pan></code>.
          </p>
<p>
</p>
<pre class="programlisting"><span class="comment">// these tokens expose the iterator_range of the matched input sequence</span>
<span class="identifier">lex</span><span class="special">::</span><span class="identifier">token_def</span><span class="special">&lt;&gt;</span> <span class="identifier">if_</span><span class="special">,</span> <span class="identifier">else_</span><span class="special">,</span> <span class="identifier">while_</span><span class="special">;</span