Re: push parser documentation

[Bob Rossi]

On Sat, Aug 04, 2007 at 02:26:29PM -0400, Joel E. Denny wrote:
> On Sat, 4 Aug 2007, Bob Rossi wrote:
> 
> > > Moreover, to keep users safe, I wonder if impure push mode should have a 
> > > global variable that counts yypstate instances.  If yypstate_new detects 
> > > more than 1 instance, it should invoke yyerror with a message about 
> > > %pure-parser and then return NULL.
> > > 
> > > What do you think?
> > 
> > I'm not sure. There are some unfortunate limitations this would impose
> > on the user. Say they wanted to create all of the objects up front but
> > then there program is "smart enough" to ensure they are only used one at
> > a time. At least with the new documentation, they are warned...
> 
> If a user needs multiple objects, he should declare %pure-parser, so I 
> don't really see this as a limitation.  Does that alleviate your concern? 
> Again, I feel that impure push parsers are only for backward compatibility 
> with Yacc pull parsing, which also, because of its global variables, can 
> support only one parser instance at a time.

Yes, that does alleviate my concern.

> > > > +When the @code{%push-parser} or @code{%push-pull-parser} declaration 
> > > > is used
> > > > +then it is important to understand that all references to the 
> > > > @code{yyparse}
> > > > +function in this manual corresponds to the @code{yypush_parser} 
> > > > function 
> > > > +unless otherwise stated.
> > > 
> > > I'm afraid I don't understand what you mean in that last paragraph.  Can 
> > > we drop it?
> > 
> > OK, This sentence seemed important to me. I'll describe the problem, let
> > me know what a good solution is. There are lots of places in the manual
> > where it says "X happens when pure parser is used" or "X is in yyparse
> > function". I wanted to make it clear the the yyparse function is the
> > same as the yypush_parse function in that regards. Maybe that is just
> > obvious to the uesr?
> 
> There are statements in the manual for which this isn't true.  For 
> example, in section 1.7 Bison Output: the Parser File:
> 
>   The Bison parser file is C code which defines a function named
>   `yyparse' which implements that grammar.  This function does not make a
>   complete C program: you must supply some additional functions.  One is
>   the lexical analyzer.
> 
> The last statement is true of yyparse or yypull_parse but not 
> yypush_parse.
> 
> Another in section 2.1.2.1 Explanation of `input':
> 
>   The parser function `yyparse' continues to process input until a
>   grammatical error is seen or the lexical analyzer says there are no more
>   input tokens; we will arrange for the latter to happen at end-of-input.
> 
> This is only true of pull parsers.
> 
> I didn't search any further for additional examples, but I think you can 
> see the problem.  The manual was written mostly with traditional Yacc pull 
> parsing in mind.  I'm guessing it makes many more statements that don't 
> make sense for push parsing.  I feel that readers will understand that the 
> push parsing documentation shows a way to modify the functionality 
> described in the rest of the manual, and I don't think you should claim 
> that the rest of the manual applies to push parsing.
> 
> Does this make sense to you?

Yes, it does. Thanks. I like inventing problems to solve :)

Bob Rossi