interface shape
  method area() as word
end interface

class square implements shape
  private word side
  public method init(s as word)
    self.side = s
  end method
  public method area() as word
    return self.side * self.side
  end method
end class

program main
  var sq as square
  var s as shape
  sq = new square(4)
  s = sq
  print s.area()
  delete s
end program