Find Perfect Numbers

perfect.purs

-- http://www.mrpowell.net/progra/javascript/project4/project4.htm

-- A perfect number is a number where the sum of all the divisors is equal to two times the number. For example.
-- The divisors of the number 6 are 1, 2 , 3 and 6. 2 times 6 is 12. 
-- 2 * 6 = 1 + 2 + 3 + 6 
-- Write a Java script program which will output the first nine perfect numbers. 

import Data.Foldable (fold, sum)
import Data.List (List(..), (:), range, filter, reverse)
import Data.Int (toNumber)
import Math ((%))

divisors :: Int -> List Int
divisors n =
  filter (\d -> (toNumber n) % (toNumber d) == 0.0) $ range 1 n

isPerfect :: Int -> Boolean
isPerfect n =
  (2 * n) == sum (divisors n)

perfects :: List Int
perfects =
  go Nil 1
  where
    -- Yeahhh... this whole thing is O(n^2) or worse, so good luck finding more than 4
    go :: List Int -> Int -> List Int
    go list@(a : b : c : d : Nil) _ =
      list
    go soFar curr =
      let l = if isPerfect curr then (curr : soFar) else soFar
      in
        go l (curr + 1)