[antlr-interest] How to do "not" in a syntactic predicate?

[Kaleb Pederson]

On Fri, Oct 16, 2009 at 4:39 AM, Naveen Chawla
<naveen.chwl at googlemail.com> wrote:
> So, does anybody have a way of doing "Take *a* IF not followed by *b* (both
> syntactic constructs)" ?
>
> i.e.
> q: (a !b)=> a;                        //("!" or "not" doesn't exist in
> ANTLR)

I think that would be a nice syntax for ANTLR to support.

I would guess that you could generally accomplish the same thing by
placing the "opposite" syntactic predicate on your other
alternative(s) in your production.  In other words:

(a b)=> alternative_1
| alternative_2 ...

Rather than:

(a !b)=> alternative_2
| alternative_1

--
Kaleb Pederson
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Blog - http://kalebpederson.com