1999-05-03 04:20:49 +00:00
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Bison is a tool used to write parsers, such as the parser for GNU cc.
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It is similar to Yacc, which is included in the base FreeBSD system.
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1999-05-03 03:18:08 +00:00
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The main difference between Bison and Yacc that I know of is that
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Bison supports the @N construction, which gives you access to
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the starting and ending line number and character number associated
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with any of the symbols in the current rule.
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Also, Bison supports the command `%expect N' which says not to mention
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the conflicts if there are N shift/reduce conflicts and no reduce/reduce
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conflicts.
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The differences in the algorithms stem mainly from the horrible
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kludges that Johnson had to perpetrate to make Yacc fit in a PDP-11.
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Also, Bison uses a faster but less space-efficient encoding for the
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parse tables (see Corbett's PhD thesis from Berkeley, "Static
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Semantics in Compiler Error Recovery", June 1985, Report No. UCB/CSD
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85/251), and more modern technique for generating the lookahead sets.
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(See "Efficient Construction of LALR(1) Lookahead Sets" by F. DeRemer
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and A. Pennello, in ACM TOPLS Vol 4 No 4, October 1982. Their
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technique is the standard one now.)
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