NEWS

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