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
  12   removed.
  13
  14 * Error token location.
  15   During error recovery, the location of the syntax error is updated
  16   to cover the whole sequence covered by the error token: it includes
  17   the shifted symbols thrown away during the first part of the error
  18   recovery, and the lookahead rejected during the second part.
  19
  20 * Goto numbers are no longer arbitrarily limited to 16-bit counts.
  21
  22 Changes in version 1.875d, 2004-05-21:
  23
  24 * Unescaped newlines are no longer allowed in character constants or
  25   string literals.  They were never portable, and GCC 3.4.0 has
  26   dropped support for them.  Better diagnostics are now generated if
  27   forget a closing quote.
  28
  29 * NUL bytes are no longer allowed in Bison string literals, unfortunately.
  30
  31 * %token numbers can now be hexadecimal integers, e.g., `%token FOO 0x12d'.
  32   This is a GNU extension.
  33
  34 * A new directive "%expect-rr N" specifies the expected number of
  35   reduce/reduce conflicts in GLR parsers.
  36
  37 * Experimental %destructor support has been added to lalr1.cc.
  38
  39 Changes in version 1.875c, 2003-08-25:
  40
  41   (Just bug fixes.)
  42
  43 Changes in version 1.875b, 2003-06-17:
  44
  45 * GLR grammars now support locations.
  46
  47 * Semicolon changes:
  48   - Semicolons are now allowed before "|" in grammar rules, as POSIX requires.
  49   - Stray semicolons are no longer allowed at the start of a grammar.
  50   - Semicolons are now required after in-grammar declarations.
  51
  52 Changes in version 1.875a, 2003-02-01:
  53
  54 * For now, %expect-count violations are now just warnings, not errors.
  55   This is for compatibility with Bison 1.75 and earlier (when there are
  56   reduce/reduce conflicts) and with Bison 1.30 and earlier (when there
  57   are too many or too few shift/reduce conflicts).  However, in future
  58   versions of Bison we plan to improve the %expect machinery so that
  59   these violations will become errors again.
  60
  61 * New configure option --disable-yacc, to disable installation of the
  62   yacc command and -ly library introduced in 1.875 for POSIX conformance.
  63 \f
  64 Changes in version 1.875, 2003-01-01:
  65
  66 * The documentation license has been upgraded to version 1.2
  67   of the GNU Free Documentation License.
  68
  69 * syntax error processing
  70
  71   - In Yacc-style parsers YYLLOC_DEFAULT is now used to compute error
  72     locations too.  This fixes bugs in error-location computation.
  73
  74   - %destructor
  75     It is now possible to reclaim the memory associated to symbols
  76     discarded during error recovery.  This feature is still experimental.
  77
  78   - %error-verbose
  79     This new directive is preferred over YYERROR_VERBOSE.
  80
  81   - #defining yyerror to steal internal variables is discouraged.
  82     It is not guaranteed to work forever.
  83
  84 * POSIX conformance
  85
  86   - Semicolons are once again optional at the end of grammar rules.
  87     This reverts to the behavior of Bison 1.33 and earlier, and improves
  88     compatibility with Yacc.
  89
  90   - `parse error' -> `syntax error'
  91     Bison now uniformly uses the term `syntax error'; formerly, the code
  92     and manual sometimes used the term `parse error' instead.  POSIX
  93     requires `syntax error' in diagnostics, and it was thought better to
  94     be consistent.
  95
  96   - The documentation now emphasizes that yylex and yyerror must be
  97     declared before use.  C99 requires this.
  98
  99   - Bison now parses C99 lexical constructs like UCNs and
 100     backslash-newline within C escape sequences, as POSIX 1003.1-2001 requires.
 101
 102   - File names are properly escaped in C output.  E.g., foo\bar.y is
 103     output as "foo\\bar.y".
 104
 105   - Yacc command and library now available
 106     The Bison distribution now installs a `yacc' command, as POSIX requires.
 107     Also, Bison now installs a small library liby.a containing
 108     implementations of Yacc-compatible yyerror and main functions.
 109     This library is normally not useful, but POSIX requires it.
 110
 111   - Type clashes now generate warnings, not errors.
 112
 113   - If the user does not define YYSTYPE as a macro, Bison now declares it
 114     using typedef instead of defining it as a macro.
 115     For consistency, YYLTYPE is also declared instead of defined.
 116
 117 * Other compatibility issues
 118
 119   - %union directives can now have a tag before the `{', e.g., the
 120     directive `%union foo {...}' now generates the C code
 121     `typedef union foo { ... } YYSTYPE;'; this is for Yacc compatibility.
 122     The default union tag is `YYSTYPE', for compatibility with Solaris 9 Yacc.
 123     For consistency, YYLTYPE's struct tag is now `YYLTYPE' not `yyltype'.
 124     This is for compatibility with both Yacc and Bison 1.35.
 125
 126   - `;' is output before the terminating `}' of an action, for
 127     compatibility with Bison 1.35.
 128
 129   - Bison now uses a Yacc-style format for conflict reports, e.g.,
 130     `conflicts: 2 shift/reduce, 1 reduce/reduce'.
 131
 132   - `yystype' and `yyltype' are now obsolescent macros instead of being
 133     typedefs or tags; they are no longer documented and are planned to be
 134     withdrawn in a future release.
 135
 136 * GLR parser notes
 137
 138   - GLR and inline
 139     Users of Bison have to decide how they handle the portability of the
 140     C keyword `inline'.
 141
 142   - `parsing stack overflow...' -> `parser stack overflow'
 143     GLR parsers now report `parser stack overflow' as per the Bison manual.
 144
 145 * Bison now warns if it detects conflicting outputs to the same file,
 146   e.g., it generates a warning for `bison -d -o foo.h foo.y' since
 147   that command outputs both code and header to foo.h.
 148
 149 * #line in output files
 150   - --no-line works properly.
 151
 152 * Bison can no longer be built by a K&R C compiler; it requires C89 or
 153   later to be built.  This change originally took place a few versions
 154   ago, but nobody noticed until we recently asked someone to try
 155   building Bison with a K&R C compiler.
 156 \f
 157 Changes in version 1.75, 2002-10-14:
 158
 159 * Bison should now work on 64-bit hosts.
 160
 161 * Indonesian translation thanks to Tedi Heriyanto.
 162
 163 * GLR parsers
 164   Fix spurious parse errors.
 165
 166 * Pure parsers
 167   Some people redefine yyerror to steal yyparse' private variables.
 168   Reenable this trick until an official feature replaces it.
 169
 170 * Type Clashes
 171   In agreement with POSIX and with other Yaccs, leaving a default
 172   action is valid when $$ is untyped, and $1 typed:
 173
 174         untyped: ... typed;
 175
 176   but the converse remains an error:
 177
 178         typed: ... untyped;
 179
 180 * Values of mid-rule actions
 181   The following code:
 182
 183         foo: { ... } { $$ = $1; } ...
 184
 185   was incorrectly rejected: $1 is defined in the second mid-rule
 186   action, and is equal to the $$ of the first mid-rule action.
 187 \f
 188 Changes in version 1.50, 2002-10-04:
 189
 190 * GLR parsing
 191   The declaration
 192      %glr-parser
 193   causes Bison to produce a Generalized LR (GLR) parser, capable of handling
 194   almost any context-free grammar, ambiguous or not.  The new declarations
 195   %dprec and %merge on grammar rules allow parse-time resolution of
 196   ambiguities.  Contributed by Paul Hilfinger.
 197
 198   Unfortunately Bison 1.50 does not work properly on 64-bit hosts
 199   like the Alpha, so please stick to 32-bit hosts for now.
 200
 201 * Output Directory
 202   When not in Yacc compatibility mode, when the output file was not
 203   specified, running `bison foo/bar.y' created `foo/bar.c'.  It
 204   now creates `bar.c'.
 205
 206 * Undefined token
 207   The undefined token was systematically mapped to 2 which prevented
 208   the use of 2 by the user.  This is no longer the case.
 209
 210 * Unknown token numbers
 211   If yylex returned an out of range value, yyparse could die.  This is
 212   no longer the case.
 213
 214 * Error token
 215   According to POSIX, the error token must be 256.
 216   Bison extends this requirement by making it a preference: *if* the
 217   user specified that one of her tokens is numbered 256, then error
 218   will be mapped onto another number.
 219
 220 * Verbose error messages
 221   They no longer report `..., expecting error or...' for states where
 222   error recovery is possible.
 223
 224 * End token
 225   Defaults to `$end' instead of `$'.
 226
 227 * Error recovery now conforms to documentation and to POSIX
 228   When a Bison-generated parser encounters a syntax error, it now pops
 229   the stack until it finds a state that allows shifting the error
 230   token.  Formerly, it popped the stack until it found a state that
 231   allowed some non-error action other than a default reduction on the
 232   error token.  The new behavior has long been the documented behavior,
 233   and has long been required by POSIX.  For more details, please see
 234   <http://mail.gnu.org/pipermail/bug-bison/2002-May/001452.html>.
 235
 236 * Traces
 237   Popped tokens and nonterminals are now reported.
 238
 239 * Larger grammars
 240   Larger grammars are now supported (larger token numbers, larger grammar
 241   size (= sum of the LHS and RHS lengths), larger LALR tables).
 242   Formerly, many of these numbers ran afoul of 16-bit limits;
 243   now these limits are 32 bits on most hosts.
 244
 245 * Explicit initial rule
 246   Bison used to play hacks with the initial rule, which the user does
 247   not write.  It is now explicit, and visible in the reports and
 248   graphs as rule 0.
 249
 250 * Useless rules
 251   Before, Bison reported the useless rules, but, although not used,
 252   included them in the parsers.  They are now actually removed.
 253
 254 * Useless rules, useless nonterminals
 255   They are now reported, as a warning, with their locations.
 256
 257 * Rules never reduced
 258   Rules that can never be reduced because of conflicts are now
 259   reported.
 260
 261 * Incorrect `Token not used'
 262   On a grammar such as
 263
 264            %token useless useful
 265            %%
 266            exp: '0' %prec useful;
 267
 268   where a token was used to set the precedence of the last rule,
 269   bison reported both `useful' and `useless' as useless tokens.
 270
 271 * Revert the C++ namespace changes introduced in 1.31
 272   as they caused too many portability hassles.
 273
 274 * Default locations
 275   By an accident of design, the default computation of @$ was
 276   performed after another default computation was performed: @$ = @1.
 277   The latter is now removed: YYLLOC_DEFAULT is fully responsible of
 278   the computation of @$.
 279
 280 * Token end-of-file
 281   The token end of file may be specified by the user, in which case,
 282   the user symbol is used in the reports, the graphs, and the verbose
 283   error messages instead of `$end', which remains being the default.
 284   For instance
 285      %token MYEOF 0
 286   or
 287      %token MYEOF 0 "end of file"
 288
 289 * Semantic parser
 290   This old option, which has been broken for ages, is removed.
 291
 292 * New translations
 293   Brazilian Portuguese, thanks to Alexandre Folle de Menezes.
 294   Croatian, thanks to Denis Lackovic.
 295
 296 * Incorrect token definitions
 297   When given `%token 'a' "A"', Bison used to output `#define 'a' 65'.
 298
 299 * Token definitions as enums
 300   Tokens are output both as the traditional #define's, and, provided
 301   the compiler supports ANSI C or is a C++ compiler, as enums.
 302   This lets debuggers display names instead of integers.
 303
 304 * Reports
 305   In addition to --verbose, bison supports --report=THINGS, which
 306   produces additional information:
 307   - itemset
 308     complete the core item sets with their closure
 309   - lookahead [changed to `look-ahead' in 1.875e and later]
 310     explicitly associate look-ahead tokens to items
 311   - solved
 312     describe shift/reduce conflicts solving.
 313     Bison used to systematically output this information on top of
 314     the report.  Solved conflicts are now attached to their states.
 315
 316 * Type clashes
 317   Previous versions don't complain when there is a type clash on
 318   the default action if the rule has a mid-rule action, such as in:
 319
 320       %type <foo> bar
 321       %%
 322       bar: '0' {} '0';
 323
 324   This is fixed.
 325
 326 * GNU M4 is now required when using Bison.
 327 \f
 328 Changes in version 1.35, 2002-03-25:
 329
 330 * C Skeleton
 331   Some projects use Bison's C parser with C++ compilers, and define
 332   YYSTYPE as a class.  The recent adjustment of C parsers for data
 333   alignment and 64 bit architectures made this impossible.
 334
 335   Because for the time being no real solution for C++ parser
 336   generation exists, kludges were implemented in the parser to
 337   maintain this use.  In the future, when Bison has C++ parsers, this
 338   kludge will be disabled.
 339
 340   This kludge also addresses some C++ problems when the stack was
 341   extended.
 342 \f
 343 Changes in version 1.34, 2002-03-12:
 344
 345 * File name clashes are detected
 346   $ bison foo.y -d -o foo.x
 347   fatal error: header and parser would both be named `foo.x'
 348
 349 * A missing `;' at the end of a rule triggers a warning
 350   In accordance with POSIX, and in agreement with other
 351   Yacc implementations, Bison will mandate this semicolon in the near
 352   future.  This eases the implementation of a Bison parser of Bison
 353   grammars by making this grammar LALR(1) instead of LR(2).  To
 354   facilitate the transition, this release introduces a warning.
 355
 356 * Revert the C++ namespace changes introduced in 1.31, as they caused too
 357   many portability hassles.
 358
 359 * DJGPP support added.
 360
 361 * Fix test suite portability problems.
 362 \f
 363 Changes in version 1.33, 2002-02-07:
 364
 365 * Fix C++ issues
 366   Groff could not be compiled for the definition of size_t was lacking
 367   under some conditions.
 368
 369 * Catch invalid @n
 370   As is done with $n.
 371 \f
 372 Changes in version 1.32, 2002-01-23:
 373
 374 * Fix Yacc output file names
 375
 376 * Portability fixes
 377
 378 * Italian, Dutch translations
 379 \f
 380 Changes in version 1.31, 2002-01-14:
 381
 382 * Many Bug Fixes
 383
 384 * GNU Gettext and %expect
 385   GNU Gettext asserts 10 s/r conflicts, but there are 7.  Now that
 386   Bison dies on incorrect %expectations, we fear there will be
 387   too many bug reports for Gettext, so _for the time being_, %expect
 388   does not trigger an error when the input file is named `plural.y'.
 389
 390 * Use of alloca in parsers
 391   If YYSTACK_USE_ALLOCA is defined to 0, then the parsers will use
 392   malloc exclusively.  Since 1.29, but was not NEWS'ed.
 393
 394   alloca is used only when compiled with GCC, to avoid portability
 395   problems as on AIX.
 396
 397 * When the generated parser lacks debugging code, YYDEBUG is now 0
 398   (as POSIX requires) instead of being undefined.
 399
 400 * User Actions
 401   Bison has always permitted actions such as { $$ = $1 }: it adds the
 402   ending semicolon.  Now if in Yacc compatibility mode, the semicolon
 403   is no longer output: one has to write { $$ = $1; }.
 404
 405 * Better C++ compliance
 406   The output parsers try to respect C++ namespaces.
 407   [This turned out to be a failed experiment, and it was reverted later.]
 408
 409 * Reduced Grammars
 410   Fixed bugs when reporting useless nonterminals.
 411
 412 * 64 bit hosts
 413   The parsers work properly on 64 bit hosts.
 414
 415 * Error messages
 416   Some calls to strerror resulted in scrambled or missing error messages.
 417
 418 * %expect
 419   When the number of shift/reduce conflicts is correct, don't issue
 420   any warning.
 421
 422 * The verbose report includes the rule line numbers.
 423
 424 * Rule line numbers are fixed in traces.
 425
 426 * Swedish translation
 427
 428 * Parse errors
 429   Verbose parse error messages from the parsers are better looking.
 430   Before: parse error: unexpected `'/'', expecting `"number"' or `'-'' or `'(''
 431      Now: parse error: unexpected '/', expecting "number" or '-' or '('
 432
 433 * Fixed parser memory leaks.
 434   When the generated parser was using malloc to extend its stacks, the
 435   previous allocations were not freed.
 436
 437 * Fixed verbose output file.
 438   Some newlines were missing.
 439   Some conflicts in state descriptions were missing.
 440
 441 * Fixed conflict report.
 442   Option -v was needed to get the result.
 443
 444 * %expect
 445   Was not used.
 446   Mismatches are errors, not warnings.
 447
 448 * Fixed incorrect processing of some invalid input.
 449
 450 * Fixed CPP guards: 9foo.h uses BISON_9FOO_H instead of 9FOO_H.
 451
 452 * Fixed some typos in the documentation.
 453
 454 * %token MY_EOF 0 is supported.
 455   Before, MY_EOF was silently renumbered as 257.
 456
 457 * doc/refcard.tex is updated.
 458
 459 * %output, %file-prefix, %name-prefix.
 460   New.
 461
 462 * --output
 463   New, aliasing `--output-file'.
 464 \f
 465 Changes in version 1.30, 2001-10-26:
 466
 467 * `--defines' and `--graph' have now an optional argument which is the
 468   output file name. `-d' and `-g' do not change; they do not take any
 469   argument.
 470
 471 * `%source_extension' and `%header_extension' are removed, failed
 472   experiment.
 473
 474 * Portability fixes.
 475 \f
 476 Changes in version 1.29, 2001-09-07:
 477
 478 * The output file does not define const, as this caused problems when used
 479   with common autoconfiguration schemes.  If you still use ancient compilers
 480   that lack const, compile with the equivalent of the C compiler option
 481   `-Dconst='.  autoconf's AC_C_CONST macro provides one way to do this.
 482
 483 * Added `-g' and `--graph'.
 484
 485 * The Bison manual is now distributed under the terms of the GNU FDL.
 486
 487 * The input and the output files has automatically a similar extension.
 488
 489 * Russian translation added.
 490
 491 * NLS support updated; should hopefully be less troublesome.
 492
 493 * Added the old Bison reference card.
 494
 495 * Added `--locations' and `%locations'.
 496
 497 * Added `-S' and `--skeleton'.
 498
 499 * `%raw', `-r', `--raw' is disabled.
 500
 501 * Special characters are escaped when output.  This solves the problems
 502   of the #line lines with path names including backslashes.
 503
 504 * New directives.
 505   `%yacc', `%fixed_output_files', `%defines', `%no_parser', `%verbose',
 506   `%debug', `%source_extension' and `%header_extension'.
 507
 508 * @$
 509   Automatic location tracking.
 510 \f
 511 Changes in version 1.28, 1999-07-06:
 512
 513 * Should compile better now with K&R compilers.
 514
 515 * Added NLS.
 516
 517 * Fixed a problem with escaping the double quote character.
 518
 519 * There is now a FAQ.
 520 \f
 521 Changes in version 1.27:
 522
 523 * The make rule which prevented bison.simple from being created on
 524   some systems has been fixed.
 525 \f
 526 Changes in version 1.26:
 527
 528 * Bison now uses automake.
 529
 530 * New mailing lists: <bug-bison@gnu.org> and <help-bison@gnu.org>.
 531
 532 * Token numbers now start at 257 as previously documented, not 258.
 533
 534 * Bison honors the TMPDIR environment variable.
 535
 536 * A couple of buffer overruns have been fixed.
 537
 538 * Problems when closing files should now be reported.
 539
 540 * Generated parsers should now work even on operating systems which do
 541   not provide alloca().
 542 \f
 543 Changes in version 1.25, 1995-10-16:
 544
 545 * Errors in the input grammar are not fatal; Bison keeps reading
 546 the grammar file, and reports all the errors found in it.
 547
 548 * Tokens can now be specified as multiple-character strings: for
 549 example, you could use "<=" for a token which looks like <=, instead
 550 of chosing a name like LESSEQ.
 551
 552 * The %token_table declaration says to write a table of tokens (names
 553 and numbers) into the parser file.  The yylex function can use this
 554 table to recognize multiple-character string tokens, or for other
 555 purposes.
 556
 557 * The %no_lines declaration says not to generate any #line preprocessor
 558 directives in the parser file.
 559
 560 * The %raw declaration says to use internal Bison token numbers, not
 561 Yacc-compatible token numbers, when token names are defined as macros.
 562
 563 * The --no-parser option produces the parser tables without including
 564 the parser engine; a project can now use its own parser engine.
 565 The actions go into a separate file called NAME.act, in the form of
 566 a switch statement body.
 567 \f
 568 Changes in version 1.23:
 569
 570 The user can define YYPARSE_PARAM as the name of an argument to be
 571 passed into yyparse.  The argument should have type void *.  It should
 572 actually point to an object.  Grammar actions can access the variable
 573 by casting it to the proper pointer type.
 574
 575 Line numbers in output file corrected.
 576 \f
 577 Changes in version 1.22:
 578
 579 --help option added.
 580 \f
 581 Changes in version 1.20:
 582
 583 Output file does not redefine const for C++.
 584
 585 Local Variables:
 586 mode: outline
 587 End:
 588
 589 -----
 590
 591 Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004
 592 Free Software Foundation, Inc.
 593
 594 This file is part of Bison, the GNU Compiler Compiler.
 595
 596 Bison is free software; you can redistribute it and/or modify
 597 it under the terms of the GNU General Public License as published by
 598 the Free Software Foundation; either version 2, or (at your option)
 599 any later version.
 600
 601 Bison is distributed in the hope that it will be useful,
 602 but WITHOUT ANY WARRANTY; without even the implied warranty of
 603 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 604 GNU General Public License for more details.
 605
 606 You should have received a copy of the GNU General Public License
 607 along with autoconf; see the file COPYING.  If not, write to
 608 the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 609 Boston, MA 02111-1307, USA.