les expect a number as the first
character?</p>
<h2>Tree output (and what to do about it)</h2>
<p>But if we leave the negative examples for a second; what happens if the parse
succeeds? It turns out, not much:</p>
<pre class="sh_ruby"><code>
  parse "1 + 2 + 3"  # =&gt; "1 + 2 + 3"@0
</code></pre>
<p>The only notable difference between input and output is that the output has an
extra &#8216;@0&#8217; appended to it. This is related to line number tracking and will be
explained later on (or you can skip ahea