NEWS

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