{prog  
;; class graph:
 {
  { datatype Container 
     {ContainerC {contents ItemList} {capacity Number}} }
  { datatype Item 
     {Complex {c Container}}
     {Atomic  {name String} {weight Number}} }
  { datatype ItemList 
     {Empty}
     {More {first Item} {rest ItemList}}}
 }

;; object graph:
 (ContainerC (More (Atomic "apple" 5)
                   (More (ContainerC (More (Atomic "orange" 8) (Empty))
			             8)
		         (Empty)))
             5)

;; strategy:
 {// ContainerC Atomic}

;; visitor: 
 { visitor: totalWeight 0
            totalWeight
            [before Atomic a ...]
 }
}