[antlr-interest] mild simplification and tree grammars

[Mark Wright]

On Wed, Apr 21, 2010 at 01:27:02PM +0200, Giampaolo Tomassoni wrote:
> > The solution seems simple: the actions should be called before the
> > tree rewrites, like:
> > 
> > condExpr
> > 	:    QMARK c=orExpression t=condExpr f=condExpr
> >                 {shc=true;}
> > 		-> {($c.tree.getType()==TRUE)}?   $t
> > 		-> {($c.tree.getType()==FALSE)}?  $f
> > 		->
> > 	;
> > 
> > Regards, Mark
> 
> Well, I attempted that, but then the shc var is set true even when there are
> no rewrites (the empty rewrite case in your example). This is probably
> because the disambiguating predicates are on the right side of the rewrite
> operator, while the {shc=true;} seems an action to me. So, it is of course
> to its left.
> 
> I don't see a way to put an action to the right side of the rewrite
> operator, since a {...} notation would be interpreted like a tree reference,
> if I understand it right.
> 
> Maybe all this means there is space for an enhancement in ANTLR? ;)
> 
> Giampaolo

I guess then it is necessary to repeat the predicate test in the action
code then conditionally set shc, or to call a method from the action code with
whatever parameters are necessary for it to compute whether it should set shc or not.

Regards, Mark