Ask HN: Better coding idioms for tree processing?

Is the Visitor pattern really the best we've got for tree processing?

I'm processing tree data structures, possibly with embedded links (so they're actually DAGs), iteratively, with a different processing step each time. The code is very similar in spirit to writing an LLVM pass: http://llvm.org/docs/WritingAnLLVMPass.html

If you have any links to research or articles on coding idioms for tree processing, or other insight, I'd very much appreciate it. :)