[antlr-interest] Re: updated "antlr 2 bashing list"

Terence Parr parrt at cs.usfca.edu
Tue Mar 9 17:22:25 PST 2004


On Mar 9, 2004, at 4:51 PM, lgcraymer wrote:

> Ter--
>
> I hate to say it, but I think that that's a cop out.  Building
> exception objects and stack frames costs, and there is no point when
> in guessing mode.

This never happens unless you fail and is a minor cost compared to the 
cost of nested predicates, right?

>   They are also obnoxious when debugging (especially
> C++)

Doesn't bother me in Java, but other languages might be a drag.

I can investigate not using exceptions to see what the code looks like. 
  Actually somebody who has used JavaCC could tell us what it looks like 
;)  They do not use exceptions.

> and hamper code generation for languages which do not have
> exceptions.  It would be better to have a "synpredFailed flag as part
> of the generated classes-the flag will always be in cache, so is not a
> performance issue--or to have a return flag from rules and wrap rule
> invocations (foo) in
> if (foo() == false) return;
>
> and add
> if (guessing)
>     return false;
> else {
>     <throw exception>
> }
>
> around the <throw exception>s in ANTLR.  Come to think of it,
> implementing this with the current ANTLR runtime would be only about
> 10 lines of code or so (maybe a little more--I think that each
> exception would have to be fixed separately).

Uh...how you gonna redo return values in 10 lines ;)

Ter
--
Professor Comp. Sci., University of San Francisco
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