<a href="references.html#curious_recurring">&quot;Curiously 
  Recurring Template Pattern&quot;</a> in template meta-programming circles. This 
  inheritance strategy gives us the power of polymorphism without the virtual 
  function overhead. In essence this is a way to implement <a href="references.html#generic_patterns">compile 
  time polymorphism</a>.</p>
<h2> parser_category_t</h2>
<p> Each derived parser has a typedef <tt>parser_category_t</tt> that defines 
  its category. By default, if one is not 