PD versions of yacc

[from allegra!ucbvax!phr (Paul Rubin)]


The parsers generated by Bison and Zoo (both written by Bob Corbett
and distributed by the Free Software Foundation) are public domain
and compatible with YACC parsers (tho they run faster).


Bison was written by Bob Corbett as part of his PhD thesis at Berkeley
on compiler error recovery. It is a more modern parser generator than
Yacc, but used a different input syntax. Stallman got a copy and hacked
it up to process Yacc input (along with some extensions), but this was
kind of a kludgy job. Then Corbett wrote Zoo (based on Bison), which
was intended as a Yacc replacement and may yet replace Yacc on some
future BSD tape. However, the GNU C compiler uses Bison's extensions,
so until someone hacks them into Zoo (not too difficult from what I've
heard.)


Bison was on some of the early GNU distribution tapes, but was withdrawn
due to bugs. Zoo does not have the bugs (it supports every documented
feature of Yacc) but lacks some of Bison's undocumented extensions.
They are based on the same code. Some version of Bison and/or Zoo
will be GNU's Yacc replacement when GNU is a more complete system.

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