[antlr-interest] Parsing optional component in Tree Walker

[Monty Zukowski]

Peter Kronenberg wrote:
> I have a tree walker that needs to deal with an optional component C.
> 
> If tree is #(ROOT A B) then call handleAB(a.getText(), b.getText()).
> If tree is #(ROOT A B C) then call handleAB(a.getText(), b.getText(), 
> true);
> 
> The handler for C has already set some stuff, but handleAB needs to know 
> about it.  Since there is likely to be recursion while walking the tree, 
> setting a variable isn't feasable.
> 
> What I've come up with is
> 
> (#(ROOT A B C)) => #(ROOT a:A b:B C) {
>    handleAB(#a.getText(), #b.getText(), true);
> }
> | #(ROOT A B) {
>    handleAB(#a.getText(), #b.getText());
> }
> 
> It seems a bit kludgy and redundant.  Is there a better way?
> I can adjust the parameters of handleAB, but I need some indication if 
> the optional C is there
> 

Consider building the tree differently.  For instance, when building the 
tree, if you see C then change the root node type to ROOTC.  Then when 
walking you can have the option at the root level.

Monty