class="mdzsyn-coresym">in</span>  @[<span class="mdzsyn-keyword">:a</span> <span class="mdzsyn-keyword">:b</span> <span class="mdzsyn-keyword">:c</span>] <span class="mdzsyn-number">3</span>) <span class="mdzsyn-comment"># -&gt; raises error</span></code></pre><p>To update a mutable data structure, use the <code class="mendoza-code">put</code> function. It takes 3
arguments, the data structure, the key, and the value, and returns the data
structure. The allowed types keys and values depend on the data struc