import qualified Data.IntMap as I
import Control.Monad
import Data.List
import Data.Maybe
import System.Random

main :: IO ()
main = do
  rd  <- replicateM 100000 $ rollIkasamaDice (take 6 $ cycle [1,2])
  rd1 <- replicateM 100000 $ rollIkasamaDice (map sqrt [1..4])
  let im  = foldr (I.update ((Just $!) . succ)) im0 rd
      im0 = I.fromList $ zip [1..6] [0,0..]
  print im

rollIkasamaDice :: [Double] -> IO Int
rollIkasamaDice dist = do
  d <- getStdRandom (randomR (0, 1)) :: IO Double
  let thr = scanl1 (+) $ map . flip (/) =<< sum $ dist
      a   = zip thr [1..] :: [(Double, Int)]

  return $ snd $ fromJust $ find ((d <=) . fst) a