NEWS

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