Sorry Daniel, i've seen your answer just after posting my reply. But i can't write !t1f <- gettime, nor t1f <- !gettime; because it's an IO ? Your method is a good help form me. Thanks, Didier Daniel Fischer a écrit :
Am Samstag 13 März 2010 21:20:58 schrieb legajid:
Hi, my following code should show time before executing listeprem, then time after execution.
import System.Time gettime :: IO ClockTime gettime = getClockTime
main=do t1d <- gettime
This gets the time, now.
let t1=last (listeprem 5000)
This doesn't do the calculation, it only creates a thunk what to calculate should t1 be demanded, takes a few nanoseconds
t1f <- gettime
This gets the time, a few nanoseconds later
putStrLn ("Methode 1 : " ++ show t1d) putStrLn (" " ++ show t1)
Now t1 is demanded, and only now it's calculated.
putStrLn (" " ++ show t1f)
Looking at the screen, t1d is displayed then, after a few seconds, t1 and t1f. But, t1d and t1f are equal. It seems like if t1d and t1f where calculated at start of procedure, before we need calculating t1 for putStrLn.
Exactly.
How can i have t1f evaluated after t1, so i can calculate time elapsed for calculation of t1?
Depends on what sort of value t1 is. If it's a simple value like an Integer (as I think it is here, derniere nombre premier avant 5000, 5000-th prime?),
{-# LANGUAGE BangPatterns #-} ... let !t1 = last (listeprem 5000) t1f <- gettime
or
let t1 = last (listeprem 5000) t1f <- t1 `seq` gettime
will do. For small values, printing takes negligible time, so
t1d <- gettime putStrLn (" " ++ show t1f) t1f <- gettime
is another option. But getClockTime isn't particularly exact, I'd suggest using System.CPUTime.getCPUTime
Thanks, Didier