X-Git-Url: https://git.saurik.com/bison.git/blobdiff_plain/ac9b0e954b1d3aed514a3bbd363da1514202af0f..62efdd2a85847c8b7559d312e7cada6ca03a2779:/NEWS diff --git a/NEWS b/NEWS index e4bb63f5..d6eed912 100644 --- a/NEWS +++ b/NEWS @@ -3,6 +3,31 @@ Bison News * 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 @@ -20,9 +45,9 @@ Bison News 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" + %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 @@ -33,9 +58,15 @@ Bison News 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. +** Unrecognized %code qualifiers are now an error not a warning. + +** %define improvements. -** %define can now be invoked via the command line. +*** 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 @@ -54,7 +85,7 @@ Bison News quietly override %define, but -D and --define do not. For further details, see the section "Bison Options" in the Bison manual. -** %define variables renamed. +*** Variables renamed. The following %define variables @@ -69,7 +100,18 @@ Bison News The old names are now deprecated but will be maintained indefinitely for backward compatibility. -** Symbols names +*** 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, @@ -77,6 +119,17 @@ Bison News 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. + ** Temporary hack for adding a semicolon to the user action. Previously, Bison appended a semicolon to every user action for @@ -111,8 +164,23 @@ Bison News 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. + +** 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: @@ -136,6 +204,51 @@ Bison News 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