[antlr-interest] backtrack=false and AST generation
John B. Brodie
jbb at acm.org
Sun Apr 18 08:05:15 PDT 2010
Greetings!
On Sun, 2010-04-18 at 16:30 +0200, Giampaolo Tomassoni wrote:
> > You can pass trees from one rule to another as a parameter(s),
> > maybe that might help, something like (probably requires more
> > work to obtain the tree you are after):
> >
> > protected
> > expression
> > : e=conditionalOrExpression conditionalExpression[$e.tree]
> > ;
> >
> > protected
> > conditionalExpression[CommonTree TheActualASTRoot]
> > : QMARK t=expression COMMA f=expression
> > -> ^(ITE ${TheActualASTRoot} $t $f)
> > |
> > ;
> >
> > Regards, Mark
>
> Thank you Mark, for your clever reply.
>
> May I ask if there is any way to do somthing like this:
>
> protected
> expression
> : e=conditionalOrExpression c=conditionalExpression[$e] -> $c
> ;
>
> protected
> conditionalExpression[conditionalOrExpression e]
> : QMARK t=expression COMMA f=expression -> ^(ITE $e $t $f)
> | -> $e
> ;
>
> It seems cleaner to me, since this way subrules are not going to "play
> dirty" with the root of their parents.
>
> Unfortunately, this notation causes a "reference to undefined label in
> rewrite rule: $e" error. The point may be "e" is not of
> conditionalOrExpression type or, well, I don't really know why. Something
> like that works with non-AST generating combined parsers (with more
> classical actions, then). But it seems not to work with rewrite actions.
>
I do not know why you get the undefined label error.
Have you considered not using a sub-rule for the then-else part?
Something like:
expression :
conditionalOrExpression (QMARK^ expression COMMA! expression) ?
;
or if you really want ITE as the root (instead of QMARK) perhaps:
expresssion :
( c=conditionalOrExpression -> $c )
( QMARK t=expression COMMA f=expression-> ^(ITE $c $t $f) )?
;
Hope this helps...
-jbb
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