X-Git-Url: https://git.saurik.com/bison.git/blobdiff_plain/9e6e7ed2b275cba4dcc75fca6a8f0768285e4c6b..31984206a710101776d1db64009aff6c7962551c:/NEWS diff --git a/NEWS b/NEWS index 2e757516..96cfa7a7 100644 --- a/NEWS +++ b/NEWS @@ -1,7 +1,233 @@ Bison News ---------- -Changes in version 2.3+: +Changes in version 2.3a+ (????-??-??): + +* 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. + +* 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 -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 directives is now + deprecated: + + %file-prefix "parser" + %name-prefix "c_" + %output "parser.c" + +* The quotes around NAME that used to be required in the following directive + are now deprecated: + + %define NAME "VALUE" + +* 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'. + +* 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 $$ or $n in a semantic action. + + The default %destructor's and %printer's are experimental. More user + feedback will help to determine whether they should become permanent + features. + + See the section `Freeing Discarded Symbols' in the Bison manual for further + details. + +Changes in version 2.3a, 2006-09-13: + +* Instead of %union, you can define and use your own union type + YYSTYPE if your grammar contains at least one tag. + Your YYSTYPE need not be a macro; it can be a typedef. + This change is for compatibility with other Yacc implementations, + and is required by POSIX. + +* Locations columns and lines start at 1. + In accordance with the GNU Coding Standards and Emacs. + +* You may now declare per-type and default %destructor's and %printer's: + + For example: + + %union { char *string; } + %token STRING1 + %token STRING2 + %type string1 + %type string2 + %union { char character; } + %token CHR + %type chr + %destructor { free ($$); } %symbol-default + %destructor { free ($$); printf ("%d", @$.first_line); } STRING1 string1 + %destructor { } + + guarantees that, when the parser discards any user-defined symbol that has a + semantic type tag other than `', it passes its semantic value to + `free'. However, when the parser discards a `STRING1' or a `string1', it + 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 + 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. + +* Bison now provides a more flexible alternative to the traditional Yacc + prologue blocks: %before-header, %start-header, %end-header, and + %after-header. + + For example, the following declaration order in the grammar file reflects the + order in which Bison will output these code blocks. However, you are free to + declare these code blocks in your grammar file in whatever order is most + convenient for you: + + %before-header { + /* Bison treats this block like a pre-prologue block: it inserts it into + * the code file before the contents of the header file. It does *not* + * insert it into the header file. This is a good place to put + * #include's that you want at the top of your code file. A common + * example is `#include "system.h"'. */ + } + %start-header { + /* Bison inserts this block into both the header file and the code file. + * In both files, the point of insertion is before any Bison-generated + * token, semantic type, location type, and class definitions. This is a + * good place to define %union dependencies, for example. */ + } + %union { + /* Unlike the traditional Yacc prologue blocks, the output order for the + * new %*-header blocks is not affected by their declaration position + * relative to any %union in the grammar file. */ + } + %end-header { + /* Bison inserts this block into both the header file and the code file. + * In both files, the point of insertion is after the Bison-generated + * definitions. This is a good place to declare or define public + * functions or data structures that depend on the Bison-generated + * definitions. */ + } + %after-header { + /* Bison treats this block like a post-prologue block: it inserts it into + * the code file after the contents of the header file. It does *not* + * insert it into the header file. This is a good place to declare or + * define internal functions or data structures that depend on the + * Bison-generated definitions. */ + } + + 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 @@ -717,21 +943,19 @@ 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 .