title: Racket list in struct
body: <p>I just started programming with Racket and now I have the following problem. 
  I have a struct with a list and I have to add up all prices in the list.</p>
  
  <pre><code>(define-struct item (name category price))
  (define some-items
  (list
     (make-item "Book1" 'Book 40.97)
     (make-item "Book2" 'Book 5.99)
     (make-item "Book3" 'Book 20.60)
     (make-item "Item" 'KitchenAccessory 2669.90)))
  </code></pre>
  
  <p>I know that I can return the price with: <code>(item-price (first some-items))</code> or <code>(item-price (car some-items))</code>.</p>
  
  <p>The problem is, that I dont know how I can add up all Items prices with this.</p>
  
  <hr>
  
  <p>Answer to Óscar López:
  May i filled the blanks not correctly, but Racket mark the code black when I press start and don't return anything.</p>
  
  <pre><code>  (define (add-prices items)
    (if (null? items)           
       0                   
        (+ (first items)                 
           (add-prices (rest items)))))
  </code></pre>