NEWS

   1 Bison News
   2 ----------
   3
   4 Changes in version 2.1a:
   5
   6 * lalr1.cc: The token and value types are now class members.
   7   The tokens where defined as free form enums and cpp macros.  YYSTYPE
   8   was defined as a free form union.  Both are now class members:
   9   tokens are enumerations of the `yy::parser::token' struct, and the
  10   semantic values have the `yy::parser::semantic_type' type.
  11
  12   If you do not want or can update to this scheme, the directive
  13   `%define "global_tokens_and_yystype" "1"' triggers the global
  14   definition of tokens and YYSTYPE.
  15
  16
  17 Changes in version 2.1, 2005-09-16:
  18
  19 * Bison-generated parsers now support the translation of diagnostics like
  20   "syntax error" into languages other than English.  The default
  21   language is still English.  For details, please see the new
  22   Internationalization section of the Bison manual.  Software
  23   distributors should also see the new PACKAGING file.  Thanks to
  24   Bruno Haible for this new feature.
  25
  26 * Wording in the Bison-generated parsers has been changed slightly to
  27   simplify translation.  In particular, the message "memory exhausted"
  28   has replaced "parser stack overflow", as the old message was not
  29   always accurate for modern Bison-generated parsers.
  30
  31 * Destructors are now called when the parser aborts, for all symbols left
  32   behind on the stack.  Also, the start symbol is now destroyed after a
  33   successful parse.  In both cases, the behavior was formerly inconsistent.
  34
  35 * When generating verbose diagnostics, Bison-generated parsers no longer
  36   quote the literal strings associated with tokens.  For example, for
  37   a syntax error associated with '%token NUM "number"' they might
  38   print 'syntax error, unexpected number' instead of 'syntax error,
  39   unexpected "number"'.
  40
  41 Changes in version 2.0, 2004-12-25:
  42
  43 * Possibly-incompatible changes
  44
  45   - Bison-generated parsers no longer default to using the alloca function
  46     (when available) to extend the parser stack, due to widespread
  47     problems in unchecked stack-overflow detection.  You can "#define
  48     YYSTACK_USE_ALLOCA 1" to require the use of alloca, but please read
  49     the manual to determine safe values for YYMAXDEPTH in that case.
  50
  51   - Error token location.
  52     During error recovery, the location of the syntax error is updated
  53     to cover the whole sequence covered by the error token: it includes
  54     the shifted symbols thrown away during the first part of the error
  55     recovery, and the lookahead rejected during the second part.
  56
  57   - Semicolon changes:
  58     . Stray semicolons are no longer allowed at the start of a grammar.
  59     . Semicolons are now required after in-grammar declarations.
  60
  61   - Unescaped newlines are no longer allowed in character constants or
  62     string literals.  They were never portable, and GCC 3.4.0 has
  63     dropped support for them.  Better diagnostics are now generated if
  64     forget a closing quote.
  65
  66   - NUL bytes are no longer allowed in Bison string literals, unfortunately.
  67
  68 * New features
  69
  70   - GLR grammars now support locations.
  71
  72   - New directive: %initial-action.
  73     This directive allows the user to run arbitrary code (including
  74     initializing @$) from yyparse before parsing starts.
  75
  76   - A new directive "%expect-rr N" specifies the expected number of
  77     reduce/reduce conflicts in GLR parsers.
  78
  79   - %token numbers can now be hexadecimal integers, e.g., `%token FOO 0x12d'.
  80     This is a GNU extension.
  81
  82   - The option `--report=lookahead' was changed to `--report=look-ahead'.
  83     The old spelling still works, but is not documented and will be
  84     removed.
  85
  86   - Experimental %destructor support has been added to lalr1.cc.
  87
  88   - New configure option --disable-yacc, to disable installation of the
  89     yacc command and -ly library introduced in 1.875 for POSIX conformance.
  90
  91 * Bug fixes
  92
  93   - For now, %expect-count violations are now just warnings, not errors.
  94     This is for compatibility with Bison 1.75 and earlier (when there are
  95     reduce/reduce conflicts) and with Bison 1.30 and earlier (when there
  96     are too many or too few shift/reduce conflicts).  However, in future
  97     versions of Bison we plan to improve the %expect machinery so that
  98     these violations will become errors again.
  99
 100   - Within Bison itself, numbers (e.g., goto numbers) are no longer
 101     arbitrarily limited to 16-bit counts.
 102
 103   - Semicolons are now allowed before "|" in grammar rules, as POSIX requires.
 104 \f
 105 Changes in version 1.875, 2003-01-01:
 106
 107 * The documentation license has been upgraded to version 1.2
 108   of the GNU Free Documentation License.
 109
 110 * syntax error processing
 111
 112   - In Yacc-style parsers YYLLOC_DEFAULT is now used to compute error
 113     locations too.  This fixes bugs in error-location computation.
 114
 115   - %destructor
 116     It is now possible to reclaim the memory associated to symbols
 117     discarded during error recovery.  This feature is still experimental.
 118
 119   - %error-verbose
 120     This new directive is preferred over YYERROR_VERBOSE.
 121
 122   - #defining yyerror to steal internal variables is discouraged.
 123     It is not guaranteed to work forever.
 124
 125 * POSIX conformance
 126
 127   - Semicolons are once again optional at the end of grammar rules.
 128     This reverts to the behavior of Bison 1.33 and earlier, and improves
 129     compatibility with Yacc.
 130
 131   - `parse error' -> `syntax error'
 132     Bison now uniformly uses the term `syntax error'; formerly, the code
 133     and manual sometimes used the term `parse error' instead.  POSIX
 134     requires `syntax error' in diagnostics, and it was thought better to
 135     be consistent.
 136
 137   - The documentation now emphasizes that yylex and yyerror must be
 138     declared before use.  C99 requires this.
 139
 140   - Bison now parses C99 lexical constructs like UCNs and
 141     backslash-newline within C escape sequences, as POSIX 1003.1-2001 requires.
 142
 143   - File names are properly escaped in C output.  E.g., foo\bar.y is
 144     output as "foo\\bar.y".
 145
 146   - Yacc command and library now available
 147     The Bison distribution now installs a `yacc' command, as POSIX requires.
 148     Also, Bison now installs a small library liby.a containing
 149     implementations of Yacc-compatible yyerror and main functions.
 150     This library is normally not useful, but POSIX requires it.
 151
 152   - Type clashes now generate warnings, not errors.
 153
 154   - If the user does not define YYSTYPE as a macro, Bison now declares it
 155     using typedef instead of defining it as a macro.
 156     For consistency, YYLTYPE is also declared instead of defined.
 157
 158 * Other compatibility issues
 159
 160   - %union directives can now have a tag before the `{', e.g., the
 161     directive `%union foo {...}' now generates the C code
 162     `typedef union foo { ... } YYSTYPE;'; this is for Yacc compatibility.
 163     The default union tag is `YYSTYPE', for compatibility with Solaris 9 Yacc.
 164     For consistency, YYLTYPE's struct tag is now `YYLTYPE' not `yyltype'.
 165     This is for compatibility with both Yacc and Bison 1.35.
 166
 167   - `;' is output before the terminating `}' of an action, for
 168     compatibility with Bison 1.35.
 169
 170   - Bison now uses a Yacc-style format for conflict reports, e.g.,
 171     `conflicts: 2 shift/reduce, 1 reduce/reduce'.
 172
 173   - `yystype' and `yyltype' are now obsolescent macros instead of being
 174     typedefs or tags; they are no longer documented and are planned to be
 175     withdrawn in a future release.
 176
 177 * GLR parser notes
 178
 179   - GLR and inline
 180     Users of Bison have to decide how they handle the portability of the
 181     C keyword `inline'.
 182
 183   - `parsing stack overflow...' -> `parser stack overflow'
 184     GLR parsers now report `parser stack overflow' as per the Bison manual.
 185
 186 * Bison now warns if it detects conflicting outputs to the same file,
 187   e.g., it generates a warning for `bison -d -o foo.h foo.y' since
 188   that command outputs both code and header to foo.h.
 189
 190 * #line in output files
 191   - --no-line works properly.
 192
 193 * Bison can no longer be built by a K&R C compiler; it requires C89 or
 194   later to be built.  This change originally took place a few versions
 195   ago, but nobody noticed until we recently asked someone to try
 196   building Bison with a K&R C compiler.
 197 \f
 198 Changes in version 1.75, 2002-10-14:
 199
 200 * Bison should now work on 64-bit hosts.
 201
 202 * Indonesian translation thanks to Tedi Heriyanto.
 203
 204 * GLR parsers
 205   Fix spurious parse errors.
 206
 207 * Pure parsers
 208   Some people redefine yyerror to steal yyparse' private variables.
 209   Reenable this trick until an official feature replaces it.
 210
 211 * Type Clashes
 212   In agreement with POSIX and with other Yaccs, leaving a default
 213   action is valid when $$ is untyped, and $1 typed:
 214
 215         untyped: ... typed;
 216
 217   but the converse remains an error:
 218
 219         typed: ... untyped;
 220
 221 * Values of mid-rule actions
 222   The following code:
 223
 224         foo: { ... } { $$ = $1; } ...
 225
 226   was incorrectly rejected: $1 is defined in the second mid-rule
 227   action, and is equal to the $$ of the first mid-rule action.
 228 \f
 229 Changes in version 1.50, 2002-10-04:
 230
 231 * GLR parsing
 232   The declaration
 233      %glr-parser
 234   causes Bison to produce a Generalized LR (GLR) parser, capable of handling
 235   almost any context-free grammar, ambiguous or not.  The new declarations
 236   %dprec and %merge on grammar rules allow parse-time resolution of
 237   ambiguities.  Contributed by Paul Hilfinger.
 238
 239   Unfortunately Bison 1.50 does not work properly on 64-bit hosts
 240   like the Alpha, so please stick to 32-bit hosts for now.
 241
 242 * Output Directory
 243   When not in Yacc compatibility mode, when the output file was not
 244   specified, running `bison foo/bar.y' created `foo/bar.c'.  It
 245   now creates `bar.c'.
 246
 247 * Undefined token
 248   The undefined token was systematically mapped to 2 which prevented
 249   the use of 2 by the user.  This is no longer the case.
 250
 251 * Unknown token numbers
 252   If yylex returned an out of range value, yyparse could die.  This is
 253   no longer the case.
 254
 255 * Error token
 256   According to POSIX, the error token must be 256.
 257   Bison extends this requirement by making it a preference: *if* the
 258   user specified that one of her tokens is numbered 256, then error
 259   will be mapped onto another number.
 260
 261 * Verbose error messages
 262   They no longer report `..., expecting error or...' for states where
 263   error recovery is possible.
 264
 265 * End token
 266   Defaults to `$end' instead of `$'.
 267
 268 * Error recovery now conforms to documentation and to POSIX
 269   When a Bison-generated parser encounters a syntax error, it now pops
 270   the stack until it finds a state that allows shifting the error
 271   token.  Formerly, it popped the stack until it found a state that
 272   allowed some non-error action other than a default reduction on the
 273   error token.  The new behavior has long been the documented behavior,
 274   and has long been required by POSIX.  For more details, please see
 275   Paul Eggert, "Reductions during Bison error handling" (2002-05-20)
 276   <http://lists.gnu.org/archive/html/bug-bison/2002-05/msg00038.html>.
 277
 278 * Traces
 279   Popped tokens and nonterminals are now reported.
 280
 281 * Larger grammars
 282   Larger grammars are now supported (larger token numbers, larger grammar
 283   size (= sum of the LHS and RHS lengths), larger LALR tables).
 284   Formerly, many of these numbers ran afoul of 16-bit limits;
 285   now these limits are 32 bits on most hosts.
 286
 287 * Explicit initial rule
 288   Bison used to play hacks with the initial rule, which the user does
 289   not write.  It is now explicit, and visible in the reports and
 290   graphs as rule 0.
 291
 292 * Useless rules
 293   Before, Bison reported the useless rules, but, although not used,
 294   included them in the parsers.  They are now actually removed.
 295
 296 * Useless rules, useless nonterminals
 297   They are now reported, as a warning, with their locations.
 298
 299 * Rules never reduced
 300   Rules that can never be reduced because of conflicts are now
 301   reported.
 302
 303 * Incorrect `Token not used'
 304   On a grammar such as
 305
 306            %token useless useful
 307            %%
 308            exp: '0' %prec useful;
 309
 310   where a token was used to set the precedence of the last rule,
 311   bison reported both `useful' and `useless' as useless tokens.
 312
 313 * Revert the C++ namespace changes introduced in 1.31
 314   as they caused too many portability hassles.
 315
 316 * Default locations
 317   By an accident of design, the default computation of @$ was
 318   performed after another default computation was performed: @$ = @1.
 319   The latter is now removed: YYLLOC_DEFAULT is fully responsible of
 320   the computation of @$.
 321
 322 * Token end-of-file
 323   The token end of file may be specified by the user, in which case,
 324   the user symbol is used in the reports, the graphs, and the verbose
 325   error messages instead of `$end', which remains being the default.
 326   For instance
 327      %token MYEOF 0
 328   or
 329      %token MYEOF 0 "end of file"
 330
 331 * Semantic parser
 332   This old option, which has been broken for ages, is removed.
 333
 334 * New translations
 335   Brazilian Portuguese, thanks to Alexandre Folle de Menezes.
 336   Croatian, thanks to Denis Lackovic.
 337
 338 * Incorrect token definitions
 339   When given `%token 'a' "A"', Bison used to output `#define 'a' 65'.
 340
 341 * Token definitions as enums
 342   Tokens are output both as the traditional #define's, and, provided
 343   the compiler supports ANSI C or is a C++ compiler, as enums.
 344   This lets debuggers display names instead of integers.
 345
 346 * Reports
 347   In addition to --verbose, bison supports --report=THINGS, which
 348   produces additional information:
 349   - itemset
 350     complete the core item sets with their closure
 351   - lookahead [changed to `look-ahead' in 1.875e and later]
 352     explicitly associate look-ahead tokens to items
 353   - solved
 354     describe shift/reduce conflicts solving.
 355     Bison used to systematically output this information on top of
 356     the report.  Solved conflicts are now attached to their states.
 357
 358 * Type clashes
 359   Previous versions don't complain when there is a type clash on
 360   the default action if the rule has a mid-rule action, such as in:
 361
 362       %type <foo> bar
 363       %%
 364       bar: '0' {} '0';
 365
 366   This is fixed.
 367
 368 * GNU M4 is now required when using Bison.
 369 \f
 370 Changes in version 1.35, 2002-03-25:
 371
 372 * C Skeleton
 373   Some projects use Bison's C parser with C++ compilers, and define
 374   YYSTYPE as a class.  The recent adjustment of C parsers for data
 375   alignment and 64 bit architectures made this impossible.
 376
 377   Because for the time being no real solution for C++ parser
 378   generation exists, kludges were implemented in the parser to
 379   maintain this use.  In the future, when Bison has C++ parsers, this
 380   kludge will be disabled.
 381
 382   This kludge also addresses some C++ problems when the stack was
 383   extended.
 384 \f
 385 Changes in version 1.34, 2002-03-12:
 386
 387 * File name clashes are detected
 388   $ bison foo.y -d -o foo.x
 389   fatal error: header and parser would both be named `foo.x'
 390
 391 * A missing `;' at the end of a rule triggers a warning
 392   In accordance with POSIX, and in agreement with other
 393   Yacc implementations, Bison will mandate this semicolon in the near
 394   future.  This eases the implementation of a Bison parser of Bison
 395   grammars by making this grammar LALR(1) instead of LR(2).  To
 396   facilitate the transition, this release introduces a warning.
 397
 398 * Revert the C++ namespace changes introduced in 1.31, as they caused too
 399   many portability hassles.
 400
 401 * DJGPP support added.
 402
 403 * Fix test suite portability problems.
 404 \f
 405 Changes in version 1.33, 2002-02-07:
 406
 407 * Fix C++ issues
 408   Groff could not be compiled for the definition of size_t was lacking
 409   under some conditions.
 410
 411 * Catch invalid @n
 412   As is done with $n.
 413 \f
 414 Changes in version 1.32, 2002-01-23:
 415
 416 * Fix Yacc output file names
 417
 418 * Portability fixes
 419
 420 * Italian, Dutch translations
 421 \f
 422 Changes in version 1.31, 2002-01-14:
 423
 424 * Many Bug Fixes
 425
 426 * GNU Gettext and %expect
 427   GNU Gettext asserts 10 s/r conflicts, but there are 7.  Now that
 428   Bison dies on incorrect %expectations, we fear there will be
 429   too many bug reports for Gettext, so _for the time being_, %expect
 430   does not trigger an error when the input file is named `plural.y'.
 431
 432 * Use of alloca in parsers
 433   If YYSTACK_USE_ALLOCA is defined to 0, then the parsers will use
 434   malloc exclusively.  Since 1.29, but was not NEWS'ed.
 435
 436   alloca is used only when compiled with GCC, to avoid portability
 437   problems as on AIX.
 438
 439 * yyparse now returns 2 if memory is exhausted; formerly it dumped core.
 440
 441 * When the generated parser lacks debugging code, YYDEBUG is now 0
 442   (as POSIX requires) instead of being undefined.
 443
 444 * User Actions
 445   Bison has always permitted actions such as { $$ = $1 }: it adds the
 446   ending semicolon.  Now if in Yacc compatibility mode, the semicolon
 447   is no longer output: one has to write { $$ = $1; }.
 448
 449 * Better C++ compliance
 450   The output parsers try to respect C++ namespaces.
 451   [This turned out to be a failed experiment, and it was reverted later.]
 452
 453 * Reduced Grammars
 454   Fixed bugs when reporting useless nonterminals.
 455
 456 * 64 bit hosts
 457   The parsers work properly on 64 bit hosts.
 458
 459 * Error messages
 460   Some calls to strerror resulted in scrambled or missing error messages.
 461
 462 * %expect
 463   When the number of shift/reduce conflicts is correct, don't issue
 464   any warning.
 465
 466 * The verbose report includes the rule line numbers.
 467
 468 * Rule line numbers are fixed in traces.
 469
 470 * Swedish translation
 471
 472 * Parse errors
 473   Verbose parse error messages from the parsers are better looking.
 474   Before: parse error: unexpected `'/'', expecting `"number"' or `'-'' or `'(''
 475      Now: parse error: unexpected '/', expecting "number" or '-' or '('
 476
 477 * Fixed parser memory leaks.
 478   When the generated parser was using malloc to extend its stacks, the
 479   previous allocations were not freed.
 480
 481 * Fixed verbose output file.
 482   Some newlines were missing.
 483   Some conflicts in state descriptions were missing.
 484
 485 * Fixed conflict report.
 486   Option -v was needed to get the result.
 487
 488 * %expect
 489   Was not used.
 490   Mismatches are errors, not warnings.
 491
 492 * Fixed incorrect processing of some invalid input.
 493
 494 * Fixed CPP guards: 9foo.h uses BISON_9FOO_H instead of 9FOO_H.
 495
 496 * Fixed some typos in the documentation.
 497
 498 * %token MY_EOF 0 is supported.
 499   Before, MY_EOF was silently renumbered as 257.
 500
 501 * doc/refcard.tex is updated.
 502
 503 * %output, %file-prefix, %name-prefix.
 504   New.
 505
 506 * --output
 507   New, aliasing `--output-file'.
 508 \f
 509 Changes in version 1.30, 2001-10-26:
 510
 511 * `--defines' and `--graph' have now an optional argument which is the
 512   output file name. `-d' and `-g' do not change; they do not take any
 513   argument.
 514
 515 * `%source_extension' and `%header_extension' are removed, failed
 516   experiment.
 517
 518 * Portability fixes.
 519 \f
 520 Changes in version 1.29, 2001-09-07:
 521
 522 * The output file does not define const, as this caused problems when used
 523   with common autoconfiguration schemes.  If you still use ancient compilers
 524   that lack const, compile with the equivalent of the C compiler option
 525   `-Dconst='.  autoconf's AC_C_CONST macro provides one way to do this.
 526
 527 * Added `-g' and `--graph'.
 528
 529 * The Bison manual is now distributed under the terms of the GNU FDL.
 530
 531 * The input and the output files has automatically a similar extension.
 532
 533 * Russian translation added.
 534
 535 * NLS support updated; should hopefully be less troublesome.
 536
 537 * Added the old Bison reference card.
 538
 539 * Added `--locations' and `%locations'.
 540
 541 * Added `-S' and `--skeleton'.
 542
 543 * `%raw', `-r', `--raw' is disabled.
 544
 545 * Special characters are escaped when output.  This solves the problems
 546   of the #line lines with path names including backslashes.
 547
 548 * New directives.
 549   `%yacc', `%fixed_output_files', `%defines', `%no_parser', `%verbose',
 550   `%debug', `%source_extension' and `%header_extension'.
 551
 552 * @$
 553   Automatic location tracking.
 554 \f
 555 Changes in version 1.28, 1999-07-06:
 556
 557 * Should compile better now with K&R compilers.
 558
 559 * Added NLS.
 560
 561 * Fixed a problem with escaping the double quote character.
 562
 563 * There is now a FAQ.
 564 \f
 565 Changes in version 1.27:
 566
 567 * The make rule which prevented bison.simple from being created on
 568   some systems has been fixed.
 569 \f
 570 Changes in version 1.26:
 571
 572 * Bison now uses automake.
 573
 574 * New mailing lists: <bug-bison@gnu.org> and <help-bison@gnu.org>.
 575
 576 * Token numbers now start at 257 as previously documented, not 258.
 577
 578 * Bison honors the TMPDIR environment variable.
 579
 580 * A couple of buffer overruns have been fixed.
 581
 582 * Problems when closing files should now be reported.
 583
 584 * Generated parsers should now work even on operating systems which do
 585   not provide alloca().
 586 \f
 587 Changes in version 1.25, 1995-10-16:
 588
 589 * Errors in the input grammar are not fatal; Bison keeps reading
 590 the grammar file, and reports all the errors found in it.
 591
 592 * Tokens can now be specified as multiple-character strings: for
 593 example, you could use "<=" for a token which looks like <=, instead
 594 of chosing a name like LESSEQ.
 595
 596 * The %token_table declaration says to write a table of tokens (names
 597 and numbers) into the parser file.  The yylex function can use this
 598 table to recognize multiple-character string tokens, or for other
 599 purposes.
 600
 601 * The %no_lines declaration says not to generate any #line preprocessor
 602 directives in the parser file.
 603
 604 * The %raw declaration says to use internal Bison token numbers, not
 605 Yacc-compatible token numbers, when token names are defined as macros.
 606
 607 * The --no-parser option produces the parser tables without including
 608 the parser engine; a project can now use its own parser engine.
 609 The actions go into a separate file called NAME.act, in the form of
 610 a switch statement body.
 611 \f
 612 Changes in version 1.23:
 613
 614 The user can define YYPARSE_PARAM as the name of an argument to be
 615 passed into yyparse.  The argument should have type void *.  It should
 616 actually point to an object.  Grammar actions can access the variable
 617 by casting it to the proper pointer type.
 618
 619 Line numbers in output file corrected.
 620 \f
 621 Changes in version 1.22:
 622
 623 --help option added.
 624 \f
 625 Changes in version 1.20:
 626
 627 Output file does not redefine const for C++.
 628
 629 Local Variables:
 630 mode: outline
 631 End:
 632
 633 -----
 634
 635 Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005
 636 Free Software Foundation, Inc.
 637
 638 This file is part of Bison, the GNU Compiler Compiler.
 639
 640 Bison is free software; you can redistribute it and/or modify
 641 it under the terms of the GNU General Public License as published by
 642 the Free Software Foundation; either version 2, or (at your option)
 643 any later version.
 644
 645 Bison is distributed in the hope that it will be useful,
 646 but WITHOUT ANY WARRANTY; without even the implied warranty of
 647 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 648 GNU General Public License for more details.
 649
 650 You should have received a copy of the GNU General Public License
 651 along with autoconf; see the file COPYING.  If not, write to
 652 the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
 653 Boston, MA 02110-1301, USA.