[antlr-interest] Tree grammars & optional AST nodes

[Terence Parr]

On Oct 20, 2006, at 11:24 PM, Nicolas Rouquette wrote:

> 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.
>
> Thanks for this suggestion; however, there's one small glitch...
> If I write:
>
> expression
>  : e1=conditionalExpression (op=assignmentOperator e2=expression)?
>    -> {$op!=null} ? ^($op $e1 $e2)
>    -> $e1
>  ;
>
> 3.0b4 produces this kind of code:
>
> if ($op!=null) {
>   // the code for ^($op $e1 $e2)
> } else {
>   // the code for $e1
> }
>
> ... and a telltale error message:
>
> missing attribute access on rule scope: op

Oh.  It wants $op.tree or something.  Which which is the problem?  ^ 
($op i guess.  Try {$op.tree} for now.

Ter