\input texinfo @c -*-texinfo-*-
@comment %**start of header
@setfilename bison.info
-@settitle Bison 1.25
+@include version.texi
+@settitle Bison @value{VERSION}
@setchapternewpage odd
@iftex
@c the smallbook format.
@c @smallbook
-@c next time, consider using @set for edition number, etc...
-
@c Set following if you have the new `shorttitlepage' command
@c @clear shorttitlepage-enabled
@c @set shorttitlepage-enabled
@end ifinfo
@comment %**end of header
+@ifinfo
+@format
+START-INFO-DIR-ENTRY
+* bison: (bison). GNU Project parser generator (yacc replacement).
+END-INFO-DIR-ENTRY
+@end format
+@end ifinfo
+
@ifinfo
This file documents the Bison parser generator.
-Copyright (C) 1988, 89, 90, 91, 92, 93, 1995 Free Software Foundation, Inc.
+Copyright (C) 1988, 89, 90, 91, 92, 93, 95, 98, 1999 Free Software Foundation, Inc.
Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
@titlepage
@title Bison
@subtitle The YACC-compatible Parser Generator
-@subtitle August 1995, Bison Version 1.25
+@subtitle @value{UPDATED}, Bison Version @value{VERSION}
@author by Charles Donnelly and Richard Stallman
@page
@vskip 0pt plus 1filll
-Copyright @copyright{} 1988, 89, 90, 91, 92, 93, 1995 Free Software
+Copyright @copyright{} 1988, 89, 90, 91, 92, 93, 95, 98, 1999 Free Software
Foundation
@sp 2
Published by the Free Software Foundation @*
59 Temple Place, Suite 330 @*
Boston, MA 02111-1307 USA @*
-Printed copies are available for $15 each.@*
-ISBN 1-882114-45-0
+Printed copies are available from the Free Software Foundation.@*
+ISBN 1-882114-44-2
Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
@node Top, Introduction, (dir), (dir)
@ifinfo
-This manual documents version 1.25 of Bison.
+This manual documents version @value{VERSION} of Bison.
@end ifinfo
@menu
Yacc-compatible. Wilfred Hansen of Carnegie Mellon University added
multicharacter string literals and other features.
-This edition corresponds to version 1.25 of Bison.
+This edition corresponds to version @value{VERSION} of Bison.
@node Conditions, Copying, Introduction, Top
@unnumbered Conditions for Using Bison
As of Bison version 1.24, we have changed the distribution terms for
-@code{yyparse} to permit using Bison's output in non-free programs.
+@code{yyparse} to permit using Bison's output in nonfree programs.
Formerly, Bison parsers could be used only in programs that were free
software.
The other GNU programming tools, such as the GNU C compiler, have never
-had such a requirement. They could always be used for non-free
+had such a requirement. They could always be used for nonfree
software. The reason Bison was different was not due to a special
policy decision; it resulted from applying the usual General Public
License to all of the Bison source code.
@display
Copyright @copyright{} 1989, 1991 Free Software Foundation, Inc.
-675 Mass Ave, Cambridge, MA 02139, USA
+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.
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., 675 Mass Ave, Cambridge, MA 02139, USA.
+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.
(@pxref{Error Recovery}). Otherwise, @code{yyparse} returns nonzero. We
have not written any error rules in this example, so any invalid input will
cause the calculator program to exit. This is not clean behavior for a
-real calculator, but it is adequate in the first example.
+real calculator, but it is adequate for the first example.
@node Rpcalc Gen, Rpcalc Compile, Rpcalc Error, RPN Calc
@subsection Running Bison to Make the Parser
It is easy to add new operators to the infix calculator as long as they are
only single-character literals. The lexical analyzer @code{yylex} passes
-back all non-number characters as tokens, so new grammar rules suffice for
+back all nonnumber characters as tokens, so new grammar rules suffice for
adding a new operator. But we want something more flexible: built-in
functions whose syntax has this form:
@item
@cindex string token
@cindex literal string token
-@cindex multi-character literal
+@cindex multicharacter literal
A @dfn{literal string token} is written like a C string constant; for
example, @code{"<="} is a literal string token. A literal string token
doesn't need to be declared unless you need to specify its semantic
By convention, a literal string token is used only to represent a token
that consists of that particular string. Thus, you should use the token
type @code{"<="} to represent the string @samp{<=} as a token. Bison
-does not enforces this convention, but if you depart from it, people who
+does not enforce this convention, but if you depart from it, people who
read your program will be confused.
All the escape sequences used in string literals in C can be used in
@end example
@noindent
-where @var{result} is the nonterminal symbol that this rule describes
+where @var{result} is the nonterminal symbol that this rule describes,
and @var{components} are various terminal and nonterminal symbols that
are put together by this rule (@pxref{Symbols}).
A rule is called @dfn{recursive} when its @var{result} nonterminal appears
also on its right hand side. Nearly all Bison grammars need to use
recursion, because that is the only way to define a sequence of any number
-of somethings. Consider this recursive definition of a comma-separated
-sequence of one or more expressions:
+of a particular thing. Consider this recursive definition of a
+comma-separated sequence of one or more expressions:
@example
@group
can use the name @var{name} to stand for this token type's code.
Alternatively, you can use @code{%left}, @code{%right}, or @code{%nonassoc}
-instead of @code{%token}, if you wish to specify precedence.
+instead of @code{%token}, if you wish to specify associativity and precedence.
@xref{Precedence Decl, ,Operator Precedence}.
You can explicitly specify the numeric code for a token type by appending
handler. In systems with multiple threads of control, a nonreentrant
program must be called only within interlocks.
-The Bison parser is not normally a reentrant program, because it uses
-statically allocated variables for communication with @code{yylex}. These
-variables include @code{yylval} and @code{yylloc}.
+Normally, Bison generates a parser which is not reentrant. This is
+suitable for most uses, and it permits compatibility with YACC. (The
+standard YACC interfaces are inherently nonreentrant, because they use
+statically allocated variables for communication with @code{yylex},
+including @code{yylval} and @code{yylloc}.)
-The Bison declaration @code{%pure_parser} says that you want the parser
-to be reentrant. It looks like this:
+Alternatively, you can generate a pure, reentrant parser. The Bison
+declaration @code{%pure_parser} says that you want the parser to be
+reentrant. It looks like this:
@example
%pure_parser
@end example
-The effect is that the two communication variables become local
-variables in @code{yyparse}, and a different calling convention is used
-for the lexical analyzer function @code{yylex}. @xref{Pure Calling,
-,Calling Conventions for Pure Parsers}, for the details of this. The
-variable @code{yynerrs} also becomes local in @code{yyparse}
-(@pxref{Error Reporting, ,The Error Reporting Function @code{yyerror}}).
-The convention for calling @code{yyparse} itself is unchanged.
+The result is that the communication variables @code{yylval} and
+@code{yylloc} become local variables in @code{yyparse}, and a different
+calling convention is used for the lexical analyzer function
+@code{yylex}. @xref{Pure Calling, ,Calling Conventions for Pure
+Parsers}, for the details of this. The variable @code{yynerrs} also
+becomes local in @code{yyparse} (@pxref{Error Reporting, ,The Error
+Reporting Function @code{yyerror}}). The convention for calling
+@code{yyparse} itself is unchanged.
+
+Whether the parser is pure has nothing to do with the grammar rules.
+You can generate either a pure parser or a nonreentrant parser from any
+valid grammar.
@node Decl Summary, , Pure Decl, Declarations
@subsection Bison Declaration Summary
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
+at 257 except for single-character tokens; Bison assigns token numbers
sequentially for all tokens starting at 3.)
@item %token_table
@item YYNTOKENS
The highest token number, plus one.
@item YYNNTS
-The number of non-terminal symbols.
+The number of nonterminal symbols.
@item YYNRULES
The number of grammar rules,
@item YYNSTATES
the grammar file has no effect on @code{yylex}.
@item
-@code{yylex} can find the multi-character token in the @code{yytname}
+@code{yylex} can find the multicharacter token in the @code{yytname}
table. The index of the token in the table is the token type's code.
-The name of a multi-character token is recorded in @code{yytname} with a
+The name of a multicharacter token is recorded in @code{yytname} with a
double-quote, the token's characters, and another double-quote. The
token's characters are not escaped in any way; they appear verbatim in
the contents of the string in the table.
@{
if (yytname[i] != 0
&& yytname[i][0] == '"'
- && strncmp (yytname[i] + 1, token_buffer, strlen (token_buffer))
+ && strncmp (yytname[i] + 1, token_buffer,
+ strlen (token_buffer))
&& yytname[i][strlen (token_buffer) + 1] == '"'
&& yytname[i][strlen (token_buffer) + 2] == 0)
break;
@cindex syntax error
The Bison parser detects a @dfn{parse error} or @dfn{syntax error}
-whenever it reads a token which cannot satisfy any syntax rule. A
+whenever it reads a token which cannot satisfy any syntax rule. An
action in the grammar can also explicitly proclaim an error, using the
macro @code{YYERROR} (@pxref{Action Features, ,Special Features for Use in Actions}).
@};
@end example
-Thus, to get the starting line number of the third component, use
-@samp{@@3.first_line}.
+Thus, to get the starting line number of the third component, you would
+use @samp{@@3.first_line}.
In order for the members of this structure to contain valid information,
you must make @code{yylex} supply this information about each token.
@noindent
Suppose the parser has seen the tokens @samp{1}, @samp{-} and @samp{2};
-should it reduce them via the rule for the addition operator? It depends
+should it reduce them via the rule for the subtraction operator? It depends
on the next token. Of course, if the next token is @samp{)}, we must
reduce; shifting is invalid because no single rule can reduce the token
sequence @w{@samp{- 2 )}} or anything starting with that. But if the next
To decide which one Bison should do, we must consider the
results. If the next operator token @var{op} is shifted, then it
must be reduced first in order to permit another opportunity to
-reduce the sum. The result is (in effect) @w{@samp{1 - (2
+reduce the difference. The result is (in effect) @w{@samp{1 - (2
@var{op} 3)}}. On the other hand, if the subtraction is reduced
before shifting @var{op}, the result is @w{@samp{(1 - 2) @var{op}
3}}. Clearly, then, the choice of shift or reduce should depend
Unfortunately, the name being declared is separated from the declaration
construct itself by a complicated syntactic structure---the ``declarator''.
-As a result, the part of Bison parser for C needs to be duplicated, with
+As a result, part of the Bison parser for C needs to be duplicated, with
all the nonterminal names changed: once for parsing a declaration in which
a typedef name can be redefined, and once for parsing a declaration in
which that can't be done. Here is a part of the duplication, with actions
@menu
* Bison Options:: All the options described in detail,
in alphabetical order by short options.
+* Environment Variables:: Variables which affect Bison execution.
* Option Cross Key:: Alphabetical list of long options.
* VMS Invocation:: Bison command syntax on VMS.
@end menu
-@node Bison Options, Option Cross Key, , Invocation
+@node Bison Options, Environment Variables, , Invocation
@section Bison Options
Bison supports both traditional single-letter options and mnemonic long
@end example
@end table
-@node Option Cross Key, VMS Invocation, Bison Options, Invocation
+@node Environment Variables, Option Cross Key, Bison Options, Invocation
+@section Environment Variables
+@cindex environment variables
+@cindex BISON_HAIRY
+@cindex BISON_SIMPLE
+
+Here is a list of environment variables which affect the way Bison
+runs.
+
+@table @samp
+@item BISON_SIMPLE
+@itemx BISON_HAIRY
+Much of the parser generated by Bison is copied verbatim from a file
+called @file{bison.simple}. If Bison cannot find that file, or if you
+would like to direct Bison to use a different copy, setting the
+environment variable @code{BISON_SIMPLE} to the path of the file will
+cause Bison to use that copy instead.
+
+When the @samp{%semantic_parser} delcaration is used, Bison copies from
+a file called @file{bison.hairy} instead. The location of this file can
+also be specified or overridden in a similar fashion, with the
+@code{BISON_HAIRY} environment variable.
+
+@end table
+
+@node Option Cross Key, VMS Invocation, Environment Variables, Invocation
@section Option Cross Key
Here is a list of options, alphabetized by long option, to help you find
tokens are parsed. @xref{Lexical Tie-ins}.
@item Literal string token
-A token which constists of two or more fixed characters.
+A token which consists of two or more fixed characters.
@xref{Symbols}.
@item Look-ahead token
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