[Haskell-cafe] Haskell performance question

I see lots of shootout examples where Haskell programs seem to perform comparably with C programs, but I find it hard to reproduce anything like those figures when testing with my own code. So here's a simple case: I have this C program: #include #define n 100000000 double a[n]; int main() { int i; for (i = 0; i do { x <- readArray a i; y <- readArray a (i+1); writeArray a (i+1) (x+y) } x <- readArray a (n-1) print x Even though 'n' is 10 times bigger in the C program it runs much faster than the Haskell program on my MacBook Pro with Haskell 6.6.1. I've tried lots of different combinations of flags that I've found in various postings to haskell-cafe but to no avail. What flags do I need to get at least within a factor of 2 or 3 of C? Am I using the wrong kind of array? Or is Haskell always going to be 15-20 times slower for this kind of numerical work? -- Dan