The following C program was described on #haskell #include <stdio.h> int main() { double x = 1.0/3.0; double y = 3.0; int i = 1; for (; i<=1000000000; i++) { x = x*y/3.0; y = x*9.0; } printf("%f\n", x+y); } Which was translated to the following Haskell: {-# OPTIONS -fexcess-precision #-} import Text.Printf main = go (1/3) 3 1 go :: Double -> Double -> Int -> IO () go !x !y !i | i == 1000000000 = printf "%f\n" (x+y) | otherwise = go (x*y/3) (x*9) (i+1) To everyone's surprise, GHC 6.6 beats GCC (3.3.5) here, at least the two test machines: $ ghc -O -fexcess-precision -fbang-patterns -optc-O3 -optc-ffast-math -optc-mfpmath=sse -optc-msse2 A.hs -o a $ time ./a 3.333333 ./a 0.96s user 0.01s system 99% cpu 0.969 total ^^^^^ Versus gcc 3.3.5: $ gcc -O3 -ffast-math -mfpmath=sse -msse2 -std=c99 t.c -o c_loop $ time ./c_loop 3.333333 ./c_loop 1.01s user 0.01s system 97% cpu 1.046 total ^^^^^ Note that newer gcc's will statically compute that loop. Note also that -fexcess-precision must currently be provided as a pragma only. I declare GHC Haskell numerics (with -fexcess-precision) not so shabby! -- Don