-- package Main
import Control.Monad

data KolakoskiStep =
    Singular Int |
    Double Int Int deriving (Show)

getNext :: [Int] -> Int -> KolakoskiStep
getNext kolakoski index = do
    let current_len = kolakoski !! index
    let last_len = kolakoski !! (index - 1)
    let last_val = last kolakoski
    let len = length kolakoski
    let last_influenced = (index /= (len - 1))
    if current_len == 1 then
        Singular (3 - last_val)
    else
        if last_len == 1 && not last_influenced then
            Singular last_val
        else Double (3 - last_val) (3 - last_val)

loop kolakoski index =
    if ((length kolakoski) < 100) then do
        case getNext kolakoski index of
            Singular a -> loop (kolakoski ++ [a]) (index + 1)
            Double a b -> loop (kolakoski ++ [a, b]) (index + 1)
    else print kolakoski



main :: IO ()
main = do
    loop [1, 2] 1