NEWS

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