 expensive operations go here...</span></span>
<span id="cb1-3"><a href="#cb1-3" tabindex="-1"></a>  df <span class="ot">&lt;-</span> <span class="fu">download_lots_of_data</span>()</span>
<span id="cb1-4"><a href="#cb1-4" tabindex="-1"></a>  <span class="fu">fit_model</span>(df)</span>
<span id="cb1-5"><a href="#cb1-5" tabindex="-1"></a>})</span></code></pre></div>
<p>The object that’s returned is a future, which for all intents and
purposes is a promise object<a href="#fn1" class="footnote-ref" id="fnre