Indeed, there is already a proposal for an enum syntax in dotty that looks almost exactly like that: enum Tree[T] { case Branch(t: Tree[T]) cas

Indeed, there is already a proposal for an enum syntax in dotty that looks almost exactly like that: enum Tree[T] { case Branch(t: Tree[T]) case Leaf(t: T) } https://github.com/lampepfl/dotty/issues/1970 https://github.com/lampepfl/dotty/issues/1970