Bison test version 2.3b is now available. 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 "Bison News" below for further details. Here is the URL where you can download Bison 2.3b: ftp://alpha.gnu.org/gnu/bison/bison-2.3b.tar.gz Here are the MD5 and SHA512 checksums: f52b1fb9fce6d60d8a2e11fa5498fce0 bison-2.3b.tar.gz 72660b254d285d7b88388d7aee613c47e7e671338ccebcb3e208e2aad816f14d45b25e579f624de375031b77ac648705ffea3a1e4c4727b4bf3f1758bfcedd47 bison-2.3b.tar.gz To try this test version, please make sure you have at least GNU m4 1.4.6 <ftp://ftp.gnu.org/gnu/m4/m4-1.4.6.tar.gz> installed, and then execute the following shell commands or their equivalents: wget ftp://alpha.gnu.org/gnu/bison/bison-2.3b.tar.gz gunzip <bison-2.3b.tar.gz | tar xf - cd bison-2.3b ./configure make make check We particularly appreciate tests on unusual hosts. Please report bugs to <[EMAIL PROTECTED]>. Bison is a parser generator that is compatible with Yacc. Please see <http://www.gnu.org/software/bison/> for more info about Bison. Here is a list of user-visible changes in version 2.3b, compared to 2.3a: Bison News ---------- 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. This directive affects the skeleton used and 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. _______________________________________________ GNU Announcement mailing list <info-gnu@gnu.org> http://lists.gnu.org/mailman/listinfo/info-gnu
