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diff --git a/Haskell-book/09/src/Cipher.purs b/Haskell-book/09/src/Cipher.purs
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+module Cipher where
+
+import Data.Char (fromCharCode, toCharCode)
+import Data.String (fromCharArray, toCharArray)
+import Prelude
+
+caesar :: Int -> String -> String
+caesar key s = fromCharArray $ map shiftRight (toCharArray s)
+  where shiftRight char = fromCharCode $ mod (ord char) 26
+        ord = (add key) <<< toCharCode
+
+unCaesar :: Int -> String -> String
+unCaesar key s = fromCharArray $ map shiftLeft (toCharArray s)
+  where shiftLeft char = fromCharCode $ ord char
+        ord chr = ((toCharCode chr) - (mod key 26)) + 26