LuaJava - unprotected error in call to Lua API

Question

I'm trying to get a simple function working in LuaJava (adding two numbers). I have very little experience with Lua, and am finding this difficult as I haven't been able to find in depth documentation for LuaJava. I can currently print out to the java console from lua, but nothing beyond that.

I have tried implementing a few methods, but get the same error every time:

PANIC: unprotected error in call to Lua API (attempt to call a nil value)

This is the code I am using:

import org.keplerproject.luajava.LuaState;
import org.keplerproject.luajava.LuaStateFactory;

public class Hello {
    public static void main(String[] args) {
        LuaState l = LuaStateFactory.newLuaState();
        l.openLibs();
        l.LdoFile("main.lua");
        l.call(0, 0);
        l.getGlobal("add");
        l.pushInteger(1);
        l.pushInteger(1);
        l.call(2, 1);
        int result = l.toInteger(1);
        l.pop(1);
        System.out.println("1 + 1 = " + result); 
    }
}

And the Lua file:

function add(a, b) 
    return a + b
end

My IDE is Eclipse. Thanks in advance for any help.

Answer 1

I am going to assume the problem is occurring on this line l.call(0, 0);.

l.LdoFile("main.lua"); does not, most likely, return a function on the stack that must be called. That is what the lua C function luaL_loadfile does. luaL_dofile is a macro around luaL_loadfile which also runs the returned chunk function.

So after l.LdoFile("main.lua"); finishes I believe you have nothing on the stack and your add function is available for use.