[antlr-interest] lexer woes

[Loring Craymer]

Setting backtracking in combined grammars only affects the parser (again, see the prefixWithSynPred code); from the code, though, setting backtracking=true in lexer grammars does introduce synpreds at all decision points.

--Loring

----- Original Message ----
> From: Gavin Lambert <antlr at mirality.co.nz>
> To: Loring Craymer <lgcraymer at yahoo.com>; Matt Benson <gudnabrsam at yahoo.com>; Antlr List <antlr-interest at antlr.org>
> Sent: Wednesday, March 5, 2008 12:09:41 AM
> Subject: Re: [antlr-interest] lexer woes
> 
> At 11:35 5/03/2008, Loring Craymer wrote:
>  >> 1) Whether backtracking mode is supported for lexers,
>  >1.)  Yes--see calls to prefixWithSynPred() in antlr.g
> 
> I think that answer is a little misleading :)
> 
> As far as I know, the "backtrack=true" option has no effect in the 
> lexer.  However, backtracking in general is supported through 
> adding your own syntactic predicates.
> 
> Note that syntactic predicates can only be used to disambiguate 
> between alts in a single rule -- you can't use them to distinguish 
> between tokens at the top level.  (If you need to do that, you'll 
> have to merge the rules.)
> 
> 




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