text
thing(void)
{
    return "delegate implementation";
}

text
operation(record delegator)
{
    text s;

    if (r_key(delegator, "delegate")) {
        if (r_key(delegator["delegate"], "thing")) {
            s = call(r_query(delegator["delegate"], "thing"));
        } else {
            s = "default implementation";
        }
    } else {
        s = "default implementation";
    }

    return s;
}

integer
main(void)
{
    record delegate, delegator;

    o_text(operation(delegator));
    o_byte('\n');

    r_link(delegator, "delegate", delegate);
    o_text(operation(delegator));
    o_byte('\n');

    r_put(delegate, "thing", thing);
    o_text(operation(delegator));
    o_byte('\n');

    return 0;
}