Bison News
----------
-Changes in version 1.75b:
+Changes in version 2.0, 2004-12-25:
-* Bison now parses C99 lexical constructs like digraphs, UCNs, and
- backslash-newline within C escape sequences, as POSIX now requires.
+* Possibly-incompatible changes
-* --no-line works properly.
+ - 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.
-Changes in version 1.75a, 2002-10-24:
+ - 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.
-* Bison can no longer be built by a K&R C compiler; it requires C89 or
- later to be built. This change originally took place a few versions
- ago, but nobody noticed until we recently asked someone to try
- building Bison with a K&R C compiler.
+ - 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:
+
+* The documentation license has been upgraded to version 1.2
+ of the GNU Free Documentation License.
+
+* syntax error processing
+
+ - In Yacc-style parsers YYLLOC_DEFAULT is now used to compute error
+ locations too. This fixes bugs in error-location computation.
+
+ - %destructor
+ It is now possible to reclaim the memory associated to symbols
+ discarded during error recovery. This feature is still experimental.
+
+ - %error-verbose
+ This new directive is preferred over YYERROR_VERBOSE.
-* %error-verbose
- This new directive is preferred over YYERROR_VERBOSE.
+ - #defining yyerror to steal internal variables is discouraged.
+ It is not guaranteed to work forever.
-* %lex-param, %parse-param
- These new directives are preferred over PARSE_PARAM and LEX_PARAM.
- In addition, they provide a means for yyerror to remain pure, and
- to access to the current location.
+* POSIX conformance
-* #line
- Bison now recognizes #line in its input, and forwards them.
+ - Semicolons are once again optional at the end of grammar rules.
+ This reverts to the behavior of Bison 1.33 and earlier, and improves
+ compatibility with Yacc.
+ - `parse error' -> `syntax error'
+ Bison now uniformly uses the term `syntax error'; formerly, the code
+ and manual sometimes used the term `parse error' instead. POSIX
+ requires `syntax error' in diagnostics, and it was thought better to
+ be consistent.
+
+ - The documentation now emphasizes that yylex and yyerror must be
+ declared before use. C99 requires this.
+
+ - Bison now parses C99 lexical constructs like UCNs and
+ backslash-newline within C escape sequences, as POSIX 1003.1-2001 requires.
+
+ - File names are properly escaped in C output. E.g., foo\bar.y is
+ output as "foo\\bar.y".
+
+ - Yacc command and library now available
+ The Bison distribution now installs a `yacc' command, as POSIX requires.
+ Also, Bison now installs a small library liby.a containing
+ implementations of Yacc-compatible yyerror and main functions.
+ This library is normally not useful, but POSIX requires it.
+
+ - Type clashes now generate warnings, not errors.
+
+ - If the user does not define YYSTYPE as a macro, Bison now declares it
+ using typedef instead of defining it as a macro.
+ For consistency, YYLTYPE is also declared instead of defined.
+
+* Other compatibility issues
+
+ - %union directives can now have a tag before the `{', e.g., the
+ directive `%union foo {...}' now generates the C code
+ `typedef union foo { ... } YYSTYPE;'; this is for Yacc compatibility.
+ The default union tag is `YYSTYPE', for compatibility with Solaris 9 Yacc.
+ For consistency, YYLTYPE's struct tag is now `YYLTYPE' not `yyltype'.
+ This is for compatibility with both Yacc and Bison 1.35.
+
+ - `;' is output before the terminating `}' of an action, for
+ compatibility with Bison 1.35.
+
+ - Bison now uses a Yacc-style format for conflict reports, e.g.,
+ `conflicts: 2 shift/reduce, 1 reduce/reduce'.
+
+ - `yystype' and `yyltype' are now obsolescent macros instead of being
+ typedefs or tags; they are no longer documented and are planned to be
+ withdrawn in a future release.
+
+* GLR parser notes
+
+ - GLR and inline
+ Users of Bison have to decide how they handle the portability of the
+ C keyword `inline'.
+
+ - `parsing stack overflow...' -> `parser stack overflow'
+ GLR parsers now report `parser stack overflow' as per the Bison manual.
+
+* Bison now warns if it detects conflicting outputs to the same file,
+ e.g., it generates a warning for `bison -d -o foo.h foo.y' since
+ that command outputs both code and header to foo.h.
+
+* #line in output files
+ - --no-line works properly.
+
+* Bison can no longer be built by a K&R C compiler; it requires C89 or
+ later to be built. This change originally took place a few versions
+ ago, but nobody noticed until we recently asked someone to try
+ building Bison with a K&R C compiler.
+\f
Changes in version 1.75, 2002-10-14:
* Bison should now work on 64-bit hosts.
was incorrectly rejected: $1 is defined in the second mid-rule
action, and is equal to the $$ of the first mid-rule action.
-
+\f
Changes in version 1.50, 2002-10-04:
* GLR parsing
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.
the user symbol is used in the reports, the graphs, and the verbose
error messages instead of `$end', which remains being the default.
For instance
- %token YYEOF 0
+ %token MYEOF 0
or
- %token YYEOF 0 "end of file"
+ %token MYEOF 0 "end of file"
* Semantic parser
This old option, which has been broken for ages, is removed.
produces additional information:
- itemset
complete the core item sets with their closure
- - lookahead
- explicitly associate lookaheads to items
+ - lookahead [changed to `look-ahead' in 1.875e and later]
+ explicitly associate look-ahead tokens to items
- solved
describe shift/reduce conflicts solving.
Bison used to systematically output this information on top of
\f
Changes in version 1.30, 2001-10-26:
-* `--defines' and `--graph' have now an optionnal argument which is the
- output file name. `-d' and `-g' do not change, they do not take any
+* `--defines' and `--graph' have now an optional argument which is the
+ output file name. `-d' and `-g' do not change; they do not take any
argument.
* `%source_extension' and `%header_extension' are removed, failed
-----
-Copyright (C) 2001, 2002 Free Software Foundation, Inc.
+Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004
+Free Software Foundation, Inc.
-This file is part of GNU Autoconf.
+This file is part of Bison, the GNU Compiler Compiler.
-GNU Autoconf is free software; you can redistribute it and/or modify
+Bison is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.
-GNU Autoconf is distributed in the hope that it will be useful,
+Bison is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
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