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

20 Feb 2006


      I'm also using GHC 6.4.1 and rxvt v2.7.10. The problem does occur in 
compiled code, but everything is OK in ghci!
   hFlush stdout did solve the problem, as expected.
   I've just started using rxvt. If you have tips on how to make ghci 
work well with rxvt, please share them with me (for instance, how to set 
the top arrow to repeat the last line, instead of moving the cursor one 
live above. I don't understand very well how those applications handle 
keyboard).

   Best,
   Maurício

Emil Axelsson wrote:
...
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  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
_______________________________________________
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
_______________________________________________
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe