ntifier">on_error</span></code> declares our error
          handler:
        </p>
<pre class="programlisting"><span class="identifier">on_error</span><span class="special">&lt;</span><span class="identifier">Action</span><span class="special">&gt;(</span><span class="identifier">rule</span><span class="special">,</span> <span class="identifier">handler</span><span class="special">)</span>
</pre>
<p>
          This will specify what we will do when we get an error. We will print out
          an error messa