[Haskell-Cafe] Quick question for a slow program

[Lanny Ripple]

The second prime generator on this page

   http://www.haskell.org/haskellwiki/Prime_numbers

is quick and easy.  I keep it nearby for all those sudden attacks of
needing to solve yet another projecteuler problem.

  -ljr

Slavomir Kaslev wrote:
> 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.
>