[Haskell-cafe] Simple program. Simple problem?

[Peter Verswyvelen]

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 <bugfact at gmail.com>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')?
> h
> 104
> You win!
> What's your guess, heads or tails ('h' or 't')?
> *10*
> You 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 <nowgate at yahoo.com> 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
>>
>> =======
>>
>> [michael at 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
>> [michael at localhost ~]$
>>
>>
>>
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>>
>
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