[antlr-interest] AntLR bug warning

Terence Parr parrt at jguru.com
Sun Feb 3 21:16:52 PST 2002


On Sunday, February 3, 2002, at 03:58  AM, Michael Labhard wrote:

> As requested here is exactly what the warning is:
>
> ANTLR Parser Generator   Version 2.7.1   1989-2000 jGuru.com
> warning: lexical nondeterminism between rules NAME_TOKEN and END_TOKEN 
> upon
> TermParser2.g:0: 	k==1:'.'
> TermParser2.g:0: 	k==2:<end-of-token>

Ok, it's a problem of lookahead.

protected GRAPHIC_TOKEN
   :
     ( '.' (GRAPHIC_TOKEN_CHAR|'.')+ )
     |
     ( GRAPHIC_TOKEN_CHAR (GRAPHIC_TOKEN_CHAR|'.')* )
   ;

can match '.' followed by something or a single char followed by 
nothing...when these lookaheads are combined it appears that '.' <end> 
is valid for this rule which it isn't.

Search the faq for info on linear approx lookahead.
Ter
PS	You might consider merging the rules to fix this.
--
Chief Scientist & Co-founder, http://www.jguru.com
Creator, ANTLR Parser Generator: http://www.antlr.org


 

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