[antlr-interest] Tree grammars & optional AST nodes

[Nicolas Rouquette]

Nicolas Rouquette <nicolas.rouquette at ...> writes:

> 
> Terence Parr <parrt <at> ...> writes:
> 
> > On Oct 19, 2006, at 5:09 PM, Nicolas Rouquette wrote:
> > 
> > >  <at> init { boolean flag=false; }
> > >   : e1=conditionalExpression (op=assignmentOperator e2=expression  
> > > {flag=true;})?
> > >     -> {flag} ? ^($op $e1 $e2)
> > >     -> $e1
> > >   ;
> > 
> > or use {$op!=null}? without the flag mumbojumbo.

Bizarre... {op!=null} works.

I surprised action.g didn't barf at this.
It seems to work which is perplexing.

-- Nicolas.