Thanks for the tip, and the lazy example.
I think I'm finally beginning to "get" monads, so I decided to test my understanding with this small example. So far so good, except for that little bump in the road. Onward and upward. Michael --- On Sun, 10/11/09, Peter Verswyvelen <[email protected]> wrote: From: Peter Verswyvelen <[email protected]> Subject: Re: [Haskell-cafe] Simple program. Simple problem? To: "michael rice" <[email protected]> Cc: [email protected] Date: Sunday, October 11, 2009, 6:42 PM btw I always find it amusing to play with interact and lazy IO: guess :: [Char] -> [String] -> [String]guess (c:cs) ~(i:is) = "What's your guess, heads or tails ('h' or 't')?" : (if [c]==i then "You win!" else "You lose!") : guess cs is main = do gen <- getStdGen let rs = randomRs (0,1::Int) gen cs = map ("ht"!!) rs interact $ unlines . guess cs . lines On Mon, Oct 12, 2009 at 12:24 AM, Peter Verswyvelen <[email protected]> wrote: It always helps to put a Debug.Trace.trace: in if trace (show (fromEnum c)) $ c == ((!!) "ht" randInt) then p What's your guess, heads or tails ('h' or 't')? h104You win!What's your guess, heads or tails ('h' or 't')?10You lose!What's your guess, heads or tails ('h' or 't')? So getChar also receives the linefeed character. An easy way to get around this, is to use getLine instead and just use the first character, as in >> fmap head getLine But of course we're hacking away here :-) On Mon, Oct 12, 2009 at 12:10 AM, michael rice <[email protected]> wrote: What is going wrong here? Michael ======= import System.Random coinToss :: StdGen -> IO () coinToss gen = putStrLn "What's your guess, heads or tails ('h' or 't')?" >> getChar >>= \c -> let (randInt, _) = randomR(0,1) gen :: (Int, StdGen) in if c == ((!!) "ht" randInt) then putStrLn "You win!" else putStrLn "You lose!" main = do gen <- getStdGen coinToss gen gen <- newStdGen main ======= [mich...@localhost ~]$ runhaskell cointoss.hs What's your guess, heads or tails ('h' or 't')? h You win! What's your guess, heads or tails ('h' or 't')? You lose! What's your guess, heads or tails ('h' or 't')? h You lose! What's your guess, heads or tails ('h' or 't')? You lose! What's your guess, heads or tails ('h' or 't')? ^Ccointoss.hs: cointoss.hs: interrupted [mich...@localhost ~]$ _______________________________________________ Haskell-Cafe mailing list [email protected] http://www.haskell.org/mailman/listinfo/haskell-cafe
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