NEWS

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