NEWS

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