NEWS

   1 Bison News
   2 ----------
   3
   4 Changes in version 1.875e:
   5
   6 * The option `--report=lookahead' was changed to `--report=look-ahead'.
   7   The old spelling still works, but is not documented and will be removed.
   8
   9 Changes in version 1.875d, 2004-05-21:
  10
  11 * Unescaped newlines are no longer allowed in character constants or
  12   string literals.  They were never portable, and GCC 3.4.0 has
  13   dropped support for them.  Better diagnostics are now generated if
  14   forget a closing quote.
  15
  16 * NUL bytes are no longer allowed in Bison string literals, unfortunately.
  17
  18 * %token numbers can now be hexadecimal integers, e.g., `%token FOO 0x12d'.
  19   This is a GNU extension.
  20
  21 * A new directive "%expect-rr N" specifies the expected number of
  22   reduce/reduce conflicts in GLR parsers.
  23
  24 * Experimental %destructor support has been added to lalr1.cc.
  25
  26 Changes in version 1.875c, 2003-08-25:
  27
  28   (Just bug fixes.)
  29
  30 Changes in version 1.875b, 2003-06-17:
  31
  32 * GLR grammars now support locations.
  33
  34 * Semicolon changes:
  35   - Semicolons are now allowed before "|" in grammar rules, as POSIX requires.
  36   - Stray semicolons are no longer allowed at the start of a grammar.
  37   - Semicolons are now required after in-grammar declarations.
  38
  39 Changes in version 1.875a, 2003-02-01:
  40
  41 * For now, %expect-count violations are now just warnings, not errors.
  42   This is for compatibility with Bison 1.75 and earlier (when there are
  43   reduce/reduce conflicts) and with Bison 1.30 and earlier (when there
  44   are too many or too few shift/reduce conflicts).  However, in future
  45   versions of Bison we plan to improve the %expect machinery so that
  46   these violations will become errors again.
  47
  48 * New configure option --disable-yacc, to disable installation of the
  49   yacc command and -ly library introduced in 1.875 for POSIX conformance.
  50 \f
  51 Changes in version 1.875, 2003-01-01:
  52
  53 * The documentation license has been upgraded to version 1.2
  54   of the GNU Free Documentation License.
  55
  56 * syntax error processing
  57
  58   - In Yacc-style parsers YYLLOC_DEFAULT is now used to compute error
  59     locations too.  This fixes bugs in error-location computation.
  60
  61   - %destructor
  62     It is now possible to reclaim the memory associated to symbols
  63     discarded during error recovery.  This feature is still experimental.
  64
  65   - %error-verbose
  66     This new directive is preferred over YYERROR_VERBOSE.
  67
  68   - #defining yyerror to steal internal variables is discouraged.
  69     It is not guaranteed to work forever.
  70
  71 * POSIX conformance
  72
  73   - Semicolons are once again optional at the end of grammar rules.
  74     This reverts to the behavior of Bison 1.33 and earlier, and improves
  75     compatibility with Yacc.
  76
  77   - `parse error' -> `syntax error'
  78     Bison now uniformly uses the term `syntax error'; formerly, the code
  79     and manual sometimes used the term `parse error' instead.  POSIX
  80     requires `syntax error' in diagnostics, and it was thought better to
  81     be consistent.
  82
  83   - The documentation now emphasizes that yylex and yyerror must be
  84     declared before use.  C99 requires this.
  85
  86   - Bison now parses C99 lexical constructs like UCNs and
  87     backslash-newline within C escape sequences, as POSIX 1003.1-2001 requires.
  88
  89   - File names are properly escaped in C output.  E.g., foo\bar.y is
  90     output as "foo\\bar.y".
  91
  92   - Yacc command and library now available
  93     The Bison distribution now installs a `yacc' command, as POSIX requires.
  94     Also, Bison now installs a small library liby.a containing
  95     implementations of Yacc-compatible yyerror and main functions.
  96     This library is normally not useful, but POSIX requires it.
  97
  98   - Type clashes now generate warnings, not errors.
  99
 100   - If the user does not define YYSTYPE as a macro, Bison now declares it
 101     using typedef instead of defining it as a macro.
 102     For consistency, YYLTYPE is also declared instead of defined.
 103
 104 * Other compatibility issues
 105
 106   - %union directives can now have a tag before the `{', e.g., the
 107     directive `%union foo {...}' now generates the C code
 108     `typedef union foo { ... } YYSTYPE;'; this is for Yacc compatibility.
 109     The default union tag is `YYSTYPE', for compatibility with Solaris 9 Yacc.
 110     For consistency, YYLTYPE's struct tag is now `YYLTYPE' not `yyltype'.
 111     This is for compatibility with both Yacc and Bison 1.35.
 112
 113   - `;' is output before the terminating `}' of an action, for
 114     compatibility with Bison 1.35.
 115
 116   - Bison now uses a Yacc-style format for conflict reports, e.g.,
 117     `conflicts: 2 shift/reduce, 1 reduce/reduce'.
 118
 119   - `yystype' and `yyltype' are now obsolescent macros instead of being
 120     typedefs or tags; they are no longer documented and are planned to be
 121     withdrawn in a future release.
 122
 123 * GLR parser notes
 124
 125   - GLR and inline
 126     Users of Bison have to decide how they handle the portability of the
 127     C keyword `inline'.
 128
 129   - `parsing stack overflow...' -> `parser stack overflow'
 130     GLR parsers now report `parser stack overflow' as per the Bison manual.
 131
 132 * Bison now warns if it detects conflicting outputs to the same file,
 133   e.g., it generates a warning for `bison -d -o foo.h foo.y' since
 134   that command outputs both code and header to foo.h.
 135
 136 * #line in output files
 137   - --no-line works properly.
 138
 139 * Bison can no longer be built by a K&R C compiler; it requires C89 or
 140   later to be built.  This change originally took place a few versions
 141   ago, but nobody noticed until we recently asked someone to try
 142   building Bison with a K&R C compiler.
 143 \f
 144 Changes in version 1.75, 2002-10-14:
 145
 146 * Bison should now work on 64-bit hosts.
 147
 148 * Indonesian translation thanks to Tedi Heriyanto.
 149
 150 * GLR parsers
 151   Fix spurious parse errors.
 152
 153 * Pure parsers
 154   Some people redefine yyerror to steal yyparse' private variables.
 155   Reenable this trick until an official feature replaces it.
 156
 157 * Type Clashes
 158   In agreement with POSIX and with other Yaccs, leaving a default
 159   action is valid when $$ is untyped, and $1 typed:
 160
 161         untyped: ... typed;
 162
 163   but the converse remains an error:
 164
 165         typed: ... untyped;
 166
 167 * Values of mid-rule actions
 168   The following code:
 169
 170         foo: { ... } { $$ = $1; } ...
 171
 172   was incorrectly rejected: $1 is defined in the second mid-rule
 173   action, and is equal to the $$ of the first mid-rule action.
 174 \f
 175 Changes in version 1.50, 2002-10-04:
 176
 177 * GLR parsing
 178   The declaration
 179      %glr-parser
 180   causes Bison to produce a Generalized LR (GLR) parser, capable of handling
 181   almost any context-free grammar, ambiguous or not.  The new declarations
 182   %dprec and %merge on grammar rules allow parse-time resolution of
 183   ambiguities.  Contributed by Paul Hilfinger.
 184
 185   Unfortunately Bison 1.50 does not work properly on 64-bit hosts
 186   like the Alpha, so please stick to 32-bit hosts for now.
 187
 188 * Output Directory
 189   When not in Yacc compatibility mode, when the output file was not
 190   specified, running `bison foo/bar.y' created `foo/bar.c'.  It
 191   now creates `bar.c'.
 192
 193 * Undefined token
 194   The undefined token was systematically mapped to 2 which prevented
 195   the use of 2 by the user.  This is no longer the case.
 196
 197 * Unknown token numbers
 198   If yylex returned an out of range value, yyparse could die.  This is
 199   no longer the case.
 200
 201 * Error token
 202   According to POSIX, the error token must be 256.
 203   Bison extends this requirement by making it a preference: *if* the
 204   user specified that one of her tokens is numbered 256, then error
 205   will be mapped onto another number.
 206
 207 * Verbose error messages
 208   They no longer report `..., expecting error or...' for states where
 209   error recovery is possible.
 210
 211 * End token
 212   Defaults to `$end' instead of `$'.
 213
 214 * Error recovery now conforms to documentation and to POSIX
 215   When a Bison-generated parser encounters a syntax error, it now pops
 216   the stack until it finds a state that allows shifting the error
 217   token.  Formerly, it popped the stack until it found a state that
 218   allowed some non-error action other than a default reduction on the
 219   error token.  The new behavior has long been the documented behavior,
 220   and has long been required by POSIX.  For more details, please see
 221   <http://mail.gnu.org/pipermail/bug-bison/2002-May/001452.html>.
 222
 223 * Traces
 224   Popped tokens and nonterminals are now reported.
 225
 226 * Larger grammars
 227   Larger grammars are now supported (larger token numbers, larger grammar
 228   size (= sum of the LHS and RHS lengths), larger LALR tables).
 229   Formerly, many of these numbers ran afoul of 16-bit limits;
 230   now these limits are 32 bits on most hosts.
 231
 232 * Explicit initial rule
 233   Bison used to play hacks with the initial rule, which the user does
 234   not write.  It is now explicit, and visible in the reports and
 235   graphs as rule 0.
 236
 237 * Useless rules
 238   Before, Bison reported the useless rules, but, although not used,
 239   included them in the parsers.  They are now actually removed.
 240
 241 * Useless rules, useless nonterminals
 242   They are now reported, as a warning, with their locations.
 243
 244 * Rules never reduced
 245   Rules that can never be reduced because of conflicts are now
 246   reported.
 247
 248 * Incorrect `Token not used'
 249   On a grammar such as
 250
 251            %token useless useful
 252            %%
 253            exp: '0' %prec useful;
 254
 255   where a token was used to set the precedence of the last rule,
 256   bison reported both `useful' and `useless' as useless tokens.
 257
 258 * Revert the C++ namespace changes introduced in 1.31
 259   as they caused too many portability hassles.
 260
 261 * Default locations
 262   By an accident of design, the default computation of @$ was
 263   performed after another default computation was performed: @$ = @1.
 264   The latter is now removed: YYLLOC_DEFAULT is fully responsible of
 265   the computation of @$.
 266
 267 * Token end-of-file
 268   The token end of file may be specified by the user, in which case,
 269   the user symbol is used in the reports, the graphs, and the verbose
 270   error messages instead of `$end', which remains being the default.
 271   For instance
 272      %token MYEOF 0
 273   or
 274      %token MYEOF 0 "end of file"
 275
 276 * Semantic parser
 277   This old option, which has been broken for ages, is removed.
 278
 279 * New translations
 280   Brazilian Portuguese, thanks to Alexandre Folle de Menezes.
 281   Croatian, thanks to Denis Lackovic.
 282
 283 * Incorrect token definitions
 284   When given `%token 'a' "A"', Bison used to output `#define 'a' 65'.
 285
 286 * Token definitions as enums
 287   Tokens are output both as the traditional #define's, and, provided
 288   the compiler supports ANSI C or is a C++ compiler, as enums.
 289   This lets debuggers display names instead of integers.
 290
 291 * Reports
 292   In addition to --verbose, bison supports --report=THINGS, which
 293   produces additional information:
 294   - itemset
 295     complete the core item sets with their closure
 296   - lookahead [changed to `look-ahead' in 1.875e and later]
 297     explicitly associate look-ahead tokens to items
 298   - solved
 299     describe shift/reduce conflicts solving.
 300     Bison used to systematically output this information on top of
 301     the report.  Solved conflicts are now attached to their states.
 302
 303 * Type clashes
 304   Previous versions don't complain when there is a type clash on
 305   the default action if the rule has a mid-rule action, such as in:
 306
 307       %type <foo> bar
 308       %%
 309       bar: '0' {} '0';
 310
 311   This is fixed.
 312
 313 * GNU M4 is now required when using Bison.
 314 \f
 315 Changes in version 1.35, 2002-03-25:
 316
 317 * C Skeleton
 318   Some projects use Bison's C parser with C++ compilers, and define
 319   YYSTYPE as a class.  The recent adjustment of C parsers for data
 320   alignment and 64 bit architectures made this impossible.
 321
 322   Because for the time being no real solution for C++ parser
 323   generation exists, kludges were implemented in the parser to
 324   maintain this use.  In the future, when Bison has C++ parsers, this
 325   kludge will be disabled.
 326
 327   This kludge also addresses some C++ problems when the stack was
 328   extended.
 329 \f
 330 Changes in version 1.34, 2002-03-12:
 331
 332 * File name clashes are detected
 333   $ bison foo.y -d -o foo.x
 334   fatal error: header and parser would both be named `foo.x'
 335
 336 * A missing `;' at the end of a rule triggers a warning
 337   In accordance with POSIX, and in agreement with other
 338   Yacc implementations, Bison will mandate this semicolon in the near
 339   future.  This eases the implementation of a Bison parser of Bison
 340   grammars by making this grammar LALR(1) instead of LR(2).  To
 341   facilitate the transition, this release introduces a warning.
 342
 343 * Revert the C++ namespace changes introduced in 1.31, as they caused too
 344   many portability hassles.
 345
 346 * DJGPP support added.
 347
 348 * Fix test suite portability problems.
 349 \f
 350 Changes in version 1.33, 2002-02-07:
 351
 352 * Fix C++ issues
 353   Groff could not be compiled for the definition of size_t was lacking
 354   under some conditions.
 355
 356 * Catch invalid @n
 357   As is done with $n.
 358 \f
 359 Changes in version 1.32, 2002-01-23:
 360
 361 * Fix Yacc output file names
 362
 363 * Portability fixes
 364
 365 * Italian, Dutch translations
 366 \f
 367 Changes in version 1.31, 2002-01-14:
 368
 369 * Many Bug Fixes
 370
 371 * GNU Gettext and %expect
 372   GNU Gettext asserts 10 s/r conflicts, but there are 7.  Now that
 373   Bison dies on incorrect %expectations, we fear there will be
 374   too many bug reports for Gettext, so _for the time being_, %expect
 375   does not trigger an error when the input file is named `plural.y'.
 376
 377 * Use of alloca in parsers
 378   If YYSTACK_USE_ALLOCA is defined to 0, then the parsers will use
 379   malloc exclusively.  Since 1.29, but was not NEWS'ed.
 380
 381   alloca is used only when compiled with GCC, to avoid portability
 382   problems as on AIX.
 383
 384 * When the generated parser lacks debugging code, YYDEBUG is now 0
 385   (as POSIX requires) instead of being undefined.
 386
 387 * User Actions
 388   Bison has always permitted actions such as { $$ = $1 }: it adds the
 389   ending semicolon.  Now if in Yacc compatibility mode, the semicolon
 390   is no longer output: one has to write { $$ = $1; }.
 391
 392 * Better C++ compliance
 393   The output parsers try to respect C++ namespaces.
 394   [This turned out to be a failed experiment, and it was reverted later.]
 395
 396 * Reduced Grammars
 397   Fixed bugs when reporting useless nonterminals.
 398
 399 * 64 bit hosts
 400   The parsers work properly on 64 bit hosts.
 401
 402 * Error messages
 403   Some calls to strerror resulted in scrambled or missing error messages.
 404
 405 * %expect
 406   When the number of shift/reduce conflicts is correct, don't issue
 407   any warning.
 408
 409 * The verbose report includes the rule line numbers.
 410
 411 * Rule line numbers are fixed in traces.
 412
 413 * Swedish translation
 414
 415 * Parse errors
 416   Verbose parse error messages from the parsers are better looking.
 417   Before: parse error: unexpected `'/'', expecting `"number"' or `'-'' or `'(''
 418      Now: parse error: unexpected '/', expecting "number" or '-' or '('
 419
 420 * Fixed parser memory leaks.
 421   When the generated parser was using malloc to extend its stacks, the
 422   previous allocations were not freed.
 423
 424 * Fixed verbose output file.
 425   Some newlines were missing.
 426   Some conflicts in state descriptions were missing.
 427
 428 * Fixed conflict report.
 429   Option -v was needed to get the result.
 430
 431 * %expect
 432   Was not used.
 433   Mismatches are errors, not warnings.
 434
 435 * Fixed incorrect processing of some invalid input.
 436
 437 * Fixed CPP guards: 9foo.h uses BISON_9FOO_H instead of 9FOO_H.
 438
 439 * Fixed some typos in the documentation.
 440
 441 * %token MY_EOF 0 is supported.
 442   Before, MY_EOF was silently renumbered as 257.
 443
 444 * doc/refcard.tex is updated.
 445
 446 * %output, %file-prefix, %name-prefix.
 447   New.
 448
 449 * --output
 450   New, aliasing `--output-file'.
 451 \f
 452 Changes in version 1.30, 2001-10-26:
 453
 454 * `--defines' and `--graph' have now an optional argument which is the
 455   output file name. `-d' and `-g' do not change; they do not take any
 456   argument.
 457
 458 * `%source_extension' and `%header_extension' are removed, failed
 459   experiment.
 460
 461 * Portability fixes.
 462 \f
 463 Changes in version 1.29, 2001-09-07:
 464
 465 * The output file does not define const, as this caused problems when used
 466   with common autoconfiguration schemes.  If you still use ancient compilers
 467   that lack const, compile with the equivalent of the C compiler option
 468   `-Dconst='.  autoconf's AC_C_CONST macro provides one way to do this.
 469
 470 * Added `-g' and `--graph'.
 471
 472 * The Bison manual is now distributed under the terms of the GNU FDL.
 473
 474 * The input and the output files has automatically a similar extension.
 475
 476 * Russian translation added.
 477
 478 * NLS support updated; should hopefully be less troublesome.
 479
 480 * Added the old Bison reference card.
 481
 482 * Added `--locations' and `%locations'.
 483
 484 * Added `-S' and `--skeleton'.
 485
 486 * `%raw', `-r', `--raw' is disabled.
 487
 488 * Special characters are escaped when output.  This solves the problems
 489   of the #line lines with path names including backslashes.
 490
 491 * New directives.
 492   `%yacc', `%fixed_output_files', `%defines', `%no_parser', `%verbose',
 493   `%debug', `%source_extension' and `%header_extension'.
 494
 495 * @$
 496   Automatic location tracking.
 497 \f
 498 Changes in version 1.28, 1999-07-06:
 499
 500 * Should compile better now with K&R compilers.
 501
 502 * Added NLS.
 503
 504 * Fixed a problem with escaping the double quote character.
 505
 506 * There is now a FAQ.
 507 \f
 508 Changes in version 1.27:
 509
 510 * The make rule which prevented bison.simple from being created on
 511   some systems has been fixed.
 512 \f
 513 Changes in version 1.26:
 514
 515 * Bison now uses automake.
 516
 517 * New mailing lists: <bug-bison@gnu.org> and <help-bison@gnu.org>.
 518
 519 * Token numbers now start at 257 as previously documented, not 258.
 520
 521 * Bison honors the TMPDIR environment variable.
 522
 523 * A couple of buffer overruns have been fixed.
 524
 525 * Problems when closing files should now be reported.
 526
 527 * Generated parsers should now work even on operating systems which do
 528   not provide alloca().
 529 \f
 530 Changes in version 1.25, 1995-10-16:
 531
 532 * Errors in the input grammar are not fatal; Bison keeps reading
 533 the grammar file, and reports all the errors found in it.
 534
 535 * Tokens can now be specified as multiple-character strings: for
 536 example, you could use "<=" for a token which looks like <=, instead
 537 of chosing a name like LESSEQ.
 538
 539 * The %token_table declaration says to write a table of tokens (names
 540 and numbers) into the parser file.  The yylex function can use this
 541 table to recognize multiple-character string tokens, or for other
 542 purposes.
 543
 544 * The %no_lines declaration says not to generate any #line preprocessor
 545 directives in the parser file.
 546
 547 * The %raw declaration says to use internal Bison token numbers, not
 548 Yacc-compatible token numbers, when token names are defined as macros.
 549
 550 * The --no-parser option produces the parser tables without including
 551 the parser engine; a project can now use its own parser engine.
 552 The actions go into a separate file called NAME.act, in the form of
 553 a switch statement body.
 554 \f
 555 Changes in version 1.23:
 556
 557 The user can define YYPARSE_PARAM as the name of an argument to be
 558 passed into yyparse.  The argument should have type void *.  It should
 559 actually point to an object.  Grammar actions can access the variable
 560 by casting it to the proper pointer type.
 561
 562 Line numbers in output file corrected.
 563 \f
 564 Changes in version 1.22:
 565
 566 --help option added.
 567 \f
 568 Changes in version 1.20:
 569
 570 Output file does not redefine const for C++.
 571
 572 Local Variables:
 573 mode: outline
 574 End:
 575
 576 -----
 577
 578 Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004
 579 Free Software Foundation, Inc.
 580
 581 This file is part of Bison, the GNU Compiler Compiler.
 582
 583 Bison is free software; you can redistribute it and/or modify
 584 it under the terms of the GNU General Public License as published by
 585 the Free Software Foundation; either version 2, or (at your option)
 586 any later version.
 587
 588 Bison is distributed in the hope that it will be useful,
 589 but WITHOUT ANY WARRANTY; without even the implied warranty of
 590 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 591 GNU General Public License for more details.
 592
 593 You should have received a copy of the GNU General Public License
 594 along with autoconf; see the file COPYING.  If not, write to
 595 the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 596 Boston, MA 02111-1307, USA.