CVS Bison has two directives for writing verbatim code to the parser
header file. However, they are still experimental, so I can't promise
what they'll look like in the next stable release:
1. %requires {CODE} inserts CODE that YYSTYPE and YYLTYPE depend upon.
That is, it inserts CODE near the top of the parser header file.
2. %provides {CODE} is what you probably want. It exposes additional
definitions/declarations in the parser header file. They could
potentially depend upon YYSTYPE and YYLTYPE since it inserts CODE
near the
bottom of the parser header file.