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

[Jim Idle]

Use a semantic predicate rather than syntactic. You possibly need a bated predicate here too:

 

{ input.LA(1) == A && input.LA(2) != B}?=>

 

However, if you need that kind of syntactic predicate, then I suggest you may be approaching your problem incorrectly.

 

Jim

 

From: antlr-interest-bounces at antlr.org [mailto:antlr-interest-bounces at antlr.org] On Behalf Of Naveen Chawla
Sent: Monday, October 05, 2009 7:02 AM
To: antlr-interest at antlr.org
Subject: [antlr-interest] How to do "not" in a syntactic predicate?

 

If I do

 

(a ~b)=> a

 

meaning "take this alternative if you encounter an a when not followed by b"

 

I get a syntax error: unexpected token b

Is it the right syntax to use '~'?

 

N



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