an class="p">{</span><span class="nx">tokens</span><span class="p">}</span> <span class="o">=</span> <span class="k">this</span>
    <span class="nv">levels = </span><span class="mi">0</span>
    <span class="k">while</span> <span class="nv">token = </span><span class="nx">tokens</span><span class="p">[</span><span class="nx">i</span><span class="p">]</span>
      <span class="k">return</span> <span class="nx">action</span><span class="p">.</span><span class="nx">call</span> <span class="k">this</span><span