Haskell Quiz/Weird Numbers/Solution Ninju

module Main where
import System.Environment

main :: IO ()
main = do args <- getArgs
          let max = read (head args)
          if length args == 1
            then do putStrLn $ "The weird numbers up to " ++ (head args) ++ ":"
                    print $ takeWhile (<= max) weirdNumbers
            else putStrLn "Usage: weird_numbers LIMIT"

weirdNumbers :: [Integer]
weirdNumbers = filter weird [70..]
               where
               weird n = sum (divisors n) > n && (not . any (==n) . map sum . subsets . divisors) n

divisors :: Integer -> [Integer]
divisors n = filter ((==0) . (mod n)) [1..(n `div` 2)]

subsets :: [a] -> [[a]]
subsets [] = [[]]
subsets (x:xs) = subsets xs ++ map (x:) (subsets xs)