The input file for the Bison utility is a Bison grammar file. The general form of a Bison grammar file is as follows:
%{
C declarations
%}
Bison declarations
%%
Grammar rules
%%
Additional C code
The `%%', `%{' and `%}' are punctuation that appears in every Bison grammar file to separate the sections.
The C declarations may define types and variables used in the actions.
You can also use preprocessor commands to define macros used there, and use
#include to include header files that do any of these things.
The Bison declarations declare the names of the terminal and nonterminal symbols, and may also describe operator precedence and the data types of semantic values of various symbols.
The grammar rules define how to construct each nonterminal symbol from its parts.
The additional C code can contain any C code you want to use. Often the
definition of the lexical analyzer yylex goes here, plus subroutines
called by the actions in the grammar rules. In a simple program, all the
rest of the program can go here.
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