SQL & PL/SQL

I'm trying to make a library that takes arbitrary data (well varchars, dates, numbers, collections and objects) and returns a Javascript Object Notation representation. I would like this to work something like:

lv_json_string := to_json(ANYDATA.CONVERTVARCHAR2('My data'));

I've got the basic types working, now I'm tackling objects. I can iterate over them and get their values but when the object contains a nested object it seems to be impossible to get at the object. Ideally I would be able to get an attribute back as ANYDATA regardless of type, at the moment I have a case statement that looks something like:

        CASE p_type_code
            WHEN DBMS_TYPES.TYPECODE_VARCHAR2 THEN
                lv_error := p_data.getVarchar2(lv_varchar2);
                RETURN ANYDATA.convertVarchar2(lv_varchar2);
            WHEN DBMS_TYPES.TYPECODE_NUMBER THEN
                lv_error := p_data.getNumber(lv_number);
                RETURN ANYDATA.convertNumber(lv_number);
            WHEN DBMS_TYPES.TYPECODE_OBJECT THEN
                ....

This is executed for each attribute and then I call to_json again recursively. When I have an object type, I cannot get at it. How do I:

a) Get at any attribute as an ANYDATA value? (this has to be a 'fresh' one so I can carry on iterating with the current one).
b) Get an arbitrary object out of an ANYDATA value and back in again?

A note on (b): I've tried using EXECUTE IMMEDIATE to set up a variable of the right type and do something similar to what I've got for the other types. The problem is that I always get an error about type mismatches. The same code hardcoded for a test type and run without execute immediate works fine, I think passing the current ANYDATA object into another block messes it's state up somehow. Here's that piece of code:

                EXECUTE IMMEDIATE '
                    DECLARE
                        lv_data   ANYDATA := :data;
                        lv_error  BINARY_INTEGER;
                        lv_object ' || lv_type_name || ';
                    BEGIN
                        lv_error := lv_data.getObject(lv_object);
                        :result := ANYDATA.convertObject(lv_object);
                    END;' USING IN p_data, OUT lv_result;

Any ideas people?