[antlr-interest] syntactic predicates and exceptions

Terence Parr parrt at cs.usfca.edu
Wed Nov 16 10:39:58 PST 2005


On Nov 16, 2005, at 10:30 AM, Pete Gonzalez wrote:

> Terence Parr wrote:
>> Hi.  First, are you parsing C# or are you parsing simple field/ 
>> value  pairs?
>
> We are parsing field/value pairs, but the grammar was created by  
> modifying an example grammar for C# from your web site.  This may  
> seem like overkill for simple field/value pairs, but the  
> application requires parsers for several different languages with  
> syntax similar to C#, so it made sense to use a common framework.

Ah.  Makes sense.

> The exceptions I see right now are MismatchedCharException (1870  
> times) and NoViableAltForCharException (3755 times).

The *LEXER* is backtracking?  Oh gawd, it will kill you.  See what  
the java grammar does for matching numbers...I think it avoids them.   
An exception per char is deadly.

>> Thanks very much for the valuable info.  I'm going to try for no-  
>> exceptions to see what happens.  Note that v3 should make syn  
>> preds  MUCH less needed.
>
> How hard is it to convert 2.0 grammars for Antlr 3.0?  How usable  
> is the current "early access" build?  What's the ETA for the  
> official 3.0 release?  These seem like basic questions, but I  
> didn't see them in the FAQ.  :-)

We don't have a faq yet ;)  Gotta figure out why the wiki was  
crashing and get that going again.

I'll be doing an auto-converter to 3.0.  Current version I just  
released is pretty usable if you ask me, but I'm going to try it out  
on a real app soon to see if it does anything useful.  It crashes on  
bad input at the moment etc...  I wouldn't bet my job on it yet ;)   
3.0 eta will be next summer probably.

Ter


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