Bison News
----------
-Changes in version 1.875e:
+Changes in version 2.1a:
-* New directive: %initial-action.
- This directive allows the user to run arbitrary code (including
- initializing @$) from yyparse before parsing starts.
+* Bison now allows multiple %union declarations, and concatenates
+ their contents together.
-* The option `--report=lookahead' was changed to `--report=look-ahead'.
- The old spelling still works, but is not documented and will be removed.
+* New warning: unused values
+ Typed right-hand side symbols whose value are not used are reported.
+ For instance:
-Changes in version 1.875d, 2004-05-21:
+ exp: exp "?" exp ":" exp { $1 ? $1 : $3; }
+ | exp "+" exp
+ ;
-* Unescaped newlines are no longer allowed in character constants or
- string literals. They were never portable, and GCC 3.4.0 has
- dropped support for them. Better diagnostics are now generated if
- forget a closing quote.
+ will trigger a warning about $$ and $5 in the first rule, and $3 in
+ the second ($1 is copied to $$ by the default rule). This example
+ most likely contains three errors, and should be rewritten as:
-* NUL bytes are no longer allowed in Bison string literals, unfortunately.
+ exp: exp "?" exp ":" exp { $$ = $1 ? $3 : $5; }
+ | exp "+" exp { $$ = $1 + $3; }
+ ;
-* %token numbers can now be hexadecimal integers, e.g., `%token FOO 0x12d'.
- This is a GNU extension.
+ However, if the original actions were really intended, the warnings
+ can be suppressed by letting Bison believe the values are used, e.g.:
-* A new directive "%expect-rr N" specifies the expected number of
- reduce/reduce conflicts in GLR parsers.
+ exp: exp "?" exp ":" exp { $1 ? $1 : $3; (void) ($$, $5); }
+ | exp "+" exp { $$ = $1; (void) $3; }
+ ;
-* Experimental %destructor support has been added to lalr1.cc.
+ If there are mid-rule actions, the warning is issued if no action
+ uses it. The following triggers no warning: $1 and $3 are used.
-Changes in version 1.875c, 2003-08-25:
+ exp: exp { push ($1); } '+' exp { push ($3); sum (); };
- (Just bug fixes.)
+ Mid-rule actions that use $$ cause the corresponding value to be
+ set, therefore the following action must use it. The following rule
+ triggers a warning about $2.
-Changes in version 1.875b, 2003-06-17:
+ exp: '1' { $$ = 1; } '+' exp { $$ = $1 + $4; };
-* GLR grammars now support locations.
+ The warning is intended to help catching lost values and memory leaks.
+ If a value is ignored, its associated memory typically is not reclaimed.
-* Semicolon changes:
- - Semicolons are now allowed before "|" in grammar rules, as POSIX requires.
- - Stray semicolons are no longer allowed at the start of a grammar.
- - Semicolons are now required after in-grammar declarations.
+* %destructor vs. YYABORT, YYACCEPT, and YYERROR.
+ Destructors are now called when user code invokes YYABORT, YYACCEPT,
+ and YYERROR, for all objects on the stack, other than objects
+ corresponding to the right-hand side of the current rule.
+
+* %expect, %expect-rr
+ Incorrect numbers of expected conflicts are now actual errors,
+ instead of warnings.
+
+* GLR, YACC parsers.
+ The %parse-params are available in the %destructor's (and the
+ experimental %printer's) as per the documentation.
+
+* Bison now warns if it finds a stray `$' or `@' in an action.
+
+* %require "VERSION"
+ To specify that the grammar file depends on features implemented in
+ Bison version VERSION or higher.
+
+* lalr1.cc: The token and value types are now class members.
+ The tokens were defined as free form enums and cpp macros. YYSTYPE
+ was defined as a free form union. They are now class members:
+ tokens are enumerations of the `yy::parser::token' struct, and the
+ semantic values have the `yy::parser::semantic_type' type.
+
+ If you do not want or can update to this scheme, the directive
+ `%define "global_tokens_and_yystype" "1"' triggers the global
+ definition of tokens and YYSTYPE. This change is suitable both
+ for previous releases of Bison, and this one.
+
+ If you wish to update, then make sure older version of Bison will
+ fail using `%require "2.1a"'.
+
+* DJGPP support added.
+
+Changes in version 2.1, 2005-09-16:
+
+* The C++ lalr1.cc skeleton supports %lex-param.
+
+* Bison-generated parsers now support the translation of diagnostics like
+ "syntax error" into languages other than English. The default
+ language is still English. For details, please see the new
+ Internationalization section of the Bison manual. Software
+ distributors should also see the new PACKAGING file. Thanks to
+ Bruno Haible for this new feature.
+
+* Wording in the Bison-generated parsers has been changed slightly to
+ simplify translation. In particular, the message "memory exhausted"
+ has replaced "parser stack overflow", as the old message was not
+ always accurate for modern Bison-generated parsers.
+
+* Destructors are now called when the parser aborts, for all symbols left
+ behind on the stack. Also, the start symbol is now destroyed after a
+ successful parse. In both cases, the behavior was formerly inconsistent.
+
+* When generating verbose diagnostics, Bison-generated parsers no longer
+ quote the literal strings associated with tokens. For example, for
+ a syntax error associated with '%token NUM "number"' they might
+ print 'syntax error, unexpected number' instead of 'syntax error,
+ unexpected "number"'.
+
+Changes in version 2.0, 2004-12-25:
-Changes in version 1.875a, 2003-02-01:
+* Possibly-incompatible changes
-* For now, %expect-count violations are now just warnings, not errors.
- This is for compatibility with Bison 1.75 and earlier (when there are
- reduce/reduce conflicts) and with Bison 1.30 and earlier (when there
- are too many or too few shift/reduce conflicts). However, in future
- versions of Bison we plan to improve the %expect machinery so that
- these violations will become errors again.
+ - Bison-generated parsers no longer default to using the alloca function
+ (when available) to extend the parser stack, due to widespread
+ problems in unchecked stack-overflow detection. You can "#define
+ YYSTACK_USE_ALLOCA 1" to require the use of alloca, but please read
+ the manual to determine safe values for YYMAXDEPTH in that case.
-* New configure option --disable-yacc, to disable installation of the
- yacc command and -ly library introduced in 1.875 for POSIX conformance.
+ - Error token location.
+ During error recovery, the location of the syntax error is updated
+ to cover the whole sequence covered by the error token: it includes
+ the shifted symbols thrown away during the first part of the error
+ recovery, and the lookahead rejected during the second part.
+
+ - Semicolon changes:
+ . Stray semicolons are no longer allowed at the start of a grammar.
+ . Semicolons are now required after in-grammar declarations.
+
+ - Unescaped newlines are no longer allowed in character constants or
+ string literals. They were never portable, and GCC 3.4.0 has
+ dropped support for them. Better diagnostics are now generated if
+ forget a closing quote.
+
+ - NUL bytes are no longer allowed in Bison string literals, unfortunately.
+
+* New features
+
+ - GLR grammars now support locations.
+
+ - New directive: %initial-action.
+ This directive allows the user to run arbitrary code (including
+ initializing @$) from yyparse before parsing starts.
+
+ - A new directive "%expect-rr N" specifies the expected number of
+ reduce/reduce conflicts in GLR parsers.
+
+ - %token numbers can now be hexadecimal integers, e.g., `%token FOO 0x12d'.
+ This is a GNU extension.
+
+ - The option `--report=lookahead' was changed to `--report=look-ahead'.
+ The old spelling still works, but is not documented and will be
+ removed.
+
+ - Experimental %destructor support has been added to lalr1.cc.
+
+ - New configure option --disable-yacc, to disable installation of the
+ yacc command and -ly library introduced in 1.875 for POSIX conformance.
+
+* Bug fixes
+
+ - For now, %expect-count violations are now just warnings, not errors.
+ This is for compatibility with Bison 1.75 and earlier (when there are
+ reduce/reduce conflicts) and with Bison 1.30 and earlier (when there
+ are too many or too few shift/reduce conflicts). However, in future
+ versions of Bison we plan to improve the %expect machinery so that
+ these violations will become errors again.
+
+ - Within Bison itself, numbers (e.g., goto numbers) are no longer
+ arbitrarily limited to 16-bit counts.
+
+ - Semicolons are now allowed before "|" in grammar rules, as POSIX requires.
\f
Changes in version 1.875, 2003-01-01:
allowed some non-error action other than a default reduction on the
error token. The new behavior has long been the documented behavior,
and has long been required by POSIX. For more details, please see
- <http://mail.gnu.org/pipermail/bug-bison/2002-May/001452.html>.
+ Paul Eggert, "Reductions during Bison error handling" (2002-05-20)
+ <http://lists.gnu.org/archive/html/bug-bison/2002-05/msg00038.html>.
* Traces
Popped tokens and nonterminals are now reported.
alloca is used only when compiled with GCC, to avoid portability
problems as on AIX.
+* yyparse now returns 2 if memory is exhausted; formerly it dumped core.
+
* When the generated parser lacks debugging code, YYDEBUG is now 0
(as POSIX requires) instead of being undefined.
-----
-Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004
-Free Software Foundation, Inc.
+Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003,
+2004, 2005, 2006 Free Software Foundation, Inc.
This file is part of Bison, the GNU Compiler Compiler.
You should have received a copy of the GNU General Public License
along with autoconf; see the file COPYING. If not, write to
-the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
-Boston, MA 02111-1307, USA.
+the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+Boston, MA 02110-1301, USA.
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