Saving/restoring bison parse state

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).


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


---------------------------------------------------------------------------
Tim Hollebeek
email: tim@wfn-shop.princeton.edu
URL: http://wfn-shop.princeton.edu/~tim
[There was discussion a year or so ago about backtracking versions of yacc.
The grammar of C++ is so awful that you need them to parse C++ reasonably.
-John]
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