NEWS

   1 Bison News
   2 ----------
   3
   4 Changes in version 2.0a, ????-??-??:
   5
   6 * Bison-generated C parsers use the _ macro to translate strings from
   7   English to the user's language, e.g., _("syntax error").  By default,
   8   _ is defined to be a no-op macro so the strings are not translated.
   9
  10 Changes in version 2.0, 2004-12-25:
  11
  12 * Possibly-incompatible changes
  13
  14   - Bison-generated parsers no longer default to using the alloca function
  15     (when available) to extend the parser stack, due to widespread
  16     problems in unchecked stack-overflow detection.  You can "#define
  17     YYSTACK_USE_ALLOCA 1" to require the use of alloca, but please read
  18     the manual to determine safe values for YYMAXDEPTH in that case.
  19
  20   - Error token location.
  21     During error recovery, the location of the syntax error is updated
  22     to cover the whole sequence covered by the error token: it includes
  23     the shifted symbols thrown away during the first part of the error
  24     recovery, and the lookahead rejected during the second part.
  25
  26   - Semicolon changes:
  27     . Stray semicolons are no longer allowed at the start of a grammar.
  28     . Semicolons are now required after in-grammar declarations.
  29
  30   - Unescaped newlines are no longer allowed in character constants or
  31     string literals.  They were never portable, and GCC 3.4.0 has
  32     dropped support for them.  Better diagnostics are now generated if
  33     forget a closing quote.
  34
  35   - NUL bytes are no longer allowed in Bison string literals, unfortunately.
  36
  37 * New features
  38
  39   - GLR grammars now support locations.
  40
  41   - New directive: %initial-action.
  42     This directive allows the user to run arbitrary code (including
  43     initializing @$) from yyparse before parsing starts.
  44
  45   - A new directive "%expect-rr N" specifies the expected number of
  46     reduce/reduce conflicts in GLR parsers.
  47
  48   - %token numbers can now be hexadecimal integers, e.g., `%token FOO 0x12d'.
  49     This is a GNU extension.
  50
  51   - The option `--report=lookahead' was changed to `--report=look-ahead'.
  52     The old spelling still works, but is not documented and will be
  53     removed.
  54
  55   - Experimental %destructor support has been added to lalr1.cc.
  56
  57   - New configure option --disable-yacc, to disable installation of the
  58     yacc command and -ly library introduced in 1.875 for POSIX conformance.
  59
  60 * Bug fixes
  61
  62   - For now, %expect-count violations are now just warnings, not errors.
  63     This is for compatibility with Bison 1.75 and earlier (when there are
  64     reduce/reduce conflicts) and with Bison 1.30 and earlier (when there
  65     are too many or too few shift/reduce conflicts).  However, in future
  66     versions of Bison we plan to improve the %expect machinery so that
  67     these violations will become errors again.
  68
  69   - Within Bison itself, numbers (e.g., goto numbers) are no longer
  70     arbitrarily limited to 16-bit counts.
  71
  72   - Semicolons are now allowed before "|" in grammar rules, as POSIX requires.
  73 \f
  74 Changes in version 1.875, 2003-01-01:
  75
  76 * The documentation license has been upgraded to version 1.2
  77   of the GNU Free Documentation License.
  78
  79 * syntax error processing
  80
  81   - In Yacc-style parsers YYLLOC_DEFAULT is now used to compute error
  82     locations too.  This fixes bugs in error-location computation.
  83
  84   - %destructor
  85     It is now possible to reclaim the memory associated to symbols
  86     discarded during error recovery.  This feature is still experimental.
  87
  88   - %error-verbose
  89     This new directive is preferred over YYERROR_VERBOSE.
  90
  91   - #defining yyerror to steal internal variables is discouraged.
  92     It is not guaranteed to work forever.
  93
  94 * POSIX conformance
  95
  96   - Semicolons are once again optional at the end of grammar rules.
  97     This reverts to the behavior of Bison 1.33 and earlier, and improves
  98     compatibility with Yacc.
  99
 100   - `parse error' -> `syntax error'
 101     Bison now uniformly uses the term `syntax error'; formerly, the code
 102     and manual sometimes used the term `parse error' instead.  POSIX
 103     requires `syntax error' in diagnostics, and it was thought better to
 104     be consistent.
 105
 106   - The documentation now emphasizes that yylex and yyerror must be
 107     declared before use.  C99 requires this.
 108
 109   - Bison now parses C99 lexical constructs like UCNs and
 110     backslash-newline within C escape sequences, as POSIX 1003.1-2001 requires.
 111
 112   - File names are properly escaped in C output.  E.g., foo\bar.y is
 113     output as "foo\\bar.y".
 114
 115   - Yacc command and library now available
 116     The Bison distribution now installs a `yacc' command, as POSIX requires.
 117     Also, Bison now installs a small library liby.a containing
 118     implementations of Yacc-compatible yyerror and main functions.
 119     This library is normally not useful, but POSIX requires it.
 120
 121   - Type clashes now generate warnings, not errors.
 122
 123   - If the user does not define YYSTYPE as a macro, Bison now declares it
 124     using typedef instead of defining it as a macro.
 125     For consistency, YYLTYPE is also declared instead of defined.
 126
 127 * Other compatibility issues
 128
 129   - %union directives can now have a tag before the `{', e.g., the
 130     directive `%union foo {...}' now generates the C code
 131     `typedef union foo { ... } YYSTYPE;'; this is for Yacc compatibility.
 132     The default union tag is `YYSTYPE', for compatibility with Solaris 9 Yacc.
 133     For consistency, YYLTYPE's struct tag is now `YYLTYPE' not `yyltype'.
 134     This is for compatibility with both Yacc and Bison 1.35.
 135
 136   - `;' is output before the terminating `}' of an action, for
 137     compatibility with Bison 1.35.
 138
 139   - Bison now uses a Yacc-style format for conflict reports, e.g.,
 140     `conflicts: 2 shift/reduce, 1 reduce/reduce'.
 141
 142   - `yystype' and `yyltype' are now obsolescent macros instead of being
 143     typedefs or tags; they are no longer documented and are planned to be
 144     withdrawn in a future release.
 145
 146 * GLR parser notes
 147
 148   - GLR and inline
 149     Users of Bison have to decide how they handle the portability of the
 150     C keyword `inline'.
 151
 152   - `parsing stack overflow...' -> `parser stack overflow'
 153     GLR parsers now report `parser stack overflow' as per the Bison manual.
 154
 155 * Bison now warns if it detects conflicting outputs to the same file,
 156   e.g., it generates a warning for `bison -d -o foo.h foo.y' since
 157   that command outputs both code and header to foo.h.
 158
 159 * #line in output files
 160   - --no-line works properly.
 161
 162 * Bison can no longer be built by a K&R C compiler; it requires C89 or
 163   later to be built.  This change originally took place a few versions
 164   ago, but nobody noticed until we recently asked someone to try
 165   building Bison with a K&R C compiler.
 166 \f
 167 Changes in version 1.75, 2002-10-14:
 168
 169 * Bison should now work on 64-bit hosts.
 170
 171 * Indonesian translation thanks to Tedi Heriyanto.
 172
 173 * GLR parsers
 174   Fix spurious parse errors.
 175
 176 * Pure parsers
 177   Some people redefine yyerror to steal yyparse' private variables.
 178   Reenable this trick until an official feature replaces it.
 179
 180 * Type Clashes
 181   In agreement with POSIX and with other Yaccs, leaving a default
 182   action is valid when $$ is untyped, and $1 typed:
 183
 184         untyped: ... typed;
 185
 186   but the converse remains an error:
 187
 188         typed: ... untyped;
 189
 190 * Values of mid-rule actions
 191   The following code:
 192
 193         foo: { ... } { $$ = $1; } ...
 194
 195   was incorrectly rejected: $1 is defined in the second mid-rule
 196   action, and is equal to the $$ of the first mid-rule action.
 197 \f
 198 Changes in version 1.50, 2002-10-04:
 199
 200 * GLR parsing
 201   The declaration
 202      %glr-parser
 203   causes Bison to produce a Generalized LR (GLR) parser, capable of handling
 204   almost any context-free grammar, ambiguous or not.  The new declarations
 205   %dprec and %merge on grammar rules allow parse-time resolution of
 206   ambiguities.  Contributed by Paul Hilfinger.
 207
 208   Unfortunately Bison 1.50 does not work properly on 64-bit hosts
 209   like the Alpha, so please stick to 32-bit hosts for now.
 210
 211 * Output Directory
 212   When not in Yacc compatibility mode, when the output file was not
 213   specified, running `bison foo/bar.y' created `foo/bar.c'.  It
 214   now creates `bar.c'.
 215
 216 * Undefined token
 217   The undefined token was systematically mapped to 2 which prevented
 218   the use of 2 by the user.  This is no longer the case.
 219
 220 * Unknown token numbers
 221   If yylex returned an out of range value, yyparse could die.  This is
 222   no longer the case.
 223
 224 * Error token
 225   According to POSIX, the error token must be 256.
 226   Bison extends this requirement by making it a preference: *if* the
 227   user specified that one of her tokens is numbered 256, then error
 228   will be mapped onto another number.
 229
 230 * Verbose error messages
 231   They no longer report `..., expecting error or...' for states where
 232   error recovery is possible.
 233
 234 * End token
 235   Defaults to `$end' instead of `$'.
 236
 237 * Error recovery now conforms to documentation and to POSIX
 238   When a Bison-generated parser encounters a syntax error, it now pops
 239   the stack until it finds a state that allows shifting the error
 240   token.  Formerly, it popped the stack until it found a state that
 241   allowed some non-error action other than a default reduction on the
 242   error token.  The new behavior has long been the documented behavior,
 243   and has long been required by POSIX.  For more details, please see
 244   Paul Eggert, "Reductions during Bison error handling" (2002-05-20)
 245   <http://lists.gnu.org/archive/html/bug-bison/2002-05/msg00038.html>.
 246
 247 * Traces
 248   Popped tokens and nonterminals are now reported.
 249
 250 * Larger grammars
 251   Larger grammars are now supported (larger token numbers, larger grammar
 252   size (= sum of the LHS and RHS lengths), larger LALR tables).
 253   Formerly, many of these numbers ran afoul of 16-bit limits;
 254   now these limits are 32 bits on most hosts.
 255
 256 * Explicit initial rule
 257   Bison used to play hacks with the initial rule, which the user does
 258   not write.  It is now explicit, and visible in the reports and
 259   graphs as rule 0.
 260
 261 * Useless rules
 262   Before, Bison reported the useless rules, but, although not used,
 263   included them in the parsers.  They are now actually removed.
 264
 265 * Useless rules, useless nonterminals
 266   They are now reported, as a warning, with their locations.
 267
 268 * Rules never reduced
 269   Rules that can never be reduced because of conflicts are now
 270   reported.
 271
 272 * Incorrect `Token not used'
 273   On a grammar such as
 274
 275            %token useless useful
 276            %%
 277            exp: '0' %prec useful;
 278
 279   where a token was used to set the precedence of the last rule,
 280   bison reported both `useful' and `useless' as useless tokens.
 281
 282 * Revert the C++ namespace changes introduced in 1.31
 283   as they caused too many portability hassles.
 284
 285 * Default locations
 286   By an accident of design, the default computation of @$ was
 287   performed after another default computation was performed: @$ = @1.
 288   The latter is now removed: YYLLOC_DEFAULT is fully responsible of
 289   the computation of @$.
 290
 291 * Token end-of-file
 292   The token end of file may be specified by the user, in which case,
 293   the user symbol is used in the reports, the graphs, and the verbose
 294   error messages instead of `$end', which remains being the default.
 295   For instance
 296      %token MYEOF 0
 297   or
 298      %token MYEOF 0 "end of file"
 299
 300 * Semantic parser
 301   This old option, which has been broken for ages, is removed.
 302
 303 * New translations
 304   Brazilian Portuguese, thanks to Alexandre Folle de Menezes.
 305   Croatian, thanks to Denis Lackovic.
 306
 307 * Incorrect token definitions
 308   When given `%token 'a' "A"', Bison used to output `#define 'a' 65'.
 309
 310 * Token definitions as enums
 311   Tokens are output both as the traditional #define's, and, provided
 312   the compiler supports ANSI C or is a C++ compiler, as enums.
 313   This lets debuggers display names instead of integers.
 314
 315 * Reports
 316   In addition to --verbose, bison supports --report=THINGS, which
 317   produces additional information:
 318   - itemset
 319     complete the core item sets with their closure
 320   - lookahead [changed to `look-ahead' in 1.875e and later]
 321     explicitly associate look-ahead tokens to items
 322   - solved
 323     describe shift/reduce conflicts solving.
 324     Bison used to systematically output this information on top of
 325     the report.  Solved conflicts are now attached to their states.
 326
 327 * Type clashes
 328   Previous versions don't complain when there is a type clash on
 329   the default action if the rule has a mid-rule action, such as in:
 330
 331       %type <foo> bar
 332       %%
 333       bar: '0' {} '0';
 334
 335   This is fixed.
 336
 337 * GNU M4 is now required when using Bison.
 338 \f
 339 Changes in version 1.35, 2002-03-25:
 340
 341 * C Skeleton
 342   Some projects use Bison's C parser with C++ compilers, and define
 343   YYSTYPE as a class.  The recent adjustment of C parsers for data
 344   alignment and 64 bit architectures made this impossible.
 345
 346   Because for the time being no real solution for C++ parser
 347   generation exists, kludges were implemented in the parser to
 348   maintain this use.  In the future, when Bison has C++ parsers, this
 349   kludge will be disabled.
 350
 351   This kludge also addresses some C++ problems when the stack was
 352   extended.
 353 \f
 354 Changes in version 1.34, 2002-03-12:
 355
 356 * File name clashes are detected
 357   $ bison foo.y -d -o foo.x
 358   fatal error: header and parser would both be named `foo.x'
 359
 360 * A missing `;' at the end of a rule triggers a warning
 361   In accordance with POSIX, and in agreement with other
 362   Yacc implementations, Bison will mandate this semicolon in the near
 363   future.  This eases the implementation of a Bison parser of Bison
 364   grammars by making this grammar LALR(1) instead of LR(2).  To
 365   facilitate the transition, this release introduces a warning.
 366
 367 * Revert the C++ namespace changes introduced in 1.31, as they caused too
 368   many portability hassles.
 369
 370 * DJGPP support added.
 371
 372 * Fix test suite portability problems.
 373 \f
 374 Changes in version 1.33, 2002-02-07:
 375
 376 * Fix C++ issues
 377   Groff could not be compiled for the definition of size_t was lacking
 378   under some conditions.
 379
 380 * Catch invalid @n
 381   As is done with $n.
 382 \f
 383 Changes in version 1.32, 2002-01-23:
 384
 385 * Fix Yacc output file names
 386
 387 * Portability fixes
 388
 389 * Italian, Dutch translations
 390 \f
 391 Changes in version 1.31, 2002-01-14:
 392
 393 * Many Bug Fixes
 394
 395 * GNU Gettext and %expect
 396   GNU Gettext asserts 10 s/r conflicts, but there are 7.  Now that
 397   Bison dies on incorrect %expectations, we fear there will be
 398   too many bug reports for Gettext, so _for the time being_, %expect
 399   does not trigger an error when the input file is named `plural.y'.
 400
 401 * Use of alloca in parsers
 402   If YYSTACK_USE_ALLOCA is defined to 0, then the parsers will use
 403   malloc exclusively.  Since 1.29, but was not NEWS'ed.
 404
 405   alloca is used only when compiled with GCC, to avoid portability
 406   problems as on AIX.
 407
 408 * When the generated parser lacks debugging code, YYDEBUG is now 0
 409   (as POSIX requires) instead of being undefined.
 410
 411 * User Actions
 412   Bison has always permitted actions such as { $$ = $1 }: it adds the
 413   ending semicolon.  Now if in Yacc compatibility mode, the semicolon
 414   is no longer output: one has to write { $$ = $1; }.
 415
 416 * Better C++ compliance
 417   The output parsers try to respect C++ namespaces.
 418   [This turned out to be a failed experiment, and it was reverted later.]
 419
 420 * Reduced Grammars
 421   Fixed bugs when reporting useless nonterminals.
 422
 423 * 64 bit hosts
 424   The parsers work properly on 64 bit hosts.
 425
 426 * Error messages
 427   Some calls to strerror resulted in scrambled or missing error messages.
 428
 429 * %expect
 430   When the number of shift/reduce conflicts is correct, don't issue
 431   any warning.
 432
 433 * The verbose report includes the rule line numbers.
 434
 435 * Rule line numbers are fixed in traces.
 436
 437 * Swedish translation
 438
 439 * Parse errors
 440   Verbose parse error messages from the parsers are better looking.
 441   Before: parse error: unexpected `'/'', expecting `"number"' or `'-'' or `'(''
 442      Now: parse error: unexpected '/', expecting "number" or '-' or '('
 443
 444 * Fixed parser memory leaks.
 445   When the generated parser was using malloc to extend its stacks, the
 446   previous allocations were not freed.
 447
 448 * Fixed verbose output file.
 449   Some newlines were missing.
 450   Some conflicts in state descriptions were missing.
 451
 452 * Fixed conflict report.
 453   Option -v was needed to get the result.
 454
 455 * %expect
 456   Was not used.
 457   Mismatches are errors, not warnings.
 458
 459 * Fixed incorrect processing of some invalid input.
 460
 461 * Fixed CPP guards: 9foo.h uses BISON_9FOO_H instead of 9FOO_H.
 462
 463 * Fixed some typos in the documentation.
 464
 465 * %token MY_EOF 0 is supported.
 466   Before, MY_EOF was silently renumbered as 257.
 467
 468 * doc/refcard.tex is updated.
 469
 470 * %output, %file-prefix, %name-prefix.
 471   New.
 472
 473 * --output
 474   New, aliasing `--output-file'.
 475 \f
 476 Changes in version 1.30, 2001-10-26:
 477
 478 * `--defines' and `--graph' have now an optional argument which is the
 479   output file name. `-d' and `-g' do not change; they do not take any
 480   argument.
 481
 482 * `%source_extension' and `%header_extension' are removed, failed
 483   experiment.
 484
 485 * Portability fixes.
 486 \f
 487 Changes in version 1.29, 2001-09-07:
 488
 489 * The output file does not define const, as this caused problems when used
 490   with common autoconfiguration schemes.  If you still use ancient compilers
 491   that lack const, compile with the equivalent of the C compiler option
 492   `-Dconst='.  autoconf's AC_C_CONST macro provides one way to do this.
 493
 494 * Added `-g' and `--graph'.
 495
 496 * The Bison manual is now distributed under the terms of the GNU FDL.
 497
 498 * The input and the output files has automatically a similar extension.
 499
 500 * Russian translation added.
 501
 502 * NLS support updated; should hopefully be less troublesome.
 503
 504 * Added the old Bison reference card.
 505
 506 * Added `--locations' and `%locations'.
 507
 508 * Added `-S' and `--skeleton'.
 509
 510 * `%raw', `-r', `--raw' is disabled.
 511
 512 * Special characters are escaped when output.  This solves the problems
 513   of the #line lines with path names including backslashes.
 514
 515 * New directives.
 516   `%yacc', `%fixed_output_files', `%defines', `%no_parser', `%verbose',
 517   `%debug', `%source_extension' and `%header_extension'.
 518
 519 * @$
 520   Automatic location tracking.
 521 \f
 522 Changes in version 1.28, 1999-07-06:
 523
 524 * Should compile better now with K&R compilers.
 525
 526 * Added NLS.
 527
 528 * Fixed a problem with escaping the double quote character.
 529
 530 * There is now a FAQ.
 531 \f
 532 Changes in version 1.27:
 533
 534 * The make rule which prevented bison.simple from being created on
 535   some systems has been fixed.
 536 \f
 537 Changes in version 1.26:
 538
 539 * Bison now uses automake.
 540
 541 * New mailing lists: <bug-bison@gnu.org> and <help-bison@gnu.org>.
 542
 543 * Token numbers now start at 257 as previously documented, not 258.
 544
 545 * Bison honors the TMPDIR environment variable.
 546
 547 * A couple of buffer overruns have been fixed.
 548
 549 * Problems when closing files should now be reported.
 550
 551 * Generated parsers should now work even on operating systems which do
 552   not provide alloca().
 553 \f
 554 Changes in version 1.25, 1995-10-16:
 555
 556 * Errors in the input grammar are not fatal; Bison keeps reading
 557 the grammar file, and reports all the errors found in it.
 558
 559 * Tokens can now be specified as multiple-character strings: for
 560 example, you could use "<=" for a token which looks like <=, instead
 561 of chosing a name like LESSEQ.
 562
 563 * The %token_table declaration says to write a table of tokens (names
 564 and numbers) into the parser file.  The yylex function can use this
 565 table to recognize multiple-character string tokens, or for other
 566 purposes.
 567
 568 * The %no_lines declaration says not to generate any #line preprocessor
 569 directives in the parser file.
 570
 571 * The %raw declaration says to use internal Bison token numbers, not
 572 Yacc-compatible token numbers, when token names are defined as macros.
 573
 574 * The --no-parser option produces the parser tables without including
 575 the parser engine; a project can now use its own parser engine.
 576 The actions go into a separate file called NAME.act, in the form of
 577 a switch statement body.
 578 \f
 579 Changes in version 1.23:
 580
 581 The user can define YYPARSE_PARAM as the name of an argument to be
 582 passed into yyparse.  The argument should have type void *.  It should
 583 actually point to an object.  Grammar actions can access the variable
 584 by casting it to the proper pointer type.
 585
 586 Line numbers in output file corrected.
 587 \f
 588 Changes in version 1.22:
 589
 590 --help option added.
 591 \f
 592 Changes in version 1.20:
 593
 594 Output file does not redefine const for C++.
 595
 596 Local Variables:
 597 mode: outline
 598 End:
 599
 600 -----
 601
 602 Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005
 603 Free Software Foundation, Inc.
 604
 605 This file is part of Bison, the GNU Compiler Compiler.
 606
 607 Bison is free software; you can redistribute it and/or modify
 608 it under the terms of the GNU General Public License as published by
 609 the Free Software Foundation; either version 2, or (at your option)
 610 any later version.
 611
 612 Bison is distributed in the hope that it will be useful,
 613 but WITHOUT ANY WARRANTY; without even the implied warranty of
 614 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 615 GNU General Public License for more details.
 616
 617 You should have received a copy of the GNU General Public License
 618 along with autoconf; see the file COPYING.  If not, write to
 619 the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 620 Boston, MA 02111-1307, USA.