CODEWITHSUNDEEP
javalualuaj
nerdinand
nerdinand

Reputation: 876

Passing arguments to a lua function with luaj

I'm trying to call a lua function in a Java program using LuaJ. It works fine when I'm not passing any arguments to the closure: 

String script = "print 'Hello World!'";
InputStream input = new ByteArrayInputStream(script.getBytes());
Prototype prototype = LuaC.compile(input, "script");
LuaValue globals = JsePlatform.standardGlobals();
LuaClosure closure = new LuaClosure(prototype, globals);
closure.call();

But now I'm trying a lua script with a top-level function that takes an argument and I just can't figure out how to pass in the argument from Java. Here's what I got so far:

String script = "function something(argument)\n"+
                            "test_string = 'Hello World!'\n"+
                            "print(test_string)\n"+
                            "print(argument)\n"+
                "end";

InputStream input = new ByteArrayInputStream(script.getBytes());
Prototype prototype = LuaC.compile(input, "script");
LuaValue globals = JsePlatform.standardGlobals();
LuaClosure closure = new LuaClosure(prototype, globals);
closure.invokemethod("something", CoerceJavaToLua.coerce("Foo"));

This results in an Exception on the invokemethod line:

org.luaj.vm2.LuaError: attempt to index ? (a function value)

Thanks for your help!

Upvotes: 5

Views: 3243

Answers (2)

Jim Roseborough
Jim Roseborough

Reputation: 201

In lua, the top-level scope is an anonymous function with variable arguments. These are accessed using ... In your example, you don't need the function named something, the chunk itself can be used as an unnamed function.

For example, this code in luaj-3.0-beta1

String script = "argument = ...\n"+
 "test_string = 'Hello World!'\n"+
 "print(test_string)\n"+
 "print(argument)\n";

Globals globals = JsePlatform.standardGlobals();
LuaValue chunk = globals.loadString(script, "myscript");
chunk.call( LuaValue.valueOf("some-arg-value") );

Produced this result for me:

Hello World!
some-arg-value

You can pass in any number of arguments this way.

Upvotes: 4

hjpotter92
hjpotter92

Reputation: 80629

Since you receive

org.luaj.vm2.LuaError: attempt to index ? (a function value)

as your error; this means that your function is not being created at all.

Try it without \n and give spaces in the variable script. Like this:

String script = "function something(argument) " + 
        " test_string = 'Hello World!'; " + 
        " print( test_string ); " + 
        " print( argument ); " + 
        " end";

Upvotes: -1

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