[antlr-interest] Strange ambiguous decision warning

[Martin Probst]

Am 02.04.2008 um 10:32 schrieb Jeroen Steenbeeke:
> I simplified your grammar a bit to illustrate the problem
>> sequenceType    :    (EMPTY_SEQUENCE '(' ')')
>>                        | (itemType occurrenceIndicator) =>  
>> (itemType occurrenceIndicator)
>>                      | itemType ;
>> itemType    :    atomicType ;
>> atomicType    :    qNameOrIdent ;
>> qNameOrIdent    :    EMPTY_SEQUENCE;
> Every single choice in sequenceType can start with EMPTY_SEQUENCE,  
> so ANTLR does not have a clue which one to pick.

Well, generally yes, but I thought the point of the LL(*) algorithm is  
to disambiguate such decisions by taking the next token into  
consideration. I.e. in this case:
* EMPTY_SEQUENCE -> itemType
* EMPTY_SEQUENCE ( ) -> direct match
* EMPTY_SEQUENCE + -> itemType occurrenceIndicator

Btw. as far as I can see the grammar does not allow a sequenceType  
declaration to be followed by an open parenthesis, which should rule  
out such an ambiguity (and such an error should of course be flagged  
in the rule where the following '(' occurs, I think).

Best regards,
Martin