cipher.hs

import Data.Char

shouldcipher :: Char -> Bool
shouldcipher c = isLetter (c) && isAscii (c)

cipherchar :: Int -> Char -> Char
cipherchar shift c
  | shouldcipher c = chr (ord (c) + shift)
  | otherwise = c

cipher :: Int -> [Char] -> [Char]
cipher shift plaintext = map (betterchipherchar shift) plaintext

decipher :: Int -> [Char] -> [Char]
decipher shift ciphertext = cipher (- shift) ciphertext

wraparound shift c
  | isLower (c) && ord (c) + shift > ord 'z' = True
  | isUpper (c) && ord (c) + shift > ord 'Z' = True
  | otherwise = False

betterchipherchar :: Int -> Char -> Char
betterchipherchar shift c
  | shouldcipher c = chr (ord (c) + adjustedshift)
  | otherwise = c
  where
    adjustedshift =
      let shift' = shift `mod` 26
       in if (wraparound shift' c)
            then shift' - 26
            else shift'


-- import Test.QuickCheck
-- quickCheck ((\n -> (\s -> ((decipher n (cipher n s)) == s))) :: Int -> [Char] -> Bool)