NEWS

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