X-Git-Url: https://git.saurik.com/bison.git/blobdiff_plain/f1b238df182101b9c9d3808bf2d5e2333e27c50f..86408959da5eddf26493eef64f049034a7849e2a:/NEWS?ds=sidebyside diff --git a/NEWS b/NEWS index 99814004..64a25704 100644 --- a/NEWS +++ b/NEWS @@ -62,6 +62,14 @@ Bison News * Changes in version 2.5 (????-??-??): +** Grammar symbol names can now contain non-initial dashes: + + Consistently with directives (such as %error-verbose) and with + %define variables (e.g. push-pull), grammar symbol names may contain + dashes in any position except the beginning. This is a GNU + extension over POSIX Yacc. Thus, use of this extension is reported + by -Wyacc and rejected in Yacc mode (--yacc). + ** Named references: Historically, Yacc and Bison have supported positional references @@ -108,27 +116,27 @@ Bison News %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. + The default-reduction optimization in the parser tables can also be + adjusted using `%define lr.default-reductions'. For details on both + of these features, see the new section `Tuning LR' in the Bison + manual. These features are experimental. More user feedback will help to stabilize them. -** LAC (lookahead correction) for syntax error handling: +** LAC (Lookahead Correction) for syntax error handling: Canonical LR, IELR, and LALR can suffer from a couple of problems upon encountering a syntax error. First, the parser might perform additional parser stack reductions before discovering the syntax - error. Such reductions perform user semantic actions that are + error. Such reductions can perform user semantic actions that are unexpected because they are based on an invalid token, and they cause error recovery to begin in a different syntactic context than the one in which the invalid token was encountered. Second, when - verbose error messages are enabled (with %error-verbose or `#define - YYERROR_VERBOSE'), the expected token list in the syntax error - message can both contain invalid tokens and omit valid tokens. + verbose error messages are enabled (with %error-verbose or the + obsolete `#define YYERROR_VERBOSE'), the expected token list in the + syntax error message can both contain invalid tokens and omit valid + tokens. The culprits for the above problems are %nonassoc, default reductions in inconsistent states, and parser state merging. Thus, @@ -136,11 +144,11 @@ Bison News %nonassoc is used or if default reductions are enabled for inconsistent states. - LAC is a new mechanism within the parsing algorithm that completely - solves these problems for canonical LR, IELR, and LALR without - sacrificing %nonassoc, default reductions, or state mering. When - LAC is in use, canonical LR and IELR behave exactly the same for - both syntactically acceptable and syntactically unacceptable input. + LAC is a new mechanism within the parsing algorithm that solves + these problems for canonical LR, IELR, and LALR without sacrificing + %nonassoc, default reductions, or state merging. When LAC is in + use, canonical LR and IELR behave almost exactly the same for both + syntactically acceptable and syntactically unacceptable input. While LALR still does not support the full language-recognition power of canonical LR and IELR, LAC at least enables LALR's syntax error handling to correctly reflect LALR's language-recognition @@ -151,20 +159,14 @@ Bison News %define parse.lac full - See the documentation for `%define parse.lac' in the section `Bison - Declaration Summary' in the Bison manual for additional details. + See the new section `LAC' in the Bison manual for additional + details including a few caveats. LAC is an experimental feature. More user feedback will help to stabilize it. -** Unrecognized %code qualifiers are now errors not warnings. - ** %define improvements: -*** Unrecognized variables are now errors not warnings. - -*** 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 @@ -210,13 +212,73 @@ Bison News %define api.push-pull push -** Grammar symbol names can now contain dashes: +*** Unrecognized variables are now errors not warnings. + +*** Multiple invocations for any variable is now an error not a warning. + +** Unrecognized %code qualifiers are now errors not warnings. + +** Character literals not of length one: - Consistently with directives (such as %error-verbose) and variables - (e.g. push-pull), grammar 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). + 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 start reporting an error instead. + +** 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. + +** C++ parsers use YYRHSLOC: + + Similarly to the C parsers, the C++ parsers now define the YYRHSLOC + macro and use it in the default YYLLOC_DEFAULT. You are encouraged + to use it. If, for instance, your location structure has "first" + and "last" members, instead of + + # define YYLLOC_DEFAULT(Current, Rhs, N) \ + do \ + if (N) \ + { \ + (Current).first = (Rhs)[1].location.first; \ + (Current).last = (Rhs)[N].location.last; \ + } \ + else \ + { \ + (Current).first = (Current).last = (Rhs)[0].location.last; \ + } \ + while (false) + + use: + + # define YYLLOC_DEFAULT(Current, Rhs, N) \ + do \ + if (N) \ + { \ + (Current).first = YYRHSLOC (Rhs, 1).first; \ + (Current).last = YYRHSLOC (Rhs, N).last; \ + } \ + else \ + { \ + (Current).first = (Current).last = YYRHSLOC (Rhs, 0).last; \ + } \ + while (false) + +** YYLLOC_DEFAULT in C++: + + The default implementation of YYLLOC_DEFAULT used to be issued in + the header file. It is now output in the implementation file, after + the user %code sections so that its #ifndef guard does not try to + override the user's YYLLOC_DEFAULT if provided. ** YYFAIL now produces warnings and Java parsers no longer implement it: @@ -250,26 +312,13 @@ Bison News 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 start reporting an error instead. - ** Verbose syntax error message fixes: - When %error-verbose or `#define YYERROR_VERBOSE' is specified, - syntax error messages produced by the generated parser include the - unexpected token as well as a list of expected tokens. The effect - of %nonassoc on these verbose messages has been corrected in two - ways, but a complete fix requires LAC, described above: + When %error-verbose or the obsolete `#define YYERROR_VERBOSE' is + specified, syntax error messages produced by the generated parser + include the unexpected token as well as a list of expected tokens. + The effect of %nonassoc on these verbose messages has been corrected + in two ways, but a more complete fix requires LAC, described above: *** When %nonassoc is used, there can exist parser states that accept no tokens, and so the parser does not always require a lookahead token @@ -301,54 +350,23 @@ Bison News canonical LR. However, LAC is still experimental and is disabled by default. -** 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. +** Java skeleton fixes: -** C++ parsers use YYRHSLOC: +*** A location handling bug has been fixed. - Similarly to the C parsers, the C++ parsers now define the YYRHSLOC - macro and use it in the default YYLLOC_DEFAULT. You are encouraged - to use it. If, for instance, your location structure has "first" - and "last" members, instead of +*** The top element of each of the value stack and location stack is now + cleared when popped so that it can be garbage collected. - # define YYLLOC_DEFAULT(Current, Rhs, N) \ - do \ - if (N) \ - { \ - (Current).first = (Rhs)[1].location.first; \ - (Current).last = (Rhs)[N].location.last; \ - } \ - else \ - { \ - (Current).first = (Current).last = (Rhs)[0].location.last; \ - } \ - while (false) +*** Parser traces now print the top element of the stack. - use: +** -W/--warnings fixes: - # define YYLLOC_DEFAULT(Current, Rhs, N) \ - do \ - if (N) \ - { \ - (Current).first = YYRHSLOC (Rhs, 1).first; \ - (Current).last = YYRHSLOC (Rhs, N).last; \ - } \ - else \ - { \ - (Current).first = (Current).last = YYRHSLOC (Rhs, 0).last; \ - } \ - while (false) +*** Bison now properly recognizes the "no-" versions of categories: -** YYLLOC_DEFAULT in C++: + For example, given the following command line, Bison now enables all + warnings except warnings for incompatibilities with POSIX Yacc: - The default implementation of YYLLOC_DEFAULT used to be issued in - the header file. It is now output in the implementation file, after - the user %code sections so that its #ifndef guard does not try to - override the user's YYLLOC_DEFAULT if provided. + bison -Wall,no-yacc gram.y * Changes in version 2.4.3 (2010-08-05): @@ -1511,9 +1529,7 @@ End: ----- -Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, -2004, 2005, 2006, 2007, 2008, 2009, 2010 Free Software Foundation, -Inc. +Copyright (C) 1995-2011 Free Software Foundation, Inc. This file is part of Bison, the GNU Parser Generator.