anchor.diff:  (defun cart-update ()
     (when (has-form?)
       (cart-add-undo)
  -    (filter #'cart-update-item (form-alists))
  +    (@ #'cart-update-item (form-alists))
       (action-redirect)))
   
   (defun cart (x)
  
positive.code:       (+! total (number (assoc-value 'price (cart-find-article i.)))))))
  
  (defun cart-items ()
    (template-list #'tpl-cart-item (filter [cart-find-article _.] (cart-current))))
  
  (defun cart-num-items ()
    (length (cart-current)))
  
negative.code: ; Copyright (c) 2012,2014–2015 Sven Michael Klose <pixel@copei.de>
  
  (defun cart-current ()      (!?   (session 'cart)      (phphash-alist !)))
  (defun cart-undos ()        (!?   (session 'cart-undo) (array-list !)))
  