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Declarations for `rpcalc'
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
%% /* Grammar rules and actions follow */
The C declarations section (Note: The C Declarations Section
Declarations.) 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: Value Type.). 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
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.
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