[antlr-interest] Using previously matched parser rule in decision making

[John B. Brodie]

Greetings!

On Mon, 2010-03-08 at 13:50 +1100, Kieran Simpson wrote:
> I have
> 
> ruleA: ruleB;
> 
> ruleC: ruleB;
> 
> ruleB: ruleD;
> 
> In ruleB I want to different target language actions to execute based on
> whether it was ruleA or ruleC that was previously matched.  If my
> understanding of syntatic/semantic predicates is correct, they only look
> forwards, not backwards.
> 
> Is there a way (without refactoring the grammar) to in rule B know which
> rule it was invoked from (A or C) and make decisions accordingly?

Off the top of my head, pass a parameter.....

ruleA : ruleB[true];
ruleC : ruleB[false];
ruleB [boolean fromA] : ruleD
  { if( fromA )then
       ....do this stuff....
    else
       ....do that stuff....
   };

(the above probably is not precisely the correct meta-syntax, but
hopefully you get the idea...)

   -jbb