The Epilogue is copied verbatim to the end of the parser
implementation file, just as the Prologue is copied to the
beginning. This is the most convenient place to put anything that you
want to have in the parser implementation file but which need not come
before the definition of
yyparse. For example, the definitions
yyerror often go here. Because C requires
functions to be declared before being used, you often need to declare
yyerror in the Prologue, even
if you define them in the Epilogue. See Parser C-Language Interface.
If the last section is empty, you may omit the ‘%%’ that separates it from the grammar rules.
The Bison parser itself contains many macros and identifiers whose names start with ‘yy’ or ‘YY’, so it is a good idea to avoid using any such names (except those documented in this manual) in the epilogue of the grammar file.