Saving/restoring bison parse state

From: tim@wagner.Princeton.EDU (Tim Hollebeek)


> I'm writing a C documentation tool based on a bison grammar for C. One of
> the things I want to do is handle BOTH blocks of #ifdef/#else/#endif
> constructs.
>
> I have the practical aspects down as far as my program is concerned, so
> I just need to get bison to cooperate. I.e.:


> /* some C code */
> /***** save all bison state info here *****/
> #ifdef FOO
> /* branch 1 */
> /***** restore bison state info here *****/
> #else
> /* branch 2 */
> #endif
>
> Has anyone tried something like this before? A quick look at the bison
> output suggests it should work fine if I simply save the globals in the
> YYPURE ifdef, as well as all the local variables in yyparse (probably using
> a hacked version of bison.simple).


We face the same problem with conditional compilation as we are
working on re-engineering of existing programs. One of our first idea
was saving and restoring parse state. What we did with a quite easy
hacking of bison.simple.


> Are there any disadvantages to this approach I have missed? Any better
> ways of accomplishing the same thing?


In our case it simply didn't work because of situations such as:


...
#ifdef SUNOS
/* source code for SUNOS */
#endif
/* common code */
#ifdef SOLARIS
/* source code for SOLARIS */
#endif
/* common code */
#ifdef SUNOS
/* source code for SUNOS */
#endif
....


Where we want to consider all the code related to SUNOS or SOLARIS
together and independantly. In a such case you simply can't say when
to save and restore the parsing state (conditions can be more
complicated than what is above with #if).


We also have problem with the fact that our saving and restoring
primitives are completely dependant on bison implementation, and then,
may not work with different (futur) versions.


Just send me a mail if you are interessed on our hack.
--
Stéphane S. Somé
http://www.csi.uottawa.ca/~tcl/kbre/
SITE: School of Information Technology and Engineering
University of/d'Ottawa
Ottawa, Canada, K1N 6N5
--

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