Josephus problem

gistfile1.hs

import Data.Sequence as Seq
import System.Environment

survivor :: Int -> [a] -> a
survivor k soldiers = viewnext k (Seq.fromList soldiers)
  where
    viewnext l list    = killnext l (Seq.viewl list)
    killnext l (x:<xs) | Seq.null xs = x
                       | l == 1      = viewnext k xs
                       | otherwise   = viewnext (l-1) (xs|>x)

main = do
    args <- getArgs
    let k = read (args!!0) :: Int
        n = read (args!!1) :: Int
    print $ survivor k [1..n]