Using Haskell's GHCI through a Java Program

Question

What I would like to do is wrap my Java program around the GHCI. In my mind it should work like this:

1. Starting my Java program
2. Write down some Haskell function as Input for Java (i.e. reverse [1,2,3,4])
3. See the appropriate Haskell Output on my Java Console

Because I did not want to mess around with any language bridges I tried the clumsy way and used the Runtime.exec() approach.

This is my Code:

public static void main(String[] args) throws Exception {
Runtime r = Runtime.getRuntime();
Process p = r.exec("ghci");
OutputStream output = p.getOutputStream();
output.write("let x = 5\r\n".getBytes());
output.write("x".getBytes());

int tmp;
String result = "";
while ((tmp = p.getInputStream().read()) != -1) {
  result += (char) tmp;
}

System.out.println(result);
p.destroy();  }

My problem here is that the read() method always returns a -1 and I cannot get the output. I dont even know if what I wrote created any Output.

Help would be appreciated. Thanks!

Answer 1

It is clear that Process p = r.exec("ghci"); did not successful for which read() method always returns a -1. Provide full path and check.

Process p = r.exec("/fullpath/ghci  2>&1");
p.waitFor();//You need to use this line of code

For confirmation first execute ls command first

Process p = r.exec("ls 2>&1");

Also modify your codes like below and try:-

public static void main(String[] args) throws Exception {
    Runtime r = Runtime.getRuntime();
    Process p = r.exec("ghci");
            p.waitFor();
    OutputStream output = p.getOutputStream();
    ByteArrayOutputStream byte1=new ByteArrayOutputStream();
    output.write(byte1.toByteArray());
    String result=byte1.toString();
    System.out.println(result);
    p.destroy();  
}