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

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+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