project euler #1

pe1.hs

-- http://projecteuler.net/index.php?section=problems&id=1
--
-- If we list all the natural numbers below 10 that are multiples of 3 or 5, we
-- get 3, 5, 6 and 9. The sum of these multiples is 23.
--
-- Find the sum of all the multiples of 3 or 5 below 1000.

main :: IO ()
main = print answer

answer :: Integer
answer =
    sum [ n
        | n <- [1..999]
        , n `isMultipleOf` 3 || n `isMultipleOf` 5
        ]
  where
    isMultipleOf x y = x `mod` y == 0