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(bison.info)Rpcalc Decls

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Declarations for `rpcalc'
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   Here are the C and Bison declarations for the reverse polish notation
calculator.  As in C, comments are placed between `/*...*/'.

     /* Reverse polish notation calculator. */
     
     %{
     #define YYSTYPE double
     #include <math.h>
     %}
     
     %token NUM
     
     %% /* Grammar rules and actions follow */

   The C declarations section (Note: The C Declarations Section.
) contains two preprocessor directives.

   The `#define' directive defines the macro `YYSTYPE', thus specifying
the C data type for semantic values of both tokens and groupings (Note:
Data Types of Semantic Values.).  The Bison parser will use
whatever type `YYSTYPE' is defined as; if you don't define it, `int' is
the default.  Because we specify `double', each token and each
expression has an associated value, which is a floating point number.

   The `#include' directive is used to declare the exponentiation
function `pow'.

   The second section, Bison declarations, provides information to
Bison about the token types (*note The Bison Declarations Section:
Bison Declarations.).  Each terminal symbol that is not a
single-character literal must be declared here.  (Single-character
literals normally don't need to be declared.)  In this example, all the
arithmetic operators are designated by single-character literals, so the
only terminal symbol that needs to be declared is `NUM', the token type
for numeric constants.