l structure looks like this, in pseudocode:</p>
<div class="sourceCode" id="cb4"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span class="va">server</span> <span class="op">&lt;-</span> <span class="kw">function</span><span class="op">(</span><span class="va">input</span>, <span class="va">output</span>, <span class="va">session</span><span class="op">)</span> <span class="op">{</span>
  
  <span class="va">output</span><span class="op">$</span><span class="va">alluvial_plot</span> <span c