How to get the values in ABCL using Java

Question

I am searching the API for handling the values in Armed Bear Common Lisp (ABCL) implementation of the Common Lisp language in the JVM, using Java.

It works when a function returns (only) a list or a string.

When it returns multiple values I only can fetch the first returned value.

I do not know how to fetch the other values.

This is my test.lisp file :

(defun get-list ()
   (list "abc" 12 'a 'b))

(defun get-value ()
    (values "abc" 12 'a 'b))

And my Java code is :

public static void main(String[] args) throws Exception {
    Interpreter interpreter = Interpreter.createInstance();

    LispObject lobj = interpreter.eval("(load \"test.lisp\")");
    org.armedbear.lisp.Package defaultPackage = Packages.findPackage("CL-USER");

    Symbol myFunctionSym = defaultPackage.findAccessibleSymbol("GET-LIST");
    Function myFunction = (Function) myFunctionSym.getSymbolFunction();
    LispObject o = myFunction.execute();

    System.out.println(o.listp());    // this return false

    Symbol myFunctionSym2 = defaultPackage.findAccessibleSymbol("GET-VALUE");
    Function myFunction2 = (Function) myFunctionSym.getSymbolFunction();

    LispObject o2 = myFunction.execute();

}

Answer 1

You could use multiple-value-bind, etc. on the Lisp side to assign to separate variables, and then access them individually in Java. Or you could call multiple-value-bind from Java. That's not the answer you are looking for. I assume what you'd really like is a method that you can call in Java that will get values other than the first one directly. I don't have that answer, but no one else has provided that answer.

However, poking around in the source and in javadoc, I see that classes Primitives and Symbol have methods VALUES and MULTIPLE_VALUE_BIND. I would guess that these are not designed to be called in user source code, but they might at least help you find the answer you want.

And finally, I think this might be something that you need to ask on the ABCL mailing list. You could report the full answer back here as an answer to your own question.

Answer 2

Is multiple-value-bind or nth-value what you are looking for, or is there something more to this question?

Answer 3

After a call to a function that returns multiple values, the values are associated with the executing LispThread until the next call into Lisp.

One may access the values object as a list of LispObject instances via a call to getValues() as evidenced by the following code:

org.armedbear.lisp.Package cl = Packages.findPackage("CL"); Symbol valuesSymbol = cl.findAccessibleSymbol("VALUES"); LispObject[] valuesArgs = { LispInteger.getInstance(1), LispInteger.getInstance(2) }; LispObject result = valuesSymbol.execute(valuesArgs); LispObject[] values = LispThread.currentThread().getValues(); for (LispObject value: values) { System.out.println("value ==> " + value.printObject()); }

Answer 4

I think there are two copy paste errors with your code above (you want to use myFunctionSym2 and myFunction2 in the last two lines, i.e.

Function myFunction2 = (Function) myFunctionSym2.getSymbolFunction();
LispObject o2 = myFunction2.execute();
System.out.println(o2.listp()); // additional line added by me

With this, it works for me.