I think you're slightly missing the point. It's not the use of recursive functions or data structures that is interesting. It's that, in Go, you can add a new t

I think you're slightly missing the point. It's not the use of recursive functions or data structures that is interesting. It's that, in Go, you can add a new type which covers externally defined types, and those types are now instances of the new type automatically. In other languages, to unify two types like this with a common interface, you would probably have to define a wrapper class which proxies the calls to the real objects. Even though the methods for the two classes have matching type signatures and do the same thing already.