Not that this is a very good benchmark, but I compiled the nearly equivalent C and Haskell (1st, recursive version) programs from this blog post: http://donsbot.wordpress.com/2008/06/04/haskell-as-fast-as-c-working-at-a-hi... There, in both versions, 1e9 iterations take 1.8s. However, in my timing on 32-bit Linux machines, the C version is 5-10 times faster. Does the bitness of the OS make a big difference? Here are my timings on a 3.4GHz Pentium D: C : 4.072s (GCC 4.2.4) Haskell : 22.481s (GHC 6.10.2 and 6.8.2 are about the same here) I used the exact same compiler options as in the blog post. I only added import System import Text.Printf to the Haskell program, which seems to be missing. Suspiciously, "ghc -O2 --make" is almost as fast at 24.438s (6.10.2)