No. The code can be rewritten without visitors using iterators for traversal, for example). But it'll look badly. Visitors in the linked example are real class

No. The code can be rewritten without visitors using iterators for traversal, for example). But it'll look badly. Visitors in the linked example are real classic visitors. The code _within_ the visitor methods, of course, uses pattern matching, but the pattern itself is not materially different from C++. Exhaustiveness checking for pattern matching is also "best effort" for complex matching.