[antlr-interest] Advice with backtracking/ambiguity

[Jim Idle]

Remember antlr.markmail.org as it will give you lots of examples of this. You need:

fragment DIGITS : ('0'..'9')+ ;
DATE
: DIGITS
  (
      (SLASH DIGITS SLASH DIGITS)=> SLASH DIGITS SLASH DIGITS
    | {$type = DIGITS; }
;

SLASH : '/' ;

Jim

> -----Original Message-----
> From: antlr-interest-bounces at antlr.org [mailto:antlr-interest-
> bounces at antlr.org] On Behalf Of Ken Williams
> Sent: Wednesday, June 02, 2010 1:04 PM
> To: antlr-interest at antlr.org
> Subject: [antlr-interest] Advice with backtracking/ambiguity
> 
> Hi,
> 
> Here's a simple grammar demonstrating something I'm working with:
> 
> ------------------------------
> grammar testg;
> 
> options {
>     backtrack=true;
>     memoize=true;
>     output=AST;
> }
> 
> cite    :    token+ EOF ;
> 
> token    :    DATE | SLASH | DIGITS ;
> 
> DATE    :    DIGITS SLASH DIGITS SLASH DIGITS ;
> 
> WS    :    ( ' ' | '\t'| '\f' | '\n' | '\r' ) {skip();} ;
> 
> SLASH    :    '/' ;
> DIGITS    :    ('0'..'9')+ ;
> --------------------------------
> 
> 
> As you can see, there's an ambiguity with DATE.  What I'm trying to do
> is to
> use the DATE rule when it can succeed, and use DATE & SLASH otherwise.