I'm trying to write a program in Haskell that writes a large file at the end, and it seems like that output alone is taking way longer than it should. I don't understand why Haskell shouldn't be able to write data as quickly as C, so I wrote two test files:

-- Test.hs

import Control.Loop

import Data.ByteString.Builder

import System.IO

main :: IO ()

main =

  numLoop 0 1000000 $ \_ ->

    hPutBuilder stdout $ char7 ' '

// test.c

#include <stdio.h>

int main() {

  int i;

  for (i = 0; i < 1000000; i++) {

    fprintf(stdout, " ");

  }

  return 0;

}

I compiled them both with -O2, and ran them redirecting their outputs to /dev/null. For the Haskell version I got times aroudn 0.3 seconds, while the C version was around 0.03. Is there any reason why in simple IO the Haskell version would be slower by an order of magnitude?