anchor.diff:        (+! total (number (assoc-value 'price (cart-find-article i.)))))))
   
   (defun cart-items ()
  -  (template-list #'tpl-cart-item (filter [cart-find-article _.] (cart-current))))
  +  (template-list #'tpl-cart-item (@ [cart-find-article _.] (cart-current))))
   
   (defun cart-num-items ()
     (length (cart-current)))
  
positive.code:   (not (zero? (length (cart-current)))))
  
  (defmacro filter-cart (&rest body)
    `(= (cart-current) (filter [,@body] (cart-current))))
  
  (defun cart-redirect ()
    (action-redirect :update 'cart))
  
negative.code: (defun cart-update ()
    (when (has-form?)
      (cart-add-undo)
      (@ #'cart-update-item (form-alists))
      (action-redirect)))
  
  (defun cart (x)
  