Request features to simplify AST

[dzpao]

Is it possible to provide a feature that simplifies the AST by removing certain Rules from the resulting AST?
I'm not sure if anyone has mentioned a similar requirement before. I tried to retrieve it but couldn't find it.

I tried this to make some changes on my fork. Looks like it works, but I'm not sure if there are any errors. Anyway, I still send you a PR, you can dispose it at will, merge or close it.

Thank you in advance.