How do I use helper functions in Lumen?
<pre><code>    $credentials = app_path();
</code></pre>

<p>Results in:</p>

<blockquote>
  <p>[Symfony\Component\Debug\Exception\FatalThrowableError]   Call to
  undefined function App\LtClasses\app_path()</p>
</blockquote>

<p>But it's listed as a helper here: <a href="https://laravel.com/docs/5.3/helpers#method-app-path" rel="noreferrer">https://laravel.com/docs/5.3/helpers#method-app-path</a></p>