reworking functions and errorhandling

Main.hs

@@ -72,6 +72,34 @@ data Based = Decode {
              deriving(Show, Data, Typeable) 
 
 -- helper functions
+
+convertToByteString :: String -> Either String BS.ByteString
+convertToByteString str =
+   case BSU.fromString str of
+     Just bs -> Right bs
+     Nothing -> Left "Failed to convert string to ByteString."
+
+decodeFromBase91 :: C.ByteString -> Either String BS.ByteString
+   case B91.decode bs =
+      Just bs -> Right decoded
+      Nothing -> Left "Failed to decode from Base91."
+
+
+encodeToBase64 :: C.ByteString -> Either String BS.ByteString
+encodeToBase64 bs =
+   case B64.encode bs of
+     encoded | BS.null encoded -> Left "Failed to encode base64."
+             | otherwise -> Right encoded
+
+decodeFromBase64 :: C.ByteString -> Either String BS.ByteString
+decodeFromBase64 bs =
+   case B64L.decodeLenient bs of 
+     decoded | BS.null decoded -> Left "Failed to decode from base64."
+             | otherwise -> Right decoded
+             -- | otherwise -> Right (BSU.toString decoded)
+     -- Left err -> Left $ "Failed to decode from base64: " ++ err
+     -- Right decoded -> Right decoded
+
 binToInt :: [Int] -> Int
 binToInt [] = 0
 binToInt (x : xs) = x + 2 * binToInt xs
@@ -82,13 +110,33 @@ octToInt (x : xs) = x + 8 * octToInt xs
 
 -- base functions
 -- without the show func, sequences like \n will not be shown as characters but will be executed as newline
-dec91 = C.unpack . B91.decode
+
+-- dec91 = C.unpack . B91.decode
+dec91 :: C.ByteString -> Either String String
+dec91 input = do
+   decoded <- decodeFromBase91 input
+   -- return $ C.unpack decoded
+   -- is the same as
+   return (C.unpack decoded)
+   
 enc91 = B91.encode . BSU.fromString
 dec85 = C.unpack . U.fromRight . B85.decode . BSU.fromString
 enc85 = C.unpack . B85.encode . BSU.fromString
--- dec64 = C.unpack . U.fromRight . B64.decode . BSU.fromString
+
-dec64 = C.unpack . B64L.decodeLenient . BSU.fromString
+-- dec64 = C.unpack . B64L.decodeLenient . BSU.fromString
-enc64 = C.unpack . B64.encode . BSU.fromString
+dec64 :: String -> Either String String
+dec64 input = do
+   byteString <- convertToByteString input
+   decoded <- decodeFromBase64 byteString
+   return $ BSU.toString decoded
+
+-- enc64 = C.unpack . B64.encode . BSU.fromString
+enc64 :: String -> Either String String
+enc64 input = do
+   byteString <- convertToByteString input
+   encoded <- encodeToBase64 byteString
+   return $ BS.unpack encoded
+
 dec64url = C.unpack . U.fromRight . B64U.decode . BSU.fromString
 enc64url = C.unpack . B64U.encode . BSU.fromString
 decurl = HB.urlDecode