NEWS

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