Unless I'm missing something, enums are closed, thus overlap with sum types for the use-cases. Subclasses are an implementation detail in this context. Here is

Unless I'm missing something, enums are closed, thus overlap with sum types for the use-cases. Subclasses are an implementation detail in this context. Here is an example that uses subclasses to implement generalized enums, aka sum types: enum List { Cons(head, tail) {...} Nil {...} int length() { switch (this) { case Cons(head, tail): return 1 + length(tail) case Nil: return 0 } } } Mind you, this is syntactic sugar and you can do it by hand with enums + sublcasses. But the whole point of clean languages is to remove unnecessary boilerplate :)