map_insert.hs

import qualified Data.Map as M
import System.Random
import System.Environment
import Control.Monad


insert :: Int -> M.Map Int Int -> [Int] -> M.Map Int Int
insert n m randoms
    | n < 1     = m
    | otherwise = insert (n - 1) new_map new_randoms
        where el = head randoms
              new_randoms = tail randoms
              new_map = M.insert n el m

main = do
    g <- getStdGen
    n <- liftM (read . head) getArgs :: IO Int
    putStrLn . show . M.size $ insert n M.empty $ randomRs (1, 100) g