Running haskell executable using Java ProcessBuilder: why does hGetLine only return after closing outputStream?

I am terminating a FM-SBLEX Saldo program in a Java library.

Saldo is written in Haskell and searches the lexicon for strings given to stdin, for example

echo "ord"|./sblex/bin/saldo dicts/saldo.dict

      

        
        
        
      

    

outputs something like the following to stdout

{"ord":{"s_1":{"word":"ord","head":"sanna mina ord","pos":"abm","param":"invar 1:3-3","inhs":[],"id":"sanna_mina_ord..abm.1","p":"abm_i_till_exempel","attr":"3"},...

      

        
        
        
      

    

If I run it with

./sblex/bin/saldo dicts/saldo.dict

      

        
        
        
      

    

it searches every line I typed in the console until I submit an EOF.

In my Java library, I run it with ProcessBuilder and set up a stream to output stdout and stderr to my stdout program, and another stream writes word and newline and then clears the outputStream

On the console, saldo returns results every time I hit return, but in my wrapper, it only returns results for all of my input once when I close the outputStream (see close () commented out in the following code block)

    ProcessBuilder pb = new ProcessBuilder(binPath, dictPath);

    pb.redirectErrorStream(true);
    saldoProcess = pb.start();

    new Thread(new Reader(saldoProcess.getInputStream())).start();
    new Thread(new Writer(saldoProcess.getOutputStream())).start();

    saldoProcess.waitFor();
    System.out.println("saldo exited.");
    Thread.sleep(2000);

      

        
        
        
      

    

Shutting down Writer:

    public void run() {
        try {
            outputStream.write("ord\n".getBytes());
            outputStream.flush();
            //outputStream.close();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

      

        
        
        
      

    

Haskell code that reads input

run' :: Language a => a -> (String -> [Tok]) -> (String -> [[String]]) -> AnaType -> Stats -> IO Stats
run' l tokenizer f a st = 
 do b <- hIsEOF stdin
    if b then return st 
     else do 
       s <- hGetLine stdin
       analyze l a f (tokenizer s) st >>= run' l tokenizer f a

      

        
        
        
      

    

If binPath = "cat" and dictPath = "-" then my java program prints the input after every reset. Any idea why this haskell program only deals with input after closing the output stream?

NB: as the answer shows, there was no hGetLine that didn't return (as I assumed), but output that was buffered because the Haskell implementation I use by default to block the buffer if it is not run from the console.