title: New Lumen 5.5 Project 'Undefined variable: app'
body: <p>I am new to Lumen and just tried to create an app. I am getting an error that states at Application->Laravel\Lumen\Concerns{closure}(8, 'Undefined variable: app', '/Users/test/Sites/books/routes/web.php', 14, array('router' => object(Router))) when I try to use this bit of code:</p>
  
  <pre><code>$app-&gt;group(['prefix' =&gt; 'book/'], function() use ($app) {
      $app-&gt;get('/','BooksController@index'); //get all the routes    
      $app-&gt;post('/','BooksController@store'); //store single route
      $app-&gt;get('/{id}/', 'BooksController@show'); //get single route
      $app-&gt;put('/{id}/','BooksController@update'); //update single route
      $app-&gt;delete('/{id}/','BooksController@destroy'); //delete single route
  });
  </code></pre>
  
  <p>According to the documents <a href="https://lumen.laravel.com/docs/5.5/routing" rel="nofollow noreferrer">https://lumen.laravel.com/docs/5.5/routing</a> this should work. I am following a tutorial found at <a href="https://paulund.co.uk/creating-a-rest-api-with-lumen" rel="nofollow noreferrer">https://paulund.co.uk/creating-a-rest-api-with-lumen</a> I know that 5.5 just came out a few days ago, so there might not be anyone that knows the answer yet, but any help would be appreciated. </p>