import System.Time( getClockTime )

add_up 0 acc = acc
add_up n acc = add_up (n - 1) (acc + n)

time = getClockTime >>= print >> return ""

main = do
    time
    print (add_up 10000000 0)
    time
    print (add_up 5000000 0)
    time
    print (add_up 10000000 0)
    time
    return ()

{-
c:\ghc\ghc-6.4\code>ghc 493959.hs

c:\ghc\ghc-6.4\code>main
Thu Sep 22 17:57:10 GMT Daylight Time 2005
Heap exhausted;
Current maximum heap size is 268435456 bytes (256 Mb);
use `+RTS -M<size>' to increase it.

c:\ghc\ghc-6.4\code>main
Thu Sep 22 17:58:10 GMT Daylight Time 2005
50000005000000
Thu Sep 22 17:58:13 GMT Daylight Time 2005
12500002500000
Thu Sep 22 17:58:15 GMT Daylight Time 2005
50000005000000
Thu Sep 22 17:58:15 GMT Daylight Time 2005

-}