Bison News
----------
-Changes in version 2.3a+ (????-??-??):
+Changes in version ?.? (????-??-??):
-* Previously, Bison sometimes generated parser tables with states that were
- unreachable due to conflicts in predecessor states. Bison now:
+*
+
+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.
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".
+ "useless in parser due to conflicts".
-* The -g and --graph options now output graphs in Graphviz DOT format,
- not VCG format.
+ This feature can be disabled with the following directive:
-* 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".
+ %define lr.keep_unreachable_states
-* The grammar file may now specify the name of the parser header file using
- %defines. For example:
+ See the %define entry in the `Bison Declaration Summary' in the Bison manual
+ for further discussion.
- %defines "parser.h"
+* 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:
%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"
+* An Alternative to `%{...%}' -- `%code QUALIFIER {CODE}'
-* Bison 2.3a provided a new set of directives as a more flexible alternative to
+ 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
3. `%code provides {CODE}' replaces `%end-header {CODE}'
4. `%code top {CODE}' replaces `%before-header {CODE}'
- See the %code entries in `Appendix A Bison Symbols' in the Bison manual for a
- summary of the new functionality. See the new section `Prologue
+ 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.
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 flag `--warnings=midrule-values' or
+ To enable these warnings, specify the option `--warnings=midrule-values' or
`-W', which is a synonym for `--warnings=all'.
-* Bison now recognizes two separate kinds of default %destructor's and
+* 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
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
-----
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-2004, 2005, 2006, 2007 Free Software Foundation, Inc.
+2004, 2005, 2006, 2007, 2008 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.
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+along with this program. If not, see <http://www.gnu.org/licenses/>.
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