mirror of
https://git.FreeBSD.org/ports.git
synced 2024-10-29 21:39:24 +00:00
23 lines
1.1 KiB
Plaintext
23 lines
1.1 KiB
Plaintext
Bison is a tool used to write parsers, such as the parser for GNU cc.
|
|
It is similar to Yacc, which is included in the base FreeBSD system.
|
|
|
|
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.)
|