[antlr-interest] lexer woes
Loring Craymer
lgcraymer at yahoo.com
Wed Mar 5 11:58:24 PST 2008
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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