[antlr-interest] Working with tree walkers in V3

[Terence Parr]

On Feb 21, 2007, at 3:31 AM, Mark Bednarczyk wrote:

> I'm having difficulty accessing values from my tree walker. The  
> tree is
> built and has hierachy of nodes in it. The walker properly matches  
> on the
> various rules and that's where my problems start. I can't seem to  
> get the
> grasp on all the special $ prefixed attributes. Everything throws  
> NULL ptrs
> exceptions when I access them.
>
> It would be nice if there was a way to tell the rule to return  
> whatever
> value it matched such as:
>
> modifier returns [String ret]
> @finally {
> $ret = $text; // Will throw NULL Ptr exception
> }
>     :   'public'
>     |   'protected'
>     |   'private'
>     |   'static'
>     |   'final'
>     |   'synchronized'
>     |   'transient'
>     |   'volatile'
>     |	  'field'
>     ;
>
> Again, this is all in "tree grammar".

Hmm..that seems ok.  Generates:

             retval.ret = input.getTokenStream().toString(
               input.getTreeAdaptor().getTokenStartIndex(retval.start),
               input.getTreeAdaptor().getTokenStopIndex 
(retval.start)); // Will throw NULL Ptr exception

which should work.  Note it's @after now in 3.0b7 :)

Ter