NEWS

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