Original is here:
https://inventwithpython.com/bigbookpython/project80.html
Haskell version:
{-| Vigniere Cipher console program based on the version in _The Big Book of
Small Python Projects_ by Al Sweigart. -}
{-# LANGUAGE LambdaCase #-} -- Used to enable LambdaCase syntax to simplify a code section.
module Main where
import Data.Char (chr, isAlpha, isUpper, ord, toUpper)
import System.Clipboard (setClipboardString)
import Data.List (mapAccumL) -- used to map while holding an accumulator
import Data.Foldable (traverse_) -- used to turn a list into an fstring-like structure
type VigenereKey = [Int] -- ^ Type synonym for the key structure (list of keys) to make it a bit more readable.
makeKey :: String -> VigenereKey -- ^ Converts a string to a list of offsets
makeKey = fmap (subtract 65 . ord . toUpper) . filter isAlpha
data VigDirection = Encrypt | Decrypt -- ^ Enum type to avoid using strings; idiomatic.
encrypt, decrypt :: VigenereKey -> String -> String -- ^ Convenient synonyms to avoid directly using applyKey.
encrypt = applyKey Encrypt; decrypt = applyKey Decrypt
{-| Actual encryption decryption function, takes advantage of the fact that
encryption and decryption are just one function apart. -}
applyKey :: VigDirection -> VigenereKey -> String -> String
applyKey vigDirection [] text = text
applyKey vigDirection key text =
{-mapAccumL allows us to map with an accumulator, which is basically a mutable variable,
from left to right with the accumulator being updated by the mapping function.
The result is a tuple of the final accumulator and the mapped data structure.
Haskell's pervasive laziness allows me to use an infinite list generated by cycle as an accumulator!-}
snd $ mapAccumL adjustAlphaNumerics (cycle key) text
where
adjustAlphaNumerics keySpool@(keyShift:restOfKeys) character
| not $ isAlpha character = (keySpool, character) -- Keep the accumulator unchanged, return character.
| otherwise = -- take the first element off the accumulator, encrypt / decrypt the character
( restOfKeys
, chr . (+ shiftFactor) . flip mod 26
. shiftEncryptOrDecrypt . subtract shiftFactor
$ ord character)
where
shiftFactor
| isUpper character = 65
| otherwise = 97
shiftEncryptOrDecrypt = case vigDirection of
Encrypt -> (+ keyShift)
Decrypt -> subtract keyShift
main :: IO () -- ^ Actual user-facing code. "Imperative shell, functional core."
main = do -- Build a basic schematic of the program in main.
introduction
getAndProcessInputs >>= -- Bind to allow the following function to act directly
-- on the output of the preceding IO action.
showResultsAndCopyToClipboard
where -- fill out the details in the where clause.
introduction = putStrLn
"Haskell Vigenere Cipher, by Liam Zhu Liam.Zhu@protonmail.com\n\
\Adapted from Vigenere Cipher in _The Big Book of Small Python\n\
\Projects_ by Al Sweigart al@inventwithpython.com.\n\
\The Vigenere cipher is a polyalphabetic substitution cipher that was\n\
\powerful enough to remain unbroken for centuries."
getAndProcessInputs = do
programMode <- getProgramMode
key <- makeKey <$> entryPrompt "Please specify the key to use.\n\
\It can be a word or any combination of letters."
text <- entryPrompt $ "Enter the message you wish to " <> case programMode of
Encrypt -> "encrypt."
Decrypt -> "decrypt."
let processedMessage = (case programMode of
Encrypt -> encrypt
Decrypt -> decrypt) key text
pure (programMode, processedMessage)
{-| Here, we need a separate definition for getProgramMode since it loops/recurses into itself.
We direct bind the LambdaCase for concision here; the LambdaCase reads the result and
chooses either to return a Encrypt or Decrypt enum, or show an error and loop back into itself.-}
getProgramMode = entryPrompt "Do you want to (e)ncrypt or (d)ecrypt?" >>= \case
"e" -> pure Encrypt
"d" -> pure Decrypt
_ -> do
putStrLn "Unrecognized input."
getProgramMode
showResultsAndCopyToClipboard (programMode, processedMessage) = do
setClipboardString processedMessage
traverse_ putStrLn -- traverse is used here to apply putStrLn to a list, which would
-- be an f-string in Python.
[ case programMode of; Encrypt -> "Encrypted message:"; Decrypt -> "Decrypted message:"
, processedMessage
, "Full " <> (case programMode of; Encrypt -> "encrypted"; Decrypt -> "decrypted")
<> " text copied to clipboard."
]
entryPrompt :: String -> IO String -- ^ Supporting prompt function.
entryPrompt str = do
putStrLn str
putStr "> "
getLine
A relatively simple program, with the user-facing IO section being quite large, helped in part by the "pure" section being tiny. I took the liberty of choosing a more Haskelly idiom with the main being outlined and then defined through the where clause over a Pythonic block-oriented approach.
Even then, because of the complexity of the Vigenere enciphering code, we still end up beating the Python version by around 5-10%, with more verbose comments to make clear some unique Haskell features / idioms.
Haskell in general can easily beat out Python when it comes to data transformation code, but starts to lag when it comes to the IO layer (imperative side), especially when you take a more principled Haskell approach, name your blocks, and build an outline.
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