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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 "Efficient Construction of LALR(1) Lookahead Sets" by F. DeRemer 
and A. Pennello, in ACM TOPLS Vol 4 No 4, October 1982.  Their 
technique is the standard one now.) 
 
	paul rubin 
	free software foundation