{-# LANGUAGE DeriveFunctor #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE OverloadedStrings #-}
module Crypto.Classical.Cipher.Substitution where
import Crypto.Classical.Types
import Crypto.Classical.Util
import qualified Data.ByteString.Lazy.Char8 as B
import Data.Char
import Data.Map.Strict (Map)
import qualified Data.Map.Strict as M
newtype Substitution a = Substitution { _substitution :: a }
deriving (Eq,Show,Functor)
instance Applicative Substitution where
pure = Substitution
Substitution f <*> Substitution a = Substitution $ f a
instance Monad Substitution where
return = pure
Substitution a >>= f = f a
instance Cipher (Map Char Char) Substitution where
encrypt m = pure . B.map f
where f c | isLower c = f $ toUpper c
| otherwise = M.findWithDefault c c m
decrypt m = encrypt (mapInverse m)