[antlr-interest] Can antlr v3 lex star | tristar properly?
Kevin J. Cummings
cummings at kjchome.homeip.net
Wed Nov 21 14:48:36 PST 2007
Guntis Ozols wrote:
> Citēju "Kevin J. Cummings" <cummings at kjchome.homeip.net>:
>
>> Guntis Ozols wrote:
>>> Thanks, guys!
>>>
>>> I've finally found (thanks to Jim Idle) a solution that both works and
>>> is based on syntactic predicates:
>>> STAR : '*' (('**') => '**' { type = TRISTAR; } | );
>>>
>>> Solution by Kay Röpke also works:
>>> TRISTAR : {input.LA(3) == '*'}? => '*' '*' '*';
>>> STAR : '*';
>>>
>>> I still do not understand why
>>> STAR : '*' ;
>>> TRISTAR : ('***') => '***';
>>> does not work as expected, I think it is a bug in v3.
>> What happens if you reverse the order of STAR and TRISTAR in the
>> previous example, ie don't recognize STAR before you've check for
>> TRISTAR. I was under the impression that ANTLR was dependent upon the
>> order of certain productions.
>
> Does not work
I'm surprised, in ANTLR 2, I've done the following, which works fine:
> protected
> DIGIT : '0' .. '9'
> ;
>
> protected
> DIGITS : ( DIGIT ) + // Just digits
> ;
>
> protected
> FLOAT : DIGITS '.' DIGITS
> ;
>
> protected
> UINT : DIGITS
> ;
>
> NUM : ( DIGITS '.' ) => FLOAT
> | UINT
> ;
So if the similar construct doesn't work in ANTLR 3, then I'd consider
it a regression. Terry may feel differently. B^)
--
Kevin J. Cummings
kjchome at rcn.com
cummings at kjchome.homeip.net
cummings at kjc386.framingham.ma.us
Registered Linux User #1232 (http://counter.li.org)
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