import Data.Char↲
↲
 main = interact parse↲
↲
parse :: String -> String↲
parse [] = []↲
parse (x:xs)↲
    | x == '@' = runlength xs↲
    | otherwise = x : parse xs↲
↲
runlength :: String -> String↲
runlength (x:y:xs) = replicate n y ++ parse xs↲
    where n = digitToInt x
