NEWS

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