bison is a general-purpose parser generator that converts an annotated context-free grammar into an LALR(1) or GLR parser for that grammer. Bison is upward compatible with Yacc -- all properly-written Yacc grammars ought to work with Bison with no change. The msys-bison-bin (sub)package provides the bison executable and associated development files. The msys-bison-lang (sub)package provides i18n support for the bison executable, while the msys-bison-rtm (sub)package provides i18n support for applications created with bison.