrime :: Int -> Int -> Bool relPrime x y = gcd x y == 1 euler :: Int -> Int euler n = length (filter (relPrime n) (mkList n)) sumEuler :: Int -> Int sumEuler = sum . (map euler) . mkList sumFibEuler :: Int -> Int -> Int sumFibEuler a b = fib a + sumEuler b parSumFibEuler :: Int -> Int -> Int parSumFibEuler a b = f `par` (e `pseq` (e + f)) where f = fib a e = sumEuler b secDiff :: ClockTime -> ClockTime -> Float secDiff (TOD secs1 psecs1) (TOD secs2 psecs2) = fromInteger (psecs2 - psecs1) / 1e12 + fromInteger (secs2 - secs1) r1 :: Int r1 = sumFibEuler 38 5300 main :: IO () main = do t0 <- getClockTime pseq r1 (return()) t1 <- getClockTime putStrLn ("Sum: " ++ show r1) putStrLn ("time: " ++ show (secDiff t0 t1) ++ " seconds")