2016 Update

Task/Caesar-cipher/Haskell/caesar-cipher-1.hs

@@ -0,0 +1,16 @@
+module Caesar (caesar, uncaesar) where
+
+import Data.Char
+
+caesar, uncaesar :: (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
+uncaesar k = caesar (-k)
+
+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

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

@@ -0,0 +1,32 @@
+{-# LANGUAGE LambdaCase #-}
+module Main where
+
+import Control.Error (tryRead, tryAt)
+import Control.Monad.Trans (liftIO)
+import Control.Monad.Trans.Except (ExceptT, runExceptT)
+
+import Data.Char
+import System.Exit (die)
+import System.Environment (getArgs)
+
+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

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

@@ -1,17 +0,0 @@
-import Data.Char (ord, chr)
-import Data.Ix (inRange)
-
-caesar :: Int -> String -> String
-caesar k = map f
-  where
-    f c
-      | inRange ('a','z') c = tr 'a' k c
-      | inRange ('A','Z') c = tr 'A' k c
-      | otherwise = c
-
-unCaesar :: Int -> String -> String
-unCaesar k = caesar (-k)
-
--- char addition
-tr :: Char -> Int -> Char -> Char
-tr base offset char = chr $ ord base + (ord char - ord base + offset) `mod` 26