Help with Exceptions on I/O

[Hal Daume]

you can write this a bit more simply as:

main =3D do=20
  (do do-the-major stuff here
      putStr "File created...")
    `catch` (\_ -> show the error)
  getLine    -- look ma, no <-
  return ()

now, your problem is almost certainly with buffering.  in the main do,
put

  hSetBuffering stdout NoBuffering
  hSetBuffering stdin  NoBuffering

you'll need to import System.IO to get these.

 --
 Hal Daume III                                   | hdaume@isi.edu
 "Arrest this man, he talks in maths."           | www.isi.edu/~hdaume

-----Original Message-----
From: haskell-cafe-admin@haskell.org
[mailto:haskell-cafe-admin@haskell.org] On Behalf Of Alexandre Weffort
Thenorio
Sent: Tuesday, August 12, 2003 4:17 PM
To: haskell@haskell.org
Cc: haskell-cafe@haskell.org
Subject: Help with Exceptions on I/O


I have a program which creates textfiles out of other files. Since the
program is runned from windows I output some text strings (Like "File
created succefully") and I need to stop the program before it quits so
that
the user can read the line outputted to know what went on and then he
can
press ENTER to quit the program.

I managed to do this fine if no error occurs but when a error occurs I
am
having problems.

The code goes like that

main :: IO()
main =3Dcatch (do
                     Do all the needed stuff here
                     putStr "File created Successfully. Press RETURN to
quit"
                     dummy <- getLine --Halts the program so the user
can
read the above line)
                     putStr "Exiting now..." --needed since I can't
finish a
do function with the "dummy<- getLine" line) (\_ -> do putStr "\nFile
not
found. Press RETURN (ENTER) to quit."
     dumb <- getLine
     putStr "\nExiting...")

So when the program runs, if the input file is found the program writes
successfull creation of file but if the file doesn't exist, after the
user
gives the input filename and press enter, the program creates a new line
and
Halts (Probably because of the getLine function) without writing out
anything, then when the user press ENTER again it writes the line at the
first putStr (File not...), then writes the next putStr line under it
(Exiting...) and exits. I don't know why it doesn't wirte the first
line,
halts and then when user press enter it writes the second and quits.

Can anybody help me as I am not very familiar with exception and
catches.


Another question I have is: Is there any other function rather than
getLine
that halts a program and continues when a user press any key (Instead of
ENTER) and besides this is an ugly code since getLine wasn't made for
that
but I couldn't find anything else myself.

Thank you in advance.

Best Regards

Alex=20