Module Visitor Pattern for manipulating BinaryModules

[jtenner]

The visitor pattern looks something like this in pseudocode:

fn do_visit_type(ctx, value, visitor) {
  use #(ctx, value) <- try(do_visit(ctx, value, visitor.on_enter_type))
  use #(ctx, value) <- try(case value {
    Variant -> do_visit(ctx, value, visitor.on_enter_variant)
    // ..
  })
  use #(ctx, child_element) <- try(do_visit_child_element(ctx, value.child_element, visitor))
  
  use #(ctx, value) <- try(case value {
    Variant -> do_visit(ctx, value, visitor.on_exit_variant)
    // ..
  })
 
  do_visit(ctx, value, visitor.on_exit_type)   
}

Steps:

1. Visit Type on_enter
2. Visit variant on_enter
3. Visit all children elements (based on type too)
4. Visit variant on_exit
5. Visit Type on_exit

What do you think?