NEWS

   1 Bison News
   2 ----------
   3
   4 Changes in version 1.875e:
   5
   6 * New directive: %initial-action.
   7   This directive allows the user to run arbitrary code (including
   8   initializing @$) from yyparse before parsing starts.
   9
  10 * The option `--report=lookahead' was changed to `--report=look-ahead'.
  11   The old spelling still works, but is not documented and will be removed.
  12
  13 Changes in version 1.875d, 2004-05-21:
  14
  15 * Unescaped newlines are no longer allowed in character constants or
  16   string literals.  They were never portable, and GCC 3.4.0 has
  17   dropped support for them.  Better diagnostics are now generated if
  18   forget a closing quote.
  19
  20 * NUL bytes are no longer allowed in Bison string literals, unfortunately.
  21
  22 * %token numbers can now be hexadecimal integers, e.g., `%token FOO 0x12d'.
  23   This is a GNU extension.
  24
  25 * A new directive "%expect-rr N" specifies the expected number of
  26   reduce/reduce conflicts in GLR parsers.
  27
  28 * Experimental %destructor support has been added to lalr1.cc.
  29
  30 Changes in version 1.875c, 2003-08-25:
  31
  32   (Just bug fixes.)
  33
  34 Changes in version 1.875b, 2003-06-17:
  35
  36 * GLR grammars now support locations.
  37
  38 * Semicolon changes:
  39   - Semicolons are now allowed before "|" in grammar rules, as POSIX requires.
  40   - Stray semicolons are no longer allowed at the start of a grammar.
  41   - Semicolons are now required after in-grammar declarations.
  42
  43 Changes in version 1.875a, 2003-02-01:
  44
  45 * For now, %expect-count violations are now just warnings, not errors.
  46   This is for compatibility with Bison 1.75 and earlier (when there are
  47   reduce/reduce conflicts) and with Bison 1.30 and earlier (when there
  48   are too many or too few shift/reduce conflicts).  However, in future
  49   versions of Bison we plan to improve the %expect machinery so that
  50   these violations will become errors again.
  51
  52 * New configure option --disable-yacc, to disable installation of the
  53   yacc command and -ly library introduced in 1.875 for POSIX conformance.
  54 \f
  55 Changes in version 1.875, 2003-01-01:
  56
  57 * The documentation license has been upgraded to version 1.2
  58   of the GNU Free Documentation License.
  59
  60 * syntax error processing
  61
  62   - In Yacc-style parsers YYLLOC_DEFAULT is now used to compute error
  63     locations too.  This fixes bugs in error-location computation.
  64
  65   - %destructor
  66     It is now possible to reclaim the memory associated to symbols
  67     discarded during error recovery.  This feature is still experimental.
  68
  69   - %error-verbose
  70     This new directive is preferred over YYERROR_VERBOSE.
  71
  72   - #defining yyerror to steal internal variables is discouraged.
  73     It is not guaranteed to work forever.
  74
  75 * POSIX conformance
  76
  77   - Semicolons are once again optional at the end of grammar rules.
  78     This reverts to the behavior of Bison 1.33 and earlier, and improves
  79     compatibility with Yacc.
  80
  81   - `parse error' -> `syntax error'
  82     Bison now uniformly uses the term `syntax error'; formerly, the code
  83     and manual sometimes used the term `parse error' instead.  POSIX
  84     requires `syntax error' in diagnostics, and it was thought better to
  85     be consistent.
  86
  87   - The documentation now emphasizes that yylex and yyerror must be
  88     declared before use.  C99 requires this.
  89
  90   - Bison now parses C99 lexical constructs like UCNs and
  91     backslash-newline within C escape sequences, as POSIX 1003.1-2001 requires.
  92
  93   - File names are properly escaped in C output.  E.g., foo\bar.y is
  94     output as "foo\\bar.y".
  95
  96   - Yacc command and library now available
  97     The Bison distribution now installs a `yacc' command, as POSIX requires.
  98     Also, Bison now installs a small library liby.a containing
  99     implementations of Yacc-compatible yyerror and main functions.
 100     This library is normally not useful, but POSIX requires it.
 101
 102   - Type clashes now generate warnings, not errors.
 103
 104   - If the user does not define YYSTYPE as a macro, Bison now declares it
 105     using typedef instead of defining it as a macro.
 106     For consistency, YYLTYPE is also declared instead of defined.
 107
 108 * Other compatibility issues
 109
 110   - %union directives can now have a tag before the `{', e.g., the
 111     directive `%union foo {...}' now generates the C code
 112     `typedef union foo { ... } YYSTYPE;'; this is for Yacc compatibility.
 113     The default union tag is `YYSTYPE', for compatibility with Solaris 9 Yacc.
 114     For consistency, YYLTYPE's struct tag is now `YYLTYPE' not `yyltype'.
 115     This is for compatibility with both Yacc and Bison 1.35.
 116
 117   - `;' is output before the terminating `}' of an action, for
 118     compatibility with Bison 1.35.
 119
 120   - Bison now uses a Yacc-style format for conflict reports, e.g.,
 121     `conflicts: 2 shift/reduce, 1 reduce/reduce'.
 122
 123   - `yystype' and `yyltype' are now obsolescent macros instead of being
 124     typedefs or tags; they are no longer documented and are planned to be
 125     withdrawn in a future release.
 126
 127 * GLR parser notes
 128
 129   - GLR and inline
 130     Users of Bison have to decide how they handle the portability of the
 131     C keyword `inline'.
 132
 133   - `parsing stack overflow...' -> `parser stack overflow'
 134     GLR parsers now report `parser stack overflow' as per the Bison manual.
 135
 136 * Bison now warns if it detects conflicting outputs to the same file,
 137   e.g., it generates a warning for `bison -d -o foo.h foo.y' since
 138   that command outputs both code and header to foo.h.
 139
 140 * #line in output files
 141   - --no-line works properly.
 142
 143 * Bison can no longer be built by a K&R C compiler; it requires C89 or
 144   later to be built.  This change originally took place a few versions
 145   ago, but nobody noticed until we recently asked someone to try
 146   building Bison with a K&R C compiler.
 147 \f
 148 Changes in version 1.75, 2002-10-14:
 149
 150 * Bison should now work on 64-bit hosts.
 151
 152 * Indonesian translation thanks to Tedi Heriyanto.
 153
 154 * GLR parsers
 155   Fix spurious parse errors.
 156
 157 * Pure parsers
 158   Some people redefine yyerror to steal yyparse' private variables.
 159   Reenable this trick until an official feature replaces it.
 160
 161 * Type Clashes
 162   In agreement with POSIX and with other Yaccs, leaving a default
 163   action is valid when $$ is untyped, and $1 typed:
 164
 165         untyped: ... typed;
 166
 167   but the converse remains an error:
 168
 169         typed: ... untyped;
 170
 171 * Values of mid-rule actions
 172   The following code:
 173
 174         foo: { ... } { $$ = $1; } ...
 175
 176   was incorrectly rejected: $1 is defined in the second mid-rule
 177   action, and is equal to the $$ of the first mid-rule action.
 178 \f
 179 Changes in version 1.50, 2002-10-04:
 180
 181 * GLR parsing
 182   The declaration
 183      %glr-parser
 184   causes Bison to produce a Generalized LR (GLR) parser, capable of handling
 185   almost any context-free grammar, ambiguous or not.  The new declarations
 186   %dprec and %merge on grammar rules allow parse-time resolution of
 187   ambiguities.  Contributed by Paul Hilfinger.
 188
 189   Unfortunately Bison 1.50 does not work properly on 64-bit hosts
 190   like the Alpha, so please stick to 32-bit hosts for now.
 191
 192 * Output Directory
 193   When not in Yacc compatibility mode, when the output file was not
 194   specified, running `bison foo/bar.y' created `foo/bar.c'.  It
 195   now creates `bar.c'.
 196
 197 * Undefined token
 198   The undefined token was systematically mapped to 2 which prevented
 199   the use of 2 by the user.  This is no longer the case.
 200
 201 * Unknown token numbers
 202   If yylex returned an out of range value, yyparse could die.  This is
 203   no longer the case.
 204
 205 * Error token
 206   According to POSIX, the error token must be 256.
 207   Bison extends this requirement by making it a preference: *if* the
 208   user specified that one of her tokens is numbered 256, then error
 209   will be mapped onto another number.
 210
 211 * Verbose error messages
 212   They no longer report `..., expecting error or...' for states where
 213   error recovery is possible.
 214
 215 * End token
 216   Defaults to `$end' instead of `$'.
 217
 218 * Error recovery now conforms to documentation and to POSIX
 219   When a Bison-generated parser encounters a syntax error, it now pops
 220   the stack until it finds a state that allows shifting the error
 221   token.  Formerly, it popped the stack until it found a state that
 222   allowed some non-error action other than a default reduction on the
 223   error token.  The new behavior has long been the documented behavior,
 224   and has long been required by POSIX.  For more details, please see
 225   <http://mail.gnu.org/pipermail/bug-bison/2002-May/001452.html>.
 226
 227 * Traces
 228   Popped tokens and nonterminals are now reported.
 229
 230 * Larger grammars
 231   Larger grammars are now supported (larger token numbers, larger grammar
 232   size (= sum of the LHS and RHS lengths), larger LALR tables).
 233   Formerly, many of these numbers ran afoul of 16-bit limits;
 234   now these limits are 32 bits on most hosts.
 235
 236 * Explicit initial rule
 237   Bison used to play hacks with the initial rule, which the user does
 238   not write.  It is now explicit, and visible in the reports and
 239   graphs as rule 0.
 240
 241 * Useless rules
 242   Before, Bison reported the useless rules, but, although not used,
 243   included them in the parsers.  They are now actually removed.
 244
 245 * Useless rules, useless nonterminals
 246   They are now reported, as a warning, with their locations.
 247
 248 * Rules never reduced
 249   Rules that can never be reduced because of conflicts are now
 250   reported.
 251
 252 * Incorrect `Token not used'
 253   On a grammar such as
 254
 255            %token useless useful
 256            %%
 257            exp: '0' %prec useful;
 258
 259   where a token was used to set the precedence of the last rule,
 260   bison reported both `useful' and `useless' as useless tokens.
 261
 262 * Revert the C++ namespace changes introduced in 1.31
 263   as they caused too many portability hassles.
 264
 265 * Default locations
 266   By an accident of design, the default computation of @$ was
 267   performed after another default computation was performed: @$ = @1.
 268   The latter is now removed: YYLLOC_DEFAULT is fully responsible of
 269   the computation of @$.
 270
 271 * Token end-of-file
 272   The token end of file may be specified by the user, in which case,
 273   the user symbol is used in the reports, the graphs, and the verbose
 274   error messages instead of `$end', which remains being the default.
 275   For instance
 276      %token MYEOF 0
 277   or
 278      %token MYEOF 0 "end of file"
 279
 280 * Semantic parser
 281   This old option, which has been broken for ages, is removed.
 282
 283 * New translations
 284   Brazilian Portuguese, thanks to Alexandre Folle de Menezes.
 285   Croatian, thanks to Denis Lackovic.
 286
 287 * Incorrect token definitions
 288   When given `%token 'a' "A"', Bison used to output `#define 'a' 65'.
 289
 290 * Token definitions as enums
 291   Tokens are output both as the traditional #define's, and, provided
 292   the compiler supports ANSI C or is a C++ compiler, as enums.
 293   This lets debuggers display names instead of integers.
 294
 295 * Reports
 296   In addition to --verbose, bison supports --report=THINGS, which
 297   produces additional information:
 298   - itemset
 299     complete the core item sets with their closure
 300   - lookahead [changed to `look-ahead' in 1.875e and later]
 301     explicitly associate look-ahead tokens to items
 302   - solved
 303     describe shift/reduce conflicts solving.
 304     Bison used to systematically output this information on top of
 305     the report.  Solved conflicts are now attached to their states.
 306
 307 * Type clashes
 308   Previous versions don't complain when there is a type clash on
 309   the default action if the rule has a mid-rule action, such as in:
 310
 311       %type <foo> bar
 312       %%
 313       bar: '0' {} '0';
 314
 315   This is fixed.
 316
 317 * GNU M4 is now required when using Bison.
 318 \f
 319 Changes in version 1.35, 2002-03-25:
 320
 321 * C Skeleton
 322   Some projects use Bison's C parser with C++ compilers, and define
 323   YYSTYPE as a class.  The recent adjustment of C parsers for data
 324   alignment and 64 bit architectures made this impossible.
 325
 326   Because for the time being no real solution for C++ parser
 327   generation exists, kludges were implemented in the parser to
 328   maintain this use.  In the future, when Bison has C++ parsers, this
 329   kludge will be disabled.
 330
 331   This kludge also addresses some C++ problems when the stack was
 332   extended.
 333 \f
 334 Changes in version 1.34, 2002-03-12:
 335
 336 * File name clashes are detected
 337   $ bison foo.y -d -o foo.x
 338   fatal error: header and parser would both be named `foo.x'
 339
 340 * A missing `;' at the end of a rule triggers a warning
 341   In accordance with POSIX, and in agreement with other
 342   Yacc implementations, Bison will mandate this semicolon in the near
 343   future.  This eases the implementation of a Bison parser of Bison
 344   grammars by making this grammar LALR(1) instead of LR(2).  To
 345   facilitate the transition, this release introduces a warning.
 346
 347 * Revert the C++ namespace changes introduced in 1.31, as they caused too
 348   many portability hassles.
 349
 350 * DJGPP support added.
 351
 352 * Fix test suite portability problems.
 353 \f
 354 Changes in version 1.33, 2002-02-07:
 355
 356 * Fix C++ issues
 357   Groff could not be compiled for the definition of size_t was lacking
 358   under some conditions.
 359
 360 * Catch invalid @n
 361   As is done with $n.
 362 \f
 363 Changes in version 1.32, 2002-01-23:
 364
 365 * Fix Yacc output file names
 366
 367 * Portability fixes
 368
 369 * Italian, Dutch translations
 370 \f
 371 Changes in version 1.31, 2002-01-14:
 372
 373 * Many Bug Fixes
 374
 375 * GNU Gettext and %expect
 376   GNU Gettext asserts 10 s/r conflicts, but there are 7.  Now that
 377   Bison dies on incorrect %expectations, we fear there will be
 378   too many bug reports for Gettext, so _for the time being_, %expect
 379   does not trigger an error when the input file is named `plural.y'.
 380
 381 * Use of alloca in parsers
 382   If YYSTACK_USE_ALLOCA is defined to 0, then the parsers will use
 383   malloc exclusively.  Since 1.29, but was not NEWS'ed.
 384
 385   alloca is used only when compiled with GCC, to avoid portability
 386   problems as on AIX.
 387
 388 * When the generated parser lacks debugging code, YYDEBUG is now 0
 389   (as POSIX requires) instead of being undefined.
 390
 391 * User Actions
 392   Bison has always permitted actions such as { $$ = $1 }: it adds the
 393   ending semicolon.  Now if in Yacc compatibility mode, the semicolon
 394   is no longer output: one has to write { $$ = $1; }.
 395
 396 * Better C++ compliance
 397   The output parsers try to respect C++ namespaces.
 398   [This turned out to be a failed experiment, and it was reverted later.]
 399
 400 * Reduced Grammars
 401   Fixed bugs when reporting useless nonterminals.
 402
 403 * 64 bit hosts
 404   The parsers work properly on 64 bit hosts.
 405
 406 * Error messages
 407   Some calls to strerror resulted in scrambled or missing error messages.
 408
 409 * %expect
 410   When the number of shift/reduce conflicts is correct, don't issue
 411   any warning.
 412
 413 * The verbose report includes the rule line numbers.
 414
 415 * Rule line numbers are fixed in traces.
 416
 417 * Swedish translation
 418
 419 * Parse errors
 420   Verbose parse error messages from the parsers are better looking.
 421   Before: parse error: unexpected `'/'', expecting `"number"' or `'-'' or `'(''
 422      Now: parse error: unexpected '/', expecting "number" or '-' or '('
 423
 424 * Fixed parser memory leaks.
 425   When the generated parser was using malloc to extend its stacks, the
 426   previous allocations were not freed.
 427
 428 * Fixed verbose output file.
 429   Some newlines were missing.
 430   Some conflicts in state descriptions were missing.
 431
 432 * Fixed conflict report.
 433   Option -v was needed to get the result.
 434
 435 * %expect
 436   Was not used.
 437   Mismatches are errors, not warnings.
 438
 439 * Fixed incorrect processing of some invalid input.
 440
 441 * Fixed CPP guards: 9foo.h uses BISON_9FOO_H instead of 9FOO_H.
 442
 443 * Fixed some typos in the documentation.
 444
 445 * %token MY_EOF 0 is supported.
 446   Before, MY_EOF was silently renumbered as 257.
 447
 448 * doc/refcard.tex is updated.
 449
 450 * %output, %file-prefix, %name-prefix.
 451   New.
 452
 453 * --output
 454   New, aliasing `--output-file'.
 455 \f
 456 Changes in version 1.30, 2001-10-26:
 457
 458 * `--defines' and `--graph' have now an optional argument which is the
 459   output file name. `-d' and `-g' do not change; they do not take any
 460   argument.
 461
 462 * `%source_extension' and `%header_extension' are removed, failed
 463   experiment.
 464
 465 * Portability fixes.
 466 \f
 467 Changes in version 1.29, 2001-09-07:
 468
 469 * The output file does not define const, as this caused problems when used
 470   with common autoconfiguration schemes.  If you still use ancient compilers
 471   that lack const, compile with the equivalent of the C compiler option
 472   `-Dconst='.  autoconf's AC_C_CONST macro provides one way to do this.
 473
 474 * Added `-g' and `--graph'.
 475
 476 * The Bison manual is now distributed under the terms of the GNU FDL.
 477
 478 * The input and the output files has automatically a similar extension.
 479
 480 * Russian translation added.
 481
 482 * NLS support updated; should hopefully be less troublesome.
 483
 484 * Added the old Bison reference card.
 485
 486 * Added `--locations' and `%locations'.
 487
 488 * Added `-S' and `--skeleton'.
 489
 490 * `%raw', `-r', `--raw' is disabled.
 491
 492 * Special characters are escaped when output.  This solves the problems
 493   of the #line lines with path names including backslashes.
 494
 495 * New directives.
 496   `%yacc', `%fixed_output_files', `%defines', `%no_parser', `%verbose',
 497   `%debug', `%source_extension' and `%header_extension'.
 498
 499 * @$
 500   Automatic location tracking.
 501 \f
 502 Changes in version 1.28, 1999-07-06:
 503
 504 * Should compile better now with K&R compilers.
 505
 506 * Added NLS.
 507
 508 * Fixed a problem with escaping the double quote character.
 509
 510 * There is now a FAQ.
 511 \f
 512 Changes in version 1.27:
 513
 514 * The make rule which prevented bison.simple from being created on
 515   some systems has been fixed.
 516 \f
 517 Changes in version 1.26:
 518
 519 * Bison now uses automake.
 520
 521 * New mailing lists: <bug-bison@gnu.org> and <help-bison@gnu.org>.
 522
 523 * Token numbers now start at 257 as previously documented, not 258.
 524
 525 * Bison honors the TMPDIR environment variable.
 526
 527 * A couple of buffer overruns have been fixed.
 528
 529 * Problems when closing files should now be reported.
 530
 531 * Generated parsers should now work even on operating systems which do
 532   not provide alloca().
 533 \f
 534 Changes in version 1.25, 1995-10-16:
 535
 536 * Errors in the input grammar are not fatal; Bison keeps reading
 537 the grammar file, and reports all the errors found in it.
 538
 539 * Tokens can now be specified as multiple-character strings: for
 540 example, you could use "<=" for a token which looks like <=, instead
 541 of chosing a name like LESSEQ.
 542
 543 * The %token_table declaration says to write a table of tokens (names
 544 and numbers) into the parser file.  The yylex function can use this
 545 table to recognize multiple-character string tokens, or for other
 546 purposes.
 547
 548 * The %no_lines declaration says not to generate any #line preprocessor
 549 directives in the parser file.
 550
 551 * The %raw declaration says to use internal Bison token numbers, not
 552 Yacc-compatible token numbers, when token names are defined as macros.
 553
 554 * The --no-parser option produces the parser tables without including
 555 the parser engine; a project can now use its own parser engine.
 556 The actions go into a separate file called NAME.act, in the form of
 557 a switch statement body.
 558 \f
 559 Changes in version 1.23:
 560
 561 The user can define YYPARSE_PARAM as the name of an argument to be
 562 passed into yyparse.  The argument should have type void *.  It should
 563 actually point to an object.  Grammar actions can access the variable
 564 by casting it to the proper pointer type.
 565
 566 Line numbers in output file corrected.
 567 \f
 568 Changes in version 1.22:
 569
 570 --help option added.
 571 \f
 572 Changes in version 1.20:
 573
 574 Output file does not redefine const for C++.
 575
 576 Local Variables:
 577 mode: outline
 578 End:
 579
 580 -----
 581
 582 Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004
 583 Free Software Foundation, Inc.
 584
 585 This file is part of Bison, the GNU Compiler Compiler.
 586
 587 Bison is free software; you can redistribute it and/or modify
 588 it under the terms of the GNU General Public License as published by
 589 the Free Software Foundation; either version 2, or (at your option)
 590 any later version.
 591
 592 Bison is distributed in the hope that it will be useful,
 593 but WITHOUT ANY WARRANTY; without even the implied warranty of
 594 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 595 GNU General Public License for more details.
 596
 597 You should have received a copy of the GNU General Public License
 598 along with autoconf; see the file COPYING.  If not, write to
 599 the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 600 Boston, MA 02111-1307, USA.