Disappearance of rhs[], prhs[], and user control of table generation.

[David M. Warme]

Bison developers,

While examining the "git" repository for bison, I discovered a change
that will be very detrimental to our particular application that makes
extensive use of bison.  The relevant change is discussed here:

http://lists.gnu.org/archive/html/bison-patches/2008-11/msg00291.html

We have a rather large code base (several hundred grammars, most of
which weigh in as "large and complex").  All of these grammars are used
in a way that depends upon having the yyrhs[] and yyprhs[] tables
available.  Outright removal of these tables would be a huge problem for
us.

Further examination yielded very confusing results, however.  The patch
referenced above dates from November 2008, yet looking at the latest
released version of bison (version 2.4.3, dated August 2010) it appears
that yyrhs[] and yyprhs[] are still being generated.

Certainly parsers can be smaller and faster if bison drops tables that
it doesn't need.  But it would be handy if the user could specify tables
that should always be produced (even when bison doesn't think it needs
them), e.g.:

%generate-tables        yyrhs yyprhs yytname

or even the following:

        %{
        typedef short        my_short;
        %}

        ...

        %generate-tables {my_short}        yyrhs yyprhs
        %generate-tables                   yytname

which would also give the user the ability to force a certain choice of
type for said tables.  (The temptation was to use <my_short>, but
currently that syntax is used to specify %union member names, not type
names, so I switched to curly braces instead.)

Questions:

1. What is the current state (and future fate) of the yyrhs[] and
   yyprhs[] tables?

2. Would you be willing to retain the ability to generate these tables
   (and perhaps other similar tables) if we contributed a declaration
   (like the one shown above) that would permit the user to force
   generation of tables he or she really wants/needs?

David


David M. Warme, Ph.D.
Principal Computer Scientist
Group W, Inc.
Fairfax, Virginia, USA.