September 2017 Update

Task/Caesar-cipher/Haskell/caesar-cipher-2.hs

@@ -1,32 +1,23 @@
-{-# LANGUAGE LambdaCase #-}
-module Main where
+import Data.Char (ord, chr, isUpper, isAlpha)
 
-import Control.Error (tryRead, tryAt)
-import Control.Monad.Trans (liftIO)
-import Control.Monad.Trans.Except (ExceptT, runExceptT)
+caesar, uncaesar :: Int -> String -> String
+caesar = (<$>) . tr
 
-import Data.Char
-import System.Exit (die)
-import System.Environment (getArgs)
+uncaesar = caesar . negate
+
+tr :: Int -> Char -> Char
+tr offset c
+  | isAlpha c = chr $ intAlpha + mod ((ord c - intAlpha) + offset) 26
+  | otherwise = c
+  where
+    intAlpha =
+      ord
+        (if isUpper c
+           then 'A'
+           else 'a')
 
 main :: IO ()
-main = runExceptT parseKey >>= \case
-           Left err -> die err
-           Right k  -> interact $ caesar k
-
-parseKey :: (Read a, Integral a) => ExceptT String IO a
-parseKey = liftIO getArgs >>=
-           flip (tryAt "Not enough arguments") 0 >>=
-           tryRead "Key is not a valid integer"
-
-caesar :: (Integral a) => a -> String -> String
-caesar k = map f
-    where f c = case generalCategory c of
-              LowercaseLetter -> addChar 'a' k c
-              UppercaseLetter -> addChar 'A' k c
-              _               -> c
-
-addChar :: (Integral a) => Char -> a -> Char -> Char
-addChar b o c = chr $ fromIntegral (b' + (c' - b' + o) `mod` 26)
-    where b' = fromIntegral $ ord b
-          c' = fromIntegral $ ord c
+main = mapM_ print [encoded, decoded]
+  where
+    encoded = caesar (-114) "Curio, Cesare venne, e vide e vinse ? "
+    decoded = uncaesar (-114) encoded