X-Git-Url: https://git.saurik.com/bison.git/blobdiff_plain/8589431355773d9d34105d644ba0ec2d944853e5..66f0441da3d12c9a68787ff24315cdbd513d14ad:/NEWS diff --git a/NEWS b/NEWS index 31a44a0c..18e71b7d 100644 --- a/NEWS +++ b/NEWS @@ -3,21 +3,105 @@ Bison News Changes in version 2.3a+ (????-??-??): +* 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 -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 +* 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 + "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. + +* 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. + +* 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 @@ -38,7 +122,9 @@ Changes in version 2.3a+ (????-??-??): To enable these warnings, specify the flag `--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 @@ -61,76 +147,6 @@ Changes in version 2.3a+ (????-??-??): 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. It replaces - the traditional Yacc prologue, `%{CODE%}', for most purposes. Compare - with: - - - `%{CODE%}' appearing after the first `%union {CODE}' in a 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. 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. Compare with: - - - `%{CODE%}' appearing before the first `%union {CODE}' in a 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. That is, this directive inserts your CODE - both into the parser header file and into the parser code file after - Bison's required definitions. Compare with: - - - `%end-header {CODE}', which only Bison 2.3a supported. - - 4. %code-top {CODE} - - Occasionally it is desirable to insert code near the top of the parser - code file. For example: - - %code-top { - #define _GNU_SOURCE - #include - } - - Compare with: - - - `%{CODE%}' appearing before the first `%union {CODE}' in a 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. - - The prologue alternatives are experimental. More user feedback will help to - determine whether they should become permanent features. - - 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 @@ -955,21 +971,19 @@ End: ----- 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 .