[antlr-interest] predicate question

[Gerald Rosenberg]

Is the question whether

a : {p1}? {action();} {p2}? A | A ;

should perform differently from

a : {p1}? {action(); return true;}? {p2}? A | A ;

 From a high level the-grammar-as-a-language point of view, seems 
like those two rules should match equivalently.



At 06:20 PM 5/5/2008, Terence Parr wrote:
>Consider:
>
>parser grammar T;
>
>a : {p1}? {action} {p2}? A
>   | A
>   ;
>
>Someone pointed out that p2 should not be tested out of context (i.e.,
>before action executes).  ANTLR v2 (PCCTS) correctly ignored preds
>after actions.  v3 definitely walks right over actions looking for
>preds.   I propose to prevent p2 from being hoisted into the decision
>for rule 'a'.  Right now it generates enclosed DFA.  After fix, it
>would only see p1.  Not sure how to fix just yet, but i'll figure it
>out.
>
>Contrary opinions?
>
>Ter
>
>
>
>