* Copying This Manual:: License for copying this manual.
* Index:: Cross-references to the text.
-@detailmenu --- The Detailed Node Listing ---
+@detailmenu
+ --- The Detailed Node Listing ---
The Concepts of Bison
a semantic value (the value of an integer,
the name of an identifier, etc.).
* Semantic Actions:: Each rule can have an action containing C code.
+* GLR Parsers:: Writing parsers for general context-free languages
+* Locations Overview:: Tracking Locations.
* Bison Parser:: What are Bison's input and output,
how is the output used?
* Stages:: Stages in writing and running Bison grammars.
Operator precedence is introduced.
* Simple Error Recovery:: Continuing after syntax errors.
* Location Tracking Calc:: Demonstrating the use of @@@var{n} and @@$.
-* Multi-function Calc:: Calculator with memory and trig functions.
- It uses multiple data-types for semantic values.
+* Multi-function Calc:: Calculator with memory and trig functions.
+ It uses multiple data-types for semantic values.
* Exercises:: Ideas for improving the multi-function calculator.
Reverse Polish Notation Calculator
* Rules:: How to write grammar rules.
* Recursion:: Writing recursive rules.
* Semantics:: Semantic values and actions.
+* Locations:: Locations and actions.
* Declarations:: All kinds of Bison declarations are described here.
* Multiple Parsers:: Putting more than one Bison parser in one program.
Outline of a Bison Grammar
-* Prologue:: Syntax and usage of the prologue (declarations section).
+* Prologue:: Syntax and usage of the prologue.
* Bison Declarations:: Syntax and usage of the Bison declarations section.
* Grammar Rules:: Syntax and usage of the grammar rules section.
-* Epilogue:: Syntax and usage of the epilogue (additional code section).
+* Epilogue:: Syntax and usage of the epilogue.
Defining Language Semantics
This says when, why and how to use the exceptional
action in the middle of a rule.
+Tracking Locations
+
+* Location Type:: Specifying a data type for locations.
+* Actions and Locations:: Using locations in actions.
+* Location Default Action:: Defining a general way to compute locations.
+
Bison Declarations
* Token Decl:: Declaring terminal symbols.
of the token it has read.
* Token Positions:: How @code{yylex} must return the text position
(line number, etc.) of the token, if the
- actions want that.
+ actions want that.
* Pure Calling:: How the calling convention differs
in a pure parser (@pxref{Pure Decl, ,A Pure (Reentrant) Parser}).
* Tie-in Recovery:: Lexical tie-ins have implications for how
error recovery rules must be written.
-Understanding or Debugging Your Parser
+Debugging Your Parser
* Understanding:: Understanding the structure of your parser.
* Tracing:: Tracing the execution of your parser.
* Bison Options:: All the options described in detail,
in alphabetical order by short options.
* Option Cross Key:: Alphabetical list of long options.
+* Yacc Library:: Yacc-compatible @code{yylex} and @code{main}.
Frequently Asked Questions
@example
%@{
- #define YYSTYPE const char*
+ #include <stdio.h>
+ #define YYSTYPE char const *
+ int yylex (void);
+ void yyerror (char const *);
%@}
%token TYPENAME ID
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 "";
@example
%@{
- #define YYSTYPE const char*
+ #define YYSTYPE char const *
static YYSTYPE stmtMerge (YYSTYPE x0, YYSTYPE x1);
%@}
@end example
@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
@example
%@{
-#if ! defined __GNUC__ && ! defined inline
-# define inline
-#endif
+ #if __STDC_VERSION__ < 199901 && ! defined __GNUC__ && ! defined inline
+ #define inline
+ #endif
%@}
@end example
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
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
/* 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
@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
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
@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);
@}
@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
;
/* Location tracking calculator. */
%@{
-#define YYSTYPE int
-#include <math.h>
+ #define YYSTYPE int
+ #include <math.h>
+ int yylex (void);
+ void yyerror (char const *);
%@}
/* Bison declarations. */
%left NEG
%right '^'
-%% /* Grammar follows */
+%% /* The grammar follows. */
@end example
@noindent
@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.
| '(' exp ')' @{ $$ = $2; @}
;
@end group
-/* End of grammar */
+/* End of grammar. */
%%
@end smallexample
@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
#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);
@}
@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,
@group
/* The symbol table: a chain of `struct symrec'. */
-symrec *sym_table = (symrec *) 0;
+symrec *sym_table;
@end group
@group
@}
@}
@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
@smallexample
symrec *
-putsym (char *sym_name, int sym_type)
+putsym (char const *sym_name, int sym_type)
@{
symrec *ptr;
ptr = (symrec *) malloc (sizeof (symrec));
@}
symrec *
-getsym (const char *sym_name)
+getsym (char const *sym_name)
@{
symrec *ptr;
for (ptr = sym_table; ptr != (symrec *) 0;
@example
%@{
-@var{Prologue}
+ @var{Prologue}
%@}
@var{Bison declarations}
* 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
@smallexample
%@{
-#include <stdio.h>
-#include "ptypes.h"
+ #include <stdio.h>
+ #include "ptypes.h"
%@}
%union @{
@}
%@{
-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{}
@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
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.
parameter information to it in a reentrant way. To do so, use the
declaration @code{%parse-param}:
-@deffn {Directive} %parse-param @{@var{argument-declaration}@}, @{@var{argument-name}@}
+@deffn {Directive} %parse-param @{@var{argument-declaration}@}
@findex %parse-param
-Declare that @code{argument-name} is an additional @code{yyparse}
-argument. This argument is also passed to @code{yyerror}. The
-@var{argument-declaration} is used when declaring functions or
-prototypes.
+Declare that an argument declared by @code{argument-declaration} is an
+additional @code{yyparse} argument. This argument is also passed to
+@code{yyerror}. The @var{argument-declaration} is used when declaring
+functions or prototypes. The last identifier in
+@var{argument-declaration} must be the argument name.
@end deffn
Here's an example. Write this in the parser:
@example
-%parse-param @{int *nastiness@}, @{nastiness@}
-%parse-param @{int *randomness@}, @{randomness@}
+%parse-param @{int *nastiness@}
+%parse-param @{int *randomness@}
@end example
@noindent
@code{%lex-param} just like @code{%parse-param} (@pxref{Parser
Function}).
-@deffn {Directive} lex-param @{@var{argument-declaration}@}, @{@var{argument-name}@}
+@deffn {Directive} lex-param @{@var{argument-declaration}@}
@findex %lex-param
-Declare that @code{argument-name} is an additional @code{yylex}
-argument.
+Declare that @code{argument-declaration} is an additional @code{yylex}
+argument declaration.
@end deffn
For instance:
@example
-%parse-param @{int *nastiness@}, @{nastiness@}
-%lex-param @{int *nastiness@}, @{nastiness@}
-%parse-param @{int *randomness@}, @{randomness@}
+%parse-param @{int *nastiness@}
+%lex-param @{int *nastiness@}
+%parse-param @{int *randomness@}
@end example
@noindent
@example
@group
void
-yyerror (const char *s)
+yyerror (char const *s)
@{
@end group
@group
@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@}, @{nastiness@}} is used, then:
+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 *nastiness, char const *msg); /* Yacc parsers. */
+void yyerror (int *nastiness, char const *msg); /* GLR parsers. */
@end example
Finally, GLR and Yacc parsers share the same @code{yyerror} calling
%locations
/* Pure yylex. */
%pure-parser
-%lex-param @{int *nastiness@}, @{nastiness@}
+%lex-param @{int *nastiness@}
/* Pure yyparse. */
-%parse-param @{int *nastiness@}, @{nastiness@}
-%parse-param @{int *randomness@}, @{randomness@}
+%parse-param @{int *nastiness@}
+%parse-param @{int *randomness@}
@end example
@noindent
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
@example
@group
%@{
-int hexflag;
+ int hexflag;
+ int yylex (void);
+ void yyerror (char const *);
%@}
%%
@dots{}
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)
@noindent
will produce @file{output.c++} and @file{outfile.h++}.
+For compatibility with @acronym{POSIX}, the standard Bison
+distribution also contains a shell script called @command{yacc} that
+invokes Bison with the @option{-y} option.
+
@menu
* Bison Options:: All the options described in detail,
in alphabetical order by short options.
* Option Cross Key:: Alphabetical list of long options.
+* Yacc Library:: Yacc-compatible @code{yylex} and @code{main}.
@end menu
@node Bison Options
@file{y.tab.c}, and the other outputs are called @file{y.output} and
@file{y.tab.h}. The purpose of this option is to imitate Yacc's output
file name conventions. Thus, the following shell script can substitute
-for Yacc:
+for Yacc, and the Bison distribution contains such a script for
+compatibility with @acronym{POSIX}:
@example
-bison -y $*
+#! /bin/sh
+bison -y "$@"
@end example
@end table
@end example
@end ifinfo
+@node Yacc Library
+@section Yacc Library
+
+The Yacc library contains default implementations of the
+@code{yyerror} and @code{main} functions. These default
+implementations are normally not useful, but @acronym{POSIX} requires
+them. To use the Yacc library, link your program with the
+@option{-ly} option. Note that Bison's implementation of the Yacc
+library is distributed under the terms of the @acronym{GNU} General
+Public License (@pxref{Copying}).
+
+If you use the Yacc library's @code{yyerror} function, you should
+declare @code{yyerror} as follows:
+
+@example
+int yyerror (char const *);
+@end example
+
+Bison ignores the @code{int} value returned by this @code{yyerror}.
+If you use the Yacc library's @code{main} function, your
+@code{yyparse} function should have the following type signature:
+
+@example
+int yyparse (void);
+@end example
+
@c ================================================= Invoking Bison
@node FAQ
@end deffn
@deffn {Macro} YYERROR_VERBOSE
-An obsolete macro that you define with @code{#define} in the Bison
-declarations section to request verbose, specific error message strings
+An obsolete macro that you define with @code{#define} in the prologue
+to request verbose, specific error message strings
when @code{yyerror} is called. It doesn't matter what definition you
use for @code{YYERROR_VERBOSE}, just whether you define it. Using
@code{%error-verbose} is preferred.
@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
@xref{Precedence Decl, ,Operator Precedence}.
@end deffn
-@deffn {Directive} %lex-param @{@var{argument-declaration}@}. @{@var{argument-name}"@}
+@deffn {Directive} %lex-param @{@var{argument-declaration}@}
Bison declaration to specifying an additional parameter that
@code{yylex} should accept. @xref{Pure Calling,, Calling Conventions
for Pure Parsers}.
Summary}.
@end deffn
-@deffn {Directive} %parse-param @{@var{argument-declaration}@}, @{@var{argument-name}@}
+@deffn {Directive} %parse-param @{@var{argument-declaration}@}
Bison declaration to specifying an additional parameter that
@code{yyparse} should accept. @xref{Parser Function,, The Parser
Function @code{yyparse}}.
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