gets perfect numbers

quitegood.hs

-- usage
-- quitegood test_size tolerance

import System.Environment
import Data.List

getDivisors :: Int -> [Int]
getDivisors n = 
    (1:) $ nub $ concat [ [x, div n x] | x <- [2..limit], rem n x == 0 ]
    where limit = (floor.sqrt.fromIntegral) n

isPerfect :: Int -> Int -> Bool
isPerfect num tol = do
    let val = (sum $ getDivisors num)
    if val - num >= -tol && val - num <= -tol 
    then True else False

main :: IO()
main = do
    args <- getArgs
    let size = (abs $ read $ head args :: Int)
    let tolerance = (abs $ read $ last args :: Int)
    print [n | n <- [2..(size)], isPerfect n tolerance]