[antlr-interest] Problem with lexical nondeterminism - ANTLR 2.7.7

clive.i.hill at jpmorgan.com clive.i.hill at jpmorgan.com
Thu Jan 3 13:02:13 PST 2008


Thanks to Gavin, Troy, and Harald for getting back.

If I try your suggestions with APAC_NUMERIC_TICKER above NUMER I still get 
the same issue.  Harold your suggestion would work if it matches NUMBER 
first but it was actually an APAC_NUMERIC_TICKER.  The match actually 
happens the other way around.

I'll try and read up some more on syntactic predicates, but I've attached 
my new grammar file in case anyone has any more suggestions.

Thanks,

Clive






Gavin Lambert <antlr at mirality.co.nz> 
Sent by: antlr-interest-bounces at antlr.org
03/01/2008 20:00

To
"Daniels, Troy \(US SSA\)" <troy.daniels at baesystems.com>, 
<antlr-interest at antlr.org>
cc

Subject
Re: [antlr-interest] Problem with lexical nondeterminism - ANTLR 2.7.7






At 04:00 4/01/2008, Daniels, Troy \(US SSA\) wrote:

>The problem is that your rules are ambiguous with fixed 
>look-ahead, which is what antlr 2 uses.  Given 4 digits and k=4 
>look-ahead, either rule could match, hence the warning when 
>compiling the grammar.  You need a semantic predicate to 
>disambiguate it:
>
>APAC_NUMERIC_TICKER
>     : (DIGIT+ COMMA) => ((DIGIT)+ (COMMA) (CHAR) (CHAR))
>     ;

That's actually a syntactic predicate :)

But yeah, that should do the trick.  Although you don't need that 
many parentheses.  You may also need to make sure that 
APAC_NUMERIC_TICKER is listed before NUMBER in the grammar file.





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