NEWS

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