[antlr-interest] question about tree parsing (2.x)

[Monty Zukowski]

Bryan Ewbank wrote:
> Yes; you can do this; you are probably seeing ambiguity warnings about
> the loop because both "ID4" and "." will match an ID4 node.  The trick
> is a syntactic predicate.  Change this:
> 
> 
>>bottomNode 
>>    :    #( 
>>            ID3 
>>            ( 
>>                    ID4 
>>                |   . // catch all for ID5 | ID6 
>>            ) // '+' volontary removed, exit should get 1 level up, no? 
>>        ) 
>>    ; 
> 
> 
> To this:
> 
> 
>>bottomNode 
>>    :    #( 
>>            ID3 
>>            ( 
>>                (ID4) =>  ID4 
>>                |   . // catch all for ID5 | ID6 
>>            )+
>>        ) 
>>    ; 
> 
> 
> The "(ID4) => ID4" tells ANTLR to use that selection if an ID4 is seen.
> 
> I don't see why you removed the "+" unless you only want to match the
> first child of ID3.  To match all ID4 children of ID3, you need the
> "+".

Instead of a syntactic predicate you could replace '.' with ~(ID4)

Monty