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Re: push parser

From: Bob Rossi
Subject: Re: push parser
Date: Sun, 17 Dec 2006 13:42:30 -0500
User-agent: Mutt/1.5.12-2006-07-14

On Sat, Dec 16, 2006 at 05:04:42PM -0500, Joel E. Denny wrote:
> On Sat, 16 Dec 2006, Bob Rossi wrote:
> > > BTW, after knowing all of this, if I were to write the patch, I would do
> > > it this way. I would leave the pure-parser option set to false. But I
> > > would write a new macro, b4_pure_or_push (or something), and replace all
> > > calls to b4_pure that are supposed to be b4_pure_or_push.
> At the moment, that would be every call to b4_pure.  And b4_pure would 
> never be used outside of b4_pure_or_push.
> Let's say we one day develop another kind of modifier like %push-parser.  
> I'll call it xyz and %xyz-parser.  Let's say we decide that all xyz 
> parsers must also be pure parsers.  Are we then going to write 
> b4_pure_or_push_or_xyz?  And then b4_pure_or_push_or_xyz_or_abc?
> > > That would
> > > leave bison with the ability to perform all combinations of checks,
> > > which I don't think it can currently do now.
> Assuming my patch, here are all 4 combinations, each with a check that 
> will be true iff that combination is true:
>      pure   push   check
>   -----------------------------
>   1  false  false  !pure_parser
>   2  false  true   false
>   3  true   false  pure_parser && !push_parser
>   4  true   true   pure_parser && push_parser
> So, assuming my patch, all checks are possible.  Notice that, since all 
> push parsers are pure, #2 is a fallacy.  We can check it and we'll get the 
> right answer, but what's the point?

One more point about this, even though it's already been committed. One
of the last things on my list is to make sure that the correct variables
are declared either in yyparse or in the struct yypstate depending on
the options choosen by the user. Currently, I declare all the variables
in the parser, just to make life easy. 

With the patch that has been applied, it makes it hard (unless I'm
missing something). The problem is, when %push-parser is used, bison
wants to declare some variables in the yypstate.  However, it does not 
want to declare some variables in the yypushparse function. When
%pure-parser it used, bison wants to declare some variables in the
yyparse function. 

How will you decide when to declare the variable in the yyparse
function? You want to declare them when %pure-parser is used in pure
mode but not when %push-parser is used.

If you have thought this case through, then I'm on board with this patch

Thanks for your time,
Bob Rossi

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