* 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
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
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:
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,
-----
-Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003,
-2004, 2005, 2006, 2007, 2008, 2009 Free Software Foundation, Inc.
+Copyright (C) 1995-2010 Free Software Foundation, Inc.
This file is part of Bison, the GNU Parser Generator.
projects / bison.git / blobdiff