title: Macro with arguments with default values, where default value is previous argument
body: <p>I have a macro defined like this:</p>
  
  <pre><code>`define some_macro(ARG0, ARG1 = ARG0) \
    ...
  </code></pre>
  
  <p>I'd like the expansion <code>some_macro(2)</code> to expand to <code>some_macro(2, 2)</code>. It expands to <code>some_macro(2, ARG0)</code>, because in the default value specification for <code>ARG1</code> the text <code>ARG0</code> is used and not the value of the <code>ARG0</code> argument.</p>
  
  <p>Is it possible to specify the default of the second argument to be the value of <code>ARG0</code>?</p>