ge using phoenix:
        </p>
<pre class="programlisting"><span class="identifier">on_error</span><span class="special">&lt;</span><span class="identifier">fail</span><span class="special">&gt;</span>
<span class="special">(</span>
    <span class="identifier">xml</span>
  <span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span>
        <span class="special">&lt;&lt;</span> <span class="identifier">val</span><span class="special">