本地验证通过了，但是提交上去一直报RE,请大佬帮忙看下

module Main where

import Control.Monad.Reader
import Control.Monad.State
import Data.Char

main :: IO ()
main = do
  n <- read <$> getLine
  m <- reverse <$> getLine {- for high-precision calculations, start with single digits and work backwards -}
  putStrLn . flip runReader n . flip evalStateT 0 $ judge 0 m

type CarryBaseEnv = StateT Int {- carry -} (Reader Int {- base -})

addBaseN :: Char -> Char -> CarryBaseEnv Char
addBaseN ch1 ch2 = do
  baseN <- ask
  carry <- get
  let [num1, num2] = digitToInt <$> [ch1, ch2]
      (carryNext, rest) = divMod (num1 + num2 + carry) baseN
  put carryNext
  return . intToDigit $ rest

addBaseN' :: String -> String -> CarryBaseEnv String
addBaseN' str1 str2 = do
  put 0
  eachBit <- foldl (\x y -> (:) <$> y <*> x) (return mempty) $ uncurry addBaseN <$> zip str1 str2
  carry <- get
  return . (if carry == 1 then ('1' :) else id) . reverse $ eachBit

judge :: Int -> String -> CarryBaseEnv String
judge n str = if n < 30
      then
        let rStr = reverse str
         in if str == rStr then return . showString "STEP=" $ show n else addBaseN' str rStr >>= (judge (n + 1))
      else return "Impossible!"