class animal =
  object (self)
    (*functions go here...*)
  end
class dog =
  object (self)
    inherit animal
    (*functions go here...*)
  end
class cat =
  object (self)
    inherit animal
    (*functions go here...*)
  end
class lab =
  object (self)
    inherit dog
    (*functions go here...*)
  end
class collie =
  object (self)
    inherit dog
    (*functions go here...*)
  end