NEWS

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