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Emphasize that yylex and yyerror must be declared before being used.

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E.g., one should typically declare them in the prologue.  Use GNU
coding style in examples.  Put "const" consistently after the type it
modifies.  Mention that C99 supports "inline".  Mention that yyerror
traditionally returns "int".
This commit is contained in:
Paul Eggert
2002-11-30 07:42:37 +00:00
parent 6b0d38ab2c
commit 38a92d500a
1 changed files with 127 additions and 90 deletions
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217
doc/bison.texinfo
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@@ -685,7 +685,10 @@ Let's consider an example, vastly simplified from a C++ grammar.
@example
%@{
#define YYSTYPE const char*
#include <stdio.h>
#define YYSTYPE char const *
int yylex (void);
void yyerror (char const *);
%@}
%token TYPENAME ID
@@ -783,7 +786,8 @@ stmt : expr ';' %merge <stmtMerge>
and define the @code{stmtMerge} function as:
@example
static YYSTYPE stmtMerge (YYSTYPE x0, YYSTYPE x1)
static YYSTYPE
stmtMerge (YYSTYPE x0, YYSTYPE x1)
@{
printf ("<OR> ");
return "";
@@ -796,7 +800,7 @@ in the C declarations at the beginning of the file:
@example
%@{
#define YYSTYPE const char*
#define YYSTYPE char const *
static YYSTYPE stmtMerge (YYSTYPE x0, YYSTYPE x1);
%@}
@end example
@@ -813,15 +817,16 @@ as both an @code{expr} and a @code{decl}, and print
@cindex @code{incline}
@cindex @acronym{GLR} parsers and @code{inline}
Note that the @acronym{GLR} parsers require an ISO C89 compiler. In
addition, they use the @code{inline} keyword, which is not C89, but a
common extension. It is up to the user of these parsers to handle
The @acronym{GLR} parsers require a compiler for @acronym{ISO} C89 or
later. In addition, they use the @code{inline} keyword, which is not
C89, but is C99 and is a common extension in pre-C99 compilers. It is
up to the user of these parsers to handle
portability issues. For instance, if using Autoconf and the Autoconf
macro @code{AC_C_INLINE}, a mere
@example
%@{
#include <config.h>
#include <config.h>
%@}
@end example
@@ -830,9 +835,9 @@ will suffice. Otherwise, we suggest
@example
%@{
#if ! defined __GNUC__ && ! defined inline
# define inline
#endif
#if __STDC_VERSION__ < 199901 && ! defined __GNUC__ && ! defined inline
#define inline
#endif
%@}
@end example
@@ -992,6 +997,9 @@ in every Bison grammar file to separate the sections.
The prologue may define types and variables used in the actions. You can
also use preprocessor commands to define macros used there, and use
@code{#include} to include header files that do any of these things.
You need to declare the lexical analyzer @code{yylex} and the error
printer @code{yyerror} here, along with any other global identifiers
used by the actions in the grammar rules.
The Bison declarations declare the names of the terminal and nonterminal
symbols, and may also describe operator precedence and the data types of
@@ -1000,10 +1008,9 @@ semantic values of various symbols.
The grammar rules define how to construct each nonterminal symbol from its
parts.
The epilogue can contain any code you want to use. Often the definition of
the lexical analyzer @code{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.
The epilogue can contain any code you want to use. Often the
definitions of functions declared in the prologue go here. In a
simple program, all the rest of the program can go here.
@node Examples
@chapter Examples
@@ -1070,8 +1077,10 @@ calculator. As in C, comments are placed between @samp{/*@dots{}*/}.
/* Reverse polish notation calculator. */
%@{
#define YYSTYPE double
#include <math.h>
#define YYSTYPE double
#include <math.h>
int yylex (void);
void yyerror (char const *);
%@}
%token NUM
@@ -1080,7 +1089,7 @@ calculator. As in C, comments are placed between @samp{/*@dots{}*/}.
@end example
The declarations section (@pxref{Prologue, , The prologue}) contains two
preprocessor directives.
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
@@ -1093,6 +1102,12 @@ which is a floating point number.
The @code{#include} directive is used to declare the exponentiation
function @code{pow}.
The forward declarations for @code{yylex} and @code{yyerror} are
needed because the C language requires that functions be declared
before they are used. These functions will be defined in the
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
@@ -1381,8 +1396,9 @@ here is the definition we will use:
@group
#include <stdio.h>
/* Called by yyparse on error. */
void
yyerror (const char *s) /* Called by yyparse on error. */
yyerror (char const *s)
@{
printf ("%s\n", s);
@}
@@ -1482,23 +1498,25 @@ parentheses nested to arbitrary depth. Here is the Bison code for
@file{calc.y}, an infix desk-top calculator.
@example
/* Infix notation calculator--calc */
/* Infix notation calculator. */
%@{
#define YYSTYPE double
#include <math.h>
#define YYSTYPE double
#include <math.h>
#include <stdio.h>
int yylex (void);
void yyerror (char const *);
%@}
/* Bison Declarations */
/* Bison declarations. */
%token NUM
%left '-' '+'
%left '*' '/'
%left NEG /* negation--unary minus */
%right '^' /* exponentiation */
%right '^' /* exponentiation */
/* Grammar follows */
%%
input: /* empty string */
%% /* The grammar follows. */
input: /* empty */
| input line
;
@@ -1628,8 +1646,10 @@ the same as the declarations for the infix notation calculator.
/* Location tracking calculator. */
%@{
#define YYSTYPE int
#include <math.h>
#define YYSTYPE int
#include <math.h>
int yylex (void);
void yyerror (char const *);
%@}
/* Bison declarations. */
@@ -1640,7 +1660,7 @@ the same as the declarations for the infix notation calculator.
%left NEG
%right '^'
%% /* Grammar follows */
%% /* The grammar follows. */
@end example
@noindent
@@ -1863,29 +1883,30 @@ Here are the C and Bison declarations for the multi-function calculator.
@smallexample
@group
%@{
#include <math.h> /* For math functions, cos(), sin(), etc. */
#include "calc.h" /* Contains definition of `symrec' */
#include <math.h> /* For math functions, cos(), sin(), etc. */
#include "calc.h" /* Contains definition of `symrec'. */
int yylex (void);
void yyerror (char const *);
%@}
@end group
@group
%union @{
double val; /* For returning numbers. */
symrec *tptr; /* For returning symbol-table pointers. */
double val; /* For returning numbers. */
symrec *tptr; /* For returning symbol-table pointers. */
@}
@end group
%token <val> NUM /* Simple double precision number. */
%token <tptr> VAR FNCT /* Variable and Function. */
%token <val> NUM /* Simple double precision number. */
%token <tptr> VAR FNCT /* Variable and Function. */
%type <val> exp
@group
%right '='
%left '-' '+'
%left '*' '/'
%left NEG /* Negation--unary minus */
%right '^' /* Exponentiation */
%left NEG /* negation--unary minus */
%right '^' /* exponentiation */
@end group
/* Grammar follows */
%%
%% /* The grammar follows. */
@end smallexample
The above grammar introduces only two new features of the Bison language.
@@ -1946,7 +1967,7 @@ exp: NUM @{ $$ = $1; @}
| '(' exp ')' @{ $$ = $2; @}
;
@end group
/* End of grammar */
/* End of grammar. */
%%
@end smallexample
@@ -1965,33 +1986,33 @@ provides for either functions or variables to be placed in the table.
@smallexample
@group
/* Function type. */
/* Function type. */
typedef double (*func_t) (double);
@end group
@group
/* Data type for links in the chain of symbols. */
/* Data type for links in the chain of symbols. */
struct symrec
@{
char *name; /* name of symbol */
char *name; /* name of symbol */
int type; /* type of symbol: either VAR or FNCT */
union
@{
double var; /* value of a VAR */
func_t fnctptr; /* value of a FNCT */
double var; /* value of a VAR */
func_t fnctptr; /* value of a FNCT */
@} value;
struct symrec *next; /* link field */
struct symrec *next; /* link field */
@};
@end group
@group
typedef struct symrec symrec;
/* The symbol table: a chain of `struct symrec'. */
/* The symbol table: a chain of `struct symrec'. */
extern symrec *sym_table;
symrec *putsym (const char *, func_t);
symrec *getsym (const char *);
symrec *putsym (char const *, func_t);
symrec *getsym (char const *);
@end group
@end smallexample
@@ -2003,17 +2024,9 @@ function that initializes the symbol table. Here it is, and
#include <stdio.h>
@group
int
main (void)
@{
init_table ();
return yyparse ();
@}
@end group
@group
/* Called by yyparse on error. */
void
yyerror (const char *s) /* Called by yyparse on error. */
yyerror (char const *s)
@{
printf ("%s\n", s);
@}
@@ -2022,13 +2035,13 @@ yyerror (const char *s) /* Called by yyparse on error. */
@group
struct init
@{
char *fname;
double (*fnct)(double);
char const *fname;
double (*fnct) (double);
@};
@end group
@group
struct init arith_fncts[] =
struct init const arith_fncts[] =
@{
"sin", sin,
"cos", cos,
@@ -2042,7 +2055,7 @@ struct init arith_fncts[] =
@group
/* The symbol table: a chain of `struct symrec'. */
symrec *sym_table = (symrec *) 0;
symrec *sym_table;
@end group
@group
@@ -2059,6 +2072,15 @@ init_table (void)
@}
@}
@end group
@group
int
main (void)
@{
init_table ();
return yyparse ();
@}
@end group
@end smallexample
By simply editing the initialization list and adding the necessary include
@@ -2073,7 +2095,7 @@ found, a pointer to that symbol is returned; otherwise zero is returned.
@smallexample
symrec *
putsym (char *sym_name, int sym_type)
putsym (char const *sym_name, int sym_type)
@{
symrec *ptr;
ptr = (symrec *) malloc (sizeof (symrec));
@@ -2087,7 +2109,7 @@ putsym (char *sym_name, int sym_type)
@}
symrec *
getsym (const char *sym_name)
getsym (char const *sym_name)
@{
symrec *ptr;
for (ptr = sym_table; ptr != (symrec *) 0;
@@ -2245,7 +2267,7 @@ appropriate delimiters:
@example
%@{
@var{Prologue}
@var{Prologue}
%@}
@var{Bison declarations}
@@ -2268,7 +2290,7 @@ continues until end of line.
* Epilogue:: Syntax and usage of the epilogue.
@end menu
@node Prologue, Bison Declarations, , Grammar Outline
@node Prologue
@subsection The prologue
@cindex declarations section
@cindex Prologue
@@ -2292,8 +2314,8 @@ can be done with two @var{Prologue} blocks, one before and one after the
@smallexample
%@{
#include <stdio.h>
#include "ptypes.h"
#include <stdio.h>
#include "ptypes.h"
%@}
%union @{
@@ -2302,8 +2324,8 @@ can be done with two @var{Prologue} blocks, one before and one after the
@}
%@{
static void print_token_value (FILE *, int, YYSTYPE);
#define YYPRINT(F, N, L) print_token_value (F, N, L)
static void print_token_value (FILE *, int, YYSTYPE);
#define YYPRINT(F, N, L) print_token_value (F, N, L)
%@}
@dots{}
@@ -2331,7 +2353,7 @@ There must always be at least one grammar rule, and the first
@samp{%%} (which precedes the grammar rules) may never be omitted even
if it is the first thing in the file.
@node Epilogue, , Grammar Rules, Grammar Outline
@node Epilogue
@subsection The epilogue
@cindex additional C code section
@cindex epilogue
@@ -2341,14 +2363,17 @@ The @var{Epilogue} is copied verbatim to the end of the parser file, just as
the @var{Prologue} is copied to the beginning. This is the most convenient
place to put anything that you want to have in the parser file but which need
not come before the definition of @code{yyparse}. For example, the
definitions of @code{yylex} and @code{yyerror} often go here.
definitions of @code{yylex} and @code{yyerror} often go here. Because
C requires functions to be declared before being used, you often need
to declare functions like @code{yylex} and @code{yyerror} in the Prologue,
even if you define them int he Epilogue.
@xref{Interface, ,Parser C-Language Interface}.
If the last section is empty, you may omit the @samp{%%} that separates it
from the grammar rules.
The Bison parser itself contains many static variables whose names start
with @samp{yy} and many macros whose names start with @samp{YY}. It is a
The Bison parser itself contains many macros and identifiers whose
names start with @samp{yy} or @samp{YY}, so it is a
good idea to avoid using any such names (except those documented in this
manual) in the epilogue of the grammar file.
@@ -4166,7 +4191,7 @@ The following definition suffices in simple programs:
@example
@group
void
yyerror (const char *s)
yyerror (char const *s)
@{
@end group
@group
@@ -4187,15 +4212,15 @@ parsers, but not for the Yacc parser, for historical reasons. I.e., if
@code{yyerror} are:
@example
void yyerror (const char *msg); /* Yacc parsers. */
void yyerror (YYLTYPE *locp, const char *msg); /* GLR parsers. */
void yyerror (char const *msg); /* Yacc parsers. */
void yyerror (YYLTYPE *locp, char const *msg); /* GLR parsers. */
@end example
If @samp{%parse-param @{int *nastiness@}} is used, then:
@example
void yyerror (int *randomness, const char *msg); /* Yacc parsers. */
void yyerror (int *randomness, const char *msg); /* GLR parsers. */
void yyerror (int *randomness, char const *msg); /* Yacc parsers. */
void yyerror (int *randomness, char const *msg); /* GLR parsers. */
@end example
Finally, GLR and Yacc parsers share the same @code{yyerror} calling
@@ -4222,14 +4247,20 @@ int yylex (YYSTYPE *lvalp, YYLTYPE *llocp, int *nastiness);
int yyparse (int *nastiness, int *randomness);
void yyerror (YYLTYPE *locp,
int *nastiness, int *randomness,
const char *msg);
char const *msg);
@end example
@noindent
Please, note that the prototypes are only indications of how the code
produced by Bison will use @code{yyerror}; you still have freedom on the
exit value, and even on making @code{yyerror} a variadic function. It
is precisely to enable this that the message is always passed last.
The prototypes are only indications of how the code produced by Bison
uses @code{yyerror}. Bison-generated code always ignores the returned
value, so @code{yyerror} can return any type, including @code{void}.
Also, @code{yyerror} can be a variadic function; that is why the
message is always passed last.
Traditionally @code{yyerror} returns an @code{int} that is always
ignored, but this is purely for historical reasons, and @code{void} is
preferable since it more accurately describes the return type for
@code{yyerror}.
@vindex yynerrs
The variable @code{yynerrs} contains the number of syntax errors
@@ -5383,7 +5414,9 @@ as an identifier if it appears in that context. Here is how you can do it:
@example
@group
%@{
int hexflag;
int hexflag;
int yylex (void);
void yyerror (char const *);
%@}
%%
@dots{}
@@ -5981,7 +6014,12 @@ Here is an example of @code{YYPRINT} suitable for the multi-function
calculator (@pxref{Mfcalc Decl, ,Declarations for @code{mfcalc}}):
@smallexample
#define YYPRINT(file, type, value) print_token_value (file, type, value)
%@{
static void print_token_value (FILE *, int, YYSTYPE);
#define YYPRINT(file, type, value) print_token_value (file, type, value)
%@}
@dots{} %% @dots{} %% @dots{}
static void
print_token_value (FILE *file, int type, YYSTYPE value)
@@ -6420,9 +6458,8 @@ after a syntax error. @xref{Error Recovery}.
@end deffn
@deffn {Function} yyerror
User-supplied function to be called by @code{yyparse} on error. The
function receives one argument, a pointer to a character string
containing an error message. @xref{Error Reporting, ,The Error
User-supplied function to be called by @code{yyparse} on error.
@xref{Error Reporting, ,The Error
Reporting Function @code{yyerror}}.
@end deffn