dart outs

For those who like to play X01 Games.
Update: with an unexpected application to Project Euler #109!

import Control.Applicative (liftA2)
import Data.List (sort, nub, sortBy, maximum)
import Data.Ord (comparing)
import System.Environment (getArgs)
  
data Dart n = Single n | Double n | Triple n | Bull | None deriving Show
  
main = mapM_ print . out . read . head =<< getArgs
  
out n = check . sort' . map (map dart) $ sortBy (comparing maximum) sums
 where
  check ns = if null ns then [None] else head ns
  sort'    = sortBy (comparing $ sum . map ease)
  sums     = nub $ filter ((== n) . sum) combos
  
---------------------------------------------------------------------------
  
combos = concat $ zipWith combosOf [1..3] $ repeat segments
  
segments = concat $ replicate 3 $ sort $ 50 : liftA2 (*) [1..3] [1..20]
   
dart n
  | n == 50    = Bull
  | n `elem` s = Single n
  | n `elem` d = Double (n `div` 2)
  | n `elem` t = Triple (n `div` 3)
 where
  [s,d,t] = liftA2 (map . (*)) [1..3] [[1..20]]
                  
ease (Single _) = 1
ease (Bull)     = 2
ease (Double _) = 3
ease (Triple _) = 4
                   
combosOf 0 _      = [[]]
combosOf _ []     = []
combosOf k (x:xs) = map (x:) (combosOf (k-1) xs) ++ combosOf k xs