;; Container = "(" 
;;   <contents> List(Item) <capacity> int ")" .
;; Item : Container | Simple.
;; List(S) ~ {S}.
;; Simple =  <name> Ident <weight> int.

;; test case

;; ( //begin container 1: weight 6: over weight
;; apple 1 //item
;;   ( //begin container 2; weight 2: over weight
;;   pencil 1 //item
;;    ( //begin container 3: weight 1
;;    apple 1 //item
;;    1) //capacity
;;  orange 1
;;  1) //capacity
;; orange 1
;; kiwi 1
;; 5) //capacity

(define-struct Container (contents capacity))
(define-struct Simple (name weight))