abstract class edible
    string name
    procedure eat();    -- (virtual)
end class

class foodbox2
    sequence contents = {}
    procedure add(edible food)
        if food.eat=NULL then -- (optional)
            throw("eat() not implemented")
        end if
        this.contents = append(this.contents,food)
    end procedure
    procedure dine()
        integer l = length(this.contents)
        string s = iff(l=1?"":"s")
        printf(1,"foodbox2 contains %d item%s\n",{l,s})
        for i=1 to l do
            -- this.contents[i].eat() -- not supported, sorry!
            -- compiler needs some more type hints, such as:
            edible food = this.contents[i]
            food.eat()
        end for
    end procedure
end class
foodbox2 lunchbox2 = new()

class fruit2 extends edible
    procedure eat()
        printf(1,"mmm... %s\n",{this.name})
    end procedure
end class
fruit2 banana2 = new({"banana"})

class clay2
    string name = "common fletton"
end class
clay2 brick2 = new()

class drink extends edible
    procedure eat()
        printf(1,"slurp... %s\n",{this.name})
    end procedure
end class
drink milkshake = new({"milkshake"})

lunchbox2.add(banana2)
try
    lunchbox2.add(brick2) -- triggers typecheck
catch e
    printf(1,"%s line %d: %s\n",{e[E_FILE],e[E_LINE],e[E_USER]})
end try
lunchbox2.add(milkshake)
lunchbox2.dine()