NEWS

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