title: Boost-pp: how to determine if a macro parameter is a tuple
body: <p>A tuple is a comma-separated list enclosed by parens, e.g.</p>
  
  <pre><code>()
  (,)
  (thing,)
  (2,3)
  </code></pre>
  
  <p>If I have </p>
  
  <pre><code>#define ISTUPLE(x) \\...
  </code></pre>
  
  <p>I'd like something like <code>ISTUPLE(nope)</code> to resolve to 0 and <code>ISTUPLE((yep))</code> to resolve to 1. </p>
  
  <p><em>[FWIW, I have <a href="http://www.boost.org/doc/libs/1_34_1/libs/preprocessor/doc/ref/" rel="nofollow">_RTFM_'d</a> a plenty.]</em></p>