Функция декодирования цезаря

lab3/app/Main.hs

@@ -16,4 +16,6 @@ main = do
     let encryptedTextBits = textToBits encryptedText
     putStrLn $ concat (take 30 (map show encryptedTextBits))
     let encryptedTextFromBits = bitsToText encryptedTextBits
-    putStrLn $ take 30 encryptedTextFromBits
+    putStrLn $ take 30 encryptedTextFromBits
+    let decryptedText = decryptCaesar alphabet caesarShift encryptedTextFromBits
+    putStrLn $ take 30 decryptedText

lab3/src/Lib.hs

@@ -2,6 +2,7 @@ module Lib
     ( 
         createAlphabetFromText,
         encryptCaesar,
+        decryptCaesar,
         textToBits,
         bitsToText
     ) where
@@ -28,6 +29,12 @@ encryptCaesar alphabet shift text = map caesarChar text
   where
     caesarChar c = alphabet !! ((indexOf alphabet c + shift) `mod` length alphabet)
 
+decryptCaesar :: [Char] -> Int -> String -> String
+decryptCaesar alphabet shift = 
+  encryptCaesar alphabet (alphabetLength - (shift `mod` alphabetLength)) 
+  where
+    alphabetLength = length alphabet
+
 textToBits :: String -> [Int]
 textToBits = concatMap charToBits
     where charToBits c = [ if testBit (ord c) i then 1 else 0 | i <- [7,6..0] ]