[antlr-interest] Proposal: synpred inversion?

[Sam Harwell]

I'm having trouble remembering the case where this came up in the
(distant?) past. I'm thinking the non-greedy wildcard might actually
resolve the issue.

-----Original Message-----
From: Terence Parr [mailto:parrt at cs.usfca.edu] 
Sent: Saturday, March 21, 2009 2:26 PM
To: Sam Harwell
Cc: ANTLR Interest Mailing List
Subject: Re: [antlr-interest] Proposal: synpred inversion?


On Mar 21, 2009, at 12:24 PM, Sam Harwell wrote:

> Currently you can only invert sets in a synpred. It seems like  
> inverting the entire predicate could be useful. It could be  
> implemented by backtracking returning state.failed instead of ! 
> state.failed, though putting it in the dfa could be a bit tougher  
> (but doable).
>
> I'm particularly interested in an example of how this could  
> encourage poor grammar design, as that would be a big fault with the  
> idea.

PEGs have not-grammar-fragment but they are mostly useful in lexer.

Ter