[antlr-interest] updating text dump when writing tree grammar ast transformers

[Leo Meyerovich]

Hiya,

I'm using Patrick Hulsmeijer's JavaScript grammar & tree walker. I 
running a 3 stage pipeline: a grammar to parse, a tree grammar walker to 
transform (output=ast), and then a tree grammar walker to pretty print. 
While I verified that the AST structure is being transformed, I can't 
reuse the existing top $text attribute to easily print - it dumps the 
untransformed AST! More specifically:

//1. parser: unmodified es3

//2. transformer: modified es3walker with the following change to flip 
assignments:
expr:
   ...
    | ^( ASSIGN a=expr b=expr )  -> ^(ASSIGN $b $a)       
  ...

//3. printer: modified to print at two locations, top, and @ point of 
transformation
   program : (statement {System.out.println($statement.text);})* ;
...
expr:
   ...
    | ^( ASSIGN a=expr b=expr )  {System.out.println("//=, " + $a.text + 
", " + $b.text);}
  ...

While the print out associated with the assignment rule prints out as 
expected (reversed assignment), the whole AST dump in the program rule 
shows the unmodified source. I tried playing a bit with token settings 
as described near the end of chapter 7 (albeit not really for the 
then-nonexistent tree rewrites) such as writing "-> ^(ASSIGN $b[$b, 
$b.text] ...)", but did not bump into anything that compiled.

Will I need to write an explicit pretty printer action for every rule, 
or is there a way to do tree transforms that will propagate associated text?

As a side note, has anybody had success with rewrite=true for tree 
grammar transformers? My AST gets butchered when I add a transform to 
the assignment arm of the expression rule (perhaps I just need to add 
explicit identity transforms to the rest of the arms of the expression 
rule?). I suspect inplace transforms would be best for my task so it'd 
be nice :)

This is all on build 2008-04-09.18.

Thanks!

- Leo

(ps: I'll post my transforms and a short explanation when/if I get this 
working, which hopefully will aid the coming release of this very useful 
feature)