Haskell: how to transfer the contents of one descriptor to another in real time

Question

I am writing a program that launches an external subprocess interactively, and I need the contents of the output descriptor to be output to stdout as soon as it is available. I tried something like this:

main = do processInfo <- createProcess (proc "ghci" []){std_out = CreatePipe,
                                                    std_in  = CreatePipe }
       case processInfo of
          (Just hIn, Just hOut, _, _) -> do mainloop hIn hOut
                                          hClose hIn
                                          hClose hOut
       _                              -> do error "Unable to start process"

mainloop :: Handle -> Handle -> IO ()
mainloop inh outh = 
    do ineof <- hIsEOF outh
       if ineof
          then return ()
          else do inpStr <- hGetLine outh
                  putStrLn inpStr
                  mainloop inh outh

But this will not work, since it only recognizes the output line by line, therefore, no output on the process output descriptor that does not end with a new line is displayed. I tried the same with hGetContents, but it gives the same result. I read the documentation of both System.Process and System.IO and actually did not find anything convincing.

Answer 1

hSetBuffering - , , ( , Unix) . stdin

hSetBuffering hIn NoBuffering

, . , , .

Answer 2

Haskell, , . hSetBuffering, , ?

Answer 3

- , gGetLine, ( ). hGetChar, . btw, - hFlush.