[Jtsummers]

> If you instead use visitor pattern, you will be looking at all the code related to Variable, Function, Literal in those files respectively.

I've never organized visitor pattern code that way. Usually it's something like:

  TypeChecker
    visitFunction
    visitVariable
    visitLiteral
  PrettyPrinter
    visitFunction
    visitVariable
    visitLiteral

So related functions (across the types you're visiting) are kept together, you're not revisiting the Function module to add a new visitor there. That would almost defeat the purpose of the pattern.

https://en.wikipedia.org/wiki/Visitor_pattern - See the UML diagram here.