[Haskell-cafe] Re: process

Jules Bean writes:

Well that depends entirely what your program is supposed to do.

Your email doesn't tell us (a) what your program was supposed to do or (b) what goes wrong. Therefore we are forced to guess!

The following slight variation of your program works fine for me. I don't have anything called 'prog1' on my system, so I used 'bc' which is a calculator program standard on unixes, which works by line-by-line interaction. I varied your program just a tiny bit to get some interesting output:

module Main where import System.Process import System.IO

main :: IO () main = do putStrLn "Running BC" (inp,out,err,pid) <- runInteractiveProcess "bc" [] Nothing Nothing hSetBuffering inp LineBuffering hSetBuffering out LineBuffering hSetBuffering err LineBuffering hPutStrLn inp "1+3" a <- hGetLine out hPutStrLn inp a a <- hGetLine out hPutStrLn inp "quit" waitForProcess pid putStrLn a

This program asks 'bc' to calculate "1+3". The reply is stored in 'a'. Then the program sends 'a' back to bc, effectively asking bc to calculate "4". Since the "4" evaluates just to "4", 'a' gets the value "4" once more.

Then I have to send "quit" to bc. That is the command that "bc" interprets as an instruction to quit; without that command, 'waitForProcess pid' will wait forever (it's waiting for bc to quit).

Finally my program outputs "4" the result of the last calculation.

Is this close to what you're trying to do?

Jules

Thanks, but I still puzzle over the same problem. I wrote the following lines to test exactely your code: module Main where main :: IO () main = f where f = do a <- getLine if a == "quit" then return () else putStrLn a >> f running the program in the console works without any problems ("1+3" is the result :) ), but with runInteractiveProcess I do not get any output except "Running BC", and every IO action after the first hPutStrLn inp "1+3" is never reached (the program hang-up there - no error is thrown) - thats my problem...