NEWS

   1 Bison News
   2 ----------
   3
   4 Changes in version 2.1a:
   5
   6 * DJGPP support added.
   7
   8 * %require "VERSION"
   9   To specify the youngest version of Bison accepted by the grammar file.
  10
  11 * lalr1.cc: The token and value types are now class members.
  12   The tokens where defined as free form enums and cpp macros.  YYSTYPE
  13   was defined as a free form union.  Both are now class members:
  14   tokens are enumerations of the `yy::parser::token' struct, and the
  15   semantic values have the `yy::parser::semantic_type' type.
  16
  17   If you do not want or can update to this scheme, the directive
  18   `%define "global_tokens_and_yystype" "1"' triggers the global
  19   definition of tokens and YYSTYPE.  This change is suitable both
  20   for previous releases of Bison, and this one.
  21
  22   If you wish to update, then make sure older version of Bison will
  23   fail using `%require "2.1a"'.
  24
  25 Changes in version 2.1, 2005-09-16:
  26
  27 * Bison-generated parsers now support the translation of diagnostics like
  28   "syntax error" into languages other than English.  The default
  29   language is still English.  For details, please see the new
  30   Internationalization section of the Bison manual.  Software
  31   distributors should also see the new PACKAGING file.  Thanks to
  32   Bruno Haible for this new feature.
  33
  34 * Wording in the Bison-generated parsers has been changed slightly to
  35   simplify translation.  In particular, the message "memory exhausted"
  36   has replaced "parser stack overflow", as the old message was not
  37   always accurate for modern Bison-generated parsers.
  38
  39 * Destructors are now called when the parser aborts, for all symbols left
  40   behind on the stack.  Also, the start symbol is now destroyed after a
  41   successful parse.  In both cases, the behavior was formerly inconsistent.
  42
  43 * When generating verbose diagnostics, Bison-generated parsers no longer
  44   quote the literal strings associated with tokens.  For example, for
  45   a syntax error associated with '%token NUM "number"' they might
  46   print 'syntax error, unexpected number' instead of 'syntax error,
  47   unexpected "number"'.
  48
  49 Changes in version 2.0, 2004-12-25:
  50
  51 * Possibly-incompatible changes
  52
  53   - Bison-generated parsers no longer default to using the alloca function
  54     (when available) to extend the parser stack, due to widespread
  55     problems in unchecked stack-overflow detection.  You can "#define
  56     YYSTACK_USE_ALLOCA 1" to require the use of alloca, but please read
  57     the manual to determine safe values for YYMAXDEPTH in that case.
  58
  59   - Error token location.
  60     During error recovery, the location of the syntax error is updated
  61     to cover the whole sequence covered by the error token: it includes
  62     the shifted symbols thrown away during the first part of the error
  63     recovery, and the lookahead rejected during the second part.
  64
  65   - Semicolon changes:
  66     . Stray semicolons are no longer allowed at the start of a grammar.
  67     . Semicolons are now required after in-grammar declarations.
  68
  69   - Unescaped newlines are no longer allowed in character constants or
  70     string literals.  They were never portable, and GCC 3.4.0 has
  71     dropped support for them.  Better diagnostics are now generated if
  72     forget a closing quote.
  73
  74   - NUL bytes are no longer allowed in Bison string literals, unfortunately.
  75
  76 * New features
  77
  78   - GLR grammars now support locations.
  79
  80   - New directive: %initial-action.
  81     This directive allows the user to run arbitrary code (including
  82     initializing @$) from yyparse before parsing starts.
  83
  84   - A new directive "%expect-rr N" specifies the expected number of
  85     reduce/reduce conflicts in GLR parsers.
  86
  87   - %token numbers can now be hexadecimal integers, e.g., `%token FOO 0x12d'.
  88     This is a GNU extension.
  89
  90   - The option `--report=lookahead' was changed to `--report=look-ahead'.
  91     The old spelling still works, but is not documented and will be
  92     removed.
  93
  94   - Experimental %destructor support has been added to lalr1.cc.
  95
  96   - New configure option --disable-yacc, to disable installation of the
  97     yacc command and -ly library introduced in 1.875 for POSIX conformance.
  98
  99 * Bug fixes
 100
 101   - For now, %expect-count violations are now just warnings, not errors.
 102     This is for compatibility with Bison 1.75 and earlier (when there are
 103     reduce/reduce conflicts) and with Bison 1.30 and earlier (when there
 104     are too many or too few shift/reduce conflicts).  However, in future
 105     versions of Bison we plan to improve the %expect machinery so that
 106     these violations will become errors again.
 107
 108   - Within Bison itself, numbers (e.g., goto numbers) are no longer
 109     arbitrarily limited to 16-bit counts.
 110
 111   - Semicolons are now allowed before "|" in grammar rules, as POSIX requires.
 112 \f
 113 Changes in version 1.875, 2003-01-01:
 114
 115 * The documentation license has been upgraded to version 1.2
 116   of the GNU Free Documentation License.
 117
 118 * syntax error processing
 119
 120   - In Yacc-style parsers YYLLOC_DEFAULT is now used to compute error
 121     locations too.  This fixes bugs in error-location computation.
 122
 123   - %destructor
 124     It is now possible to reclaim the memory associated to symbols
 125     discarded during error recovery.  This feature is still experimental.
 126
 127   - %error-verbose
 128     This new directive is preferred over YYERROR_VERBOSE.
 129
 130   - #defining yyerror to steal internal variables is discouraged.
 131     It is not guaranteed to work forever.
 132
 133 * POSIX conformance
 134
 135   - Semicolons are once again optional at the end of grammar rules.
 136     This reverts to the behavior of Bison 1.33 and earlier, and improves
 137     compatibility with Yacc.
 138
 139   - `parse error' -> `syntax error'
 140     Bison now uniformly uses the term `syntax error'; formerly, the code
 141     and manual sometimes used the term `parse error' instead.  POSIX
 142     requires `syntax error' in diagnostics, and it was thought better to
 143     be consistent.
 144
 145   - The documentation now emphasizes that yylex and yyerror must be
 146     declared before use.  C99 requires this.
 147
 148   - Bison now parses C99 lexical constructs like UCNs and
 149     backslash-newline within C escape sequences, as POSIX 1003.1-2001 requires.
 150
 151   - File names are properly escaped in C output.  E.g., foo\bar.y is
 152     output as "foo\\bar.y".
 153
 154   - Yacc command and library now available
 155     The Bison distribution now installs a `yacc' command, as POSIX requires.
 156     Also, Bison now installs a small library liby.a containing
 157     implementations of Yacc-compatible yyerror and main functions.
 158     This library is normally not useful, but POSIX requires it.
 159
 160   - Type clashes now generate warnings, not errors.
 161
 162   - If the user does not define YYSTYPE as a macro, Bison now declares it
 163     using typedef instead of defining it as a macro.
 164     For consistency, YYLTYPE is also declared instead of defined.
 165
 166 * Other compatibility issues
 167
 168   - %union directives can now have a tag before the `{', e.g., the
 169     directive `%union foo {...}' now generates the C code
 170     `typedef union foo { ... } YYSTYPE;'; this is for Yacc compatibility.
 171     The default union tag is `YYSTYPE', for compatibility with Solaris 9 Yacc.
 172     For consistency, YYLTYPE's struct tag is now `YYLTYPE' not `yyltype'.
 173     This is for compatibility with both Yacc and Bison 1.35.
 174
 175   - `;' is output before the terminating `}' of an action, for
 176     compatibility with Bison 1.35.
 177
 178   - Bison now uses a Yacc-style format for conflict reports, e.g.,
 179     `conflicts: 2 shift/reduce, 1 reduce/reduce'.
 180
 181   - `yystype' and `yyltype' are now obsolescent macros instead of being
 182     typedefs or tags; they are no longer documented and are planned to be
 183     withdrawn in a future release.
 184
 185 * GLR parser notes
 186
 187   - GLR and inline
 188     Users of Bison have to decide how they handle the portability of the
 189     C keyword `inline'.
 190
 191   - `parsing stack overflow...' -> `parser stack overflow'
 192     GLR parsers now report `parser stack overflow' as per the Bison manual.
 193
 194 * Bison now warns if it detects conflicting outputs to the same file,
 195   e.g., it generates a warning for `bison -d -o foo.h foo.y' since
 196   that command outputs both code and header to foo.h.
 197
 198 * #line in output files
 199   - --no-line works properly.
 200
 201 * Bison can no longer be built by a K&R C compiler; it requires C89 or
 202   later to be built.  This change originally took place a few versions
 203   ago, but nobody noticed until we recently asked someone to try
 204   building Bison with a K&R C compiler.
 205 \f
 206 Changes in version 1.75, 2002-10-14:
 207
 208 * Bison should now work on 64-bit hosts.
 209
 210 * Indonesian translation thanks to Tedi Heriyanto.
 211
 212 * GLR parsers
 213   Fix spurious parse errors.
 214
 215 * Pure parsers
 216   Some people redefine yyerror to steal yyparse' private variables.
 217   Reenable this trick until an official feature replaces it.
 218
 219 * Type Clashes
 220   In agreement with POSIX and with other Yaccs, leaving a default
 221   action is valid when $$ is untyped, and $1 typed:
 222
 223         untyped: ... typed;
 224
 225   but the converse remains an error:
 226
 227         typed: ... untyped;
 228
 229 * Values of mid-rule actions
 230   The following code:
 231
 232         foo: { ... } { $$ = $1; } ...
 233
 234   was incorrectly rejected: $1 is defined in the second mid-rule
 235   action, and is equal to the $$ of the first mid-rule action.
 236 \f
 237 Changes in version 1.50, 2002-10-04:
 238
 239 * GLR parsing
 240   The declaration
 241      %glr-parser
 242   causes Bison to produce a Generalized LR (GLR) parser, capable of handling
 243   almost any context-free grammar, ambiguous or not.  The new declarations
 244   %dprec and %merge on grammar rules allow parse-time resolution of
 245   ambiguities.  Contributed by Paul Hilfinger.
 246
 247   Unfortunately Bison 1.50 does not work properly on 64-bit hosts
 248   like the Alpha, so please stick to 32-bit hosts for now.
 249
 250 * Output Directory
 251   When not in Yacc compatibility mode, when the output file was not
 252   specified, running `bison foo/bar.y' created `foo/bar.c'.  It
 253   now creates `bar.c'.
 254
 255 * Undefined token
 256   The undefined token was systematically mapped to 2 which prevented
 257   the use of 2 by the user.  This is no longer the case.
 258
 259 * Unknown token numbers
 260   If yylex returned an out of range value, yyparse could die.  This is
 261   no longer the case.
 262
 263 * Error token
 264   According to POSIX, the error token must be 256.
 265   Bison extends this requirement by making it a preference: *if* the
 266   user specified that one of her tokens is numbered 256, then error
 267   will be mapped onto another number.
 268
 269 * Verbose error messages
 270   They no longer report `..., expecting error or...' for states where
 271   error recovery is possible.
 272
 273 * End token
 274   Defaults to `$end' instead of `$'.
 275
 276 * Error recovery now conforms to documentation and to POSIX
 277   When a Bison-generated parser encounters a syntax error, it now pops
 278   the stack until it finds a state that allows shifting the error
 279   token.  Formerly, it popped the stack until it found a state that
 280   allowed some non-error action other than a default reduction on the
 281   error token.  The new behavior has long been the documented behavior,
 282   and has long been required by POSIX.  For more details, please see
 283   Paul Eggert, "Reductions during Bison error handling" (2002-05-20)
 284   <http://lists.gnu.org/archive/html/bug-bison/2002-05/msg00038.html>.
 285
 286 * Traces
 287   Popped tokens and nonterminals are now reported.
 288
 289 * Larger grammars
 290   Larger grammars are now supported (larger token numbers, larger grammar
 291   size (= sum of the LHS and RHS lengths), larger LALR tables).
 292   Formerly, many of these numbers ran afoul of 16-bit limits;
 293   now these limits are 32 bits on most hosts.
 294
 295 * Explicit initial rule
 296   Bison used to play hacks with the initial rule, which the user does
 297   not write.  It is now explicit, and visible in the reports and
 298   graphs as rule 0.
 299
 300 * Useless rules
 301   Before, Bison reported the useless rules, but, although not used,
 302   included them in the parsers.  They are now actually removed.
 303
 304 * Useless rules, useless nonterminals
 305   They are now reported, as a warning, with their locations.
 306
 307 * Rules never reduced
 308   Rules that can never be reduced because of conflicts are now
 309   reported.
 310
 311 * Incorrect `Token not used'
 312   On a grammar such as
 313
 314            %token useless useful
 315            %%
 316            exp: '0' %prec useful;
 317
 318   where a token was used to set the precedence of the last rule,
 319   bison reported both `useful' and `useless' as useless tokens.
 320
 321 * Revert the C++ namespace changes introduced in 1.31
 322   as they caused too many portability hassles.
 323
 324 * Default locations
 325   By an accident of design, the default computation of @$ was
 326   performed after another default computation was performed: @$ = @1.
 327   The latter is now removed: YYLLOC_DEFAULT is fully responsible of
 328   the computation of @$.
 329
 330 * Token end-of-file
 331   The token end of file may be specified by the user, in which case,
 332   the user symbol is used in the reports, the graphs, and the verbose
 333   error messages instead of `$end', which remains being the default.
 334   For instance
 335      %token MYEOF 0
 336   or
 337      %token MYEOF 0 "end of file"
 338
 339 * Semantic parser
 340   This old option, which has been broken for ages, is removed.
 341
 342 * New translations
 343   Brazilian Portuguese, thanks to Alexandre Folle de Menezes.
 344   Croatian, thanks to Denis Lackovic.
 345
 346 * Incorrect token definitions
 347   When given `%token 'a' "A"', Bison used to output `#define 'a' 65'.
 348
 349 * Token definitions as enums
 350   Tokens are output both as the traditional #define's, and, provided
 351   the compiler supports ANSI C or is a C++ compiler, as enums.
 352   This lets debuggers display names instead of integers.
 353
 354 * Reports
 355   In addition to --verbose, bison supports --report=THINGS, which
 356   produces additional information:
 357   - itemset
 358     complete the core item sets with their closure
 359   - lookahead [changed to `look-ahead' in 1.875e and later]
 360     explicitly associate look-ahead tokens to items
 361   - solved
 362     describe shift/reduce conflicts solving.
 363     Bison used to systematically output this information on top of
 364     the report.  Solved conflicts are now attached to their states.
 365
 366 * Type clashes
 367   Previous versions don't complain when there is a type clash on
 368   the default action if the rule has a mid-rule action, such as in:
 369
 370       %type <foo> bar
 371       %%
 372       bar: '0' {} '0';
 373
 374   This is fixed.
 375
 376 * GNU M4 is now required when using Bison.
 377 \f
 378 Changes in version 1.35, 2002-03-25:
 379
 380 * C Skeleton
 381   Some projects use Bison's C parser with C++ compilers, and define
 382   YYSTYPE as a class.  The recent adjustment of C parsers for data
 383   alignment and 64 bit architectures made this impossible.
 384
 385   Because for the time being no real solution for C++ parser
 386   generation exists, kludges were implemented in the parser to
 387   maintain this use.  In the future, when Bison has C++ parsers, this
 388   kludge will be disabled.
 389
 390   This kludge also addresses some C++ problems when the stack was
 391   extended.
 392 \f
 393 Changes in version 1.34, 2002-03-12:
 394
 395 * File name clashes are detected
 396   $ bison foo.y -d -o foo.x
 397   fatal error: header and parser would both be named `foo.x'
 398
 399 * A missing `;' at the end of a rule triggers a warning
 400   In accordance with POSIX, and in agreement with other
 401   Yacc implementations, Bison will mandate this semicolon in the near
 402   future.  This eases the implementation of a Bison parser of Bison
 403   grammars by making this grammar LALR(1) instead of LR(2).  To
 404   facilitate the transition, this release introduces a warning.
 405
 406 * Revert the C++ namespace changes introduced in 1.31, as they caused too
 407   many portability hassles.
 408
 409 * DJGPP support added.
 410
 411 * Fix test suite portability problems.
 412 \f
 413 Changes in version 1.33, 2002-02-07:
 414
 415 * Fix C++ issues
 416   Groff could not be compiled for the definition of size_t was lacking
 417   under some conditions.
 418
 419 * Catch invalid @n
 420   As is done with $n.
 421 \f
 422 Changes in version 1.32, 2002-01-23:
 423
 424 * Fix Yacc output file names
 425
 426 * Portability fixes
 427
 428 * Italian, Dutch translations
 429 \f
 430 Changes in version 1.31, 2002-01-14:
 431
 432 * Many Bug Fixes
 433
 434 * GNU Gettext and %expect
 435   GNU Gettext asserts 10 s/r conflicts, but there are 7.  Now that
 436   Bison dies on incorrect %expectations, we fear there will be
 437   too many bug reports for Gettext, so _for the time being_, %expect
 438   does not trigger an error when the input file is named `plural.y'.
 439
 440 * Use of alloca in parsers
 441   If YYSTACK_USE_ALLOCA is defined to 0, then the parsers will use
 442   malloc exclusively.  Since 1.29, but was not NEWS'ed.
 443
 444   alloca is used only when compiled with GCC, to avoid portability
 445   problems as on AIX.
 446
 447 * yyparse now returns 2 if memory is exhausted; formerly it dumped core.
 448
 449 * When the generated parser lacks debugging code, YYDEBUG is now 0
 450   (as POSIX requires) instead of being undefined.
 451
 452 * User Actions
 453   Bison has always permitted actions such as { $$ = $1 }: it adds the
 454   ending semicolon.  Now if in Yacc compatibility mode, the semicolon
 455   is no longer output: one has to write { $$ = $1; }.
 456
 457 * Better C++ compliance
 458   The output parsers try to respect C++ namespaces.
 459   [This turned out to be a failed experiment, and it was reverted later.]
 460
 461 * Reduced Grammars
 462   Fixed bugs when reporting useless nonterminals.
 463
 464 * 64 bit hosts
 465   The parsers work properly on 64 bit hosts.
 466
 467 * Error messages
 468   Some calls to strerror resulted in scrambled or missing error messages.
 469
 470 * %expect
 471   When the number of shift/reduce conflicts is correct, don't issue
 472   any warning.
 473
 474 * The verbose report includes the rule line numbers.
 475
 476 * Rule line numbers are fixed in traces.
 477
 478 * Swedish translation
 479
 480 * Parse errors
 481   Verbose parse error messages from the parsers are better looking.
 482   Before: parse error: unexpected `'/'', expecting `"number"' or `'-'' or `'(''
 483      Now: parse error: unexpected '/', expecting "number" or '-' or '('
 484
 485 * Fixed parser memory leaks.
 486   When the generated parser was using malloc to extend its stacks, the
 487   previous allocations were not freed.
 488
 489 * Fixed verbose output file.
 490   Some newlines were missing.
 491   Some conflicts in state descriptions were missing.
 492
 493 * Fixed conflict report.
 494   Option -v was needed to get the result.
 495
 496 * %expect
 497   Was not used.
 498   Mismatches are errors, not warnings.
 499
 500 * Fixed incorrect processing of some invalid input.
 501
 502 * Fixed CPP guards: 9foo.h uses BISON_9FOO_H instead of 9FOO_H.
 503
 504 * Fixed some typos in the documentation.
 505
 506 * %token MY_EOF 0 is supported.
 507   Before, MY_EOF was silently renumbered as 257.
 508
 509 * doc/refcard.tex is updated.
 510
 511 * %output, %file-prefix, %name-prefix.
 512   New.
 513
 514 * --output
 515   New, aliasing `--output-file'.
 516 \f
 517 Changes in version 1.30, 2001-10-26:
 518
 519 * `--defines' and `--graph' have now an optional argument which is the
 520   output file name. `-d' and `-g' do not change; they do not take any
 521   argument.
 522
 523 * `%source_extension' and `%header_extension' are removed, failed
 524   experiment.
 525
 526 * Portability fixes.
 527 \f
 528 Changes in version 1.29, 2001-09-07:
 529
 530 * The output file does not define const, as this caused problems when used
 531   with common autoconfiguration schemes.  If you still use ancient compilers
 532   that lack const, compile with the equivalent of the C compiler option
 533   `-Dconst='.  autoconf's AC_C_CONST macro provides one way to do this.
 534
 535 * Added `-g' and `--graph'.
 536
 537 * The Bison manual is now distributed under the terms of the GNU FDL.
 538
 539 * The input and the output files has automatically a similar extension.
 540
 541 * Russian translation added.
 542
 543 * NLS support updated; should hopefully be less troublesome.
 544
 545 * Added the old Bison reference card.
 546
 547 * Added `--locations' and `%locations'.
 548
 549 * Added `-S' and `--skeleton'.
 550
 551 * `%raw', `-r', `--raw' is disabled.
 552
 553 * Special characters are escaped when output.  This solves the problems
 554   of the #line lines with path names including backslashes.
 555
 556 * New directives.
 557   `%yacc', `%fixed_output_files', `%defines', `%no_parser', `%verbose',
 558   `%debug', `%source_extension' and `%header_extension'.
 559
 560 * @$
 561   Automatic location tracking.
 562 \f
 563 Changes in version 1.28, 1999-07-06:
 564
 565 * Should compile better now with K&R compilers.
 566
 567 * Added NLS.
 568
 569 * Fixed a problem with escaping the double quote character.
 570
 571 * There is now a FAQ.
 572 \f
 573 Changes in version 1.27:
 574
 575 * The make rule which prevented bison.simple from being created on
 576   some systems has been fixed.
 577 \f
 578 Changes in version 1.26:
 579
 580 * Bison now uses automake.
 581
 582 * New mailing lists: <bug-bison@gnu.org> and <help-bison@gnu.org>.
 583
 584 * Token numbers now start at 257 as previously documented, not 258.
 585
 586 * Bison honors the TMPDIR environment variable.
 587
 588 * A couple of buffer overruns have been fixed.
 589
 590 * Problems when closing files should now be reported.
 591
 592 * Generated parsers should now work even on operating systems which do
 593   not provide alloca().
 594 \f
 595 Changes in version 1.25, 1995-10-16:
 596
 597 * Errors in the input grammar are not fatal; Bison keeps reading
 598 the grammar file, and reports all the errors found in it.
 599
 600 * Tokens can now be specified as multiple-character strings: for
 601 example, you could use "<=" for a token which looks like <=, instead
 602 of chosing a name like LESSEQ.
 603
 604 * The %token_table declaration says to write a table of tokens (names
 605 and numbers) into the parser file.  The yylex function can use this
 606 table to recognize multiple-character string tokens, or for other
 607 purposes.
 608
 609 * The %no_lines declaration says not to generate any #line preprocessor
 610 directives in the parser file.
 611
 612 * The %raw declaration says to use internal Bison token numbers, not
 613 Yacc-compatible token numbers, when token names are defined as macros.
 614
 615 * The --no-parser option produces the parser tables without including
 616 the parser engine; a project can now use its own parser engine.
 617 The actions go into a separate file called NAME.act, in the form of
 618 a switch statement body.
 619 \f
 620 Changes in version 1.23:
 621
 622 The user can define YYPARSE_PARAM as the name of an argument to be
 623 passed into yyparse.  The argument should have type void *.  It should
 624 actually point to an object.  Grammar actions can access the variable
 625 by casting it to the proper pointer type.
 626
 627 Line numbers in output file corrected.
 628 \f
 629 Changes in version 1.22:
 630
 631 --help option added.
 632 \f
 633 Changes in version 1.20:
 634
 635 Output file does not redefine const for C++.
 636
 637 Local Variables:
 638 mode: outline
 639 End:
 640
 641 -----
 642
 643 Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005
 644 Free Software Foundation, Inc.
 645
 646 This file is part of Bison, the GNU Compiler Compiler.
 647
 648 Bison is free software; you can redistribute it and/or modify
 649 it under the terms of the GNU General Public License as published by
 650 the Free Software Foundation; either version 2, or (at your option)
 651 any later version.
 652
 653 Bison is distributed in the hope that it will be useful,
 654 but WITHOUT ANY WARRANTY; without even the implied warranty of
 655 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 656 GNU General Public License for more details.
 657
 658 You should have received a copy of the GNU General Public License
 659 along with autoconf; see the file COPYING.  If not, write to
 660 the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
 661 Boston, MA 02110-1301, USA.