Convert mistyped text from English keyboard to Russian

en2ru.hs

import Data.Maybe (maybe)
import Data.Char (toUpper)
import System.IO (hGetContents, stdin)
import Control.Monad (liftM, forM_)

ruKeysL = "ёйцукенгшщзхъфывапролджэячсмитьбю"
ruKeysU = map toUpper ruKeysL
ruKeysP = ".,"

enKeysL = "`qwertyuiop[]asdfghjkl;\'zxcvbnm,."
enKeysU = "~QWERTYUIOP{}ASDFGHJKL:\"ZXCVBNM<>"
enKeysP = "/?"

ruKeys = ruKeysL ++ ruKeysU ++ ruKeysP
enKeys = enKeysL ++ enKeysU ++ enKeysP

en2ruChar :: Char -> Char
en2ruChar c = maybe c id (lookup c (zip enKeys ruKeys))

en2ruStr :: String -> String
en2ruStr = map en2ruChar

en2ru :: String -> IO ()
en2ru = putStrLn . en2ruStr

main :: IO ()
main = 
  do putStrLn "Paste your text here"
     putStrLn "Print in the end this line: 'xxx'"
     input' <- liftM lines (hGetContents stdin)
-- weird construction to postpone output until input is fully recieved
     if elem "xxx" input'
        then return ()
        else return ()
     let input = takeWhile (/= "xxx") input'
     forM_ input en2ru