(bison.info) Grammar in Bison

 
 From Formal Rules to Bison Input
 ================================
 
    A formal grammar is a mathematical construct.  To define the language
 for Bison, you must write a file expressing the grammar in Bison syntax:
 a "Bison grammar" file.   Bison Grammar Files Grammar File.
 
    A nonterminal symbol in the formal grammar is represented in Bison
 input as an identifier, like an identifier in C.  By convention, it
 should be in lower case, such as `expr', `stmt' or `declaration'.
 
    The Bison representation for a terminal symbol is also called a
 "token type".  Token types as well can be represented as C-like
 identifiers.  By convention, these identifiers should be upper case to
 distinguish them from nonterminals: for example, `INTEGER',
 `IDENTIFIER', `IF' or `RETURN'.  A terminal symbol that stands for a
 particular keyword in the language should be named after that keyword
 converted to upper case.  The terminal symbol `error' is reserved for
 error recovery.   Symbols.
 
    A terminal symbol can also be represented as a character literal,
 just like a C character constant.  You should do this whenever a token
 is just a single character (parenthesis, plus-sign, etc.): use that
 same character in a literal as the terminal symbol for that token.
 
    A third way to represent a terminal symbol is with a C string
 constant containing several characters.   Symbols, for more
 information.
 
    The grammar rules also have an expression in Bison syntax.  For
 example, here is the Bison rule for a C `return' statement.  The
 semicolon in quotes is a literal character token, representing part of
 the C syntax for the statement; the naked semicolon, and the colon, are
 Bison punctuation used in every rule.
 
      stmt:   RETURN expr ';'
              ;
 
  Syntax of Grammar Rules Rules.
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