cata.hs

import Data.Char
import Control.Monad
import Control.Applicative

para :: (a -> b -> [a] -> b) -> b -> [a] -> b
para f e [] = e
para f e (x:xs) = para f (f x e xs) xs

main = do
  n <- getLine
  let digits = map (\d -> ord d - ord '0') n
  let isMagic = para (\d b ds -> b && d > sum ds) True digits
  when isMagic $ putStrLn n
  main

tr.pl

$_=<>;/^(.)(.*)/;$s=$1;$t=$2;$t=~tr/[a-y]z/[b-z]a/;print"$s$t"