X-Git-Url: https://git.saurik.com/bison.git/blobdiff_plain/35fe08345edf43644a80a5987a50937c67e7c937..66f0441da3d12c9a68787ff24315cdbd513d14ad:/NEWS diff --git a/NEWS b/NEWS index d8e845cb..18e71b7d 100644 --- a/NEWS +++ b/NEWS @@ -3,9 +3,150 @@ 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" + +* 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 + 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 flag `--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. + Changes in version 2.3a, 2006-09-13: * Instead of %union, you can define and use your own union type @@ -39,6 +180,10 @@ 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 @@ -109,6 +254,9 @@ 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. @@ -823,21 +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 .