 stream changes length under
our feet.</p>             </td>             <td class="code">               <div class="highlight"><pre>  <span class="nv">scanTokens: </span><span class="nf">(block) -&gt;</span>
    <span class="p">{</span><span class="nx">tokens</span><span class="p">}</span> <span class="o">=</span> <span class="k">this</span>
    <span class="nv">i = </span><span class="mi">0</span>
    <span class="nx">i</span> <span class="o">+=</span> <span class="nx">block</span><span class="p">.</span>