> expr : ID suffix;
will try to match the sep '.'. backtrack takes first alt that wins and the
decision for suffix needs to backtrack due to your program rule. therefore it
attempts '.' expr and fails.
allowing ;;;;…;;;;… as a program is not a good idea ;)
T
On Nov 26, 2011, at 4:21 AM, franck102 wrote:
> I think I am missing something fundamental about backtracking. The grammar
> below won't parse input such as
>
> a=b.
> c=d;
>
> ... even though I would expect it to backtrack after realizing that a=b.c
> leads to a dead-end. What am I missing?
>
> Thanks!
>
> PS: I am not looking for refactoring options, I have the issue in a complex
> grammar that can't easily be refactored.
>
> =====================================
> grammar Test;
>
> options {
> output=AST;
> backtrack=true;
> }
>
> program
> : statement* EOF
> ;
>
> statement
> : ID '=' expr
> | sep
> ;
>
> expr : ID suffix;
>
> suffix : ( '.' expr )*
> ;
>
> sep : ';' | '.';
>
> // LEXER
> // ==========================================
>
> ID
> : ('a'..'z'|'A'..'Z'|'_') ('a'..'z'|'A'..'Z'|'0'..'9'|'_')*
> ;
>
>
> WS : ( ' '
> | '\t'
> | '\r'
> | '\n'
> ) {$channel=HIDDEN;}
> ;
>
>
> --
> View this message in context:
> http://antlr.1301665.n2.nabble.com/Confused-about-backtracking-tp7033712p7033712.html
> Sent from the ANTLR mailing list archive at Nabble.com.
>
> List: http://www.antlr.org/mailman/listinfo/antlr-interest
> Unsubscribe:
> http://www.antlr.org/mailman/options/antlr-interest/your-email-address
List: http://www.antlr.org/mailman/listinfo/antlr-interest
Unsubscribe:
http://www.antlr.org/mailman/options/antlr-interest/your-email-address
--
You received this message because you are subscribed to the Google Groups
"il-antlr-interest" group.
To post to this group, send email to il-antlr-inter...@googlegroups.com.
To unsubscribe from this group, send email to
il-antlr-interest+unsubscr...@googlegroups.com.
For more options, visit this group at
http://groups.google.com/group/il-antlr-interest?hl=en.
