[Haskell-Cafe] Quick question for a slow program

7 Jun 2008

      Hello,

I was just brushing my haskell-fu skills writing a solution for Google
Treasure Hunt Problem 4. Hers is what it looks like:
...
primes = sieve [2..]
    where
      sieve (p:xs) = p : sieve [x | x <- xs, x `mod` p /= 0]
sumOf n l = sum (take n l) : sumOf n (tail l)
find l = foldl1 aux l
    where
      aux (x:xs) (y:ys) | x == y = x : aux xs ys
                        | x < y  = aux xs (y:ys)
                        | x > y  = aux (x:xs) ys
puzzle = find (reverse [primes, p7, p17, p41, p541])
    where
      p7 = sumOf 7 primes
      p17 = sumOf 17 primes
      p41 = sumOf 41 primes
      p541 = sumOf 541 primes
main = do mapM (\x -> putStrLn $ show x) puzzle
While the code is quite readable and straight forward it is as slow as
tortoise with four legs broken. What optimizations would you suggest,
while still keeping the code clear and highlevel?

Thank you in advance.

Cheers.

-- 
Slavomir Kaslev