[Haskell-cafe] Re: Unexpected results with simple IO

[Emil Axelsson]

What version of GHC are you using?
Your code works for me in rxvt in Cygwin, with GHC 6.4.1. But I remember having 
that same problem earlier (in some earlier GHC version, so it may be fixed by now).

The solution was to run hFlush after each putStr, like so:

   import System.IO (hFlush, stdout)

   do putStr "..."
      hHlush stdout
      ...

If I remember correctly, the problem only occurred in GHCi and Hugs -- not when 
compiling the code.

/ Emil



Maurício skrev:
>   You're right... I was running the example in rxvt, in cygwin. Now I 
> tried in Windows command shell and it works.
> 
>   Thanks,
>   Maurício
> 
> Cale Gibbard wrote:
>> That doesn't happen for me at all, it works just fine. Maybe it's
>> something wrong with your terminal? You could possibly try playing
>> with the buffering settings on stdout, using hSetBuffering in
>> System.IO.
>>
>>  - Cale
>>
>> On 17/02/06, Maurício <briqueabraque at yahoo.com> wrote:
>>
>>>   Dear Haskell users,
>>>
>>>   I have a problem using IO. The small test program below asks the user
>>> to guess from a list of random numbers between 1 and 10. Everything
>>> works well excepts for one problem: all the messages ("Guess a
>>> number...", "Right..." and "Wrong...") are printed after the program
>>> finishes, i.e., I have to use it blind. I'm afraid I misunderstand
>>> something important about lazyness or monads... What am I doing wrong?
>>>
>>>   Thanks,
>>>   Maurício
>>>
>>> module Main where
>>> import Random
>>>
>>> main = do
>>>    r_gen <- getStdGen --random generator
>>>    let r_list = (randomRs (1,10) r_gen) --random list
>>>    guess_loop (r_list)
>>>
>>> guess_loop (r:r_others) = do
>>>    putStrLn "Guess a number between 1 and 10:"
>>>    n <- readLn
>>>    if n==r
>>>       then do
>>>          putStrLn "Right! :)"
>>>          return ()
>>>       else do
>>>          putStrLn "Wrong... :("
>>>          guess_loop r_others
>>>
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> 
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