Changes in version 2.3a+ (????-??-??):
+* 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
+ "never reduced because of 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.
+
+* 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.
+
* The -g and --graph options now output graphs in Graphviz DOT format,
not VCG format.
+* An experimental directive %language specifies the language of the
+ generated parser, which can be C (the default) or C++. This
+ directive affects the skeleton used, and the names of the generated
+ files if the grammar file's name ends in ".y".
+
* The grammar file may now specify the name of the parser header file using
%defines. For example:
%defines "parser.h"
-* The `=' that used to be required in the following declarations is now
+* The `=' that used to be required in the following directives is now
deprecated:
%file-prefix "parser"
%name-prefix "c_"
%output "parser.c"
+* The quotes around NAME that used to be required in the following directive
+ are now deprecated:
+
+ %define NAME "VALUE"
+
+* 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
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.
-* The Yacc prologue alternatives from Bison 2.3a have been rewritten as the
- following directives:
-
- 1. %code {CODE}
-
- Other than semantic actions, this is probably the most common place you
- should write verbatim code for the parser implementation. For C/C++, it
- replaces the traditional Yacc prologue, `%{CODE%}', for most purposes.
- For Java, it inserts your CODE into the parser class. Compare with:
-
- - `%{CODE%}' appearing after the first `%union {CODE}' in a C/C++
- based grammar file. While Bison will continue to support `%{CODE%}'
- for backward compatibility, `%code {CODE}' is cleaner as its
- functionality does not depend on its position in the grammar file
- relative to any `%union {CODE}'. Specifically, `%code {CODE}'
- always inserts your CODE into the parser code file after the usual
- contents of the parser header file.
- - `%after-header {CODE}', which only Bison 2.3a supported.
-
- 2. %requires {CODE}
-
- This is the right place to write dependency code for externally exposed
- definitions required by Bison. For C/C++, such exposed definitions are
- those usually appearing in the parser header file. Thus, this is the
- right place to define types referenced in `%union {CODE}' directives,
- and it is the right place to override Bison's default YYSTYPE and
- YYLTYPE definitions. For Java, this is the right place to write import
- directives. Compare with:
-
- - `%{CODE%}' appearing before the first `%union {CODE}' in a C/C++
- based grammar file. Unlike `%{CODE%}', `%requires {CODE}' inserts
- your CODE both into the parser code file and into the parser header
- file since Bison's required definitions should depend on it in both
- places.
- - `%start-header {CODE}', which only Bison 2.3a supported.
-
- 3. %provides {CODE}
-
- This is the right place to write additional definitions you would like
- Bison to expose externally. For C/C++, this directive inserts your CODE
- both into the parser header file and into the parser code file after
- Bison's required definitions. For Java, it inserts your CODE into the
- parser java file after the parser class. Compare with:
-
- - `%end-header {CODE}', which only Bison 2.3a supported.
-
- 4. %code-top {CODE}
-
- Occasionally for C/C++ it is desirable to insert code near the top of
- the parser code file. For example:
-
- %code-top {
- #define _GNU_SOURCE
- #include <stdio.h>
- }
-
- For Java, `%code-top {CODE}' is currently unused. Compare with:
-
- - `%{CODE%}' appearing before the first `%union {CODE}' in a C/C++
- based grammar file. `%code-top {CODE}' is cleaner as its
- functionality does not depend on its position in the grammar file
- relative to any `%union {CODE}'.
- - `%before-header {CODE}', which only Bison 2.3a supported.
-
- If you have multiple occurrences of any one of the above four directives,
- Bison will concatenate the contents in the order they appear in the grammar
- file.
-
- Also see the new section `Prologue Alternatives' in the Bison manual.
-
Changes in version 2.3a, 2006-09-13:
* Instead of %union, you can define and use your own union type
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
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.
-----
Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003,
-2004, 2005, 2006 Free Software Foundation, Inc.
+2004, 2005, 2006, 2007 Free Software Foundation, Inc.
This file is part of Bison, the GNU Compiler Compiler.
-Bison is free software; you can redistribute it and/or modify
+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, or (at your option)
-any later version.
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
-Bison is distributed in the hope that it will be useful,
+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 autoconf; see the file COPYING. If not, write to
-the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
-Boston, MA 02110-1301, USA.
+along with this program. If not, see <http://www.gnu.org/licenses/>.
projects / bison.git / blobdiff