From phr Tue Jul  8 10:36:19 1986
Date: Tue, 8 Jul 86 00:52:24 EDT
From: phr (Paul Rubin)
To: riferguson%watmath.waterloo.edu@CSNET-RELAY.ARPA, tower
Subject: Re:  Bison documentation?

The main difference between Bison and Yacc that I know of is that
Bison supports the @N construction, which gives you access to
the starting and ending line number and character number associated
with any of the symbols in the current rule.

Also, Bison supports the command `%expect N' which says not to mention
the conflicts if there are N shift/reduce conflicts and no reduce/reduce
conflicts.

The differences in the algorithms stem mainly from the horrible
kludges that Johnson had to perpetrate to make Yacc fit in a PDP-11.

Also, Bison uses a faster but less space-efficient encoding for the
parse tables (see Corbett's PhD thesis from Berkeley, "Static
Semantics in Compiler Error Recovery", June 1985, Report No. UCB/CSD
85/251), and more modern technique for generating the lookahead sets.
(See Frank DeRemer and Thomas Pennello, "Efficient Computation of
LALR(1) Look-Ahead Sets", ACM Transactions on Programming Languages
and Systems (TOPLAS) 4, 4 (October 1982), 615-649.  Their
technique is the standard one now.)

	paul rubin
	free software foundation


[DeRemer-Pennello reference corrected by Paul Eggert <eggert@cs.ucla.edu>,
 2004-06-21.]