@ifinfo
This file documents the Bison parser generator.
-Copyright (C) 1988, 1989, 1990, 1991, 1992, 1993, 1995, 1998, 1999, 2000
+Copyright (C) 1988, 1989, 1990, 1991, 1992, 1993, 1995, 1998, 1999,
+2000, 2001
Free Software Foundation, Inc.
Permission is granted to make and distribute verbatim copies of
@page
@vskip 0pt plus 1filll
Copyright @copyright{} 1988, 1989, 1990, 1991, 1992, 1993, 1995, 1998,
-1999, 2000
+1999, 2000, 2001
Free Software Foundation, Inc.
@sp 2
@contents
-@node Top, Introduction, (dir), (dir)
+@ifnottex
+@node Top
+@top Bison
-@ifinfo
-This manual documents version @value{VERSION} of Bison.
-@end ifinfo
+This manual documents version @value{VERSION} of Bison, updated
+@value{UPDATED}.
+@end ifnottex
@menu
* Introduction::
* Invocation:: How to run Bison (to produce the parser source file).
* Table of Symbols:: All the keywords of the Bison language are explained.
* Glossary:: Basic concepts are explained.
+* Copying This Manual:: License for copying this manual.
* Index:: Cross-references to the text.
- --- The Detailed Node Listing ---
+@detailmenu --- The Detailed Node Listing ---
The Concepts of Bison
* Infix Calc:: Infix (algebraic) notation calculator.
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.
* Exercises:: Ideas for improving the multi-function calculator.
Reverse Polish Notation Calculator
-* Decls: Rpcalc Decls. Bison and C declarations for rpcalc.
+* Decls: Rpcalc Decls. Prologue (declarations) for rpcalc.
* Rules: Rpcalc Rules. Grammar Rules for rpcalc, with explanation.
* Lexer: Rpcalc Lexer. The lexical analyzer.
* Main: Rpcalc Main. The controlling function.
* Rpcalc Line::
* Rpcalc Expr::
+Location Tracking Calculator: @code{ltcalc}
+
+* Decls: Ltcalc Decls. Bison and C declarations for ltcalc.
+* Rules: Ltcalc Rules. Grammar rules for ltcalc, with explanations.
+* Lexer: Ltcalc Lexer. The lexical analyzer.
+
Multi-Function Calculator: @code{mfcalc}
* Decl: Mfcalc Decl. Bison declarations for multi-function calculator.
Outline of a Bison Grammar
-* C Declarations:: Syntax and usage of the C declarations section.
+* Prologue:: Syntax and usage of the prologue (declarations section).
* Bison Declarations:: Syntax and usage of the Bison declarations section.
* Grammar Rules:: Syntax and usage of the grammar rules section.
-* C Code:: Syntax and usage of the additional C code section.
+* Epilogue:: Syntax and usage of the epilogue (additional code section).
Defining Language Semantics
in alphabetical order by short options.
* Option Cross Key:: Alphabetical list of long options.
* VMS Invocation:: Bison command syntax on VMS.
+
+Copying This Manual
+
+* GNU Free Documentation License:: License for copying this manual.
+
+@end detailmenu
@end menu
-@node Introduction, Conditions, Top, Top
+@node Introduction
@unnumbered Introduction
@cindex introduction
This edition corresponds to version @value{VERSION} of Bison.
-@node Conditions, Copying, Introduction, Top
+@node Conditions
@unnumbered Conditions for Using Bison
As of Bison version 1.24, we have changed the distribution terms for
practical conditions for using Bison match the practical conditions for
using the other GNU tools.
-@node Copying, Concepts, Conditions, Top
-@unnumbered GNU GENERAL PUBLIC LICENSE
-@center Version 2, June 1991
-
-@display
-Copyright @copyright{} 1989, 1991 Free Software Foundation, Inc.
-59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
-
-Everyone is permitted to copy and distribute verbatim copies
-of this license document, but changing it is not allowed.
-@end display
-
-@unnumberedsec Preamble
-
- The licenses for most software are designed to take away your
-freedom to share and change it. By contrast, the GNU General Public
-License is intended to guarantee your freedom to share and change free
-software---to make sure the software is free for all its users. This
-General Public License applies to most of the Free Software
-Foundation's software and to any other program whose authors commit to
-using it. (Some other Free Software Foundation software is covered by
-the GNU Library General Public License instead.) You can apply it to
-your programs, too.
-
- When we speak of free software, we are referring to freedom, not
-price. Our General Public Licenses are designed to make sure that you
-have the freedom to distribute copies of free software (and charge for
-this service if you wish), that you receive source code or can get it
-if you want it, that you can change the software or use pieces of it
-in new free programs; and that you know you can do these things.
-
- To protect your rights, we need to make restrictions that forbid
-anyone to deny you these rights or to ask you to surrender the rights.
-These restrictions translate to certain responsibilities for you if you
-distribute copies of the software, or if you modify it.
-
- For example, if you distribute copies of such a program, whether
-gratis or for a fee, you must give the recipients all the rights that
-you have. You must make sure that they, too, receive or can get the
-source code. And you must show them these terms so they know their
-rights.
-
- We protect your rights with two steps: (1) copyright the software, and
-(2) offer you this license which gives you legal permission to copy,
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-
- Also, for each author's protection and ours, we want to make certain
-that everyone understands that there is no warranty for this free
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- The precise terms and conditions for copying, distribution and
-modification follow.
-
-@iftex
-@unnumberedsec TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
-@end iftex
-@ifinfo
-@center TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
-@end ifinfo
-
-@enumerate 0
-@item
-This License applies to any program or other work which contains
-a notice placed by the copyright holder saying it may be distributed
-under the terms of this General Public License. The ``Program'', below,
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-the term ``modification''.) Each licensee is addressed as ``you''.
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-Activities other than copying, distribution and modification are not
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-is covered only if its contents constitute a work based on the
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-Whether that is true depends on what the Program does.
-
-@item
-You may copy and distribute verbatim copies of the Program's
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-@enumerate a
-@item
-You must cause the modified files to carry prominent notices
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-@end enumerate
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-the scope of this License.
-
-@item
-You may copy and distribute the Program (or a work based on it,
-under Section 2) in object code or executable form under the terms of
-Sections 1 and 2 above provided that you also do one of the following:
-
-@enumerate a
-@item
-Accompany it with the complete corresponding machine-readable
-source code, which must be distributed under the terms of Sections
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-@item
-Accompany it with a written offer, valid for at least three
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-
-@item
-Accompany it with the information you received as to the offer
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-@end enumerate
-
-The source code for a work means the preferred form of the work for
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-compelled to copy the source along with the object code.
-
-@item
-You may not copy, modify, sublicense, or distribute the Program
-except as expressly provided under this License. Any attempt
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-void, and will automatically terminate your rights under this License.
-However, parties who have received copies, or rights, from you under
-this License will not have their licenses terminated so long as such
-parties remain in full compliance.
-
-@item
-You are not required to accept this License, since you have not
-signed it. However, nothing else grants you permission to modify or
-distribute the Program or its derivative works. These actions are
-prohibited by law if you do not accept this License. Therefore, by
-modifying or distributing the Program (or any work based on the
-Program), you indicate your acceptance of this License to do so, and
-all its terms and conditions for copying, distributing or modifying
-the Program or works based on it.
-
-@item
-Each time you redistribute the Program (or any work based on the
-Program), the recipient automatically receives a license from the
-original licensor to copy, distribute or modify the Program subject to
-these terms and conditions. You may not impose any further
-restrictions on the recipients' exercise of the rights granted herein.
-You are not responsible for enforcing compliance by third parties to
-this License.
-
-@item
-If, as a consequence of a court judgment or allegation of patent
-infringement or for any other reason (not limited to patent issues),
-conditions are imposed on you (whether by court order, agreement or
-otherwise) that contradict the conditions of this License, they do not
-excuse you from the conditions of this License. If you cannot
-distribute so as to satisfy simultaneously your obligations under this
-License and any other pertinent obligations, then as a consequence you
-may not distribute the Program at all. For example, if a patent
-license would not permit royalty-free redistribution of the Program by
-all those who receive copies directly or indirectly through you, then
-the only way you could satisfy both it and this License would be to
-refrain entirely from distribution of the Program.
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-If any portion of this section is held invalid or unenforceable under
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-It is not the purpose of this section to induce you to infringe any
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-to distribute software through any other system and a licensee cannot
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-
-This section is intended to make thoroughly clear what is believed to
-be a consequence of the rest of this License.
-
-@item
-If the distribution and/or use of the Program is restricted in
-certain countries either by patents or by copyrighted interfaces, the
-original copyright holder who places the Program under this License
-may add an explicit geographical distribution limitation excluding
-those countries, so that distribution is permitted only in or among
-countries not thus excluded. In such case, this License incorporates
-the limitation as if written in the body of this License.
+@include gpl.texi
-@item
-The Free Software Foundation may publish revised and/or new versions
-of the General Public License from time to time. Such new versions will
-be similar in spirit to the present version, but may differ in detail to
-address new problems or concerns.
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-Each version is given a distinguishing version number. If the Program
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-later version'', you have the option of following the terms and conditions
-either of that version or of any later version published by the Free
-Software Foundation. If the Program does not specify a version number of
-this License, you may choose any version ever published by the Free Software
-Foundation.
-
-@item
-If you wish to incorporate parts of the Program into other free
-programs whose distribution conditions are different, write to the author
-to ask for permission. For software which is copyrighted by the Free
-Software Foundation, write to the Free Software Foundation; we sometimes
-make exceptions for this. Our decision will be guided by the two goals
-of preserving the free status of all derivatives of our free software and
-of promoting the sharing and reuse of software generally.
-
-@iftex
-@heading NO WARRANTY
-@end iftex
-@ifinfo
-@center NO WARRANTY
-@end ifinfo
-
-@item
-BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY
-FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN
-OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES
-PROVIDE THE PROGRAM ``AS IS'' WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED
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-REPAIR OR CORRECTION.
-
-@item
-IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
-WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR
-REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES,
-INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING
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-POSSIBILITY OF SUCH DAMAGES.
-@end enumerate
-
-@iftex
-@heading END OF TERMS AND CONDITIONS
-@end iftex
-@ifinfo
-@center END OF TERMS AND CONDITIONS
-@end ifinfo
-
-@page
-@unnumberedsec How to Apply These Terms to Your New Programs
-
- If you develop a new program, and you want it to be of the greatest
-possible use to the public, the best way to achieve this is to make it
-free software which everyone can redistribute and change under these terms.
-
- To do so, attach the following notices to the program. It is safest
-to attach them to the start of each source file to most effectively
-convey the exclusion of warranty; and each file should have at least
-the ``copyright'' line and a pointer to where the full notice is found.
-
-@smallexample
-@var{one line to give the program's name and a brief idea of what it does.}
-Copyright (C) 19@var{yy} @var{name of author}
-
-This program is free software; you can redistribute it and/or modify
-it under the terms of the GNU General Public License as published by
-the Free Software Foundation; either version 2 of the License, or
-(at your option) any later version.
-
-This program is distributed in the hope that it will be useful,
-but WITHOUT ANY WARRANTY; without even the implied warranty of
-MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
-GNU General Public License for more details.
-
-You should have received a copy of the GNU General Public License
-along with this program; if not, write to the Free Software
-Foundation, Inc., 59 Temple Place - Suite 330,
-Boston, MA 02111-1307, USA.
-@end smallexample
-
-Also add information on how to contact you by electronic and paper mail.
-
-If the program is interactive, make it output a short notice like this
-when it starts in an interactive mode:
-
-@smallexample
-Gnomovision version 69, Copyright (C) 19@var{yy} @var{name of author}
-Gnomovision comes with ABSOLUTELY NO WARRANTY; for details
-type `show w'.
-This is free software, and you are welcome to redistribute it
-under certain conditions; type `show c' for details.
-@end smallexample
-
-The hypothetical commands @samp{show w} and @samp{show c} should show
-the appropriate parts of the General Public License. Of course, the
-commands you use may be called something other than @samp{show w} and
-@samp{show c}; they could even be mouse-clicks or menu items---whatever
-suits your program.
-
-You should also get your employer (if you work as a programmer) or your
-school, if any, to sign a ``copyright disclaimer'' for the program, if
-necessary. Here is a sample; alter the names:
-
-@smallexample
-Yoyodyne, Inc., hereby disclaims all copyright interest in the program
-`Gnomovision' (which makes passes at compilers) written by James Hacker.
-
-@var{signature of Ty Coon}, 1 April 1989
-Ty Coon, President of Vice
-@end smallexample
-
-This General Public License does not permit incorporating your program into
-proprietary programs. If your program is a subroutine library, you may
-consider it more useful to permit linking proprietary applications with the
-library. If this is what you want to do, use the GNU Library General
-Public License instead of this License.
-
-@node Concepts, Examples, Copying, Top
+@node Concepts
@chapter The Concepts of Bison
This chapter introduces many of the basic concepts without which the
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.
+* 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.
* Grammar Layout:: Overall structure of a Bison grammar file.
@end menu
-@node Language and Grammar, Grammar in Bison, , Concepts
+@node Language and Grammar
@section Languages and Context-Free Grammars
@cindex context-free grammar
Here is a simple C function subdivided into tokens:
+@ifinfo
@example
int /* @r{keyword `int'} */
-square (x) /* @r{identifier, open-paren,} */
- /* @r{identifier, close-paren} */
- int x; /* @r{keyword `int', identifier, semicolon} */
+square (int x) /* @r{identifier, open-paren, identifier,}
+ @r{identifier, close-paren} */
@{ /* @r{open-brace} */
- return x * x; /* @r{keyword `return', identifier,} */
- /* @r{asterisk, identifier, semicolon} */
+ return x * x; /* @r{keyword `return', identifier, asterisk,
+ identifier, semicolon} */
@} /* @r{close-brace} */
@end example
+@end ifinfo
+@ifnotinfo
+@example
+int /* @r{keyword `int'} */
+square (int x) /* @r{identifier, open-paren, identifier, identifier, close-paren} */
+@{ /* @r{open-brace} */
+ return x * x; /* @r{keyword `return', identifier, asterisk, identifier, semicolon} */
+@} /* @r{close-brace} */
+@end example
+@end ifnotinfo
The syntactic groupings of C include the expression, the statement, the
declaration, and the function definition. These are represented in the
must be a `sequence of definitions and declarations'. If not, the parser
reports a syntax error.
-@node Grammar in Bison, Semantic Values, Language and Grammar, Concepts
+@node Grammar in Bison
@section From Formal Rules to Bison Input
@cindex Bison grammar
@cindex grammar, Bison
@noindent
@xref{Rules, ,Syntax of Grammar Rules}.
-@node Semantic Values, Semantic Actions, Grammar in Bison, Concepts
+@node Semantic Values
@section Semantic Values
@cindex semantic value
@cindex value, semantic
language, an expression typically has a semantic value that is a tree
structure describing the meaning of the expression.
-@node Semantic Actions, Bison Parser, Semantic Values, Concepts
+@node Semantic Actions
@section Semantic Actions
@cindex semantic actions
@cindex actions, semantic
The action says how to produce the semantic value of the sum expression
from the values of the two subexpressions.
-@node Bison Parser, Stages, Semantic Actions, Concepts
+@node Locations Overview
+@section Locations
+@cindex location
+@cindex textual position
+@cindex position, textual
+
+Many applications, like interpreters or compilers, have to produce verbose
+and useful error messages. To achieve this, one must be able to keep track of
+the @dfn{textual position}, or @dfn{location}, of each syntactic construct.
+Bison provides a mechanism for handling these locations.
+
+Each token has a semantic value. In a similar fashion, each token has an
+associated location, but the type of locations is the same for all tokens and
+groupings. Moreover, the output parser is equipped with a default data
+structure for storing locations (@pxref{Locations}, for more details).
+
+Like semantic values, locations can be reached in actions using a dedicated
+set of constructs. In the example above, the location of the whole grouping
+is @code{@@$}, while the locations of the subexpressions are @code{@@1} and
+@code{@@3}.
+
+When a rule is matched, a default action is used to compute the semantic value
+of its left hand side (@pxref{Actions}). In the same way, another default
+action is used for locations. However, the action for locations is general
+enough for most cases, meaning there is usually no need to describe for each
+rule how @code{@@$} should be formed. When building a new location for a given
+grouping, the default behavior of the output parser is to take the beginning
+of the first symbol, and the end of the last symbol.
+
+@node Bison Parser
@section Bison Output: the Parser File
@cindex Bison parser
@cindex Bison utility
expressions. As it does this, it runs the actions for the grammar rules it
uses.
-The tokens come from a function called the @dfn{lexical analyzer} that you
-must supply in some fashion (such as by writing it in C). The Bison parser
-calls the lexical analyzer each time it wants a new token. It doesn't know
-what is ``inside'' the tokens (though their semantic values may reflect
-this). Typically the lexical analyzer makes the tokens by parsing
-characters of text, but Bison does not depend on this. @xref{Lexical, ,The Lexical Analyzer Function @code{yylex}}.
+The tokens come from a function called the @dfn{lexical analyzer} that
+you must supply in some fashion (such as by writing it in C). The Bison
+parser calls the lexical analyzer each time it wants a new token. It
+doesn't know what is ``inside'' the tokens (though their semantic values
+may reflect this). Typically the lexical analyzer makes the tokens by
+parsing characters of text, but Bison does not depend on this.
+@xref{Lexical, ,The Lexical Analyzer Function @code{yylex}}.
The Bison parser file is C code which defines a function named
@code{yyparse} which implements that grammar. This function does not make
@xref{Interface, ,Parser C-Language Interface}.
Aside from the token type names and the symbols in the actions you
-write, all variable and function names used in the Bison parser file
+write, all symbols defined in the Bison parser file itself
begin with @samp{yy} or @samp{YY}. This includes interface functions
such as the lexical analyzer function @code{yylex}, the error reporting
function @code{yyerror} and the parser function @code{yyparse} itself.
or @samp{YY} in the Bison grammar file except for the ones defined in
this manual.
-@node Stages, Grammar Layout, Bison Parser, Concepts
+In some cases the Bison parser file includes system headers, and in
+those cases your code should respect the identifiers reserved by those
+headers. On some non-@sc{gnu} hosts, @code{<alloca.h>},
+@code{<stddef.h>}, and @code{<stdlib.h>} are included as needed to
+declare memory allocators and related types. In the same situation,
+C++ parsers may include @code{<cstddef>} and @code{<cstdlib>} instead.
+Other system headers may be included if you define @code{YYDEBUG} to a
+nonzero value (@pxref{Debugging, ,Debugging Your Parser}).
+
+@node Stages
@section Stages in Using Bison
@cindex stages in using Bison
@cindex using Bison
@enumerate
@item
Formally specify the grammar in a form recognized by Bison
-(@pxref{Grammar File, ,Bison Grammar Files}). For each grammatical rule in the language,
-describe the action that is to be taken when an instance of that rule
-is recognized. The action is described by a sequence of C statements.
+(@pxref{Grammar File, ,Bison Grammar Files}). For each grammatical rule
+in the language, describe the action that is to be taken when an
+instance of that rule is recognized. The action is described by a
+sequence of C statements.
@item
-Write a lexical analyzer to process input and pass tokens to the
-parser. The lexical analyzer may be written by hand in C
-(@pxref{Lexical, ,The Lexical Analyzer Function @code{yylex}}). It could also be produced using Lex, but the use
-of Lex is not discussed in this manual.
+Write a lexical analyzer to process input and pass tokens to the parser.
+The lexical analyzer may be written by hand in C (@pxref{Lexical, ,The
+Lexical Analyzer Function @code{yylex}}). It could also be produced
+using Lex, but the use of Lex is not discussed in this manual.
@item
Write a controlling function that calls the Bison-produced parser.
Link the object files to produce the finished product.
@end enumerate
-@node Grammar Layout, , Stages, Concepts
+@node Grammar Layout
@section The Overall Layout of a Bison Grammar
@cindex grammar file
@cindex file format
@example
%@{
-@var{C declarations}
+@var{Prologue (declarations)}
%@}
@var{Bison declarations}
%%
@var{Grammar rules}
%%
-@var{Additional C code}
+@var{Epilogue (additional code)}
@end example
@noindent
The @samp{%%}, @samp{%@{} and @samp{%@}} are punctuation that appears
in every Bison grammar file to separate the sections.
-The C declarations may define types and variables used in the actions.
-You can also use preprocessor commands to define macros used there, and use
+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.
The Bison declarations declare the names of the terminal and nonterminal
The grammar rules define how to construct each nonterminal symbol from its
parts.
-The additional C code can contain any C 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 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.
-@node Examples, Grammar File, Concepts, Top
+@node Examples
@chapter Examples
@cindex simple examples
@cindex examples, simple
* Infix Calc:: Infix (algebraic) notation calculator.
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.
* Exercises:: Ideas for improving the multi-function calculator.
@end menu
-@node RPN Calc, Infix Calc, , Examples
+@node RPN Calc
@section Reverse Polish Notation Calculator
@cindex reverse polish notation
@cindex polish notation calculator
@samp{.y} extension is a convention used for Bison input files.
@menu
-* Decls: Rpcalc Decls. Bison and C declarations for rpcalc.
+* Decls: Rpcalc Decls. Prologue (declarations) for rpcalc.
* Rules: Rpcalc Rules. Grammar Rules for rpcalc, with explanation.
* Lexer: Rpcalc Lexer. The lexical analyzer.
* Main: Rpcalc Main. The controlling function.
* Comp: Rpcalc Compile. Run the C compiler on the output code.
@end menu
-@node Rpcalc Decls, Rpcalc Rules, , RPN Calc
+@node Rpcalc Decls
@subsection Declarations for @code{rpcalc}
Here are the C and Bison declarations for the reverse polish notation
%% /* Grammar rules and actions follow */
@end example
-The C declarations section (@pxref{C Declarations, ,The C Declarations Section}) contains two
+The declarations section (@pxref{Prologue, , The prologue}) contains two
preprocessor directives.
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.
+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}.
-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
+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.
-@node Rpcalc Rules, Rpcalc Lexer, Rpcalc Decls, RPN Calc
+@node Rpcalc Rules
@subsection Grammar Rules for @code{rpcalc}
Here are the grammar rules for the reverse polish notation calculator.
* Rpcalc Expr::
@end menu
-@node Rpcalc Input, Rpcalc Line, , Rpcalc Rules
+@node Rpcalc Input
@subsubsection Explanation of @code{input}
Consider the definition of @code{input}:
grammatical error is seen or the lexical analyzer says there are no more
input tokens; we will arrange for the latter to happen at end of file.
-@node Rpcalc Line, Rpcalc Expr, Rpcalc Input, Rpcalc Rules
+@node Rpcalc Line
@subsubsection Explanation of @code{line}
Now consider the definition of @code{line}:
that value were ever used, but we don't use it: once rpcalc has printed the
value of the user's input line, that value is no longer needed.
-@node Rpcalc Expr, , Rpcalc Line, Rpcalc Rules
+@node Rpcalc Expr
@subsubsection Explanation of @code{expr}
The @code{exp} grouping has several rules, one for each kind of expression.
@noindent
The latter, however, is much more readable.
-@node Rpcalc Lexer, Rpcalc Main, Rpcalc Rules, RPN Calc
+@node Rpcalc Lexer
@subsection The @code{rpcalc} Lexical Analyzer
@cindex writing a lexical analyzer
@cindex lexical analyzer, writing
-The lexical analyzer's job is low-level parsing: converting characters or
-sequences of characters into tokens. The Bison parser gets its tokens by
-calling the lexical analyzer. @xref{Lexical, ,The Lexical Analyzer Function @code{yylex}}.
+The lexical analyzer's job is low-level parsing: converting characters
+or sequences of characters into tokens. The Bison parser gets its
+tokens by calling the lexical analyzer. @xref{Lexical, ,The Lexical
+Analyzer Function @code{yylex}}.
Only a simple lexical analyzer is needed for the RPN calculator. This
lexical analyzer skips blanks and tabs, then reads in numbers as
macro whose definition is the appropriate number. In this example,
therefore, @code{NUM} becomes a macro for @code{yylex} to use.
-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 Decls, ,Declarations 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 Decls,
+,Declarations for @code{rpcalc}}.)
A token type code of zero is returned if the end-of-file is encountered.
(Bison recognizes any nonpositive value as indicating the end of the
@end group
@end example
-@node Rpcalc Main, Rpcalc Error, Rpcalc Lexer, RPN Calc
+@node Rpcalc Main
@subsection The Controlling Function
@cindex controlling function
@cindex main function in simple example
@end group
@end example
-@node Rpcalc Error, Rpcalc Gen, Rpcalc Main, RPN Calc
+@node Rpcalc Error
@subsection The Error Reporting Routine
@cindex error reporting routine
cause the calculator program to exit. This is not clean behavior for a
real calculator, but it is adequate for the first example.
-@node Rpcalc Gen, Rpcalc Compile, Rpcalc Error, RPN Calc
+@node Rpcalc Gen
@subsection Running Bison to Make the Parser
@cindex running Bison (introduction)
arrange all the source code in one or more source files. For such a
simple example, the easiest thing is to put everything in one file. The
definitions of @code{yylex}, @code{yyerror} and @code{main} go at the
-end, in the ``additional C code'' section of the file (@pxref{Grammar
-Layout, ,The Overall Layout of a Bison Grammar}).
+end, in the epilogue of the file
+(@pxref{Grammar Layout, ,The Overall Layout of a Bison Grammar}).
For a large project, you would probably have several source files, and use
@code{make} to arrange to recompile them.
functions in the input file (@code{yylex}, @code{yyerror} and @code{main})
are copied verbatim to the output.
-@node Rpcalc Compile, , Rpcalc Gen, RPN Calc
+@node Rpcalc Compile
@subsection Compiling the Parser File
@cindex compiling the parser
@example
@group
# @r{List files in current directory.}
-% ls
+$ @kbd{ls}
rpcalc.tab.c rpcalc.y
@end group
@group
# @r{Compile the Bison parser.}
# @r{@samp{-lm} tells compiler to search math library for @code{pow}.}
-% cc rpcalc.tab.c -lm -o rpcalc
+$ @kbd{cc rpcalc.tab.c -lm -o rpcalc}
@end group
@group
# @r{List files again.}
-% ls
+$ @kbd{ls}
rpcalc rpcalc.tab.c rpcalc.y
@end group
@end example
example session using @code{rpcalc}.
@example
-% rpcalc
-4 9 +
+$ @kbd{rpcalc}
+@kbd{4 9 +}
13
-3 7 + 3 4 5 *+-
+@kbd{3 7 + 3 4 5 *+-}
-13
-3 7 + 3 4 5 * + - n @r{Note the unary minus, @samp{n}}
+@kbd{3 7 + 3 4 5 * + - n} @r{Note the unary minus, @samp{n}}
13
-5 6 / 4 n +
+@kbd{5 6 / 4 n +}
-3.166666667
-3 4 ^ @r{Exponentiation}
+@kbd{3 4 ^} @r{Exponentiation}
81
-^D @r{End-of-file indicator}
-%
+@kbd{^D} @r{End-of-file indicator}
+$
@end example
-@node Infix Calc, Simple Error Recovery, RPN Calc, Examples
+@node Infix Calc
@section Infix Notation Calculator: @code{calc}
@cindex infix notation calculator
@cindex @code{calc}
declarations; the higher the line number of the declaration (lower on
the page or screen), the higher the precedence. Hence, exponentiation
has the highest precedence, unary minus (@code{NEG}) is next, followed
-by @samp{*} and @samp{/}, and so on. @xref{Precedence, ,Operator Precedence}.
+by @samp{*} and @samp{/}, and so on. @xref{Precedence, ,Operator
+Precedence}.
-The other important new feature is the @code{%prec} in the grammar section
-for the unary minus operator. The @code{%prec} simply instructs Bison that
-the rule @samp{| '-' exp} has the same precedence as @code{NEG}---in this
-case the next-to-highest. @xref{Contextual Precedence, ,Context-Dependent Precedence}.
+The other important new feature is the @code{%prec} in the grammar
+section for the unary minus operator. The @code{%prec} simply instructs
+Bison that the rule @samp{| '-' exp} has the same precedence as
+@code{NEG}---in this case the next-to-highest. @xref{Contextual
+Precedence, ,Context-Dependent Precedence}.
Here is a sample run of @file{calc.y}:
@need 500
@example
-% calc
-4 + 4.5 - (34/(8*3+-3))
+$ @kbd{calc}
+@kbd{4 + 4.5 - (34/(8*3+-3))}
6.880952381
--56 + 2
+@kbd{-56 + 2}
-54
-3 ^ 2
+@kbd{3 ^ 2}
9
@end example
-@node Simple Error Recovery, Multi-function Calc, Infix Calc, Examples
+@node Simple Error Recovery
@section Simple Error Recovery
@cindex error recovery, simple
input. We won't discuss this issue further because it is not specific to
Bison programs.
-@node Multi-function Calc, Exercises, Simple Error Recovery, Examples
+@node Location Tracking Calc
+@section Location Tracking Calculator: @code{ltcalc}
+@cindex location tracking calculator
+@cindex @code{ltcalc}
+@cindex calculator, location tracking
+
+This example extends the infix notation calculator with location
+tracking. This feature will be used to improve the error messages. For
+the sake of clarity, this example is a simple integer calculator, since
+most of the work needed to use locations will be done in the lexical
+analyser.
+
+@menu
+* Decls: Ltcalc Decls. Bison and C declarations for ltcalc.
+* Rules: Ltcalc Rules. Grammar rules for ltcalc, with explanations.
+* Lexer: Ltcalc Lexer. The lexical analyzer.
+@end menu
+
+@node Ltcalc Decls
+@subsection Declarations for @code{ltcalc}
+
+The C and Bison declarations for the location tracking calculator are
+the same as the declarations for the infix notation calculator.
+
+@example
+/* Location tracking calculator. */
+
+%@{
+#define YYSTYPE int
+#include <math.h>
+%@}
+
+/* Bison declarations. */
+%token NUM
+
+%left '-' '+'
+%left '*' '/'
+%left NEG
+%right '^'
+
+%% /* Grammar follows */
+@end example
+
+@noindent
+Note there are no declarations specific to locations. Defining a data
+type for storing locations is not needed: we will use the type provided
+by default (@pxref{Location Type, ,Data Types of Locations}), which is a
+four member structure with the following integer fields:
+@code{first_line}, @code{first_column}, @code{last_line} and
+@code{last_column}.
+
+@node Ltcalc Rules
+@subsection Grammar Rules for @code{ltcalc}
+
+Whether handling locations or not has no effect on the syntax of your
+language. Therefore, grammar rules for this example will be very close
+to those of the previous example: we will only modify them to benefit
+from the new information.
+
+Here, we will use locations to report divisions by zero, and locate the
+wrong expressions or subexpressions.
+
+@example
+@group
+input : /* empty */
+ | input line
+;
+@end group
+
+@group
+line : '\n'
+ | exp '\n' @{ printf ("%d\n", $1); @}
+;
+@end group
+
+@group
+exp : NUM @{ $$ = $1; @}
+ | exp '+' exp @{ $$ = $1 + $3; @}
+ | exp '-' exp @{ $$ = $1 - $3; @}
+ | exp '*' exp @{ $$ = $1 * $3; @}
+@end group
+@group
+ | exp '/' exp
+ @{
+ if ($3)
+ $$ = $1 / $3;
+ else
+ @{
+ $$ = 1;
+ fprintf (stderr, "%d.%d-%d.%d: division by zero",
+ @@3.first_line, @@3.first_column,
+ @@3.last_line, @@3.last_column);
+ @}
+ @}
+@end group
+@group
+ | '-' exp %preg NEG @{ $$ = -$2; @}
+ | exp '^' exp @{ $$ = pow ($1, $3); @}
+ | '(' exp ')' @{ $$ = $2; @}
+@end group
+@end example
+
+This code shows how to reach locations inside of semantic actions, by
+using the pseudo-variables @code{@@@var{n}} for rule components, and the
+pseudo-variable @code{@@$} for groupings.
+
+We don't need to assign a value to @code{@@$}: the output parser does it
+automatically. By default, before executing the C code of each action,
+@code{@@$} is set to range from the beginning of @code{@@1} to the end
+of @code{@@@var{n}}, for a rule with @var{n} components. This behavior
+can be redefined (@pxref{Location Default Action, , Default Action for
+Locations}), and for very specific rules, @code{@@$} can be computed by
+hand.
+
+@node Ltcalc Lexer
+@subsection The @code{ltcalc} Lexical Analyzer.
+
+Until now, we relied on Bison's defaults to enable location
+tracking. The next step is to rewrite the lexical analyser, and make it
+able to feed the parser with the token locations, as it already does for
+semantic values.
+
+To this end, we must take into account every single character of the
+input text, to avoid the computed locations of being fuzzy or wrong:
+
+@example
+@group
+int
+yylex (void)
+@{
+ int c;
+
+ /* skip white space */
+ while ((c = getchar ()) == ' ' || c == '\t')
+ ++yylloc.last_column;
+
+ /* step */
+ yylloc.first_line = yylloc.last_line;
+ yylloc.first_column = yylloc.last_column;
+@end group
+
+@group
+ /* process numbers */
+ if (isdigit (c))
+ @{
+ yylval = c - '0';
+ ++yylloc.last_column;
+ while (isdigit (c = getchar ()))
+ @{
+ ++yylloc.last_column;
+ yylval = yylval * 10 + c - '0';
+ @}
+ ungetc (c, stdin);
+ return NUM;
+ @}
+@end group
+
+ /* return end-of-file */
+ if (c == EOF)
+ return 0;
+
+ /* return single chars and update location */
+ if (c == '\n')
+ @{
+ ++yylloc.last_line;
+ yylloc.last_column = 0;
+ @}
+ else
+ ++yylloc.last_column;
+ return c;
+@}
+@end example
+
+Basically, the lexical analyzer performs the same processing as before:
+it skips blanks and tabs, and reads numbers or single-character tokens.
+In addition, it updates @code{yylloc}, the global variable (of type
+@code{YYLTYPE}) containing the token's location.
+
+Now, each time this function returns a token, the parser has its number
+as well as its semantic value, and its location in the text. The last
+needed change is to initialize @code{yylloc}, for example in the
+controlling function:
+
+@example
+@group
+int
+main (void)
+@{
+ yylloc.first_line = yylloc.last_line = 1;
+ yylloc.first_column = yylloc.last_column = 0;
+ return yyparse ();
+@}
+@end group
+@end example
+
+Remember that computing locations is not a matter of syntax. Every
+character must be associated to a location update, whether it is in
+valid input, in comments, in literal strings, and so on.
+
+@node Multi-function Calc
@section Multi-Function Calculator: @code{mfcalc}
@cindex multi-function calculator
@cindex @code{mfcalc}
Here is a sample session with the multi-function calculator:
@example
-% mfcalc
-pi = 3.141592653589
+$ @kbd{mfcalc}
+@kbd{pi = 3.141592653589}
3.1415926536
-sin(pi)
+@kbd{sin(pi)}
0.0000000000
-alpha = beta1 = 2.3
+@kbd{alpha = beta1 = 2.3}
2.3000000000
-alpha
+@kbd{alpha}
2.3000000000
-ln(alpha)
+@kbd{ln(alpha)}
0.8329091229
-exp(ln(beta1))
+@kbd{exp(ln(beta1))}
2.3000000000
-%
+$
@end example
Note that multiple assignment and nested function calls are permitted.
* Symtab: Mfcalc Symtab. Symbol table management subroutines.
@end menu
-@node Mfcalc Decl, Mfcalc Rules, , Multi-function Calc
+@node Mfcalc Decl
@subsection Declarations for @code{mfcalc}
Here are the C and Bison declarations for the multi-function calculator.
declarations are augmented with information about their data type (placed
between angle brackets).
-The Bison construct @code{%type} is used for declaring nonterminal symbols,
-just as @code{%token} is used for declaring token types. We have not used
-@code{%type} before because nonterminal symbols are normally declared
-implicitly by the rules that define them. But @code{exp} must be declared
-explicitly so we can specify its value type. @xref{Type Decl, ,Nonterminal Symbols}.
+The Bison construct @code{%type} is used for declaring nonterminal
+symbols, just as @code{%token} is used for declaring token types. We
+have not used @code{%type} before because nonterminal symbols are
+normally declared implicitly by the rules that define them. But
+@code{exp} must be declared explicitly so we can specify its value type.
+@xref{Type Decl, ,Nonterminal Symbols}.
-@node Mfcalc Rules, Mfcalc Symtab, Mfcalc Decl, Multi-function Calc
+@node Mfcalc Rules
@subsection Grammar Rules for @code{mfcalc}
Here are the grammar rules for the multi-function calculator.
%%
@end smallexample
-@node Mfcalc Symtab, , Mfcalc Rules, Multi-function Calc
+@node Mfcalc Symtab
@subsection The @code{mfcalc} Symbol Table
@cindex symbol table example
@end smallexample
This program is both powerful and flexible. You may easily add new
-functions, and it is a simple job to modify this code to install predefined
-variables such as @code{pi} or @code{e} as well.
+functions, and it is a simple job to modify this code to install
+predefined variables such as @code{pi} or @code{e} as well.
-@node Exercises, , Multi-function Calc, Examples
+@node Exercises
@section Exercises
@cindex exercises
uninitialized variable in any way except to store a value in it.
@end enumerate
-@node Grammar File, Interface, Examples, Top
+@node Grammar File
@chapter Bison Grammar Files
Bison takes as input a context-free grammar specification and produces a
C-language function that recognizes correct instances of the grammar.
The Bison grammar input file conventionally has a name ending in @samp{.y}.
+@xref{Invocation, ,Invoking Bison}.
@menu
* Grammar Outline:: Overall layout of the grammar file.
* 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.
@end menu
-@node Grammar Outline, Symbols, , Grammar File
+@node Grammar Outline
@section Outline of a Bison Grammar
A Bison grammar file has four main sections, shown here with the
@example
%@{
-@var{C declarations}
+@var{Prologue}
%@}
@var{Bison declarations}
@var{Grammar rules}
%%
-@var{Additional C code}
+@var{Epilogue}
@end example
Comments enclosed in @samp{/* @dots{} */} may appear in any of the sections.
@menu
-* C Declarations:: Syntax and usage of the C 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.
-* C Code:: Syntax and usage of the additional C code section.
+* Epilogue:: Syntax and usage of the epilogue.
@end menu
-@node C Declarations, Bison Declarations, , Grammar Outline
-@subsection The C Declarations Section
-@cindex C declarations section
-@cindex declarations, C
+@node Prologue, Bison Declarations, , Grammar Outline
+@subsection The prologue
+@cindex declarations section
+@cindex Prologue
+@cindex declarations
-The @var{C declarations} section contains macro definitions and
+The @var{prologue} section contains macro definitions and
declarations of functions and variables that are used in the actions in the
grammar rules. These are copied to the beginning of the parser file so
that they precede the definition of @code{yyparse}. You can use
need any C declarations, you may omit the @samp{%@{} and @samp{%@}}
delimiters that bracket this section.
-@node Bison Declarations, Grammar Rules, C Declarations, Grammar Outline
+@node Bison Declarations
@subsection The Bison Declarations Section
@cindex Bison declarations (introduction)
@cindex declarations, Bison (introduction)
In some simple grammars you may not need any declarations.
@xref{Declarations, ,Bison Declarations}.
-@node Grammar Rules, C Code, Bison Declarations, Grammar Outline
+@node Grammar Rules
@subsection The Grammar Rules Section
@cindex grammar rules section
@cindex rules section for grammar
@samp{%%} (which precedes the grammar rules) may never be omitted even
if it is the first thing in the file.
-@node C Code, , Grammar Rules, Grammar Outline
-@subsection The Additional C Code Section
+@node Epilogue, , Grammar Rules, Grammar Outline
+@subsection The epilogue
@cindex additional C code section
+@cindex epilogue
@cindex C code, section for additional
-The @var{additional C code} section is copied verbatim to the end of the
-parser file, just as the @var{C declarations} section 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. @xref{Interface, ,Parser
-C-Language Interface}.
+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.
+@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
good idea to avoid using any such names (except those documented in this
-manual) in the additional C code section of the grammar file.
+manual) in the epilogue of the grammar file.
-@node Symbols, Rules, Grammar Outline, Grammar File
+@node Symbols
@section Symbols, Terminal and Nonterminal
@cindex nonterminal symbol
@cindex terminal symbol
(@pxref{Error Recovery}); you shouldn't use it for any other purpose.
In particular, @code{yylex} should never return this value.
-@node Rules, Recursion, Symbols, Grammar File
+@node Rules
@section Syntax of Grammar Rules
@cindex rule syntax
@cindex grammar rule syntax
It is customary to write a comment @samp{/* empty */} in each rule
with no components.
-@node Recursion, Semantics, Rules, Grammar File
+@node Recursion
@section Recursive Rules
@cindex recursive rule
defines two mutually-recursive nonterminals, since each refers to the
other.
-@node Semantics, Declarations, Recursion, Grammar File
+@node Semantics
@section Defining Language Semantics
@cindex defining language semantics
@cindex language semantics, defining
action in the middle of a rule.
@end menu
-@node Value Type, Multiple Types, , Semantics
+@node Value Type
@subsection Data Types of Semantic Values
@cindex semantic value type
@cindex value type, semantic
In a simple program it may be sufficient to use the same data type for
the semantic values of all language constructs. This was true in the
-RPN and infix calculator examples (@pxref{RPN Calc, ,Reverse Polish Notation Calculator}).
+RPN and infix calculator examples (@pxref{RPN Calc, ,Reverse Polish
+Notation Calculator}).
Bison's default is to use type @code{int} for all semantic values. To
specify some other type, define @code{YYSTYPE} as a macro, like this:
@end example
@noindent
-This macro definition must go in the C declarations section of the grammar
-file (@pxref{Grammar Outline, ,Outline of a Bison Grammar}).
+This macro definition must go in the prologue of the grammar file
+(@pxref{Grammar Outline, ,Outline of a Bison Grammar}).
-@node Multiple Types, Actions, Value Type, Semantics
+@node Multiple Types
@subsection More Than One Value Type
In most programs, you will need different data types for different kinds
@itemize @bullet
@item
Specify the entire collection of possible data types, with the
-@code{%union} Bison declaration (@pxref{Union Decl, ,The Collection of Value Types}).
+@code{%union} Bison declaration (@pxref{Union Decl, ,The Collection of
+Value Types}).
@item
Choose one of those types for each symbol (terminal or nonterminal) for
Decl, ,Nonterminal Symbols}).
@end itemize
-@node Actions, Action Types, Multiple Types, Semantics
+@node Actions
@subsection Actions
@cindex action
@vindex $$
semantic values associated with tokens or smaller groupings.
An action consists of C statements surrounded by braces, much like a
-compound statement in C. It can be placed at any position in the rule; it
-is executed at that position. Most rules have just one action at the end
-of the rule, following all the components. Actions in the middle of a rule
-are tricky and used only for special purposes (@pxref{Mid-Rule Actions, ,Actions in Mid-Rule}).
+compound statement in C. It can be placed at any position in the rule;
+it is executed at that position. Most rules have just one action at the
+end of the rule, following all the components. Actions in the middle of
+a rule are tricky and used only for special purposes (@pxref{Mid-Rule
+Actions, ,Actions in Mid-Rule}).
The C code in an action can refer to the semantic values of the components
matched by the rule with the construct @code{$@var{n}}, which stands for
always refers to the @code{expr} which precedes @code{bar} in the
definition of @code{foo}.
-@node Action Types, Mid-Rule Actions, Actions, Semantics
+@node Action Types
@subsection Data Types of Values in Actions
@cindex action data types
@cindex data types in actions
then you can write @code{$<itype>1} to refer to the first subunit of the
rule as an integer, or @code{$<dtype>1} to refer to it as a double.
-@node Mid-Rule Actions, , Action Types, Semantics
+@node Mid-Rule Actions
@subsection Actions in Mid-Rule
@cindex actions in mid-rule
@cindex mid-rule actions
its value with an assignment to @code{$$}, and actions later in the rule
can refer to the value using @code{$@var{n}}. Since there is no symbol
to name the action, there is no way to declare a data type for the value
-in advance, so you must use the @samp{$<@dots{}>} construct to specify a
-data type each time you refer to this value.
+in advance, so you must use the @samp{$<@dots{}>@var{n}} construct to
+specify a data type each time you refer to this value.
There is no way to set the value of the entire rule with a mid-rule
action, because assignments to @code{$$} do not have that effect. The
converted to an end-of-rule action in this way, and this is what Bison
actually does to implement mid-rule actions.
-@node Declarations, Multiple Parsers, Semantics, Grammar File
+@node Locations
+@section Tracking Locations
+@cindex location
+@cindex textual position
+@cindex position, textual
+
+Though grammar rules and semantic actions are enough to write a fully
+functional parser, it can be useful to process some additionnal informations,
+especially symbol locations.
+
+@c (terminal or not) ?
+
+The way locations are handled is defined by providing a data type, and
+actions to take when rules are matched.
+
+@menu
+* 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.
+@end menu
+
+@node Location Type
+@subsection Data Type of Locations
+@cindex data type of locations
+@cindex default location type
+
+Defining a data type for locations is much simpler than for semantic values,
+since all tokens and groupings always use the same type.
+
+The type of locations is specified by defining a macro called @code{YYLTYPE}.
+When @code{YYLTYPE} is not defined, Bison uses a default structure type with
+four members:
+
+@example
+struct
+@{
+ int first_line;
+ int first_column;
+ int last_line;
+ int last_column;
+@}
+@end example
+
+@node Actions and Locations
+@subsection Actions and Locations
+@cindex location actions
+@cindex actions, location
+@vindex @@$
+@vindex @@@var{n}
+
+Actions are not only useful for defining language semantics, but also for
+describing the behavior of the output parser with locations.
+
+The most obvious way for building locations of syntactic groupings is very
+similar to the way semantic values are computed. In a given rule, several
+constructs can be used to access the locations of the elements being matched.
+The location of the @var{n}th component of the right hand side is
+@code{@@@var{n}}, while the location of the left hand side grouping is
+@code{@@$}.
+
+Here is a basic example using the default data type for locations:
+
+@example
+@group
+exp: @dots{}
+ | exp '/' exp
+ @{
+ @@$.first_column = @@1.first_column;
+ @@$.first_line = @@1.first_line;
+ @@$.last_column = @@3.last_column;
+ @@$.last_line = @@3.last_line;
+ if ($3)
+ $$ = $1 / $3;
+ else
+ @{
+ $$ = 1;
+ printf("Division by zero, l%d,c%d-l%d,c%d",
+ @@3.first_line, @@3.first_column,
+ @@3.last_line, @@3.last_column);
+ @}
+ @}
+@end group
+@end example
+
+As for semantic values, there is a default action for locations that is
+run each time a rule is matched. It sets the beginning of @code{@@$} to the
+beginning of the first symbol, and the end of @code{@@$} to the end of the
+last symbol.
+
+With this default action, the location tracking can be fully automatic. The
+example above simply rewrites this way:
+
+@example
+@group
+exp: @dots{}
+ | exp '/' exp
+ @{
+ if ($3)
+ $$ = $1 / $3;
+ else
+ @{
+ $$ = 1;
+ printf("Division by zero, l%d,c%d-l%d,c%d",
+ @@3.first_line, @@3.first_column,
+ @@3.last_line, @@3.last_column);
+ @}
+ @}
+@end group
+@end example
+
+@node Location Default Action
+@subsection Default Action for Locations
+@vindex YYLLOC_DEFAULT
+
+Actually, actions are not the best place to compute locations. Since
+locations are much more general than semantic values, there is room in
+the output parser to redefine the default action to take for each
+rule. The @code{YYLLOC_DEFAULT} macro is invoked each time a rule is
+matched, before the associated action is run.
+
+Most of the time, this macro is general enough to suppress location
+dedicated code from semantic actions.
+
+The @code{YYLLOC_DEFAULT} macro takes three parameters. The first one is
+the location of the grouping (the result of the computation). The second one
+is an array holding locations of all right hand side elements of the rule
+being matched. The last one is the size of the right hand side rule.
+
+By default, it is defined this way:
+
+@example
+@group
+#define YYLLOC_DEFAULT(Current, Rhs, N) \
+ Current.last_line = Rhs[N].last_line; \
+ Current.last_column = Rhs[N].last_column;
+@end group
+@end example
+
+When defining @code{YYLLOC_DEFAULT}, you should consider that:
+
+@itemize @bullet
+@item
+All arguments are free of side-effects. However, only the first one (the
+result) should be modified by @code{YYLLOC_DEFAULT}.
+
+@item
+Before @code{YYLLOC_DEFAULT} is executed, the output parser sets @code{@@$}
+to @code{@@1}.
+
+@item
+For consistency with semantic actions, valid indexes for the location array
+range from 1 to @var{n}.
+@end itemize
+
+@node Declarations
@section Bison Declarations
@cindex declarations, Bison
@cindex Bison declarations
The first rule in the file also specifies the start symbol, by default.
If you want some other symbol to be the start symbol, you must declare
-it explicitly (@pxref{Language and Grammar, ,Languages and Context-Free Grammars}).
+it explicitly (@pxref{Language and Grammar, ,Languages and Context-Free
+Grammars}).
@menu
* Token Decl:: Declaring terminal symbols.
* Decl Summary:: Table of all Bison declarations.
@end menu
-@node Token Decl, Precedence Decl, , Declarations
+@node Token Decl
@subsection Token Type Names
@cindex declaring token type names
@cindex token type names, declaring
In the event that the stack type is a union, you must augment the
@code{%token} or other token declaration to include the data type
-alternative delimited by angle-brackets (@pxref{Multiple Types, ,More Than One Value Type}).
+alternative delimited by angle-brackets (@pxref{Multiple Types, ,More
+Than One Value Type}).
For example:
@code{yylex} function can use the token name or the literal string to
obtain the token type code number (@pxref{Calling Convention}).
-@node Precedence Decl, Union Decl, Token Decl, Declarations
+@node Precedence Decl
@subsection Operator Precedence
@cindex precedence declarations
@cindex declaring operator precedence
Use the @code{%left}, @code{%right} or @code{%nonassoc} declaration to
declare a token and specify its precedence and associativity, all at
once. These are called @dfn{precedence declarations}.
-@xref{Precedence, ,Operator Precedence}, for general information on operator precedence.
+@xref{Precedence, ,Operator Precedence}, for general information on
+operator precedence.
The syntax of a precedence declaration is the same as that of
@code{%token}: either
the one declared later has the higher precedence and is grouped first.
@end itemize
-@node Union Decl, Type Decl, Precedence Decl, Declarations
+@node Union Decl
@subsection The Collection of Value Types
@cindex declaring value types
@cindex value types, declaring
Note that, unlike making a @code{union} declaration in C, you do not write
a semicolon after the closing brace.
-@node Type Decl, Expect Decl, Union Decl, Declarations
+@node Type Decl
@subsection Nonterminal Symbols
@cindex declaring value types, nonterminals
@cindex value types, nonterminals, declaring
@end example
@noindent
-Here @var{nonterminal} is the name of a nonterminal symbol, and @var{type}
-is the name given in the @code{%union} to the alternative that you want
-(@pxref{Union Decl, ,The Collection of Value Types}). You can give any number of nonterminal symbols in
-the same @code{%type} declaration, if they have the same value type. Use
-spaces to separate the symbol names.
+Here @var{nonterminal} is the name of a nonterminal symbol, and
+@var{type} is the name given in the @code{%union} to the alternative
+that you want (@pxref{Union Decl, ,The Collection of Value Types}). You
+can give any number of nonterminal symbols in the same @code{%type}
+declaration, if they have the same value type. Use spaces to separate
+the symbol names.
You can also declare the value type of a terminal symbol. To do this,
use the same @code{<@var{type}>} construction in a declaration for the
terminal symbol. All kinds of token declarations allow
@code{<@var{type}>}.
-@node Expect Decl, Start Decl, Type Decl, Declarations
+@node Expect Decl
@subsection Suppressing Conflict Warnings
@cindex suppressing conflict warnings
@cindex preventing warnings about conflicts
@findex %expect
Bison normally warns if there are any conflicts in the grammar
-(@pxref{Shift/Reduce, ,Shift/Reduce Conflicts}), but most real grammars have harmless shift/reduce
-conflicts which are resolved in a predictable way and would be difficult to
-eliminate. It is desirable to suppress the warning about these conflicts
-unless the number of conflicts changes. You can do this with the
-@code{%expect} declaration.
+(@pxref{Shift/Reduce, ,Shift/Reduce Conflicts}), but most real grammars
+have harmless shift/reduce conflicts which are resolved in a predictable
+way and would be difficult to eliminate. It is desirable to suppress
+the warning about these conflicts unless the number of conflicts
+changes. You can do this with the @code{%expect} declaration.
The declaration looks like this:
%expect @var{n}
@end example
-Here @var{n} is a decimal integer. The declaration says there should be no
-warning if there are @var{n} shift/reduce conflicts and no reduce/reduce
-conflicts. The usual warning is given if there are either more or fewer
-conflicts, or if there are any reduce/reduce conflicts.
+Here @var{n} is a decimal integer. The declaration says there should be
+no warning if there are @var{n} shift/reduce conflicts and no
+reduce/reduce conflicts. An error, instead of the usual warning, is
+given if there are either more or fewer conflicts, or if there are any
+reduce/reduce conflicts.
In general, using @code{%expect} involves these steps:
it will warn you again if changes in the grammar result in additional
conflicts.
-@node Start Decl, Pure Decl, Expect Decl, Declarations
+@node Start Decl
@subsection The Start-Symbol
@cindex declaring the start symbol
@cindex start symbol, declaring
%start @var{symbol}
@end example
-@node Pure Decl, Decl Summary, Start Decl, Declarations
+@node Pure Decl
@subsection A Pure (Reentrant) Parser
@cindex reentrant parser
@cindex pure parser
You can generate either a pure parser or a nonreentrant parser from any
valid grammar.
-@node Decl Summary, , Pure Decl, Declarations
+@node Decl Summary
@subsection Bison Declaration Summary
@cindex Bison declaration summary
@cindex declaration summary
@cindex summary, Bison declaration
-Here is a summary of all Bison declarations:
+Here is a summary of the declarations used to define a grammar:
@table @code
@item %union
@item %expect
Declare the expected number of shift-reduce conflicts
(@pxref{Expect Decl, ,Suppressing Conflict Warnings}).
+@end table
-@item %yacc
-@itemx %fixed_output_files
-Pretend the option @option{--yacc} was given, i.e., imitate Yacc,
-including its naming conventions. @xref{Bison Options}, for more.
+@sp 1
+@noindent
+In order to change the behavior of @command{bison}, use the following
+directives:
+
+@table @code
+@item %debug
+In the parser file, define the macro @code{YYDEBUG} to 1 if it is not
+already defined, so that the debugging facilities are compiled.
+@xref{Debugging, ,Debugging Your Parser}.
+
+@item %defines
+Write an extra output file containing macro definitions for the token
+type names defined in the grammar and the semantic value type
+@code{YYSTYPE}, as well as a few @code{extern} variable declarations.
+
+If the parser output file is named @file{@var{name}.c} then this file
+is named @file{@var{name}.h}.@refill
+
+This output file is essential if you wish to put the definition of
+@code{yylex} in a separate source file, because @code{yylex} needs to
+be able to refer to token type codes and the variable
+@code{yylval}. @xref{Token Values, ,Semantic Values of Tokens}.@refill
+
+@item %file-prefix="@var{prefix}"
+Specify a prefix to use for all Bison output file names. The names are
+chosen as if the input file were named @file{@var{prefix}.y}.
+
+@c @item %header_extension
+@c Specify the extension of the parser header file generated when
+@c @code{%define} or @samp{-d} are used.
+@c
+@c For example, a grammar file named @file{foo.ypp} and containing a
+@c @code{%header_extension .hh} directive will produce a header file
+@c named @file{foo.tab.hh}
@item %locations
Generate the code processing the locations (@pxref{Action Features,
grammar does not use it, using @samp{%locations} allows for more
accurate parse error messages.
-@item %pure_parser
-Request a pure (reentrant) parser program (@pxref{Pure Decl, ,A Pure
-(Reentrant) Parser}).
+@item %name-prefix="@var{prefix}"
+Rename the external symbols used in the parser so that they start with
+@var{prefix} instead of @samp{yy}. The precise list of symbols renamed
+is @code{yyparse}, @code{yylex}, @code{yyerror}, @code{yynerrs},
+@code{yylval}, @code{yychar} and @code{yydebug}. For example, if you
+use @samp{%name-prefix="c_"}, the names become @code{c_parse},
+@code{c_lex}, and so on. @xref{Multiple Parsers, ,Multiple Parsers in
+the Same Program}.
-@item %no_parser
+@item %no-parser
Do not include any C code in the parser file; generate tables only. The
parser file contains just @code{#define} directives and static variable
declarations.
into a file named @file{@var{filename}.act}, in the form of a
brace-surrounded body fit for a @code{switch} statement.
-@item %no_lines
+@item %no-lines
Don't generate any @code{#line} preprocessor commands in the parser
file. Ordinarily Bison writes these commands in the parser file so that
the C compiler and debuggers will associate errors and object code with
associate errors with the parser file, treating it an independent source
file in its own right.
-@item %debug
-Output a definition of the macro @code{YYDEBUG} into the parser file, so
-that the debugging facilities are compiled. @xref{Debugging, ,Debugging
-Your Parser}.
+@item %output="@var{filename}"
+Specify the @var{filename} for the parser file.
-@item %defines
-Write an extra output file containing macro definitions for the token
-type names defined in the grammar and the semantic value type
-@code{YYSTYPE}, as well as a few @code{extern} variable declarations.
-
-If the parser output file is named @file{@var{name}.c} then this file
-is named @file{@var{name}.h}.@refill
-
-This output file is essential if you wish to put the definition of
-@code{yylex} in a separate source file, because @code{yylex} needs to
-be able to refer to token type codes and the variable
-@code{yylval}. @xref{Token Values, ,Semantic Values of Tokens}.@refill
-
-@item %verbose
-Write an extra output file containing verbose descriptions of the
-parser states and what is done for each type of look-ahead token in
-that state.
-
-This file also describes all the conflicts, both those resolved by
-operator precedence and the unresolved ones.
-
-The file's name is made by removing @samp{.tab.c} or @samp{.c} from
-the parser output file name, and adding @samp{.output} instead.@refill
-
-Therefore, if the input file is @file{foo.y}, then the parser file is
-called @file{foo.tab.c} by default. As a consequence, the verbose
-output file is called @file{foo.output}.@refill
+@item %pure-parser
+Request a pure (reentrant) parser program (@pxref{Pure Decl, ,A Pure
+(Reentrant) Parser}).
-@item %raw
-The output file @file{@var{name}.h} normally defines the tokens with
-Yacc-compatible token numbers. If this option is specified, the
-internal Bison numbers are used instead. (Yacc-compatible numbers start
-at 257 except for single-character tokens; Bison assigns token numbers
-sequentially for all tokens starting at 3.)
+@c @item %source_extension
+@c Specify the extension of the parser output file.
+@c
+@c For example, a grammar file named @file{foo.yy} and containing a
+@c @code{%source_extension .cpp} directive will produce a parser file
+@c named @file{foo.tab.cpp}
@item %token_table
Generate an array of token names in the parser file. The name of the
@item YYNSTATES
The number of parser states (@pxref{Parser States}).
@end table
+
+@item %verbose
+Write an extra output file containing verbose descriptions of the
+parser states and what is done for each type of look-ahead token in
+that state.
+
+This file also describes all the conflicts, both those resolved by
+operator precedence and the unresolved ones.
+
+The file's name is made by removing @samp{.tab.c} or @samp{.c} from
+the parser output file name, and adding @samp{.output} instead.@refill
+
+Therefore, if the input file is @file{foo.y}, then the parser file is
+called @file{foo.tab.c} by default. As a consequence, the verbose
+output file is called @file{foo.output}.@refill
+
+@item %yacc
+@itemx %fixed-output-files
+Pretend the option @option{--yacc} was given, i.e., imitate Yacc,
+including its naming conventions. @xref{Bison Options}, for more.
@end table
-@node Multiple Parsers,, Declarations, Grammar File
+
+
+
+@node Multiple Parsers
@section Multiple Parsers in the Same Program
Most programs that use Bison parse only one language and therefore contain
between different definitions of @code{yyparse}, @code{yylval}, and so on.
The easy way to do this is to use the option @samp{-p @var{prefix}}
-(@pxref{Invocation, ,Invoking Bison}). This renames the interface functions and
-variables of the Bison parser to start with @var{prefix} instead of
-@samp{yy}. You can use this to give each parser distinct names that do
-not conflict.
+(@pxref{Invocation, ,Invoking Bison}). This renames the interface
+functions and variables of the Bison parser to start with @var{prefix}
+instead of @samp{yy}. You can use this to give each parser distinct
+names that do not conflict.
The precise list of symbols renamed is @code{yyparse}, @code{yylex},
@code{yyerror}, @code{yynerrs}, @code{yylval}, @code{yychar} and
@code{@var{prefix}parse}, and so on. This effectively substitutes one
name for the other in the entire parser file.
-@node Interface, Algorithm, Grammar File, Top
+@node Interface
@chapter Parser C-Language Interface
@cindex C-language interface
@cindex interface
Keep in mind that the parser uses many C identifiers starting with
@samp{yy} and @samp{YY} for internal purposes. If you use such an
-identifier (aside from those in this manual) in an action or in additional
-C code in the grammar file, you are likely to run into trouble.
+identifier (aside from those in this manual) in an action or in epilogue
+in the grammar file, you are likely to run into trouble.
@menu
* Parser Function:: How to call @code{yyparse} and what it returns.
* Action Features:: Special features for use in actions.
@end menu
-@node Parser Function, Lexical, , Interface
+@node Parser Function
@section The Parser Function @code{yyparse}
@findex yyparse
Return immediately with value 1 (to report failure).
@end table
-@node Lexical, Error Reporting, Parser Function, Interface
+@node Lexical
@section The Lexical Analyzer Function @code{yylex}
@findex yylex
@cindex lexical analyzer
in a pure parser (@pxref{Pure Decl, ,A Pure (Reentrant) Parser}).
@end menu
-@node Calling Convention, Token Values, , Lexical
+@node Calling Convention
@subsection Calling Convention for @code{yylex}
The value that @code{yylex} returns must be the numeric code for the type
@code{%token_table} declaration. @xref{Decl Summary}.
@end itemize
-@node Token Values, Token Positions, Calling Convention, Lexical
+@node Token Values
@subsection Semantic Values of Tokens
@vindex yylval
@end example
When you are using multiple data types, @code{yylval}'s type is a union
-made from the @code{%union} declaration (@pxref{Union Decl, ,The Collection of Value Types}). So when
-you store a token's value, you must use the proper member of the union.
-If the @code{%union} declaration looks like this:
+made from the @code{%union} declaration (@pxref{Union Decl, ,The
+Collection of Value Types}). So when you store a token's value, you
+must use the proper member of the union. If the @code{%union}
+declaration looks like this:
@example
@group
@end group
@end example
-@node Token Positions, Pure Calling, Token Values, Lexical
+@node Token Positions
@subsection Textual Positions of Tokens
@vindex yylloc
-If you are using the @samp{@@@var{n}}-feature (@pxref{Action Features,
-,Special Features for Use in Actions}) in actions to keep track of the
+If you are using the @samp{@@@var{n}}-feature (@pxref{Locations, ,
+Tracking Locations}) in actions to keep track of the
textual locations of tokens and groupings, then you must provide this
information in @code{yylex}. The function @code{yyparse} expects to
find the textual location of a token just parsed in the global variable
@code{yylloc}. So @code{yylex} must store the proper data in that
-variable. The value of @code{yylloc} is a structure and you need only
+variable.
+
+By default, the value of @code{yylloc} is a structure and you need only
initialize the members that are going to be used by the actions. The
four members are called @code{first_line}, @code{first_column},
@code{last_line} and @code{last_column}. Note that the use of this
@tindex YYLTYPE
The data type of @code{yylloc} has the name @code{YYLTYPE}.
-@node Pure Calling, , Token Positions, Lexical
+@node Pure Calling
@subsection Calling Conventions for Pure Parsers
When you use the Bison declaration @code{%pure_parser} to request a
also using @code{YYPARSE_PARAM}. Then you should call @code{yyparse}
with no arguments, as usual.
-@node Error Reporting, Action Features, Lexical, Interface
+@node Error Reporting
@section The Error Reporting Function @code{yyerror}
@cindex error reporting function
@findex yyerror
@vindex yynerrs
The variable @code{yynerrs} contains the number of syntax errors
encountered so far. Normally this variable is global; but if you
-request a pure parser (@pxref{Pure Decl, ,A Pure (Reentrant) Parser}) then it is a local variable
-which only the actions can access.
+request a pure parser (@pxref{Pure Decl, ,A Pure (Reentrant) Parser})
+then it is a local variable which only the actions can access.
-@node Action Features, , Error Reporting, Interface
+@node Action Features
@section Special Features for Use in Actions
@cindex summary, action features
@cindex action features summary
@item $<@var{typealt}>$
Like @code{$$} but specifies alternative @var{typealt} in the union
-specified by the @code{%union} declaration. @xref{Action Types, ,Data Types of Values in Actions}.
+specified by the @code{%union} declaration. @xref{Action Types, ,Data
+Types of Values in Actions}.
@item $<@var{typealt}>@var{n}
Like @code{$@var{n}} but specifies alternative @var{typealt} in the
errors. This is useful primarily in error rules.
@xref{Error Recovery}.
-@item @@@var{n}
-@findex @@@var{n}
-Acts like a structure variable containing information on the line
-numbers and column numbers of the @var{n}th component of the current
-rule. The structure has four members, like this:
+@item @@$
+@findex @@$
+Acts like a structure variable containing information on the textual position
+of the grouping made by the current rule. @xref{Locations, ,
+Tracking Locations}.
-@example
-struct @{
- int first_line, last_line;
- int first_column, last_column;
-@};
-@end example
+@c Check if those paragraphs are still useful or not.
+
+@c @example
+@c struct @{
+@c int first_line, last_line;
+@c int first_column, last_column;
+@c @};
+@c @end example
+
+@c Thus, to get the starting line number of the third component, you would
+@c use @samp{@@3.first_line}.
-Thus, to get the starting line number of the third component, you would
-use @samp{@@3.first_line}.
+@c In order for the members of this structure to contain valid information,
+@c you must make @code{yylex} supply this information about each token.
+@c If you need only certain members, then @code{yylex} need only fill in
+@c those members.
-In order for the members of this structure to contain valid information,
-you must make @code{yylex} supply this information about each token.
-If you need only certain members, then @code{yylex} need only fill in
-those members.
+@c The use of this feature makes the parser noticeably slower.
+
+@item @@@var{n}
+@findex @@@var{n}
+Acts like a structure variable containing information on the textual position
+of the @var{n}th component of the current rule. @xref{Locations, ,
+Tracking Locations}.
-The use of this feature makes the parser noticeably slower.
@end table
-@node Algorithm, Error Recovery, Interface, Top
+@node Algorithm
@chapter The Bison Parser Algorithm
@cindex Bison parser algorithm
@cindex algorithm of parser
* Stack Overflow:: What happens when stack gets full. How to avoid it.
@end menu
-@node Look-Ahead, Shift/Reduce, , Algorithm
+@node Look-Ahead
@section Look-Ahead Tokens
@cindex look-ahead token
The current look-ahead token is stored in the variable @code{yychar}.
@xref{Action Features, ,Special Features for Use in Actions}.
-@node Shift/Reduce, Precedence, Look-Ahead, Algorithm
+@node Shift/Reduce
@section Shift/Reduce Conflicts
@cindex conflicts
@cindex shift/reduce conflicts
;
@end example
-@node Precedence, Contextual Precedence, Shift/Reduce, Algorithm
+@node Precedence
@section Operator Precedence
@cindex operator precedence
@cindex precedence of operators
* How Precedence:: How they work.
@end menu
-@node Why Precedence, Using Precedence, , Precedence
+@node Why Precedence
@subsection When Precedence is Needed
Consider the following ambiguous grammar fragment (ambiguous because the
contains @w{@samp{1 - 2}} and the look-ahead token is @samp{-}: shifting
makes right-associativity.
-@node Using Precedence, Precedence Examples, Why Precedence, Precedence
+@node Using Precedence
@subsection Specifying Operator Precedence
@findex %left
@findex %right
precedence is lowest, the next such declaration declares the operators
whose precedence is a little higher, and so on.
-@node Precedence Examples, How Precedence, Using Precedence, Precedence
+@node Precedence Examples
@subsection Precedence Examples
In our example, we would want the following declarations:
and so on. We assume that these tokens are more than one character long
and therefore are represented by names, not character literals.)
-@node How Precedence, , Precedence Examples, Precedence
+@node How Precedence
@subsection How Precedence Works
The first effect of the precedence declarations is to assign precedence
levels to the terminal symbols declared. The second effect is to assign
-precedence levels to certain rules: each rule gets its precedence from the
-last terminal symbol mentioned in the components. (You can also specify
-explicitly the precedence of a rule. @xref{Contextual Precedence, ,Context-Dependent Precedence}.)
-
-Finally, the resolution of conflicts works by comparing the
-precedence of the rule being considered with that of the
-look-ahead token. If the token's precedence is higher, the
-choice is to shift. If the rule's precedence is higher, the
-choice is to reduce. If they have equal precedence, the choice
-is made based on the associativity of that precedence level. The
-verbose output file made by @samp{-v} (@pxref{Invocation, ,Invoking Bison}) says
-how each conflict was resolved.
+precedence levels to certain rules: each rule gets its precedence from
+the last terminal symbol mentioned in the components. (You can also
+specify explicitly the precedence of a rule. @xref{Contextual
+Precedence, ,Context-Dependent Precedence}.)
+
+Finally, the resolution of conflicts works by comparing the precedence
+of the rule being considered with that of the look-ahead token. If the
+token's precedence is higher, the choice is to shift. If the rule's
+precedence is higher, the choice is to reduce. If they have equal
+precedence, the choice is made based on the associativity of that
+precedence level. The verbose output file made by @samp{-v}
+(@pxref{Invocation, ,Invoking Bison}) says how each conflict was
+resolved.
Not all rules and not all tokens have precedence. If either the rule or
the look-ahead token has no precedence, then the default is to shift.
-@node Contextual Precedence, Parser States, Precedence, Algorithm
+@node Contextual Precedence
@section Context-Dependent Precedence
@cindex context-dependent precedence
@cindex unary operator precedence
@end group
@end example
-@node Parser States, Reduce/Reduce, Contextual Precedence, Algorithm
+@node Parser States
@section Parser States
@cindex finite-state machine
@cindex parser state
is erroneous in the current state. This causes error processing to begin
(@pxref{Error Recovery}).
-@node Reduce/Reduce, Mystery Conflicts, Parser States, Algorithm
+@node Reduce/Reduce
@section Reduce/Reduce Conflicts
@cindex reduce/reduce conflict
@cindex conflicts, reduce/reduce
;
@end example
-@node Mystery Conflicts, Stack Overflow, Reduce/Reduce, Algorithm
+@node Mystery Conflicts
@section Mysterious Reduce/Reduce Conflicts
Sometimes reduce/reduce conflicts can occur that don't look warranted.
;
@end example
-@node Stack Overflow, , Mystery Conflicts, Algorithm
+@node Stack Overflow
@section Stack Overflow, and How to Avoid It
@cindex stack overflow
@cindex parser stack overflow
macro @code{YYINITDEPTH}. This value too must be a compile-time
constant integer. The default is 200.
-@node Error Recovery, Context Dependency, Algorithm, Top
+@node Error Recovery
@chapter Error Recovery
@cindex error recovery
@cindex recovery from errors
rest of the time. A value of 1 indicates that error messages are
currently suppressed for new syntax errors.
-@node Context Dependency, Debugging, Error Recovery, Top
+@node Context Dependency
@chapter Handling Context Dependencies
The Bison paradigm is to parse tokens first, then group them into larger
(Actually, ``kludge'' means any technique that gets its job done but is
neither clean nor robust.)
-@node Semantic Tokens, Lexical Tie-ins, , Context Dependency
+@node Semantic Tokens
@section Semantic Info in Token Types
The C language has a context dependency: the way an identifier is used
program. A true lexical tie-in has a special-purpose flag controlled by
the syntactic context.
-@node Lexical Tie-ins, Tie-in Recovery, Semantic Tokens, Context Dependency
+@node Lexical Tie-ins
@section Lexical Tie-ins
@cindex lexical tie-in
it is nonzero, all integers are parsed in hexadecimal, and tokens starting
with letters are parsed as integers if possible.
-The declaration of @code{hexflag} shown in the C declarations section of
-the parser file is needed to make it accessible to the actions
-(@pxref{C Declarations, ,The C Declarations Section}). You must also write the code in @code{yylex}
-to obey the flag.
+The declaration of @code{hexflag} shown in the prologue of the parser file
+is needed to make it accessible to the actions (@pxref{Prologue, ,The Prologue}).
+You must also write the code in @code{yylex} to obey the flag.
-@node Tie-in Recovery, , Lexical Tie-ins, Context Dependency
+@node Tie-in Recovery
@section Lexical Tie-ins and Error Recovery
Lexical tie-ins make strict demands on any error recovery rules you have.
be such that you can be sure that it always will, or always won't, have to
clear the flag.
-@node Debugging, Invocation, Context Dependency, Top
+@node Debugging
@chapter Debugging Your Parser
@findex YYDEBUG
@findex yydebug
runs, the @code{yydebug} parser-trace feature can help you figure out why.
To enable compilation of trace facilities, you must define the macro
-@code{YYDEBUG} when you compile the parser. You could use
-@samp{-DYYDEBUG=1} as a compiler option or you could put @samp{#define
-YYDEBUG 1} in the C declarations section of the grammar file
-(@pxref{C Declarations, ,The C Declarations Section}). Alternatively, use the @samp{-t} option when
-you run Bison (@pxref{Invocation, ,Invoking Bison}). We always define @code{YYDEBUG} so that
+@code{YYDEBUG} to a nonzero value when you compile the parser. You
+could use @samp{-DYYDEBUG=1} as a compiler option or you could put
+@samp{#define YYDEBUG 1} in the prologue of the grammar file
+(@pxref{Prologue, , The Prologue}). Alternatively, use the @samp{-t}
+option when you run Bison (@pxref{Invocation, ,Invoking Bison}) or the
+@code{%debug} declaration (@pxref{Decl Summary, ,Bison Declaration
+Summary}). We suggest that you always define @code{YYDEBUG} so that
debugging is always possible.
-The trace facility uses @code{stderr}, so you must add @w{@code{#include
-<stdio.h>}} to the C declarations section unless it is already there.
+The trace facility outputs messages with macro calls of the form
+@code{YYFPRINTF (YYSTDERR, @var{format}, @var{args})} where
+@var{format} and @var{args} are the usual @code{printf} format and
+arguments. If you define @code{YYDEBUG} to a nonzero value but do not
+define @code{YYFPRINTF}, @code{<stdio.h>} is automatically included
+and the macros are defined to @code{fprintf} and @code{stderr}. In
+the same situation, C++ parsers include @code{<cstdio.h>} instead, and
+use @code{std::fprintf} and @code{std::stderr}.
Once you have compiled the program with trace facilities, the way to
request a trace is to store a nonzero value in the variable @code{yydebug}.
@end itemize
To make sense of this information, it helps to refer to the listing file
-produced by the Bison @samp{-v} option (@pxref{Invocation, ,Invoking Bison}). This file
-shows the meaning of each state in terms of positions in various rules, and
-also what each state will do with each possible input token. As you read
-the successive trace messages, you can see that the parser is functioning
-according to its specification in the listing file. Eventually you will
-arrive at the place where something undesirable happens, and you will see
-which parts of the grammar are to blame.
+produced by the Bison @samp{-v} option (@pxref{Invocation, ,Invoking
+Bison}). This file shows the meaning of each state in terms of
+positions in various rules, and also what each state will do with each
+possible input token. As you read the successive trace messages, you
+can see that the parser is functioning according to its specification in
+the listing file. Eventually you will arrive at the place where
+something undesirable happens, and you will see which parts of the
+grammar are to blame.
The parser file is a C program and you can use C debuggers on it, but it's
not easy to interpret what it is doing. The parser function is a
@}
@end smallexample
-@node Invocation, Table of Symbols, Debugging, Top
+@node Invocation
@chapter Invoking Bison
@cindex invoking Bison
@cindex Bison invocation
@samp{.y}. The parser file's name is made by replacing the @samp{.y}
with @samp{.tab.c}. Thus, the @samp{bison foo.y} filename yields
@file{foo.tab.c}, and the @samp{bison hack/foo.y} filename yields
-@file{hack/foo.tab.c}.@refill
+@file{hack/foo.tab.c}. It's is also possible, in case you are writing
+C++ code instead of C in your grammar file, to name it @file{foo.ypp}
+or @file{foo.y++}. Then, the output files will take an extention like
+the given one as input (repectively @file{foo.tab.cpp} and @file{foo.tab.c++}).
+This feature takes effect with all options that manipulate filenames like
+@samp{-o} or @samp{-d}.
+
+For example :
+
+@example
+bison -d @var{infile.yxx}
+@end example
+@noindent
+will produce @file{infile.tab.cxx} and @file{infile.tab.hxx}. and
+
+@example
+bison -d @var{infile.y} -o @var{output.c++}
+@end example
+@noindent
+will produce @file{output.c++} and @file{outfile.h++}.
+
@menu
* Bison Options:: All the options described in detail,
* VMS Invocation:: Bison command syntax on VMS.
@end menu
-@node Bison Options, Environment Variables, , Invocation
+@node Bison Options
@section Bison Options
Bison supports both traditional single-letter options and mnemonic long
@item -t
@itemx --debug
-Output a definition of the macro @code{YYDEBUG} into the parser file, so
-that the debugging facilities are compiled. @xref{Debugging, ,Debugging
-Your Parser}.
+In the parser file, define the macro @code{YYDEBUG} to 1 if it is not
+already defined, so that the debugging facilities are compiled.
+@xref{Debugging, ,Debugging Your Parser}.
@item --locations
-Pretend that @code{%locactions} was specified. @xref{Decl Summary}.
+Pretend that @code{%locations} was specified. @xref{Decl Summary}.
@item -p @var{prefix}
@itemx --name-prefix=@var{prefix}
-Rename the external symbols used in the parser so that they start with
-@var{prefix} instead of @samp{yy}. The precise list of symbols renamed
-is @code{yyparse}, @code{yylex}, @code{yyerror}, @code{yynerrs},
-@code{yylval}, @code{yychar} and @code{yydebug}.
-
-For example, if you use @samp{-p c}, the names become @code{cparse},
-@code{clex}, and so on.
-
-@xref{Multiple Parsers, ,Multiple Parsers in the Same Program}.
+Pretend that @code{%name-prefix="@var{prefix}"} was specified.
+@xref{Decl Summary}.
@item -l
@itemx --no-lines
@item -n
@itemx --no-parser
-Pretend that @code{%no_parser} was specified. @xref{Decl Summary}.
-
-@item -r
-@itemx --raw
-Pretend that @code{%raw} was specified. @xref{Decl Summary}.
+Pretend that @code{%no-parser} was specified. @xref{Decl Summary}.
@item -k
@itemx --token-table
-Pretend that @code{%token_table} was specified. @xref{Decl Summary}.
+Pretend that @code{%token-table} was specified. @xref{Decl Summary}.
@end table
@noindent
@table @option
@item -d
@itemx --defines
-Pretend that @code{%verbose} was specified, i.e., write an extra output
+Pretend that @code{%defines} was specified, i.e., write an extra output
file containing macro definitions for the token type names defined in
the grammar and the semantic value type @code{YYSTYPE}, as well as a few
@code{extern} variable declarations. @xref{Decl Summary}.
+@item --defines=@var{defines-file}
+Same as above, but save in the file @var{defines-file}.
+
@item -b @var{file-prefix}
@itemx --file-prefix=@var{prefix}
-Specify a prefix to use for all Bison output file names. The names are
-chosen as if the input file were named @file{@var{prefix}.c}.
+Pretend that @code{%verbose} was specified, i.e, specify prefix to use
+for all Bison output file names. @xref{Decl Summary}.
@item -v
@itemx --verbose
Pretend that @code{%verbose} was specified, i.e, write an extra output
file containing verbose descriptions of the grammar and
-parser. @xref{Decl Summary}, for more.
+parser. @xref{Decl Summary}.
+
+@item -o @var{filename}
+@itemx --output=@var{filename}
+Specify the @var{filename} for the parser file.
-@item -o @var{outfile}
-@itemx --output-file=@var{outfile}
-Specify the name @var{outfile} for the parser file.
+The other output files' names are constructed from @var{filename} as
+described under the @samp{-v} and @samp{-d} options.
-The other output files' names are constructed from @var{outfile}
-as described under the @samp{-v} and @samp{-d} options.
+@item -g
+Output a VCG definition of the LALR(1) grammar automaton computed by
+Bison. If the grammar file is @file{foo.y}, the VCG output file will
+be @file{foo.vcg}.
+
+@item --graph=@var{graph-file}
+The behaviour of @var{--graph} is the same than @samp{-g}. The only
+difference is that it has an optionnal argument which is the name of
+the output graph filename.
@end table
-@node Environment Variables, Option Cross Key, Bison Options, Invocation
+@node Environment Variables
@section Environment Variables
@cindex environment variables
@cindex BISON_HAIRY
@end table
-@node Option Cross Key, VMS Invocation, Environment Variables, Invocation
+@node Option Cross Key
@section Option Cross Key
Here is a list of options, alphabetized by long option, to help you find
\line{ --defines \leaderfill -d}
\line{ --file-prefix \leaderfill -b}
\line{ --fixed-output-files \leaderfill -y}
+\line{ --graph \leaderfill -g}
\line{ --help \leaderfill -h}
\line{ --name-prefix \leaderfill -p}
\line{ --no-lines \leaderfill -l}
\line{ --no-parser \leaderfill -n}
-\line{ --output-file \leaderfill -o}
-\line{ --raw \leaderfill -r}
+\line{ --output \leaderfill -o}
\line{ --token-table \leaderfill -k}
\line{ --verbose \leaderfill -v}
\line{ --version \leaderfill -V}
@ifinfo
@example
--debug -t
---defines -d
+--defines=@var{defines-file} -d
--file-prefix=@var{prefix} -b @var{file-prefix}
--fixed-output-files --yacc -y
+--graph=@var{graph-file} -d
--help -h
--name-prefix=@var{prefix} -p @var{name-prefix}
--no-lines -l
--no-parser -n
---output-file=@var{outfile} -o @var{outfile}
---raw -r
+--output=@var{outfile} -o @var{outfile}
--token-table -k
--verbose -v
--version -V
@end example
@end ifinfo
-@node VMS Invocation, , Option Cross Key, Invocation
+@node VMS Invocation
@section Invoking Bison under VMS
@cindex invoking Bison under VMS
@cindex VMS
@file{foo.tab.c}. In the above example, the output file
would instead be named @file{foo_tab.c}.
-@node Table of Symbols, Glossary, Invocation, Top
+@node Table of Symbols
@appendix Bison Symbols
@cindex Bison symbols, table of
@cindex symbols in Bison, table of
@item YYLTYPE
Macro for the data type of @code{yylloc}; a structure with four
-members. @xref{Token Positions, ,Textual Positions of Tokens}.
+members. @xref{Location Type, , Data Types of Locations}.
@item yyltype
Default value for YYLTYPE.
Macro whose value indicates whether the parser is recovering from a
syntax error. @xref{Action Features, ,Special Features for Use in Actions}.
+@item YYSTACK_USE_ALLOCA
+Macro used to control the use of @code{alloca}. If defined to @samp{0},
+the parser will not use @code{alloca} but @code{malloc} when trying to
+grow its internal stacks. Do @emph{not} define @code{YYSTACK_USE_ALLOCA}
+to anything else.
+
@item YYSTYPE
Macro for the data type of semantic values; @code{int} by default.
@xref{Value Type, ,Data Types of Semantic Values}.
Reporting Function @code{yyerror}}.
@item yylex
-User-supplied lexical analyzer function, called with no arguments
-to get the next token. @xref{Lexical, ,The Lexical Analyzer Function @code{yylex}}.
+User-supplied lexical analyzer function, called with no arguments to get
+the next token. @xref{Lexical, ,The Lexical Analyzer Function
+@code{yylex}}.
@item yylval
External variable in which @code{yylex} should place the semantic
Bison declaration to create a header file meant for the scanner.
@xref{Decl Summary}.
+@item %file-prefix="@var{prefix}"
+Bison declaration to set tge prefix of the output files. @xref{Decl
+Summary}.
+
+@c @item %source_extension
+@c Bison declaration to specify the generated parser output file extension.
+@c @xref{Decl Summary}.
+@c
+@c @item %header_extension
+@c Bison declaration to specify the generated parser header file extension
+@c if required. @xref{Decl Summary}.
+
@item %left
Bison declaration to assign left associativity to token(s).
@xref{Precedence Decl, ,Operator Precedence}.
-@item %no_lines
+@item %name-prefix="@var{prefix}"
+Bison declaration to rename the external symbols. @xref{Decl Summary}.
+
+@item %no-lines
Bison declaration to avoid generating @code{#line} directives in the
parser file. @xref{Decl Summary}.
Bison declaration to assign non-associativity to token(s).
@xref{Precedence Decl, ,Operator Precedence}.
+@item %output="@var{filename}"
+Bison declaration to set the name of the parser file. @xref{Decl
+Summary}.
+
@item %prec
Bison declaration to assign a precedence to a specific rule.
@xref{Contextual Precedence, ,Context-Dependent Precedence}.
-@item %pure_parser
+@item %pure-parser
Bison declaration to request a pure (reentrant) parser.
@xref{Pure Decl, ,A Pure (Reentrant) Parser}.
-@item %raw
-Bison declaration to use Bison internal token code numbers in token
-tables instead of the usual Yacc-compatible token code numbers.
-@xref{Decl Summary}.
-
@item %right
Bison declaration to assign right associativity to token(s).
@xref{Precedence Decl, ,Operator Precedence}.
@item %start
-Bison declaration to specify the start symbol. @xref{Start Decl, ,The Start-Symbol}.
+Bison declaration to specify the start symbol. @xref{Start Decl, ,The
+Start-Symbol}.
@item %token
Bison declaration to declare token(s) without specifying precedence.
@xref{Token Decl, ,Token Type Names}.
-@item %token_table
+@item %token-table
Bison declaration to include a token name table in the parser file.
@xref{Decl Summary}.
@item %type
-Bison declaration to declare nonterminals. @xref{Type Decl, ,Nonterminal Symbols}.
+Bison declaration to declare nonterminals. @xref{Type Decl,
+,Nonterminal Symbols}.
@item %union
Bison declaration to specify several possible data types for semantic
@table @samp
@item %%
Delimiter used to separate the grammar rule section from the
-Bison declarations section or the additional C code section.
+Bison declarations section or the epilogue.
@xref{Grammar Layout, ,The Overall Layout of a Bison Grammar}.
@item %@{ %@}
All code listed between @samp{%@{} and @samp{%@}} is copied directly to
-the output file uninterpreted. Such code forms the ``C declarations''
-section of the input file. @xref{Grammar Outline, ,Outline of a Bison
+the output file uninterpreted. Such code forms the prologue of the input
+file. @xref{Grammar Outline, ,Outline of a Bison
Grammar}.
@item /*@dots{}*/
@xref{Rules, ,Syntax of Grammar Rules}.
@end table
-@node Glossary, Index, Table of Symbols, Top
+@node Glossary
@appendix Glossary
@cindex glossary
@xref{Language and Grammar, ,Languages and Context-Free Grammars}.
@end table
-@node Index, , Glossary, Top
+@node Copying This Manual
+@appendix Copying This Manual
+
+@menu
+* GNU Free Documentation License:: License for copying this manual.
+@end menu
+
+@include fdl.texi
+
+@node Index
@unnumbered Index
@printindex cp
projects / bison.git / blobdiff