import Data.List
import Numeric
import Text.Printf

-- Use the built-in function showIntAtBase.
toBin n = showIntAtBase 2 ("01" !!) n ""

-- Implement our own version.
toBin1 0 = []
toBin1 x =  (toBin1 $ x `div` 2) ++ (show $ x `mod` 2)

-- Or even more efficient (due to fusion) and universal implementation
toBin2 = foldMap show . reverse . toBase 2

toBase base = unfoldr modDiv
  where modDiv 0 = Nothing
        modDiv n = let (q, r) = (n `divMod` base) in Just (r, q)


printToBin n = putStrLn $ printf "%4d  %14s  %14s" n (toBin n) (toBin1 n)

main = do
  putStrLn $ printf "%4s  %14s  %14s" "N" "toBin" "toBin1"
  mapM_ printToBin [5, 50, 9000]