Re: reentrant parser - how?

[Hans Aberg]

[Please keep the Help-Bison cc, so that others can help.]

At 13:28 +0200 2005/05/08, Carsten Krüger wrote:
> HA> I recall Paul Eggert said that the Bison generated parser, which he
> HA> wrote, now is fully pure.
>
> Which parser?

The C-parser skeleton file. But your subsequent 
explanations suggests that this is not a question 
for Paul (sorry).

> HA> If you have some data to be passed to the
> HA> parser, that should be done via the arguments to yyparse, and there
> HA> are some macros for doing that; see the Bison manual. If yyparse
> HA> needs some local data, then there might not be support for doing that
> HA> right now. Then you need to figure out how to make the Flex generated
> HA> lexer to become pure; for that, check in the Help-Flex list
> HA> <address@hidden>.
>
> Can you explain it a litte bit more?

I do not use a fully pure parser, and I use a C++ 
parser. So you will have to hope from more input 
from somebody else.

> I try to explain my problem.
>
> My bison grammar has a BEGIN and an END token and I want to parse many
> inputfiles consecutively.
>
> Example.
>
> file1:
> START
> some command
> ...
> STOP
>
> file2:
> START
> some command
> ...
> STOP

Then you do not need fully pure parser.

> If I use only:
> yyin=fptr_1;
> yyparse();
> yyin=fptr_2;
> yyparse();
>
> The second yyparse()-call tells me, START is unexpected.
> The parser don't know, that the inputfile has changed.
> This might be usefull for include-files in C, I think.

Most likely, this is a problem that the lexer has 
not been reset. Read the Flex manual, or ask in 
the Help-Flex list. I use something like 
"lexer_.initialize(isp_)", but I do not know if 
that is the original Flex lexer function. The 
parser function yyparse() will be reset every 
time it is called anew. It only parses tokens, 
not streams.
--
  Hans Aberg