Hello all, Maybe this is a wrong place to report, but I have repeatedly performed "funny" calculation in GHCi with strange time report. The version of GHCi is: ___ ___ _ / _ \ /\ /\/ __(_) / /_\// /_/ / / | | GHC Interactive, version 6.6, for Haskell 98. / /_\\/ __ / /___| | http://www.haskell.org/ghc/ \____/\/ /_/\____/|_| Type :? for help. Loading package base ... linking ... done. Prelude> My machine: OS WinXP Pro SP2, Intel Core 2, 2GB RAM. How to reproduce error: :set +s :set -02 :cd <path to the file in the attachment> :l Primes take 10000 primes1 <provides correct result and shows correct timing, about 636 seconds> take 10000 primes2 <provides correct result, BUT INCORRECT TIMING - about -326 seconds> Yes, that is not a typo. The report of time elapsed is: minus three hundred and twenty six seconds. I'll try the newest version of the GHCi, but it is strange anyway and maybe it should be investigated... Thanks, Dusan module Primes ( primes1 ,primes2 ,primes3 ,primes2' ,primes3' ) where candidates = map (\x -> (True,x)) [2..] candidates' = [2..] skipmap f toSkip list = domap toSkip list where domap n (x:xs) | n > 1 = x : domap (n-1) xs | True = f x : domap toSkip xs domap _ [] = [] primes1 = sieve candidates where sieve (pp@(isp,p):xs) | isp = p : (sieve $ skipmap (\(_,v) -> (False,v)) p xs) | True = sieve xs primes1' = sieve candidates' where sieve (p:xs) | p > 0 = p : (sieve $ skipmap (\n -> if n>0 then (-n) else n) p xs) | True = sieve xs sieve (p:xs) = p : sieve [y | y <- xs, y `mod` p /= 0] sieve' (p:xs) = p : sieve [y | y <- xs, y `mod` p > 0] primes2 = sieve [2..] primes3 = 2 : sieve [3,5..] primes2' = sieve' [2..] primes3' = 2 : sieve' [3,5..]