ShiftString.hs

module ShiftString where

import Data.Char

data CharacterNumber
    = Lower Int
    | Upper Int

add' :: CharacterNumber -> Int -> CharacterNumber
add' (Lower a) b = Lower (a + b)
add' (Upper a) b = Upper (a + b)

mod' :: CharacterNumber -> Int -> CharacterNumber
mod' (Lower a) b = Lower (a `mod` b)
mod' (Upper a) b = Upper (a `mod` b)

let2int :: Char -> CharacterNumber
let2int c
    | isLower c = Lower (ord c - ord 'a')
    | otherwise = Upper (ord c - ord 'A')

int2let :: CharacterNumber -> Char
int2let (Lower n) = chr $ ord 'a' + n
int2let (Upper n) = chr $ ord 'A' + n

shift :: Int -> Char -> Char
shift n c = int2let $ (let2int c `add'` n) `mod'` 26

encode :: Int -> String -> String
encode n xs = [shift n x | x <- xs]