caesar_cipher.hs

import Data.Char

let2int initchr c = ord c - ord initchr

int2let initchr n = chr (ord initchr + n)

lower2int = let2int 'a'
upper2int = let2int 'A'

int2lower = int2let 'a'
int2upper = int2let 'A'

shiftcase n c int2case case2int =
  int2case ((case2int c + n) `mod` 26)

shift n c
  | isLower c = shiftcase n c int2lower lower2int
  | isUpper c = shiftcase n c int2upper upper2int
  | otherwise = c

encode n xs = [shift n x | x <- xs]