Dear Café,

I'm trying to do very small, but impressive example about optimizations possible during Haskell compilation. So far, I can demonstrate that the following two programs (if compiled) perform computation in the same time:

1)

main =

putStrLn $ show $ sum $ map (*(2::Int)) [(1::Int)..(100000000::Int)]

2)

main =

putStrLn $! show $! sumup 1 0

sumup :: Int -> Int -> Int

sumup n total =

if n<=(100000000::Int) then sumup (n+1) $! total+(2*n)

else total

Nevertheless, I expect a question on comparison with C:

3)

#include <stdio.h>

int main(void) {

long sum, i;

sum = 0;

for (i=1; i <= 100000000L; ++i) {

sum += 2*i;

}

printf("%ld\n",sum);

return 0;

}

Unfortunately, in this case the C is much more faster (it prints the result immediately), at least on my machine. Is it due to a fact that C compiler does a brutal optimization leading to compile-time evaluation, while ghc is not able to do that?

I'm using -O2 -dynamic --make ghc compiler flags. For gcc for C compilation just -O2, running Arch Linux.

Is there any option, how to force compile time evaluation? The reason, why I think it works this way is the fact, that when running out of long type values in C a code is generated that computes the values regularly (providing misleading value as a result) taking its time.

Best regards,

Dušan