[antlr-interest] Tree grammars & optional AST nodes

Nicolas Rouquette nicolas.rouquette at jpl.nasa.gov
Sat Oct 21 14:10:26 PDT 2006


Terence Parr <parrt at ...> writes:

> On Oct 20, 2006, at 11:24 PM, Nicolas Rouquette wrote:
> 
> > Terence Parr <parrt <at> ...> writes:
> >
> > expression
> >  : e1=conditionalExpression (op=assignmentOperator e2=expression)?
> >    -> {$op!=null} ? ^($op $e1 $e2)
> >    -> $e1
> >  ;
> 
> Oh.  It wants $op.tree or something.  Which which is the problem?  ^ 
> ($op i guess.  Try {$op.tree} for now.

Since 'op' is inside an optional block, $op can be NULL
and $op.tree can produce a NullPointerException.

At most, it could be {$op!=null} but 3.0b4 doesn't like it.

-- Nicolas.

> Ter
> 
> 






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