NEWS

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