X-Git-Url: https://git.saurik.com/bison.git/blobdiff_plain/1eb0b146594c8b4a8e7aa06e4fcf275739d0900f..4bb975e1ad59a39460fe6b16eec5c7830f904b6b:/NEWS diff --git a/NEWS b/NEWS index 72d73e13..57db6c2d 100644 --- a/NEWS +++ b/NEWS @@ -1,7 +1,153 @@ Bison News ---------- -* Changes in version ?.? (????-??-??): +* Changes in version 2.5 (????-??-??): + +** IELR(1) and Canonical LR(1) Support + + IELR(1) is a minimal LR(1) parser table generation algorithm. That + is, given any context-free grammar, IELR(1) generates parser tables + with the full language recognition power of canonical LR(1) but with + nearly the same number of parser states as LALR(1). This reduction in + parser states is often an order of magnitude. More importantly, + because canonical LR(1)'s extra parser states may contain duplicate + conflicts in the case of non-LR(1) grammars, the number of conflicts + for IELR(1) is often an order of magnitude less as well. This can + significantly reduce the complexity of developing of a grammar. + + Bison can now generate IELR(1) and canonical LR(1) parser tables in + place of its traditional LALR(1) parser tables, which remain the + default. You can specify the type of parser tables in the grammar + file with these directives: + + %define lr.type "LALR" + %define lr.type "IELR" + %define lr.type "canonical LR" + + The default reduction optimization in the parser tables can also be + adjusted using `%define lr.default-reductions'. See the documentation + for `%define lr.type' and `%define lr.default-reductions' in the + section `Bison Declaration Summary' in the Bison manual for the + details. + + These features are experimental. More user feedback will help to + stabilize them. + +** Multiple %define's for any variable is now an error not a warning. + +** %define can now be invoked via the command line. + + Each of these command-line options + + -D NAME[=VALUE] + --define=NAME[=VALUE] + + -F NAME[=VALUE] + --force-define=NAME[=VALUE] + + is equivalent to this grammar file declaration + + %define NAME ["VALUE"] + + except that the manner in which Bison processes multiple definitions + for the same NAME differs. Most importantly, -F and --force-define + quietly override %define, but -D and --define do not. For further + details, see the section "Bison Options" in the Bison manual. + +** %define variables renamed. + + The following %define variables + + api.push_pull + lr.keep_unreachable_states + + have been renamed to + + api.push-pull + lr.keep-unreachable-states + + The old names are now deprecated but will be maintained indefinitely + for backward compatibility. + +** Symbols names + + Consistently with directives (such as %error-verbose) and variables + (e.g. push-pull), symbol names may include dashes in any position, + similarly to periods and underscores. This is GNU extension over + POSIX Yacc whose use is reported by -Wyacc, and rejected in Yacc + mode (--yacc). + +** Temporary hack for adding a semicolon to the user action. + + Previously, Bison appended a semicolon to every user action for + reductions when the output language defaulted to C (specifically, when + neither %yacc, %language, %skeleton, or equivalent command-line + options were specified). This allowed actions such as + + exp: exp "+" exp { $$ = $1 + $3 }; + + instead of + + exp: exp "+" exp { $$ = $1 + $3; }; + + As a first step in removing this misfeature, Bison now issues a + warning when it appends a semicolon. Moreover, in cases where Bison + cannot easily determine whether a semicolon is needed (for example, an + action ending with a cpp directive or a braced compound initializer), + it no longer appends one. Thus, the C compiler might now complain + about a missing semicolon where it did not before. Future releases of + Bison will cease to append semicolons entirely. + +** Character literals not of length one. + + Previously, Bison quietly converted all character literals to length + one. For example, without warning, Bison interpreted the operators in + the following grammar to be the same token: + + exp: exp '++' + | exp '+' exp + ; + + Bison now warns when a character literal is not of length one. In + some future release, Bison will report an error instead. + +** Verbose error messages fixed for nonassociative tokens. + + When %error-verbose is specified, syntax error messages produced by + the generated parser include the unexpected token as well as a list of + expected tokens. Previously, this list erroneously included tokens + that would actually induce a syntax error because conflicts for them + were resolved with %nonassoc. Such tokens are now properly omitted + from the list. + +* Changes in version 2.4.2 (????-??-??): + +** Detection of GNU M4 1.4.6 or newer during configure is improved. + +** %code is now a permanent feature. + + A traditional Yacc prologue directive is written in the form: + + %{CODE%} + + To provide a more flexible alternative, Bison 2.3b introduced the + %code directive with the following forms for C/C++: + + %code {CODE} + %code requires {CODE} + %code provides {CODE} + %code top {CODE} + + These forms are now considered permanent features of Bison. See the + %code entries in the section "Bison Declaration Summary" in the Bison + manual for a summary of their functionality. See the section + "Prologue Alternatives" for a detailed discussion including the + advantages of %code over the traditional Yacc prologue directive. + + Bison's Java feature as a whole including its current usage of %code + is still considered experimental. + +* Changes in version 2.4.1 (2008-12-11): ** In the GLR defines file, unexpanded M4 macros in the yylval and yylloc declarations have been fixed. @@ -17,13 +163,12 @@ Bison News exp: exp "+" exp { $$ = $1 + $3; }; - This prevents the future support for languages that do not use `;' - as C/C++/Java do. Yet some grammars still depend on this `feature'. - Bison 2.4.1 restores the previous behavior in the case of C output - (specifically, when neither %language or %skeleton or equivalent - command-line options are used) to leave more time for grammars - depending on the old behavior to be adjusted. Future releases of - Bison will disable this feature. + Some grammars still depend on this `feature'. Bison 2.4.1 restores + the previous behavior in the case of C output (specifically, when + neither %language or %skeleton or equivalent command-line options + are used) to leave more time for grammars depending on the old + behavior to be adjusted. Future releases of Bison will disable this + feature. ** A few minor improvements to the Bison manual. @@ -1050,9 +1195,9 @@ End: ----- Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, -2004, 2005, 2006, 2007, 2008 Free Software Foundation, Inc. +2004, 2005, 2006, 2007, 2008, 2009 Free Software Foundation, Inc. -This file is part of Bison, the GNU Compiler Compiler. +This file is part of Bison, the GNU Parser Generator. 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