Haskell Fun Cesar Cypher

cesar.hs

-- import Data.List
import Data.Char
import Data.Maybe
import System.Environment
-- import System.IO 
import Control.Monad 
import Text.Read

-- Evaluate if a value is between two other
between :: (Ord a) => a -> a -> a -> Bool
between bottom top target = (target >= bottom) && (target <= top)

-- Do a rotation on the alphanumeric value
rotateChar :: Int -> Char -> Char
rotateChar nR input
 | between 48 57  inputOrd = rotBV 48 nR inputOrd 10
 | between 65 90  inputOrd = rotBV 65 nR inputOrd 25
 | between 97 122 inputOrd = rotBV 97 nR inputOrd 25
 | otherwise = input
 where inputOrd = ord input
       rotBV base value char modMax = let modOrd = mod (char-base) modMax 
                               in chr $ base + (mod (modOrd+value) modMax)

-- Apply rotate to a string
encrypt :: Int -> String -> String
encrypt nR (inChar:[]) = rotateChar nR inChar : []
encrypt nR (inChar:tl) = rotateChar nR inChar : encrypt nR tl 

main = do 
 args <- getArgs
 if not (length args == 1)
  then putStr "The program need 1 and only 1 argument.\n"
  else do
   let nR = readMaybe (args!!0) :: Maybe Int
   if isJust nR 
    then interact $ encrypt $ fromJust nR
    else putStr "The argument need to be an interger.\n"