[antlr-interest] how to do exceptions quickly

[Terence Parr]

On Nov 4, 2007, at 1:16 AM, Benjamin Niemann wrote:

> Hi,
>
> Terence Parr wrote:
>> I had a long conversation at Google last night with Neal Gafter,  
>> the guy who built the javac compiler when he was at Sun. He told  
>> me that exceptions can be made to execute very quickly.  The only  
>> thing you have to avoid is the actual exception object creation  
>> which has to do all of the expensive stack trace creation and so  
>> on.  He says that the actual throwing of the exception itself is  
>> not a problem.  This might be something to look at later to see if  
>> it goes quickly, because it results in cleaner backtracking code.   
>> Anyway, we can create some singleton objects, which will solve the  
>> problem.  Hooray!
>> Anyway, this might be useful to people in general.  I thought was  
>> pass along this interesting trick.
>
> As a follow-up to this long forgotten thread: I just replaced the  
> failed flag by a BacktrackingFailed exception in my Python target.  
> I got rid of all flag checking reducing the file size of the  
> generated parser by ~5% and having a small performance gain of  
> about ~2 (using the Java.g parser).
> If you are interested, look at CL 4272.

So 2% faster in python?  Perhaps python is slow to try/catch (only  
create is slow in java).

Code was much cleaner though right?

Ter