This is very typical in functional programming languages. You add functionality through compiler assisted ”pattern matching” instead of method polymorphism. Its

This is very typical in functional programming languages. You add functionality through compiler assisted ”pattern matching” instead of method polymorphism. Its benefits are more apparent if the feature is not so obviously inherent to the classes. Say you are defining the way to transmit the shapes to some random legacy system. Then you can stow away the legacy related code somewhere and still have the compiler check that you have handled all shapes.