Basket = "basket" <contents> SeveralThings.
SeveralThings ~ "(" {Thing} ")" .
Thing : Fruit | Basket.
Fruit : Apple | Orange *common* <weight> Weight.
Weight = <v> Integer.
Apple = "apple".
Orange = "orange".

SummingVisitor = <total> Integer.
PrintingVisitor = .
TraverseThingVisitor = .
TraverseBasketVisitor = .
GetWeightVisitor = <val> Integer.

Main = .