X-Git-Url: https://git.saurik.com/bison.git/blobdiff_plain/d07932ef3d14aae86149b8ff65258f520ffa3998..d67e37a74bc91e2fe254e5b7a28c62537a20e206:/NEWS diff --git a/NEWS b/NEWS index d67e3f03..9933922c 100644 --- a/NEWS +++ b/NEWS @@ -1,7 +1,278 @@ Bison News ---------- -* Changes in version ?.? (????-??-??): +* Changes in version 2.5 (????-??-??): + +** Named References Support + + Historically, Yacc and Bison have supported positional references + ($n, $$) to allow access to symbol values from inside of semantic + actions code. + + Starting from this version, Bison can also accept named references. + When no ambiguity is possible, original symbol names may be used + as named references: + + if_stmt : 'if' cond_expr 'then' then_stmt ';' + { $if_stmt = mk_if_stmt($cond_expr, $then_stmt); } + + In the more common case, explicit names may be declared: + + stmt[res] : 'if' expr[cond] 'then' stmt[then] 'else' stmt[else] ';' + { $res = mk_if_stmt($cond, $then, $else); } + + Location information is also accessible using @name syntax. When + accessing symbol names containing dots or dashes, explicit bracketing + ($[sym.1]) must be used. + + These features are experimental in this version. More user feedback + will help to stabilize them. + +** 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. + +** Unrecognized %code qualifiers are now an error not a warning. + +** %define improvements. + +*** Unrecognized variables are now an error not a warning. + +*** Multiple invocations for any variable is now an error not a warning. + +*** 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. + +*** 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. + +*** Values no longer need to be quoted in grammar file. + + If a %define value is an identifier, it no longer needs to be placed + within quotations marks. For example, + + %define api.push-pull "push" + + can be rewritten as + + %define api.push-pull push + +** Symbol 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). + +** YYFAIL now produces warnings and Java parsers no longer implement it. + + YYFAIL has existed for many years as an undocumented feature of + deterministic parsers in C generated by Bison. More recently, it was + a documented feature of Bison's experimental Java parsers. As + promised in Bison 2.4.2's NEWS entry, any appearance of YYFAIL in a + semantic action now produces a deprecation warning, and Java parsers + no longer implement YYFAIL at all. For further details, including a + discussion of how to suppress C preprocessor warnings about YYFAIL + being unused, see the Bison 2.4.2 NEWS entry. + +** `%prec IDENTIFIER' requires IDENTIFIER to be defined separately. + + As promised in Bison 2.4.2's NEWS entry, it is now an error if a token + that appears after a %prec directive is not defined by %token, %left, + %right, or %nonassoc. This is required by POSIX. + +** 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. + +** Destructor calls fixed for lookaheads altered in semantic actions. + + Previously for deterministic parsers in C, if a user semantic action + altered yychar, the parser in some cases used the old yychar value to + determine which destructor to call for the lookahead upon a syntax + error or upon parser return. This bug has been fixed. + +* Changes in version 2.4.2 (????-??-??): + +** `%prec IDENTIFIER' requires IDENTIFIER to be defined separately. + + POSIX specifies that an error be reported for any identifier that does + not appear on the LHS of a grammar rule and that is not defined by + %token, %left, %right, or %nonassoc. Bison 2.3b and later lost this + error report for the case when an identifier appears only after a + %prec directive. It is now restored. However, for backward + compatibility with recent Bison releases, it is only a warning for + now. In Bison 2.5 and later, it will return to being an error. + +** Detection of GNU M4 1.4.6 or newer during configure is improved. + +** Warnings from gcc's -Wundef option about undefined YYENABLE_NLS, + YYLTYPE_IS_TRIVIAL, and __STRICT_ANSI__ in C/C++ parsers are now + avoided. + +** %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. + +** YYFAIL is deprecated and will eventually be removed. + + YYFAIL has existed for many years as an undocumented feature of + deterministic parsers in C generated by Bison. Previously, it was + documented for Bison's experimental Java parsers. YYFAIL is no longer + documented for Java parsers and is formally deprecated in both cases. + Users are strongly encouraged to migrate to YYERROR, which is + specified by POSIX. + + Like YYERROR, you can invoke YYFAIL from a semantic action in order to + induce a syntax error. The most obvious difference from YYERROR is + that YYFAIL will automatically invoke yyerror to report the syntax + error so that you don't have to. However, there are several other + subtle differences between YYERROR and YYFAIL, and YYFAIL suffers from + inherent flaws when %error-verbose or `#define YYERROR_VERBOSE' is + used. For a more detailed discussion, see: + + http://lists.gnu.org/archive/html/bison-patches/2009-12/msg00024.html + + The upcoming Bison 2.5 will remove YYFAIL from Java parsers, but + deterministic parsers in C will continue to implement it. However, + because YYFAIL is already flawed, it seems futile to try to make new + Bison features compatible with it. Thus, during parser generation, + Bison 2.5 will produce a warning whenever it discovers YYFAIL in a + rule action. In a later release, YYFAIL will be disabled for + %error-verbose and `#define YYERROR_VERBOSE'. Eventually, YYFAIL will + be removed altogether. + + There exists at least one case where Bison 2.5's YYFAIL warning will + be a false positive. Some projects add phony uses of YYFAIL and other + Bison-defined macros for the sole purpose of suppressing C + preprocessor warnings (from GCC cpp's -Wunused-macros, for example). + To avoid Bison's future warning, such YYFAIL uses can be moved to the + epilogue (that is, after the second `%%') in the Bison input file. In + this release (2.4.2), Bison already generates its own code to suppress + C preprocessor warnings for YYFAIL, so projects can remove their own + phony uses of YYFAIL if compatibility with Bison releases prior to + 2.4.2 is not necessary. + +** Internationalization. + + Fix a regression introduced in Bison 2.4: Under some circumstances, + message translations were not installed although supported by the + host system. + +* 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. @@ -1048,10 +1319,9 @@ End: ----- -Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, -2004, 2005, 2006, 2007, 2008 Free Software Foundation, Inc. +Copyright (C) 1995-2010 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