I haven't made anything more elegant, but have a few improvements that I found made it more fun to play (and yes, I'm rather zoned out after spending most of the day solving electromagnetism problems). It's nice (and quite easy) to save the tree, so that the game is more exciting every time you play. With a bit of work and integration with darcs, you could probably interface with a public server, so the guesser can be collaboratively improved by people who have too much time on their hands or are too tired to do anything productive. Here's the improved code: \begin{code} module Main where import Data.Char ( isUpper ) data GuessTree = Answer String | GuessTreeQuestion {guessTreeQuestion :: String, guessTreeNo, guessTreeYes ::GuessTree} deriving (Show, Read) askQuestion :: String -> IO Bool askQuestion str = do putStrLn str response <- getLine return $ isYes response where isYes ('y':xs) = True isYes _ = False a :: String -> String a s@(c:_) | isUpper c = s | c `elem` "aeiou" = "an " ++ s | otherwise = "a " ++ s a "" = "nonexistent" runTree :: GuessTree -> IO GuessTree runTree (Answer name) = do response <- askQuestion $ "Is it " ++ a name ++ "?" if response then do putStrLn "Ha!" return $ Answer name else do putStrLn "What is it?" animal <- getLine putStrLn $ "Enter a question to help distinguish between " ++ a name ++ " and " ++ a animal question <- getLine a <- askQuestion $ "Is the answer yes for " ++ animal ++ "?" (if a then id else flip) (\n y -> return $ GuessTreeQuestion {guessTreeQuestion = question, guessTreeNo = n, guessTreeYes = y}) (Answer animal) (Answer name) runTree GuessTreeQuestion {guessTreeQuestion = ques, guessTreeYes = yesTree, guessTreeNo = noTree} = do response <- askQuestion $ ques if response then do a <- runTree noTree return $ GuessTreeQuestion {guessTreeQuestion = ques, guessTreeNo = a, guessTreeYes = yesTree} else do a <- runTree yesTree return $ GuessTreeQuestion {guessTreeQuestion = ques, guessTreeNo = noTree, guessTreeYes = a} run :: GuessTree -> IO GuessTree run tree = do putStrLn "Think of an animal and press enter." getLine a <- runTree tree writeFile "animaldata" $ show a r <- askQuestion "Play again?" if r then run a else return a read_animal :: IO GuessTree read_animal = (read `fmap` readFile "animaldata") `catch` \_ -> return $ Answer "bear" main = read_animal >>= run \end{code} As you can see, I also modified it so that it'll be a bit smarter about not saying things like "a David Roundy" or "a elephant". -- David Roundy Dept. of Physics Oregon State University