Bison version 2.4 is now available. Relative to 2.3, this version contains many bug fixes and many exciting new features that need more user feedback. Some of the more notable features are:
1. XML or Graphviz DOT format for the LALR(1) automaton. 2. Push parsers. 3. Java-based parsers. 4. %code, a flexible alternative to traditional Yacc prologue blocks. 5. Default %destructor and %printer directives. See "NEWS" below for further details. Here are the compressed sources: ftp://ftp.gnu.org/gnu/bison/bison-2.4.tar.gz (1.9MB) ftp://ftp.gnu.org/gnu/bison/bison-2.4.tar.bz2 (1.5MB) Here are the GPG detached signatures[*]: ftp://ftp.gnu.org/gnu/bison/bison-2.4.tar.gz.sig ftp://ftp.gnu.org/gnu/bison/bison-2.4.tar.bz2.sig Here are the MD5 and SHA1 checksums: 2b9b088b46271c7fa902a7e85f503e1e bison-2.4.tar.gz f95cc7d7f5290157a23216391dec610d bison-2.4.tar.bz2 ecd488f9fd2487c695c558443ec7b698ff9b4d64 bison-2.4.tar.gz 32c959200e630d3185f24d661c8f12de67b38684 bison-2.4.tar.bz2 [*] You can use either of the above signature files to verify that the corresponding file (without the .sig suffix) is intact. First, be sure to download both the .sig file and the corresponding tarball. Then, run a command like this: gpg --verify bison-2.4.tar.gz.sig If that command fails because you don't have the required public key, then run this command to import it: gpg --keyserver keys.gnupg.net --recv-keys F125BDF3 and rerun the `gpg --verify' command. This release was bootstrapped with the following tools: Autoconf 2.62 Automake 1.10.1 Flex 2.5.35 Gnulib v0.0-1332-g2ec9ae2 NEWS Changes relative to test version 2.3b: * %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. Other changes relative to version 2.3: * 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". However, %language is experimental and its effect on generated file names will likely evolve. * 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 now provides %code, a more flexible alternative to the traditional Yacc prologue blocks. The %code directive takes an optional qualifier field, which identifies the purpose of the code and thus the location(s) where Bison should generate it. For example, the following forms are available in the case of C/C++: 1. `%code {CODE}' -- The default for the parser source code file. 2. `%code requires {CODE}' -- Dependencies of YYSTYPE and YYLTYPE. 3. `%code provides {CODE}' -- Other definitions for the parser header file. 4. `%code top {CODE}' -- Near the top of the parser source code file. 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. 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. * 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. * 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. To insert code at other locations, try the new %code directive mentioned above. * 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. _______________________________________________ GNU Announcement mailing list <info-gnu@gnu.org> http://lists.gnu.org/mailman/listinfo/info-gnu
