X-Git-Url: https://git.saurik.com/bison.git/blobdiff_plain/12e3584054c16ab255672c07af0ffc7bb220e8bc..2c086d295967986a261ef6c2729b9edb62aac451:/NEWS diff --git a/NEWS b/NEWS index c3fe6d03..8a5fc93d 100644 --- a/NEWS +++ b/NEWS @@ -1,99 +1,212 @@ Bison News ---------- -Changes in version 2.3a+ (????-??-??): +Changes in version ?.? (????-??-??): + +* Java skeleton improvements: + + The constants for token names were moved to the Lexer interface. + Also, it is possible to add code to the parser's constructors using + "%code init" and "%define init_throws". + +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. + not VCG format. Like --graph, -g now also takes an optional FILE argument + and thus cannot be bundled with other short options. -* Bison now recognizes two separate kinds of default %destructor's and - %printer's: +* Java - 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. + 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. - 2. Place `' in a %destructor/%printer symbol list to define a default - %destructor/%printer for all grammar symbols without declared semantic - type tags. + See the new section `Java Parsers' in the Bison manual for details. - 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 current Java interface is experimental and may evolve. More user + feedback will help to stabilize it. - See the section `Freeing Discarded Symbols' in the Bison manual for further - details. +* %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: -* The Yacc prologue alternatives from Bison 2.3a have been rewritten as the - following directives: + %defines "parser.h" - 1. %code {CODE} +* 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". - 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: +* Unreachable State Removal - - `%{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. + 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: - 2. %requires {CODE} + 1. Removes unreachable states. - 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: + 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. - - `%{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. For any rule used only in such states, Bison now reports the rule as + "useless in parser due to conflicts". - 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: + This feature can be disabled with the following directive: - - `%end-header {CODE}', which only Bison 2.3a supported. + %define lr.keep_unreachable_states - 4. %code-top {CODE} + See the %define entry in the `Bison Declaration Summary' in the Bison manual + for further discussion. - Occasionally for C/C++ it is desirable to insert code near the top of - the parser code file. For example: +* Lookahead Set Correction in the `.output' Report - %code-top { - #define _GNU_SOURCE - #include - } + 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. - For Java, `%code-top {CODE}' is currently unused. Compare with: +* --report-file=FILE is a new option to override the default `.output' file + name. - - `%{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. +* The `=' that used to be required in the following directives is now + deprecated: - 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. + %file-prefix "parser" + %name-prefix "c_" + %output "parser.c" - Also see the new section `Prologue Alternatives' in the Bison manual. +* 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. Changes in version 2.3a, 2006-09-13: @@ -128,6 +241,10 @@ Changes in version 2.3a, 2006-09-13: 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 @@ -198,6 +315,9 @@ Changes in version 2.3a, 2006-09-13: 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. @@ -912,21 +1032,19 @@ End: ----- Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, -2004, 2005, 2006 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. 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 .