Question on User-Defined Types (Embedding)

[Brent Fulgham <brent.fulgham@xpsystems.com>]

Let's say I have a C++ class/structure that I want to pass in and out 
of the MzScheme runtime.

For example, let's say I have a simple structure:

    struct test
    {
        char name[10];
        long salary;
    };

Now I might have a few C routines added to Scheme's global namespace:

    proc = scheme_make_prim_w_arity(do_get_name, "get-name", 1, 1);
    scheme_add_global("get-name", proc, loc_env);

    proc = scheme_make_prim_w_arity(do_get_salary, "get-salary", 1, 1);
    scheme_add_global("get-salary", proc, loc_env);

The idea being to do something like:

Scheme>(define mytest (make-test "Brent" 1000))
Scheme>(get-name mytest)
Brent
Scheme>(get-salary mytest)
1000

I would probably implement them something like this:

    static Scheme_Object* do_get_name(int argc, Scheme_Object** argv)
    {
        struct* test = (SOME_CASTING_FOO)argv[0];
        return scheme_make_string_value(test->name);
    }

And I'd probably have some kind of "new" function:

    static Scheme_Object* do_make_test(int argc, Scheme_Object** argv)
    {
        char* title = SCHEME_STR_VAL(argv[0]);
        char* name = SCHEME_STR_VAL(argv[1]);
        long salary = SCHEME_INT_VAL(argv[2]);

        struct temp;
        temp.title = title;
        temp.name = name;  // probably copy this actually
        temp.salary = salary;

        Scheme_Object* obj = SOMEHOW_MAKE_TYPE_FROM(temp);
        scheme_add_global(title, obj, env);

        return obj;
    }

And I'd have previously created a type:

    Scheme_Type test_type;

    test_type = scheme_make_type("<test type>");


***

So, I've gotten this far, but I am now stuck as to how to go about actually
creating instances of a type.

In my real case, I wish to pass Scheme a type representing some global
data that *should not* be collected by Scheme.  In fact, Scheme will not
be creating my type, but it might inspect it, or call methods that use
it.

So how do I go about casting in and out of a Scheme_Object* ?

How do I convert a pointer to a C struct into something that MzScheme will
recognize as a "<test>" type or similar?

How should I define work-alike predicate and value-getting macros?

Help!  Help!  :-)

Thanks,

-Brent