3.1.5 The epilogue

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 of yylex and yyerror often go here. Because C requires functions to be declared before being used, you often need to declare functions like yylex and 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.