Re: push parser implemenation

[Bob Rossi]

On Wed, Apr 05, 2006 at 09:35:46AM +0000, Frans Englich wrote:
> On Wednesday 05 April 2006 00:48, Paul Eggert wrote:
> > Bob Rossi <address@hidden> writes:
> [...]
> 
> > Is there some way that we can fix that?  For example, is there someone
> > who needs push parsers, but doesn't yet know that they need them?
> 
> Heh, I might be one of them.
> 
> I googled around a bit, but I still wonder: what advantages does this 
> push-parser patch add to Bison? What does it do?
> 
> To me it seems like it makes it possible to call the parser instead of that 
> the parser calls you.. possibly solving problems wrt. blocking. Correct? 
> Something else or in addition?

Hi Frans,

Before I knew what I wanted, I was calling it an asynchronous parser.
Once I brought the discussion here, the word was quickly changed to push
parsing. 

Yes, the pull parser is a parser which asks for the tokens, and
doesn't return until it's done. This is a less desirable approach when
the parser has to read a large amount of data from a GUI application.
Also, the pull parser doesn't work at all in an application that wants
to write a parser that using streaming data, over a network socket or
unix pipe. In this case, the data is never "fully ready". So, either you
have to call your main_loop function from within bison, or you need
another solution.

The push parser is just that solution. You feed the tokens to bison.
This allows me to write a grammar that represents data that will be
coming over a stream from another application. I create the parser once
at the beggining, and feed it tokens until the other application dies.
In this particular instance, CGDB is the program using the push parser,
and GDB is the program streaming the GDB/MI protocol over stdout. This
patch will greatly improve the design and usability of CGDB.

There is 1 other potential gain of the push parser approach. For every
yyparse or xxparse grammar that you have generated, you can have more
than one parser instance working at the same time on the same grammar.
That's because all of the data associated with the parser is located
inside a single struct. I'm pretty sure this isn't possible with the
%pure-parser.

Thanks,
Bob Rossi