[Haskell-cafe] Epic failure

[Andrew Coppin]

OK, what did I do wrong here?



module Main () where

import Data.List

top = 10 ^ 8 :: Int

main = do
  let numbers = [1 .. top]
  print $ foldl' (+) 0 numbers

-- Runtime is 20 seconds.



#include <stdio.h>

int main(void)
{
  int total = 0;
  int n;

  for (n = 1, n < 100000000; n++)
  total += n;

  printf("%d", n);
}

// Runtime is 0.8 seconds.



module Main () where

import Data.List

top = 10 ^ 8 :: Int

kernel i o = if i < top then o `seq` kernel (i+1) (o+i) else o

main = do
  print $ kernel 1 0


-- Runtime is 0.5 seconds.


Clearly these two nearly identical Haskell programs should have exactly 
the same runtime. Instead, one is 40x slower. Clearly something has gone 
catastrophically wrong here. The whole point of GHC's extensive 
optimiser passes are to turn the first example into the second example - 
but something somewhere hasn't worked. Any suggestions?