[antlr-interest] resolving ambiguity

[Terence Parr]

ha! you are so right! I knew it was one of those options ;)
Ter
On May 22, 2012, at 11:05 AM, Bart Kiers wrote:

> Hi Stephen,
> 
> Explicitly tell ANTLR to match B's greedily:
> 
> b_chain : (options{greedy=true;}: B)+ -> ^(B_CHAIN B+);
> 
> 
> For input "BB", it will cause the tree ^(B_CHAIN B B) to be created, and
> ANTLR will not produce warnings when generating the parser.
> 
> Regards,
> 
> Bart.
> 
> 
> On Tue, May 22, 2012 at 6:04 PM, Stephen Siegel <siegel at udel.edu> wrote:
> 
>> No difference.
>> 
>> On May 22, 2012, at 11:42 AM, Terence Parr wrote:
>> 
>>> try (options {k=1;} : B)+
>>> Ter
>>> On May 21, 2012, at 4:12 PM, Stephen Siegel wrote:
>>> 
>>>> Thanks, Ter.  That's true, but the warnings are scary -- or at least
>> suggest I'm not doing something quite right -- and I want to make them go
>> away.  (This is an abstraction of a much larger grammar where I ran into
>> this problem.  In the larger grammar, there are a bunch of such warnings.)
>>  Is there a way to tell ANTLR that I want that behavior, so don't warn me?
>>>> -Steve
>>>> 
>>>> On May 21, 2012, at 6:14 PM, Terence Parr wrote:
>>>> 
>>>>> hi Steve, it will match greedily so that b_chain will match all B's in
>> a row.
>>>>> Ter
>>>>> On May 21, 2012, at 8:50 AM, Stephen Siegel wrote:
>>>>> 
>>>>>> In the following grammar:
>>>>>> 
>>>>>> -----------------------------------------------
>>>>>> grammar g1;
>>>>>> options { output=AST; }
>>>>>> tokens { B_CHAIN; }
>>>>>> r  :       (A | b_chain)*;
>>>>>> b_chain    :       B+ -> ^(B_CHAIN B+);
>>>>>> A  :       'A';
>>>>>> B  :       'B';
>>>>>> 
>>>>>> // BB should yield ^(BCHAIN B B)
>>>>>> -----------------------------------------------
>>>>>> 
>>>>>> there is an ambiguity since input "BB" could be parsed as (1) two
>> "b_chain"s (each with one "B") or as (2) one b_chain (with two "B"s).  I
>> want to tell ANTLR to choose option (2).
>>>>>> 
>>>>>> Right now, I get this warning:
>>>>>> 
>>>>>> -------------------------------------
>>>>>> [11:45:02] Checking Grammar g1.g...
>>>>>> [11:45:02] warning(200): g1.g:5:11:
>>>>>> Decision can match input such as "B" using multiple alternatives: 1, 2
>>>>>> 
>>>>>> As a result, alternative(s) 2 were disabled for that input
>>>>>> -------------------------------------
>>>>>> 
>>>>>> Does anyone know how to resolve the ambiguity?
>> 
>> 
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