4 Changes in version 2.1a:
 
   6 * GLR, C++ LALR(1) parsers.
 
   7   These parser skeletons are now distributed with the same special
 
   8   license exception that the C LALR(1) parser skeleton has had since
 
   9   Bison 1.24.  Hence the FSF imposes no copyright restriction on the
 
  10   output of Bison when it is generating such parsers.
 
  13   Incorrect numbers of expected conflicts are now actual errors,
 
  17   The %parse-params are available in the %destructor's (and the
 
  18   experimental %printer's) as per the documentation.
 
  20 * Bison now warns if it finds a stray `$' or `@' in an action.
 
  23   To specify that the grammar file depends on features implemented in
 
  24   Bison version VERSION or higher.
 
  26 * lalr1.cc: The token and value types are now class members.
 
  27   The tokens where defined as free form enums and cpp macros.  YYSTYPE
 
  28   was defined as a free form union.  Both are now class members:
 
  29   tokens are enumerations of the `yy::parser::token' struct, and the
 
  30   semantic values have the `yy::parser::semantic_type' type.
 
  32   If you do not want or can update to this scheme, the directive
 
  33   `%define "global_tokens_and_yystype" "1"' triggers the global
 
  34   definition of tokens and YYSTYPE.  This change is suitable both
 
  35   for previous releases of Bison, and this one.
 
  37   If you wish to update, then make sure older version of Bison will
 
  38   fail using `%require "2.1a"'.
 
  40 * DJGPP support added.
 
  42 Changes in version 2.1, 2005-09-16:
 
  44 * Bison-generated parsers now support the translation of diagnostics like
 
  45   "syntax error" into languages other than English.  The default
 
  46   language is still English.  For details, please see the new
 
  47   Internationalization section of the Bison manual.  Software
 
  48   distributors should also see the new PACKAGING file.  Thanks to
 
  49   Bruno Haible for this new feature.
 
  51 * Wording in the Bison-generated parsers has been changed slightly to
 
  52   simplify translation.  In particular, the message "memory exhausted"
 
  53   has replaced "parser stack overflow", as the old message was not
 
  54   always accurate for modern Bison-generated parsers.
 
  56 * Destructors are now called when the parser aborts, for all symbols left
 
  57   behind on the stack.  Also, the start symbol is now destroyed after a
 
  58   successful parse.  In both cases, the behavior was formerly inconsistent.
 
  60 * When generating verbose diagnostics, Bison-generated parsers no longer
 
  61   quote the literal strings associated with tokens.  For example, for
 
  62   a syntax error associated with '%token NUM "number"' they might
 
  63   print 'syntax error, unexpected number' instead of 'syntax error,
 
  66 Changes in version 2.0, 2004-12-25:
 
  68 * Possibly-incompatible changes
 
  70   - Bison-generated parsers no longer default to using the alloca function
 
  71     (when available) to extend the parser stack, due to widespread
 
  72     problems in unchecked stack-overflow detection.  You can "#define
 
  73     YYSTACK_USE_ALLOCA 1" to require the use of alloca, but please read
 
  74     the manual to determine safe values for YYMAXDEPTH in that case.
 
  76   - Error token location.
 
  77     During error recovery, the location of the syntax error is updated
 
  78     to cover the whole sequence covered by the error token: it includes
 
  79     the shifted symbols thrown away during the first part of the error
 
  80     recovery, and the lookahead rejected during the second part.
 
  83     . Stray semicolons are no longer allowed at the start of a grammar.
 
  84     . Semicolons are now required after in-grammar declarations.
 
  86   - Unescaped newlines are no longer allowed in character constants or
 
  87     string literals.  They were never portable, and GCC 3.4.0 has
 
  88     dropped support for them.  Better diagnostics are now generated if
 
  89     forget a closing quote.
 
  91   - NUL bytes are no longer allowed in Bison string literals, unfortunately.
 
  95   - GLR grammars now support locations.
 
  97   - New directive: %initial-action.
 
  98     This directive allows the user to run arbitrary code (including
 
  99     initializing @$) from yyparse before parsing starts.
 
 101   - A new directive "%expect-rr N" specifies the expected number of
 
 102     reduce/reduce conflicts in GLR parsers.
 
 104   - %token numbers can now be hexadecimal integers, e.g., `%token FOO 0x12d'.
 
 105     This is a GNU extension.
 
 107   - The option `--report=lookahead' was changed to `--report=look-ahead'.
 
 108     The old spelling still works, but is not documented and will be
 
 111   - Experimental %destructor support has been added to lalr1.cc.
 
 113   - New configure option --disable-yacc, to disable installation of the
 
 114     yacc command and -ly library introduced in 1.875 for POSIX conformance.
 
 118   - For now, %expect-count violations are now just warnings, not errors.
 
 119     This is for compatibility with Bison 1.75 and earlier (when there are
 
 120     reduce/reduce conflicts) and with Bison 1.30 and earlier (when there
 
 121     are too many or too few shift/reduce conflicts).  However, in future
 
 122     versions of Bison we plan to improve the %expect machinery so that
 
 123     these violations will become errors again.
 
 125   - Within Bison itself, numbers (e.g., goto numbers) are no longer
 
 126     arbitrarily limited to 16-bit counts.
 
 128   - Semicolons are now allowed before "|" in grammar rules, as POSIX requires.
 
 130 Changes in version 1.875, 2003-01-01:
 
 132 * The documentation license has been upgraded to version 1.2
 
 133   of the GNU Free Documentation License.
 
 135 * syntax error processing
 
 137   - In Yacc-style parsers YYLLOC_DEFAULT is now used to compute error
 
 138     locations too.  This fixes bugs in error-location computation.
 
 141     It is now possible to reclaim the memory associated to symbols
 
 142     discarded during error recovery.  This feature is still experimental.
 
 145     This new directive is preferred over YYERROR_VERBOSE.
 
 147   - #defining yyerror to steal internal variables is discouraged.
 
 148     It is not guaranteed to work forever.
 
 152   - Semicolons are once again optional at the end of grammar rules.
 
 153     This reverts to the behavior of Bison 1.33 and earlier, and improves
 
 154     compatibility with Yacc.
 
 156   - `parse error' -> `syntax error'
 
 157     Bison now uniformly uses the term `syntax error'; formerly, the code
 
 158     and manual sometimes used the term `parse error' instead.  POSIX
 
 159     requires `syntax error' in diagnostics, and it was thought better to
 
 162   - The documentation now emphasizes that yylex and yyerror must be
 
 163     declared before use.  C99 requires this.
 
 165   - Bison now parses C99 lexical constructs like UCNs and
 
 166     backslash-newline within C escape sequences, as POSIX 1003.1-2001 requires.
 
 168   - File names are properly escaped in C output.  E.g., foo\bar.y is
 
 169     output as "foo\\bar.y".
 
 171   - Yacc command and library now available
 
 172     The Bison distribution now installs a `yacc' command, as POSIX requires.
 
 173     Also, Bison now installs a small library liby.a containing
 
 174     implementations of Yacc-compatible yyerror and main functions.
 
 175     This library is normally not useful, but POSIX requires it.
 
 177   - Type clashes now generate warnings, not errors.
 
 179   - If the user does not define YYSTYPE as a macro, Bison now declares it
 
 180     using typedef instead of defining it as a macro.
 
 181     For consistency, YYLTYPE is also declared instead of defined.
 
 183 * Other compatibility issues
 
 185   - %union directives can now have a tag before the `{', e.g., the
 
 186     directive `%union foo {...}' now generates the C code
 
 187     `typedef union foo { ... } YYSTYPE;'; this is for Yacc compatibility.
 
 188     The default union tag is `YYSTYPE', for compatibility with Solaris 9 Yacc.
 
 189     For consistency, YYLTYPE's struct tag is now `YYLTYPE' not `yyltype'.
 
 190     This is for compatibility with both Yacc and Bison 1.35.
 
 192   - `;' is output before the terminating `}' of an action, for
 
 193     compatibility with Bison 1.35.
 
 195   - Bison now uses a Yacc-style format for conflict reports, e.g.,
 
 196     `conflicts: 2 shift/reduce, 1 reduce/reduce'.
 
 198   - `yystype' and `yyltype' are now obsolescent macros instead of being
 
 199     typedefs or tags; they are no longer documented and are planned to be
 
 200     withdrawn in a future release.
 
 205     Users of Bison have to decide how they handle the portability of the
 
 208   - `parsing stack overflow...' -> `parser stack overflow'
 
 209     GLR parsers now report `parser stack overflow' as per the Bison manual.
 
 211 * Bison now warns if it detects conflicting outputs to the same file,
 
 212   e.g., it generates a warning for `bison -d -o foo.h foo.y' since
 
 213   that command outputs both code and header to foo.h.
 
 215 * #line in output files
 
 216   - --no-line works properly.
 
 218 * Bison can no longer be built by a K&R C compiler; it requires C89 or
 
 219   later to be built.  This change originally took place a few versions
 
 220   ago, but nobody noticed until we recently asked someone to try
 
 221   building Bison with a K&R C compiler.
 
 223 Changes in version 1.75, 2002-10-14:
 
 225 * Bison should now work on 64-bit hosts.
 
 227 * Indonesian translation thanks to Tedi Heriyanto.
 
 230   Fix spurious parse errors.
 
 233   Some people redefine yyerror to steal yyparse' private variables.
 
 234   Reenable this trick until an official feature replaces it.
 
 237   In agreement with POSIX and with other Yaccs, leaving a default
 
 238   action is valid when $$ is untyped, and $1 typed:
 
 242   but the converse remains an error:
 
 246 * Values of mid-rule actions
 
 249         foo: { ... } { $$ = $1; } ...
 
 251   was incorrectly rejected: $1 is defined in the second mid-rule
 
 252   action, and is equal to the $$ of the first mid-rule action.
 
 254 Changes in version 1.50, 2002-10-04:
 
 259   causes Bison to produce a Generalized LR (GLR) parser, capable of handling
 
 260   almost any context-free grammar, ambiguous or not.  The new declarations
 
 261   %dprec and %merge on grammar rules allow parse-time resolution of
 
 262   ambiguities.  Contributed by Paul Hilfinger.
 
 264   Unfortunately Bison 1.50 does not work properly on 64-bit hosts
 
 265   like the Alpha, so please stick to 32-bit hosts for now.
 
 268   When not in Yacc compatibility mode, when the output file was not
 
 269   specified, running `bison foo/bar.y' created `foo/bar.c'.  It
 
 273   The undefined token was systematically mapped to 2 which prevented
 
 274   the use of 2 by the user.  This is no longer the case.
 
 276 * Unknown token numbers
 
 277   If yylex returned an out of range value, yyparse could die.  This is
 
 281   According to POSIX, the error token must be 256.
 
 282   Bison extends this requirement by making it a preference: *if* the
 
 283   user specified that one of her tokens is numbered 256, then error
 
 284   will be mapped onto another number.
 
 286 * Verbose error messages
 
 287   They no longer report `..., expecting error or...' for states where
 
 288   error recovery is possible.
 
 291   Defaults to `$end' instead of `$'.
 
 293 * Error recovery now conforms to documentation and to POSIX
 
 294   When a Bison-generated parser encounters a syntax error, it now pops
 
 295   the stack until it finds a state that allows shifting the error
 
 296   token.  Formerly, it popped the stack until it found a state that
 
 297   allowed some non-error action other than a default reduction on the
 
 298   error token.  The new behavior has long been the documented behavior,
 
 299   and has long been required by POSIX.  For more details, please see
 
 300   Paul Eggert, "Reductions during Bison error handling" (2002-05-20)
 
 301   <http://lists.gnu.org/archive/html/bug-bison/2002-05/msg00038.html>.
 
 304   Popped tokens and nonterminals are now reported.
 
 307   Larger grammars are now supported (larger token numbers, larger grammar
 
 308   size (= sum of the LHS and RHS lengths), larger LALR tables).
 
 309   Formerly, many of these numbers ran afoul of 16-bit limits;
 
 310   now these limits are 32 bits on most hosts.
 
 312 * Explicit initial rule
 
 313   Bison used to play hacks with the initial rule, which the user does
 
 314   not write.  It is now explicit, and visible in the reports and
 
 318   Before, Bison reported the useless rules, but, although not used,
 
 319   included them in the parsers.  They are now actually removed.
 
 321 * Useless rules, useless nonterminals
 
 322   They are now reported, as a warning, with their locations.
 
 324 * Rules never reduced
 
 325   Rules that can never be reduced because of conflicts are now
 
 328 * Incorrect `Token not used'
 
 331            %token useless useful
 
 333            exp: '0' %prec useful;
 
 335   where a token was used to set the precedence of the last rule,
 
 336   bison reported both `useful' and `useless' as useless tokens.
 
 338 * Revert the C++ namespace changes introduced in 1.31
 
 339   as they caused too many portability hassles.
 
 342   By an accident of design, the default computation of @$ was
 
 343   performed after another default computation was performed: @$ = @1.
 
 344   The latter is now removed: YYLLOC_DEFAULT is fully responsible of
 
 345   the computation of @$.
 
 348   The token end of file may be specified by the user, in which case,
 
 349   the user symbol is used in the reports, the graphs, and the verbose
 
 350   error messages instead of `$end', which remains being the default.
 
 354      %token MYEOF 0 "end of file"
 
 357   This old option, which has been broken for ages, is removed.
 
 360   Brazilian Portuguese, thanks to Alexandre Folle de Menezes.
 
 361   Croatian, thanks to Denis Lackovic.
 
 363 * Incorrect token definitions
 
 364   When given `%token 'a' "A"', Bison used to output `#define 'a' 65'.
 
 366 * Token definitions as enums
 
 367   Tokens are output both as the traditional #define's, and, provided
 
 368   the compiler supports ANSI C or is a C++ compiler, as enums.
 
 369   This lets debuggers display names instead of integers.
 
 372   In addition to --verbose, bison supports --report=THINGS, which
 
 373   produces additional information:
 
 375     complete the core item sets with their closure
 
 376   - lookahead [changed to `look-ahead' in 1.875e and later]
 
 377     explicitly associate look-ahead tokens to items
 
 379     describe shift/reduce conflicts solving.
 
 380     Bison used to systematically output this information on top of
 
 381     the report.  Solved conflicts are now attached to their states.
 
 384   Previous versions don't complain when there is a type clash on
 
 385   the default action if the rule has a mid-rule action, such as in:
 
 393 * GNU M4 is now required when using Bison.
 
 395 Changes in version 1.35, 2002-03-25:
 
 398   Some projects use Bison's C parser with C++ compilers, and define
 
 399   YYSTYPE as a class.  The recent adjustment of C parsers for data
 
 400   alignment and 64 bit architectures made this impossible.
 
 402   Because for the time being no real solution for C++ parser
 
 403   generation exists, kludges were implemented in the parser to
 
 404   maintain this use.  In the future, when Bison has C++ parsers, this
 
 405   kludge will be disabled.
 
 407   This kludge also addresses some C++ problems when the stack was
 
 410 Changes in version 1.34, 2002-03-12:
 
 412 * File name clashes are detected
 
 413   $ bison foo.y -d -o foo.x
 
 414   fatal error: header and parser would both be named `foo.x'
 
 416 * A missing `;' at the end of a rule triggers a warning
 
 417   In accordance with POSIX, and in agreement with other
 
 418   Yacc implementations, Bison will mandate this semicolon in the near
 
 419   future.  This eases the implementation of a Bison parser of Bison
 
 420   grammars by making this grammar LALR(1) instead of LR(2).  To
 
 421   facilitate the transition, this release introduces a warning.
 
 423 * Revert the C++ namespace changes introduced in 1.31, as they caused too
 
 424   many portability hassles.
 
 426 * DJGPP support added.
 
 428 * Fix test suite portability problems.
 
 430 Changes in version 1.33, 2002-02-07:
 
 433   Groff could not be compiled for the definition of size_t was lacking
 
 434   under some conditions.
 
 439 Changes in version 1.32, 2002-01-23:
 
 441 * Fix Yacc output file names
 
 445 * Italian, Dutch translations
 
 447 Changes in version 1.31, 2002-01-14:
 
 451 * GNU Gettext and %expect
 
 452   GNU Gettext asserts 10 s/r conflicts, but there are 7.  Now that
 
 453   Bison dies on incorrect %expectations, we fear there will be
 
 454   too many bug reports for Gettext, so _for the time being_, %expect
 
 455   does not trigger an error when the input file is named `plural.y'.
 
 457 * Use of alloca in parsers
 
 458   If YYSTACK_USE_ALLOCA is defined to 0, then the parsers will use
 
 459   malloc exclusively.  Since 1.29, but was not NEWS'ed.
 
 461   alloca is used only when compiled with GCC, to avoid portability
 
 464 * yyparse now returns 2 if memory is exhausted; formerly it dumped core.
 
 466 * When the generated parser lacks debugging code, YYDEBUG is now 0
 
 467   (as POSIX requires) instead of being undefined.
 
 470   Bison has always permitted actions such as { $$ = $1 }: it adds the
 
 471   ending semicolon.  Now if in Yacc compatibility mode, the semicolon
 
 472   is no longer output: one has to write { $$ = $1; }.
 
 474 * Better C++ compliance
 
 475   The output parsers try to respect C++ namespaces.
 
 476   [This turned out to be a failed experiment, and it was reverted later.]
 
 479   Fixed bugs when reporting useless nonterminals.
 
 482   The parsers work properly on 64 bit hosts.
 
 485   Some calls to strerror resulted in scrambled or missing error messages.
 
 488   When the number of shift/reduce conflicts is correct, don't issue
 
 491 * The verbose report includes the rule line numbers.
 
 493 * Rule line numbers are fixed in traces.
 
 495 * Swedish translation
 
 498   Verbose parse error messages from the parsers are better looking.
 
 499   Before: parse error: unexpected `'/'', expecting `"number"' or `'-'' or `'(''
 
 500      Now: parse error: unexpected '/', expecting "number" or '-' or '('
 
 502 * Fixed parser memory leaks.
 
 503   When the generated parser was using malloc to extend its stacks, the
 
 504   previous allocations were not freed.
 
 506 * Fixed verbose output file.
 
 507   Some newlines were missing.
 
 508   Some conflicts in state descriptions were missing.
 
 510 * Fixed conflict report.
 
 511   Option -v was needed to get the result.
 
 515   Mismatches are errors, not warnings.
 
 517 * Fixed incorrect processing of some invalid input.
 
 519 * Fixed CPP guards: 9foo.h uses BISON_9FOO_H instead of 9FOO_H.
 
 521 * Fixed some typos in the documentation.
 
 523 * %token MY_EOF 0 is supported.
 
 524   Before, MY_EOF was silently renumbered as 257.
 
 526 * doc/refcard.tex is updated.
 
 528 * %output, %file-prefix, %name-prefix.
 
 532   New, aliasing `--output-file'.
 
 534 Changes in version 1.30, 2001-10-26:
 
 536 * `--defines' and `--graph' have now an optional argument which is the
 
 537   output file name. `-d' and `-g' do not change; they do not take any
 
 540 * `%source_extension' and `%header_extension' are removed, failed
 
 545 Changes in version 1.29, 2001-09-07:
 
 547 * The output file does not define const, as this caused problems when used
 
 548   with common autoconfiguration schemes.  If you still use ancient compilers
 
 549   that lack const, compile with the equivalent of the C compiler option
 
 550   `-Dconst='.  autoconf's AC_C_CONST macro provides one way to do this.
 
 552 * Added `-g' and `--graph'.
 
 554 * The Bison manual is now distributed under the terms of the GNU FDL.
 
 556 * The input and the output files has automatically a similar extension.
 
 558 * Russian translation added.
 
 560 * NLS support updated; should hopefully be less troublesome.
 
 562 * Added the old Bison reference card.
 
 564 * Added `--locations' and `%locations'.
 
 566 * Added `-S' and `--skeleton'.
 
 568 * `%raw', `-r', `--raw' is disabled.
 
 570 * Special characters are escaped when output.  This solves the problems
 
 571   of the #line lines with path names including backslashes.
 
 574   `%yacc', `%fixed_output_files', `%defines', `%no_parser', `%verbose',
 
 575   `%debug', `%source_extension' and `%header_extension'.
 
 578   Automatic location tracking.
 
 580 Changes in version 1.28, 1999-07-06:
 
 582 * Should compile better now with K&R compilers.
 
 586 * Fixed a problem with escaping the double quote character.
 
 588 * There is now a FAQ.
 
 590 Changes in version 1.27:
 
 592 * The make rule which prevented bison.simple from being created on
 
 593   some systems has been fixed.
 
 595 Changes in version 1.26:
 
 597 * Bison now uses automake.
 
 599 * New mailing lists: <bug-bison@gnu.org> and <help-bison@gnu.org>.
 
 601 * Token numbers now start at 257 as previously documented, not 258.
 
 603 * Bison honors the TMPDIR environment variable.
 
 605 * A couple of buffer overruns have been fixed.
 
 607 * Problems when closing files should now be reported.
 
 609 * Generated parsers should now work even on operating systems which do
 
 610   not provide alloca().
 
 612 Changes in version 1.25, 1995-10-16:
 
 614 * Errors in the input grammar are not fatal; Bison keeps reading
 
 615 the grammar file, and reports all the errors found in it.
 
 617 * Tokens can now be specified as multiple-character strings: for
 
 618 example, you could use "<=" for a token which looks like <=, instead
 
 619 of chosing a name like LESSEQ.
 
 621 * The %token_table declaration says to write a table of tokens (names
 
 622 and numbers) into the parser file.  The yylex function can use this
 
 623 table to recognize multiple-character string tokens, or for other
 
 626 * The %no_lines declaration says not to generate any #line preprocessor
 
 627 directives in the parser file.
 
 629 * The %raw declaration says to use internal Bison token numbers, not
 
 630 Yacc-compatible token numbers, when token names are defined as macros.
 
 632 * The --no-parser option produces the parser tables without including
 
 633 the parser engine; a project can now use its own parser engine.
 
 634 The actions go into a separate file called NAME.act, in the form of
 
 635 a switch statement body.
 
 637 Changes in version 1.23:
 
 639 The user can define YYPARSE_PARAM as the name of an argument to be
 
 640 passed into yyparse.  The argument should have type void *.  It should
 
 641 actually point to an object.  Grammar actions can access the variable
 
 642 by casting it to the proper pointer type.
 
 644 Line numbers in output file corrected.
 
 646 Changes in version 1.22:
 
 650 Changes in version 1.20:
 
 652 Output file does not redefine const for C++.
 
 660 Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005
 
 661 Free Software Foundation, Inc.
 
 663 This file is part of Bison, the GNU Compiler Compiler.
 
 665 Bison is free software; you can redistribute it and/or modify
 
 666 it under the terms of the GNU General Public License as published by
 
 667 the Free Software Foundation; either version 2, or (at your option)
 
 670 Bison is distributed in the hope that it will be useful,
 
 671 but WITHOUT ANY WARRANTY; without even the implied warranty of
 
 672 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 
 673 GNU General Public License for more details.
 
 675 You should have received a copy of the GNU General Public License
 
 676 along with autoconf; see the file COPYING.  If not, write to
 
 677 the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
 
 678 Boston, MA 02110-1301, USA.