import Text.ParserCombinators.Parsec
import Control.Monad
import Data.List

left = "([{"   -- |список левых скобок
right = ")]}"  -- |список правых скобок

check = (do
    l <- oneOf left
    check
    r <- oneOf right
    when (elemIndex l left /= elemIndex r right) $ fail ""
    check)
  <|> return ()

isRightString s =
    case parse (check>>(char '\n')) "" (s ++ "\n") of
        Left _ -> False
        Right _ -> True

isGood "" = true
isGood x:xs = ((elemIndex x left) ==  (elemIndex (lastChar xs) right)) and (isGood (middlePartOf xs))

isGood "{[]}()" = False