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+module Fix where
+
+import Control.Monad.IO.Class (liftIO)
+import Control.Monad.Trans.Maybe
+import Control.Monad
+
+isValid :: String -> Bool
+isValid v = '!' `elem` v
+
+maybeExcite :: MaybeT IO String
+maybeExcite = do
+ v <- liftIO getLine
+ guard $ isValid v
+ return v
+
+doExcite :: IO ()
+doExcite = do
+ putStrLn "say something excite!"
+ excite <- runMaybeT maybeExcite
+ case excite of
+ Nothing -> putStrLn "MOAR EXCITE"
+ Just e ->
+ putStrLn
+ ("Good, was very excite: " ++ e)