* Noteworthy changes in release 2.7 (2012-12-12) [stable]
** Bug fixes
Warnings about uninitialized yylloc in yyparse have been fixed.
Restored C90 compliance (yet no report was ever made).
** Diagnostics are improved
*** Changes in the format of error messages
This used to be the format of many error reports:
input.y:2.7-12: %type redeclaration for exp
input.y:1.7-12: previous declaration
It is now:
input.y:2.7-12: error: %type redeclaration for exp
input.y:1.7-12: previous declaration
*** New format for error reports: carets
Caret errors have been added to Bison:
input.y:2.7-12: error: %type redeclaration for exp
%type <sval> exp
^^^^^^
input.y:1.7-12: previous declaration
%type <ival> exp
^^^^^^
or
input.y:3.20-23: error: ambiguous reference: '$exp'
exp: exp '+' exp { $exp = $1 + $3; };
^^^^
input.y:3.1-3: refers to: $exp at $$
exp: exp '+' exp { $exp = $1 + $3; };
^^^
input.y:3.6-8: refers to: $exp at $1
exp: exp '+' exp { $exp = $1 + $3; };
^^^
input.y:3.14-16: refers to: $exp at $3
exp: exp '+' exp { $exp = $1 + $3; };
^^^
The default behaviour for now is still not to display these unless
explictly asked with -fcaret (or -fall). However, in a later release, it
will be made the default behavior (but may still be deactivated with
-fno-caret).
** New value for %define variable: api.pure full
The %define variable api.pure requests a pure (reentrant) parser. However,
for historical reasons, using it in a location-tracking Yacc parser
resulted in a yyerror function that did not take a location as a
parameter. With this new value, the user may request a better pure parser,
where yyerror does take a location as a parameter (in location-tracking
parsers).
The use of "%define api.pure true" is deprecated in favor of this new
"%define api.pure full".
** New %define variable: api.location.type (glr.cc, lalr1.cc, lalr1.java)
The %define variable api.location.type defines the name of the type to use
for locations. When defined, Bison no longer generates the position.hh
and location.hh files, nor does the parser will include them: the user is
then responsible to define her type.
This can be used in programs with several parsers to factor their location
and position files: let one of them generate them, and the others just use
them.
This feature was actually introduced, but not documented, in Bison 2.5,
under the name "location_type" (which is maintained for backward
compatibility).
For consistency, lalr1.java's %define variables location_type and
position_type are deprecated in favor of api.location.type and
api.position.type.
** Exception safety (lalr1.cc)
The parse function now catches exceptions, uses the %destructors to
release memory (the lookahead symbol and the symbols pushed on the stack)
before re-throwing the exception.
This feature is somewhat experimental. User feedback would be
appreciated.
** Graph improvements in DOT and XSLT
The graphical presentation of the states is more readable: their shape is
now rectangular, the state number is clearly displayed, and the items are
numbered and left-justified.
The reductions are now explicitly represented as transitions to other
diamond shaped nodes.
These changes are present in both --graph output and xml2dot.xsl XSLT
processing, with minor (documented) differences.
** %language is no longer an experimental feature.
The introduction of this feature, in 2.4, was four years ago. The
--language option and the %language directive are no longer experimental.
** Documentation
The sections about shift/reduce and reduce/reduce conflicts resolution
have been fixed and extended.
Although introduced more than four years ago, XML and Graphviz reports
were not properly documented.
The translation of mid-rule actions is now described.
* Noteworthy changes in release 2.5.1 (2012-06-05) [stable]
** Future changes:
The next major release will drop support for generating parsers in K&R C.
** yacc.c: YYBACKUP works as expected.
** glr.c improvements:
*** Location support is eliminated when not requested:
GLR parsers used to include location-related code even when locations were
not requested, and therefore not even usable.
*** __attribute__ is preserved:
__attribute__ is no longer disabled when __STRICT_ANSI__ is defined (i.e.,
when -std is passed to GCC).
** lalr1.java: several fixes:
The Java parser no longer throws ArrayIndexOutOfBoundsException if the
first token leads to a syntax error. Some minor clean ups.
** Changes for C++:
*** C++11 compatibility:
C and C++ parsers use "nullptr" instead of "0" when __cplusplus is 201103L
or higher.
*** Header guards
The header files such as "parser.hh", "location.hh", etc. used a constant
name for preprocessor guards, for instance:
#ifndef BISON_LOCATION_HH
# define BISON_LOCATION_HH
...
#endif // !BISON_LOCATION_HH
The inclusion guard is now computed from "PREFIX/FILE-NAME", where lower
case characters are converted to upper case, and series of
non-alphanumerical characters are converted to an underscore.
With "bison -o lang++/parser.cc", "location.hh" would now include:
#ifndef YY_LANG_LOCATION_HH
# define YY_LANG_LOCATION_HH
...
#endif // !YY_LANG_LOCATION_HH
*** C++ locations:
The position and location constructors (and their initialize methods)
accept new arguments for line and column. Several issues in the
documentation were fixed.
** liby is no longer asking for "rpl_fprintf" on some platforms.
** Changes in the manual:
*** %printer is documented
The "%printer" directive, supported since at least Bison 1.50, is finally
documented. The "mfcalc" example is extended to demonstrate it.
For consistency with the C skeletons, the C++ parsers now also support
"yyoutput" (as an alias to "debug_stream ()").
*** Several improvements have been made:
The layout for grammar excerpts was changed to a more compact scheme.
Named references are motivated. The description of the automaton
description file (*.output) is updated to the current format. Incorrect
index entries were fixed. Some other errors were fixed.
** Building bison:
*** Conflicting prototypes with recent/modified Flex.
Fixed build problems with the current, unreleased, version of Flex, and
some modified versions of 2.5.35, which have modified function prototypes.
*** Warnings during the build procedure have been eliminated.
*** Several portability problems in the test suite have been fixed:
This includes warnings with some compilers, unexpected behavior of tools
such as diff, warning messages from the test suite itself, etc.
*** The install-pdf target work properly:
Running "make install-pdf" (or -dvi, -html, -info, and -ps) no longer
halts in the middle of its course.
* Changes in version 2.4.3 (2010-08-05):
** Bison now obeys -Werror and --warnings=error for warnings about
grammar rules that are useless in the parser due to conflicts.
** Problems with spawning M4 on at least FreeBSD 8 and FreeBSD 9 have
been fixed.
** Failures in the test suite for GCC 4.5 have been fixed.
** Failures in the test suite for some versions of Sun Studio C++ have
been fixed.
** Contrary to Bison 2.4.2's NEWS entry, it has been decided that
warnings about undefined %prec identifiers will not be converted to
errors in Bison 2.5. They will remain warnings, which should be
sufficient for POSIX while avoiding backward compatibility issues.
** Minor documentation fixes.
Changes in version 2.4 (2008-11-02):
* %language is an experimental feature.
We first introduced this feature in test release 2.3b as a cleaner
alternative to %skeleton. Since then, we have discussed the possibility of
modifying its effect on Bison's output file names. Thus, in this release,
we consider %language to be an experimental feature that will likely evolve
in future releases.
* Forward compatibility with GNU M4 has been improved.
* Several bugs in the C++ skeleton and the experimental Java skeleton have been
fixed.
Changes in version 2.3b (2008-05-27):
* The quotes around NAME that used to be required in the following directive
are now deprecated:
%define NAME "VALUE"
* The directive `%pure-parser' is now deprecated in favor of:
%define api.pure
which has the same effect except that Bison is more careful to warn about
unreasonable usage in the latter case.
* Push Parsing
Bison can now generate an LALR(1) parser in C with a push interface. That
is, instead of invoking `yyparse', which pulls tokens from `yylex', you can
push one token at a time to the parser using `yypush_parse', which will
return to the caller after processing each token. By default, the push
interface is disabled. Either of the following directives will enable it:
%define api.push_pull "push" // Just push; does not require yylex.
%define api.push_pull "both" // Push and pull; requires yylex.
See the new section `A Push Parser' in the Bison manual for details.
The current push parsing interface is experimental and may evolve. More user
feedback will help to stabilize it.
* The -g and --graph options now output graphs in Graphviz DOT format,
not VCG format. Like --graph, -g now also takes an optional FILE argument
and thus cannot be bundled with other short options.
* Java
Bison can now generate an LALR(1) parser in Java. The skeleton is
`data/lalr1.java'. Consider using the new %language directive instead of
%skeleton to select it.
See the new section `Java Parsers' in the Bison manual for details.
The current Java interface is experimental and may evolve. More user
feedback will help to stabilize it.
* %language
This new directive specifies the programming language of the generated
parser, which can be C (the default), C++, or Java. Besides the skeleton
that Bison uses, the directive affects the names of the generated files if
the grammar file's name ends in ".y".
* XML Automaton Report
Bison can now generate an XML report of the LALR(1) automaton using the new
`--xml' option. The current XML schema is experimental and may evolve. More
user feedback will help to stabilize it.
* The grammar file may now specify the name of the parser header file using
%defines. For example:
%defines "parser.h"
* When reporting useless rules, useless nonterminals, and unused terminals,
Bison now employs the terms "useless in grammar" instead of "useless",
"useless in parser" instead of "never reduced", and "unused in grammar"
instead of "unused".
* Unreachable State Removal
Previously, Bison sometimes generated parser tables containing unreachable
states. A state can become unreachable during conflict resolution if Bison
disables a shift action leading to it from a predecessor state. Bison now:
1. Removes unreachable states.
2. Does not report any conflicts that appeared in unreachable states.
WARNING: As a result, you may need to update %expect and %expect-rr
directives in existing grammar files.
3. For any rule used only in such states, Bison now reports the rule as
"useless in parser due to conflicts".
This feature can be disabled with the following directive:
%define lr.keep_unreachable_states
See the %define entry in the `Bison Declaration Summary' in the Bison manual
for further discussion.
* Lookahead Set Correction in the `.output' Report
When instructed to generate a `.output' file including lookahead sets
(using `--report=lookahead', for example), Bison now prints each reduction's
lookahead set only next to the associated state's one item that (1) is
associated with the same rule as the reduction and (2) has its dot at the end
of its RHS. Previously, Bison also erroneously printed the lookahead set
next to all of the state's other items associated with the same rule. This
bug affected only the `.output' file and not the generated parser source
code.
* --report-file=FILE is a new option to override the default `.output' file
name.
* The `=' that used to be required in the following directives is now
deprecated:
%file-prefix "parser"
%name-prefix "c_"
%output "parser.c"
* An Alternative to `%{...%}' -- `%code QUALIFIER {CODE}'
Bison 2.3a provided a new set of directives as a more flexible alternative to
the traditional Yacc prologue blocks. Those have now been consolidated into
a single %code directive with an optional qualifier field, which identifies
the purpose of the code and thus the location(s) where Bison should generate
it:
1. `%code {CODE}' replaces `%after-header {CODE}'
2. `%code requires {CODE}' replaces `%start-header {CODE}'
3. `%code provides {CODE}' replaces `%end-header {CODE}'
4. `%code top {CODE}' replaces `%before-header {CODE}'
See the %code entries in section `Bison Declaration Summary' in the Bison
manual for a summary of the new functionality. See the new section `Prologue
Alternatives' for a detailed discussion including the advantages of %code
over the traditional Yacc prologues.
The prologue alternatives are experimental. More user feedback will help to
determine whether they should become permanent features.
* Revised warning: unset or unused mid-rule values
Since Bison 2.2, Bison has warned about mid-rule values that are set but not
used within any of the actions of the parent rule. For example, Bison warns
about unused $2 in:
exp: '1' { $$ = 1; } '+' exp { $$ = $1 + $4; };
Now, Bison also warns about mid-rule values that are used but not set. For
example, Bison warns about unset $$ in the mid-rule action in:
exp: '1' { $1 = 1; } '+' exp { $$ = $2 + $4; };
However, Bison now disables both of these warnings by default since they
sometimes prove to be false alarms in existing grammars employing the Yacc
constructs $0 or $-N (where N is some positive integer).
To enable these warnings, specify the option `--warnings=midrule-values' or
`-W', which is a synonym for `--warnings=all'.
* Default %destructor or %printer with `<*>' or `<>'
Bison now recognizes two separate kinds of default %destructor's and
%printer's:
1. Place `<*>' in a %destructor/%printer symbol list to define a default
%destructor/%printer for all grammar symbols for which you have formally
declared semantic type tags.
2. Place `<>' in a %destructor/%printer symbol list to define a default
%destructor/%printer for all grammar symbols without declared semantic
type tags.
Bison no longer supports the `%symbol-default' notation from Bison 2.3a.
`<*>' and `<>' combined achieve the same effect with one exception: Bison no
longer applies any %destructor to a mid-rule value if that mid-rule value is
not actually ever referenced using either $$ or $n in a semantic action.
The default %destructor's and %printer's are experimental. More user
feedback will help to determine whether they should become permanent
features.
See the section `Freeing Discarded Symbols' in the Bison manual for further
details.
* %left, %right, and %nonassoc can now declare token numbers. This is required
by POSIX. However, see the end of section `Operator Precedence' in the Bison
manual for a caveat concerning the treatment of literal strings.
* The nonfunctional --no-parser, -n, and %no-parser options have been
completely removed from Bison.
Changes in version 2.3a, 2006-09-13:
* Instead of %union, you can define and use your own union type
YYSTYPE if your grammar contains at least one <type> tag.
Your YYSTYPE need not be a macro; it can be a typedef.
This change is for compatibility with other Yacc implementations,
and is required by POSIX.
* Locations columns and lines start at 1.
In accordance with the GNU Coding Standards and Emacs.
* You may now declare per-type and default %destructor's and %printer's:
For example:
%union { char *string; }
%token <string> STRING1
%token <string> STRING2
%type <string> string1
%type <string> string2
%union { char character; }
%token <character> CHR
%type <character> chr
%destructor { free ($$); } %symbol-default
%destructor { free ($$); printf ("%d", @$.first_line); } STRING1 string1
%destructor { } <character>
guarantees that, when the parser discards any user-defined symbol that has a
semantic type tag other than `<character>', it passes its semantic value to
`free'. However, when the parser discards a `STRING1' or a `string1', it
also prints its line number to `stdout'. It performs only the second
`%destructor' in this case, so it invokes `free' only once.
[Although we failed to mention this here in the 2.3a release, the default
%destructor's and %printer's were experimental, and they were rewritten in
future versions.]
* Except for LALR(1) parsers in C with POSIX Yacc emulation enabled (with `-y',
`--yacc', or `%yacc'), Bison no longer generates #define statements for
associating token numbers with token names. Removing the #define statements
helps to sanitize the global namespace during preprocessing, but POSIX Yacc
requires them. Bison still generates an enum for token names in all cases.
* Handling of traditional Yacc prologue blocks is now more consistent but
potentially incompatible with previous releases of Bison.
As before, you declare prologue blocks in your grammar file with the
`%{ ... %}' syntax. To generate the pre-prologue, Bison concatenates all
prologue blocks that you've declared before the first %union. To generate
the post-prologue, Bison concatenates all prologue blocks that you've
declared after the first %union.
Previous releases of Bison inserted the pre-prologue into both the header
file and the code file in all cases except for LALR(1) parsers in C. In the
latter case, Bison inserted it only into the code file. For parsers in C++,
the point of insertion was before any token definitions (which associate
token numbers with names). For parsers in C, the point of insertion was
after the token definitions.
Now, Bison never inserts the pre-prologue into the header file. In the code
file, it always inserts it before the token definitions.
* Bison now provides a more flexible alternative to the traditional Yacc
prologue blocks: %before-header, %start-header, %end-header, and
%after-header.
For example, the following declaration order in the grammar file reflects the
order in which Bison will output these code blocks. However, you are free to
declare these code blocks in your grammar file in whatever order is most
convenient for you:
%before-header {
/* Bison treats this block like a pre-prologue block: it inserts it into
* the code file before the contents of the header file. It does *not*
* insert it into the header file. This is a good place to put
* #include's that you want at the top of your code file. A common
* example is `#include "system.h"'. */
}
%start-header {
/* Bison inserts this block into both the header file and the code file.
* In both files, the point of insertion is before any Bison-generated
* token, semantic type, location type, and class definitions. This is a
* good place to define %union dependencies, for example. */
}
%union {
/* Unlike the traditional Yacc prologue blocks, the output order for the
* new %*-header blocks is not affected by their declaration position
* relative to any %union in the grammar file. */
}
%end-header {
/* Bison inserts this block into both the header file and the code file.
* In both files, the point of insertion is after the Bison-generated
* definitions. This is a good place to declare or define public
* functions or data structures that depend on the Bison-generated
* definitions. */
}
%after-header {
/* Bison treats this block like a post-prologue block: it inserts it into
* the code file after the contents of the header file. It does *not*
* insert it into the header file. This is a good place to declare or
* define internal functions or data structures that depend on the
* Bison-generated definitions. */
}
If you have multiple occurrences of any one of the above declarations, Bison
will concatenate the contents in declaration order.
[Although we failed to mention this here in the 2.3a release, the prologue
alternatives were experimental, and they were rewritten in future versions.]
* The option `--report=look-ahead' has been changed to `--report=lookahead'.
The old spelling still works, but is not documented and may be removed
in a future release.
Changes in version 2.0, 2004-12-25:
* Possibly-incompatible changes
- Bison-generated parsers no longer default to using the alloca function
(when available) to extend the parser stack, due to widespread
problems in unchecked stack-overflow detection. You can "#define
YYSTACK_USE_ALLOCA 1" to require the use of alloca, but please read
the manual to determine safe values for YYMAXDEPTH in that case.
- Error token location.
During error recovery, the location of the syntax error is updated
to cover the whole sequence covered by the error token: it includes
the shifted symbols thrown away during the first part of the error
recovery, and the lookahead rejected during the second part.
- Semicolon changes:
. Stray semicolons are no longer allowed at the start of a grammar.
. Semicolons are now required after in-grammar declarations.
- Unescaped newlines are no longer allowed in character constants or
string literals. They were never portable, and GCC 3.4.0 has
dropped support for them. Better diagnostics are now generated if
forget a closing quote.
- NUL bytes are no longer allowed in Bison string literals, unfortunately.
* New features
- GLR grammars now support locations.
- New directive: %initial-action.
This directive allows the user to run arbitrary code (including
initializing @$) from yyparse before parsing starts.
- A new directive "%expect-rr N" specifies the expected number of
reduce/reduce conflicts in GLR parsers.
- %token numbers can now be hexadecimal integers, e.g., `%token FOO 0x12d'.
This is a GNU extension.
- The option `--report=lookahead' was changed to `--report=look-ahead'.
The old spelling still works, but is not documented and will be
removed.
- Experimental %destructor support has been added to lalr1.cc.
- New configure option --disable-yacc, to disable installation of the
yacc command and -ly library introduced in 1.875 for POSIX conformance.
* Bug fixes
- For now, %expect-count violations are now just warnings, not errors.
This is for compatibility with Bison 1.75 and earlier (when there are
reduce/reduce conflicts) and with Bison 1.30 and earlier (when there
are too many or too few shift/reduce conflicts). However, in future
versions of Bison we plan to improve the %expect machinery so that
these violations will become errors again.
- Within Bison itself, numbers (e.g., goto numbers) are no longer
arbitrarily limited to 16-bit counts.
- Semicolons are now allowed before "|" in grammar rules, as POSIX requires.
Differences to the plain GNU version in the packages collection:
* We do not install the shell wrapper "yacc" (it is supplied because
POSIX requires it and we already have a yacc command).
Changes since 1.75:
* Numerous bug fixes and improvements including:
+ Compatibility (with 1.35 and Solaris yacc) changes;
+ Fixes for GCC 3.2.1;
+ Use Yacc style of conflict reports;
+ Fix bug where error locations were not being recorded correctly;
+ Fix bad interaction with flex 2.5.23.
Please see the ChangeLog file supplied with the bison source code
for more details.
* Fix Yacc output file names
* Portability fixes
* Italian, Dutch, Swedish, Russian translation
* Many Bug Fixes
* Use of alloca in parsers
* When the generated parser lacks debugging code, YYDEBUG is now 0
(as POSIX requires) instead of being undefined.
* User Actions
Bison has always permitted actions such as { $$ = $1 }: it adds the
ending semicolon. Now if in Yacc compatibility mode, the semicolon
is no longer output: one has to write { $$ = $1; }.
* Better C++ compliance
The output parsers try to respect C++ namespaces.
* Reduced Grammars
Fixed bugs when reporting useless nonterminals.
* 64 bit hosts
The parsers work properly on 64 bit hosts.
* Error messages
Some calls to strerror resulted in scrambled or missing error messages.
* The verbose report includes the rule line numbers.
* Rule line numbers are fixed in traces.
* Parse errors
Verbose parse error messages from the parsers are better looking.
* Fixed parser memory leaks.
When the generated parser was using malloc to extend its stacks, the
previous allocations were not freed.
* Fixed verbose output file.
Some newlines were missing.
Some conflicts in state descriptions were missing.
* Fixed conflict report.
Option -v was needed to get the result.
* Fixed incorrect processing of some invalid input.
* Fixed CPP guards: 9foo.h uses BISON_9FOO_H instead of 9FOO_H.
* %token MY_EOF 0 is supported.
Before, MY_EOF was silently renumbered as 257.
* doc/refcard.tex is updated.
* %output, %file-prefix, %name-prefix.
* --output
* `--defines' and `--graph' have now an optionnal argument which is the
output file name. `-d' and `-g' do not change, they do not take any
argument.
* Portability fixes.
* The output file does not define const, as this caused problems when used
with common autoconfiguration schemes. If you still use ancient compilers
that lack const, compile with the equivalent of the C compiler option
`-Dconst='. autoconf's AC_C_CONST macro provides one way to do this.
* Added `-g' and `--graph'.
* The input and the output files has automatically a similar extension.
* NLS support updated; should hopefully be less troublesome.
* Added the old Bison reference card.
* Added `--locations' and `%locations'.
* Added `-S' and `--skeleton'.
* `%raw', `-r', `--raw' is disabled.
* Special characters are escaped when output. This solves the problems
of the #line lines with path names including backslashes.
* New directives.
* @$ Automatic location tracking.
the test here depends on HAVE_LIBINTL_H, which is not set
by configure
This change makes bison use the internationalized catalogs even for
messages in getopt.c. Bug report submitted to bug-bison@gnu.org.
Changes include:
* Should compile better now with K&R compilers.
* Added NLS.
* Fixed a problem with escaping the double quote character.
* There is now a FAQ.
