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 * 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 The following change was also in version 2.0a, 2005-05-22:
  23
  24 * When generating verbose diagnostics, Bison-generated parsers no longer
  25   quote the literal strings associated with tokens.  For example, for
  26   a syntax error associated with '%token NUM "number"' they might
  27   print 'syntax error, unexpected number' instead of 'syntax error,
  28   unexpected "number"'.
  29
  30 Changes in version 2.0, 2004-12-25:
  31
  32 * Possibly-incompatible changes
  33
  34   - Bison-generated parsers no longer default to using the alloca function
  35     (when available) to extend the parser stack, due to widespread
  36     problems in unchecked stack-overflow detection.  You can "#define
  37     YYSTACK_USE_ALLOCA 1" to require the use of alloca, but please read
  38     the manual to determine safe values for YYMAXDEPTH in that case.
  39
  40   - Error token location.
  41     During error recovery, the location of the syntax error is updated
  42     to cover the whole sequence covered by the error token: it includes
  43     the shifted symbols thrown away during the first part of the error
  44     recovery, and the lookahead rejected during the second part.
  45
  46   - Semicolon changes:
  47     . Stray semicolons are no longer allowed at the start of a grammar.
  48     . Semicolons are now required after in-grammar declarations.
  49
  50   - Unescaped newlines are no longer allowed in character constants or
  51     string literals.  They were never portable, and GCC 3.4.0 has
  52     dropped support for them.  Better diagnostics are now generated if
  53     forget a closing quote.
  54
  55   - NUL bytes are no longer allowed in Bison string literals, unfortunately.
  56
  57 * New features
  58
  59   - GLR grammars now support locations.
  60
  61   - New directive: %initial-action.
  62     This directive allows the user to run arbitrary code (including
  63     initializing @$) from yyparse before parsing starts.
  64
  65   - A new directive "%expect-rr N" specifies the expected number of
  66     reduce/reduce conflicts in GLR parsers.
  67
  68   - %token numbers can now be hexadecimal integers, e.g., `%token FOO 0x12d'.
  69     This is a GNU extension.
  70
  71   - The option `--report=lookahead' was changed to `--report=look-ahead'.
  72     The old spelling still works, but is not documented and will be
  73     removed.
  74
  75   - Experimental %destructor support has been added to lalr1.cc.
  76
  77   - New configure option --disable-yacc, to disable installation of the
  78     yacc command and -ly library introduced in 1.875 for POSIX conformance.
  79
  80 * Bug fixes
  81
  82   - For now, %expect-count violations are now just warnings, not errors.
  83     This is for compatibility with Bison 1.75 and earlier (when there are
  84     reduce/reduce conflicts) and with Bison 1.30 and earlier (when there
  85     are too many or too few shift/reduce conflicts).  However, in future
  86     versions of Bison we plan to improve the %expect machinery so that
  87     these violations will become errors again.
  88
  89   - Within Bison itself, numbers (e.g., goto numbers) are no longer
  90     arbitrarily limited to 16-bit counts.
  91
  92   - Semicolons are now allowed before "|" in grammar rules, as POSIX requires.
  93 \f
  94 Changes in version 1.875, 2003-01-01:
  95
  96 * The documentation license has been upgraded to version 1.2
  97   of the GNU Free Documentation License.
  98
  99 * syntax error processing
 100
 101   - In Yacc-style parsers YYLLOC_DEFAULT is now used to compute error
 102     locations too.  This fixes bugs in error-location computation.
 103
 104   - %destructor
 105     It is now possible to reclaim the memory associated to symbols
 106     discarded during error recovery.  This feature is still experimental.
 107
 108   - %error-verbose
 109     This new directive is preferred over YYERROR_VERBOSE.
 110
 111   - #defining yyerror to steal internal variables is discouraged.
 112     It is not guaranteed to work forever.
 113
 114 * POSIX conformance
 115
 116   - Semicolons are once again optional at the end of grammar rules.
 117     This reverts to the behavior of Bison 1.33 and earlier, and improves
 118     compatibility with Yacc.
 119
 120   - `parse error' -> `syntax error'
 121     Bison now uniformly uses the term `syntax error'; formerly, the code
 122     and manual sometimes used the term `parse error' instead.  POSIX
 123     requires `syntax error' in diagnostics, and it was thought better to
 124     be consistent.
 125
 126   - The documentation now emphasizes that yylex and yyerror must be
 127     declared before use.  C99 requires this.
 128
 129   - Bison now parses C99 lexical constructs like UCNs and
 130     backslash-newline within C escape sequences, as POSIX 1003.1-2001 requires.
 131
 132   - File names are properly escaped in C output.  E.g., foo\bar.y is
 133     output as "foo\\bar.y".
 134
 135   - Yacc command and library now available
 136     The Bison distribution now installs a `yacc' command, as POSIX requires.
 137     Also, Bison now installs a small library liby.a containing
 138     implementations of Yacc-compatible yyerror and main functions.
 139     This library is normally not useful, but POSIX requires it.
 140
 141   - Type clashes now generate warnings, not errors.
 142
 143   - If the user does not define YYSTYPE as a macro, Bison now declares it
 144     using typedef instead of defining it as a macro.
 145     For consistency, YYLTYPE is also declared instead of defined.
 146
 147 * Other compatibility issues
 148
 149   - %union directives can now have a tag before the `{', e.g., the
 150     directive `%union foo {...}' now generates the C code
 151     `typedef union foo { ... } YYSTYPE;'; this is for Yacc compatibility.
 152     The default union tag is `YYSTYPE', for compatibility with Solaris 9 Yacc.
 153     For consistency, YYLTYPE's struct tag is now `YYLTYPE' not `yyltype'.
 154     This is for compatibility with both Yacc and Bison 1.35.
 155
 156   - `;' is output before the terminating `}' of an action, for
 157     compatibility with Bison 1.35.
 158
 159   - Bison now uses a Yacc-style format for conflict reports, e.g.,
 160     `conflicts: 2 shift/reduce, 1 reduce/reduce'.
 161
 162   - `yystype' and `yyltype' are now obsolescent macros instead of being
 163     typedefs or tags; they are no longer documented and are planned to be
 164     withdrawn in a future release.
 165
 166 * GLR parser notes
 167
 168   - GLR and inline
 169     Users of Bison have to decide how they handle the portability of the
 170     C keyword `inline'.
 171
 172   - `parsing stack overflow...' -> `parser stack overflow'
 173     GLR parsers now report `parser stack overflow' as per the Bison manual.
 174
 175 * Bison now warns if it detects conflicting outputs to the same file,
 176   e.g., it generates a warning for `bison -d -o foo.h foo.y' since
 177   that command outputs both code and header to foo.h.
 178
 179 * #line in output files
 180   - --no-line works properly.
 181
 182 * Bison can no longer be built by a K&R C compiler; it requires C89 or
 183   later to be built.  This change originally took place a few versions
 184   ago, but nobody noticed until we recently asked someone to try
 185   building Bison with a K&R C compiler.
 186 \f
 187 Changes in version 1.75, 2002-10-14:
 188
 189 * Bison should now work on 64-bit hosts.
 190
 191 * Indonesian translation thanks to Tedi Heriyanto.
 192
 193 * GLR parsers
 194   Fix spurious parse errors.
 195
 196 * Pure parsers
 197   Some people redefine yyerror to steal yyparse' private variables.
 198   Reenable this trick until an official feature replaces it.
 199
 200 * Type Clashes
 201   In agreement with POSIX and with other Yaccs, leaving a default
 202   action is valid when $$ is untyped, and $1 typed:
 203
 204         untyped: ... typed;
 205
 206   but the converse remains an error:
 207
 208         typed: ... untyped;
 209
 210 * Values of mid-rule actions
 211   The following code:
 212
 213         foo: { ... } { $$ = $1; } ...
 214
 215   was incorrectly rejected: $1 is defined in the second mid-rule
 216   action, and is equal to the $$ of the first mid-rule action.
 217 \f
 218 Changes in version 1.50, 2002-10-04:
 219
 220 * GLR parsing
 221   The declaration
 222      %glr-parser
 223   causes Bison to produce a Generalized LR (GLR) parser, capable of handling
 224   almost any context-free grammar, ambiguous or not.  The new declarations
 225   %dprec and %merge on grammar rules allow parse-time resolution of
 226   ambiguities.  Contributed by Paul Hilfinger.
 227
 228   Unfortunately Bison 1.50 does not work properly on 64-bit hosts
 229   like the Alpha, so please stick to 32-bit hosts for now.
 230
 231 * Output Directory
 232   When not in Yacc compatibility mode, when the output file was not
 233   specified, running `bison foo/bar.y' created `foo/bar.c'.  It
 234   now creates `bar.c'.
 235
 236 * Undefined token
 237   The undefined token was systematically mapped to 2 which prevented
 238   the use of 2 by the user.  This is no longer the case.
 239
 240 * Unknown token numbers
 241   If yylex returned an out of range value, yyparse could die.  This is
 242   no longer the case.
 243
 244 * Error token
 245   According to POSIX, the error token must be 256.
 246   Bison extends this requirement by making it a preference: *if* the
 247   user specified that one of her tokens is numbered 256, then error
 248   will be mapped onto another number.
 249
 250 * Verbose error messages
 251   They no longer report `..., expecting error or...' for states where
 252   error recovery is possible.
 253
 254 * End token
 255   Defaults to `$end' instead of `$'.
 256
 257 * Error recovery now conforms to documentation and to POSIX
 258   When a Bison-generated parser encounters a syntax error, it now pops
 259   the stack until it finds a state that allows shifting the error
 260   token.  Formerly, it popped the stack until it found a state that
 261   allowed some non-error action other than a default reduction on the
 262   error token.  The new behavior has long been the documented behavior,
 263   and has long been required by POSIX.  For more details, please see
 264   Paul Eggert, "Reductions during Bison error handling" (2002-05-20)
 265   <http://lists.gnu.org/archive/html/bug-bison/2002-05/msg00038.html>.
 266
 267 * Traces
 268   Popped tokens and nonterminals are now reported.
 269
 270 * Larger grammars
 271   Larger grammars are now supported (larger token numbers, larger grammar
 272   size (= sum of the LHS and RHS lengths), larger LALR tables).
 273   Formerly, many of these numbers ran afoul of 16-bit limits;
 274   now these limits are 32 bits on most hosts.
 275
 276 * Explicit initial rule
 277   Bison used to play hacks with the initial rule, which the user does
 278   not write.  It is now explicit, and visible in the reports and
 279   graphs as rule 0.
 280
 281 * Useless rules
 282   Before, Bison reported the useless rules, but, although not used,
 283   included them in the parsers.  They are now actually removed.
 284
 285 * Useless rules, useless nonterminals
 286   They are now reported, as a warning, with their locations.
 287
 288 * Rules never reduced
 289   Rules that can never be reduced because of conflicts are now
 290   reported.
 291
 292 * Incorrect `Token not used'
 293   On a grammar such as
 294
 295            %token useless useful
 296            %%
 297            exp: '0' %prec useful;
 298
 299   where a token was used to set the precedence of the last rule,
 300   bison reported both `useful' and `useless' as useless tokens.
 301
 302 * Revert the C++ namespace changes introduced in 1.31
 303   as they caused too many portability hassles.
 304
 305 * Default locations
 306   By an accident of design, the default computation of @$ was
 307   performed after another default computation was performed: @$ = @1.
 308   The latter is now removed: YYLLOC_DEFAULT is fully responsible of
 309   the computation of @$.
 310
 311 * Token end-of-file
 312   The token end of file may be specified by the user, in which case,
 313   the user symbol is used in the reports, the graphs, and the verbose
 314   error messages instead of `$end', which remains being the default.
 315   For instance
 316      %token MYEOF 0
 317   or
 318      %token MYEOF 0 "end of file"
 319
 320 * Semantic parser
 321   This old option, which has been broken for ages, is removed.
 322
 323 * New translations
 324   Brazilian Portuguese, thanks to Alexandre Folle de Menezes.
 325   Croatian, thanks to Denis Lackovic.
 326
 327 * Incorrect token definitions
 328   When given `%token 'a' "A"', Bison used to output `#define 'a' 65'.
 329
 330 * Token definitions as enums
 331   Tokens are output both as the traditional #define's, and, provided
 332   the compiler supports ANSI C or is a C++ compiler, as enums.
 333   This lets debuggers display names instead of integers.
 334
 335 * Reports
 336   In addition to --verbose, bison supports --report=THINGS, which
 337   produces additional information:
 338   - itemset
 339     complete the core item sets with their closure
 340   - lookahead [changed to `look-ahead' in 1.875e and later]
 341     explicitly associate look-ahead tokens to items
 342   - solved
 343     describe shift/reduce conflicts solving.
 344     Bison used to systematically output this information on top of
 345     the report.  Solved conflicts are now attached to their states.
 346
 347 * Type clashes
 348   Previous versions don't complain when there is a type clash on
 349   the default action if the rule has a mid-rule action, such as in:
 350
 351       %type <foo> bar
 352       %%
 353       bar: '0' {} '0';
 354
 355   This is fixed.
 356
 357 * GNU M4 is now required when using Bison.
 358 \f
 359 Changes in version 1.35, 2002-03-25:
 360
 361 * C Skeleton
 362   Some projects use Bison's C parser with C++ compilers, and define
 363   YYSTYPE as a class.  The recent adjustment of C parsers for data
 364   alignment and 64 bit architectures made this impossible.
 365
 366   Because for the time being no real solution for C++ parser
 367   generation exists, kludges were implemented in the parser to
 368   maintain this use.  In the future, when Bison has C++ parsers, this
 369   kludge will be disabled.
 370
 371   This kludge also addresses some C++ problems when the stack was
 372   extended.
 373 \f
 374 Changes in version 1.34, 2002-03-12:
 375
 376 * File name clashes are detected
 377   $ bison foo.y -d -o foo.x
 378   fatal error: header and parser would both be named `foo.x'
 379
 380 * A missing `;' at the end of a rule triggers a warning
 381   In accordance with POSIX, and in agreement with other
 382   Yacc implementations, Bison will mandate this semicolon in the near
 383   future.  This eases the implementation of a Bison parser of Bison
 384   grammars by making this grammar LALR(1) instead of LR(2).  To
 385   facilitate the transition, this release introduces a warning.
 386
 387 * Revert the C++ namespace changes introduced in 1.31, as they caused too
 388   many portability hassles.
 389
 390 * DJGPP support added.
 391
 392 * Fix test suite portability problems.
 393 \f
 394 Changes in version 1.33, 2002-02-07:
 395
 396 * Fix C++ issues
 397   Groff could not be compiled for the definition of size_t was lacking
 398   under some conditions.
 399
 400 * Catch invalid @n
 401   As is done with $n.
 402 \f
 403 Changes in version 1.32, 2002-01-23:
 404
 405 * Fix Yacc output file names
 406
 407 * Portability fixes
 408
 409 * Italian, Dutch translations
 410 \f
 411 Changes in version 1.31, 2002-01-14:
 412
 413 * Many Bug Fixes
 414
 415 * GNU Gettext and %expect
 416   GNU Gettext asserts 10 s/r conflicts, but there are 7.  Now that
 417   Bison dies on incorrect %expectations, we fear there will be
 418   too many bug reports for Gettext, so _for the time being_, %expect
 419   does not trigger an error when the input file is named `plural.y'.
 420
 421 * Use of alloca in parsers
 422   If YYSTACK_USE_ALLOCA is defined to 0, then the parsers will use
 423   malloc exclusively.  Since 1.29, but was not NEWS'ed.
 424
 425   alloca is used only when compiled with GCC, to avoid portability
 426   problems as on AIX.
 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.