-- import Control.Lens
import Data.Char
import Data.List

extract (x:xs) recv = extract xs $ \n s -> if '0' <= x && x <= '9' then recv (n ++ [x]) s else recv n (s ++ [x])
extract []     recv = recv [] []

assemble s = extract s $ \n s -> putStrLn n >> putStrLn s

-- assemble' = mapMOf_ both putStrLn . foldl' (\a c -> a & (if isDigit c then _1 else _2) %~ cons c) ([], [])
-- assemble'' = mapMOf_ both putStrLn . partition isDigit . reverse

main :: IO ()
main = assemble "x51ca2yz"