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