@group
%@{
- #define YYSTYPE double
#include <stdio.h>
#include <math.h>
int yylex (void);
%@}
@end group
+%define api.value.type double
%token NUM
%% /* Grammar rules and actions follow. */
The declarations section (@pxref{Prologue, , The prologue}) contains two
preprocessor directives and two forward declarations.
-The @code{#define} directive defines the macro @code{YYSTYPE}, thus
-specifying the C data type for semantic values of both tokens and
-groupings (@pxref{Value Type, ,Data Types of Semantic Values}). The
-Bison parser will use whatever type @code{YYSTYPE} is defined as; if you
-don't define it, @code{int} is the default. Because we specify
-@code{double}, each token and each expression has an associated value,
-which is a floating point number.
-
The @code{#include} directive is used to declare the exponentiation
function @code{pow}.
epilogue, but the parser calls them so they must be declared in the
prologue.
-The second section, Bison declarations, provides information to Bison
-about the token types (@pxref{Bison Declarations, ,The Bison
-Declarations Section}). 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 @code{NUM}, the token
-type for numeric constants.
+The second section, Bison declarations, provides information to Bison about
+the tokens and their types (@pxref{Bison Declarations, ,The Bison
+Declarations Section}).
+
+The @code{%define} directive defines the variable @code{api.value.type},
+thus specifying the C data type for semantic values of both tokens and
+groupings (@pxref{Value Type, ,Data Types of Semantic Values}). The Bison
+parser will use whatever type @code{api.value.type} is defined as; if you
+don't define it, @code{int} is the default. Because we specify
+@code{double}, each token and each expression has an associated value, which
+is a floating point number. C code can use @code{YYSTYPE} to refer to the
+value @code{api.value.type}.
+
+Each terminal symbol that is not a single-character literal must be
+declared. (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 @code{NUM}, the token type for numeric constants.
@node Rpcalc Rules
@subsection Grammar Rules for @code{rpcalc}
The semantic value of the token (if it has one) is stored into the
global variable @code{yylval}, which is where the Bison parser will look
-for it. (The C data type of @code{yylval} is @code{YYSTYPE}, which was
-defined at the beginning of the grammar; @pxref{Rpcalc Declarations,
-,Declarations for @code{rpcalc}}.)
+for it. (The C data type of @code{yylval} is @code{YYSTYPE}, whose value
+was defined at the beginning of the grammar via @samp{%define api.value.type
+double}; @pxref{Rpcalc Declarations,,Declarations for @code{rpcalc}}.)
A token type code of zero is returned if the end-of-input is encountered.
(Bison recognizes any nonpositive value as indicating end-of-input.)
@group
%@{
- #define YYSTYPE double
#include <math.h>
#include <stdio.h>
int yylex (void);
@group
/* Bison declarations. */
+%define api.value.type double
%token NUM
%left '-' '+'
%left '*' '/'
/* Location tracking calculator. */
%@{
- #define YYSTYPE int
#include <math.h>
int yylex (void);
void yyerror (char const *);
%@}
/* Bison declarations. */
+%define api.value.type int
%token NUM
%left '-' '+'
(@pxref{Multiple Types, ,More Than One Value Type}).
The @code{%union} declaration specifies the entire list of possible types;
-this is instead of defining @code{YYSTYPE}. The allowable types are now
+this is instead of defining @code{api.value.type}. The allowable types are now
double-floats (for @code{exp} and @code{NUM}) and pointers to entries in
the symbol table. @xref{Union Decl, ,The Collection of Value Types}.
Bison normally uses the type @code{int} for semantic values if your
program uses the same data type for all language constructs. To
-specify some other type, define @code{YYSTYPE} as a macro, like this:
+specify some other type, define the @code{%define} variable
+@code{api.value.type} like this:
+
+@example
+%define api.value.type double
+@end example
+
+@noindent
+or
+
+@example
+%define api.value.type "struct semantic_type"
+@end example
+
+The value of @code{api.value.type} should be a type name that does not
+contain parentheses or square brackets.
+
+Alternatively, instead of relying of Bison's @code{%define} support, you may
+rely on the C/C++ preprocessor and define @code{YYSTYPE} as a macro, like
+this:
@example
#define YYSTYPE double
@end example
@noindent
-@code{YYSTYPE}'s replacement list should be a type name
-that does not contain parentheses or square brackets.
This macro definition must go in the prologue of the grammar file
-(@pxref{Grammar Outline, ,Outline of a Bison Grammar}).
+(@pxref{Grammar Outline, ,Outline of a Bison Grammar}). If compatibility
+with POSIX Yacc matters to you, use this. Note however that Bison cannot
+know @code{YYSTYPE}'s value, not even whether it is defined, so there are
+services it cannot provide. Besides this works only for languages that have
+a preprocessor.
@node Multiple Types
@subsection More Than One Value Type
double val;
symrec *tptr;
@};
-typedef union YYSTYPE YYSTYPE;
@end group
@end example
@noindent
-and then your grammar can use the following
-instead of @code{%union}:
+and then your grammar can use the following instead of @code{%union}:
@example
@group
%@{
#include "parser.h"
%@}
+%define api.value.type "union YYSTYPE"
%type <val> expr
%token <tptr> ID
@end group
@item Language(s): C, C++
@item Purpose: This is the best place to write dependency code required for
-@code{YYSTYPE} and @code{YYLTYPE}.
-In other words, it's the best place to define types referenced in @code{%union}
-directives, and it's the best place to override Bison's default @code{YYSTYPE}
-and @code{YYLTYPE} definitions.
+@code{YYSTYPE} and @code{YYLTYPE}. In other words, it's the best place to
+define types referenced in @code{%union} directives. If you use
+@code{#define} to override Bison's default @code{YYSTYPE} and @code{YYLTYPE}
+definitions, then it is also the best place. However you should rather
+@code{%define} @code{api.value.type} and @code{api.location.type}.
@item Location(s): The parser header file and the parser implementation file
before the Bison-generated @code{YYSTYPE} and @code{YYLTYPE}
@end deffn
@deffn {Type} YYSTYPE
+Deprecated in favor of the @code{%define} variable @code{api.value.type}.
Data type of semantic values; @code{int} by default.
@xref{Value Type, ,Data Types of Semantic Values}.
@end deffn
projects / bison.git / commitdiff
