NEWS

   1 Bison News
   2 ----------
   3
   4 Changes in version 1.875e, 2004-12-10:
   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   Paul Eggert, "Reductions during Bison error handling" (2002-05-20)
 235   <http://lists.gnu.org/archive/html/bug-bison/2002-05/msg00038.html>.
 236
 237 * Traces
 238   Popped tokens and nonterminals are now reported.
 239
 240 * Larger grammars
 241   Larger grammars are now supported (larger token numbers, larger grammar
 242   size (= sum of the LHS and RHS lengths), larger LALR tables).
 243   Formerly, many of these numbers ran afoul of 16-bit limits;
 244   now these limits are 32 bits on most hosts.
 245
 246 * Explicit initial rule
 247   Bison used to play hacks with the initial rule, which the user does
 248   not write.  It is now explicit, and visible in the reports and
 249   graphs as rule 0.
 250
 251 * Useless rules
 252   Before, Bison reported the useless rules, but, although not used,
 253   included them in the parsers.  They are now actually removed.
 254
 255 * Useless rules, useless nonterminals
 256   They are now reported, as a warning, with their locations.
 257
 258 * Rules never reduced
 259   Rules that can never be reduced because of conflicts are now
 260   reported.
 261
 262 * Incorrect `Token not used'
 263   On a grammar such as
 264
 265            %token useless useful
 266            %%
 267            exp: '0' %prec useful;
 268
 269   where a token was used to set the precedence of the last rule,
 270   bison reported both `useful' and `useless' as useless tokens.
 271
 272 * Revert the C++ namespace changes introduced in 1.31
 273   as they caused too many portability hassles.
 274
 275 * Default locations
 276   By an accident of design, the default computation of @$ was
 277   performed after another default computation was performed: @$ = @1.
 278   The latter is now removed: YYLLOC_DEFAULT is fully responsible of
 279   the computation of @$.
 280
 281 * Token end-of-file
 282   The token end of file may be specified by the user, in which case,
 283   the user symbol is used in the reports, the graphs, and the verbose
 284   error messages instead of `$end', which remains being the default.
 285   For instance
 286      %token MYEOF 0
 287   or
 288      %token MYEOF 0 "end of file"
 289
 290 * Semantic parser
 291   This old option, which has been broken for ages, is removed.
 292
 293 * New translations
 294   Brazilian Portuguese, thanks to Alexandre Folle de Menezes.
 295   Croatian, thanks to Denis Lackovic.
 296
 297 * Incorrect token definitions
 298   When given `%token 'a' "A"', Bison used to output `#define 'a' 65'.
 299
 300 * Token definitions as enums
 301   Tokens are output both as the traditional #define's, and, provided
 302   the compiler supports ANSI C or is a C++ compiler, as enums.
 303   This lets debuggers display names instead of integers.
 304
 305 * Reports
 306   In addition to --verbose, bison supports --report=THINGS, which
 307   produces additional information:
 308   - itemset
 309     complete the core item sets with their closure
 310   - lookahead [changed to `look-ahead' in 1.875e and later]
 311     explicitly associate look-ahead tokens to items
 312   - solved
 313     describe shift/reduce conflicts solving.
 314     Bison used to systematically output this information on top of
 315     the report.  Solved conflicts are now attached to their states.
 316
 317 * Type clashes
 318   Previous versions don't complain when there is a type clash on
 319   the default action if the rule has a mid-rule action, such as in:
 320
 321       %type <foo> bar
 322       %%
 323       bar: '0' {} '0';
 324
 325   This is fixed.
 326
 327 * GNU M4 is now required when using Bison.
 328 \f
 329 Changes in version 1.35, 2002-03-25:
 330
 331 * C Skeleton
 332   Some projects use Bison's C parser with C++ compilers, and define
 333   YYSTYPE as a class.  The recent adjustment of C parsers for data
 334   alignment and 64 bit architectures made this impossible.
 335
 336   Because for the time being no real solution for C++ parser
 337   generation exists, kludges were implemented in the parser to
 338   maintain this use.  In the future, when Bison has C++ parsers, this
 339   kludge will be disabled.
 340
 341   This kludge also addresses some C++ problems when the stack was
 342   extended.
 343 \f
 344 Changes in version 1.34, 2002-03-12:
 345
 346 * File name clashes are detected
 347   $ bison foo.y -d -o foo.x
 348   fatal error: header and parser would both be named `foo.x'
 349
 350 * A missing `;' at the end of a rule triggers a warning
 351   In accordance with POSIX, and in agreement with other
 352   Yacc implementations, Bison will mandate this semicolon in the near
 353   future.  This eases the implementation of a Bison parser of Bison
 354   grammars by making this grammar LALR(1) instead of LR(2).  To
 355   facilitate the transition, this release introduces a warning.
 356
 357 * Revert the C++ namespace changes introduced in 1.31, as they caused too
 358   many portability hassles.
 359
 360 * DJGPP support added.
 361
 362 * Fix test suite portability problems.
 363 \f
 364 Changes in version 1.33, 2002-02-07:
 365
 366 * Fix C++ issues
 367   Groff could not be compiled for the definition of size_t was lacking
 368   under some conditions.
 369
 370 * Catch invalid @n
 371   As is done with $n.
 372 \f
 373 Changes in version 1.32, 2002-01-23:
 374
 375 * Fix Yacc output file names
 376
 377 * Portability fixes
 378
 379 * Italian, Dutch translations
 380 \f
 381 Changes in version 1.31, 2002-01-14:
 382
 383 * Many Bug Fixes
 384
 385 * GNU Gettext and %expect
 386   GNU Gettext asserts 10 s/r conflicts, but there are 7.  Now that
 387   Bison dies on incorrect %expectations, we fear there will be
 388   too many bug reports for Gettext, so _for the time being_, %expect
 389   does not trigger an error when the input file is named `plural.y'.
 390
 391 * Use of alloca in parsers
 392   If YYSTACK_USE_ALLOCA is defined to 0, then the parsers will use
 393   malloc exclusively.  Since 1.29, but was not NEWS'ed.
 394
 395   alloca is used only when compiled with GCC, to avoid portability
 396   problems as on AIX.
 397
 398 * When the generated parser lacks debugging code, YYDEBUG is now 0
 399   (as POSIX requires) instead of being undefined.
 400
 401 * User Actions
 402   Bison has always permitted actions such as { $$ = $1 }: it adds the
 403   ending semicolon.  Now if in Yacc compatibility mode, the semicolon
 404   is no longer output: one has to write { $$ = $1; }.
 405
 406 * Better C++ compliance
 407   The output parsers try to respect C++ namespaces.
 408   [This turned out to be a failed experiment, and it was reverted later.]
 409
 410 * Reduced Grammars
 411   Fixed bugs when reporting useless nonterminals.
 412
 413 * 64 bit hosts
 414   The parsers work properly on 64 bit hosts.
 415
 416 * Error messages
 417   Some calls to strerror resulted in scrambled or missing error messages.
 418
 419 * %expect
 420   When the number of shift/reduce conflicts is correct, don't issue
 421   any warning.
 422
 423 * The verbose report includes the rule line numbers.
 424
 425 * Rule line numbers are fixed in traces.
 426
 427 * Swedish translation
 428
 429 * Parse errors
 430   Verbose parse error messages from the parsers are better looking.
 431   Before: parse error: unexpected `'/'', expecting `"number"' or `'-'' or `'(''
 432      Now: parse error: unexpected '/', expecting "number" or '-' or '('
 433
 434 * Fixed parser memory leaks.
 435   When the generated parser was using malloc to extend its stacks, the
 436   previous allocations were not freed.
 437
 438 * Fixed verbose output file.
 439   Some newlines were missing.
 440   Some conflicts in state descriptions were missing.
 441
 442 * Fixed conflict report.
 443   Option -v was needed to get the result.
 444
 445 * %expect
 446   Was not used.
 447   Mismatches are errors, not warnings.
 448
 449 * Fixed incorrect processing of some invalid input.
 450
 451 * Fixed CPP guards: 9foo.h uses BISON_9FOO_H instead of 9FOO_H.
 452
 453 * Fixed some typos in the documentation.
 454
 455 * %token MY_EOF 0 is supported.
 456   Before, MY_EOF was silently renumbered as 257.
 457
 458 * doc/refcard.tex is updated.
 459
 460 * %output, %file-prefix, %name-prefix.
 461   New.
 462
 463 * --output
 464   New, aliasing `--output-file'.
 465 \f
 466 Changes in version 1.30, 2001-10-26:
 467
 468 * `--defines' and `--graph' have now an optional argument which is the
 469   output file name. `-d' and `-g' do not change; they do not take any
 470   argument.
 471
 472 * `%source_extension' and `%header_extension' are removed, failed
 473   experiment.
 474
 475 * Portability fixes.
 476 \f
 477 Changes in version 1.29, 2001-09-07:
 478
 479 * The output file does not define const, as this caused problems when used
 480   with common autoconfiguration schemes.  If you still use ancient compilers
 481   that lack const, compile with the equivalent of the C compiler option
 482   `-Dconst='.  autoconf's AC_C_CONST macro provides one way to do this.
 483
 484 * Added `-g' and `--graph'.
 485
 486 * The Bison manual is now distributed under the terms of the GNU FDL.
 487
 488 * The input and the output files has automatically a similar extension.
 489
 490 * Russian translation added.
 491
 492 * NLS support updated; should hopefully be less troublesome.
 493
 494 * Added the old Bison reference card.
 495
 496 * Added `--locations' and `%locations'.
 497
 498 * Added `-S' and `--skeleton'.
 499
 500 * `%raw', `-r', `--raw' is disabled.
 501
 502 * Special characters are escaped when output.  This solves the problems
 503   of the #line lines with path names including backslashes.
 504
 505 * New directives.
 506   `%yacc', `%fixed_output_files', `%defines', `%no_parser', `%verbose',
 507   `%debug', `%source_extension' and `%header_extension'.
 508
 509 * @$
 510   Automatic location tracking.
 511 \f
 512 Changes in version 1.28, 1999-07-06:
 513
 514 * Should compile better now with K&R compilers.
 515
 516 * Added NLS.
 517
 518 * Fixed a problem with escaping the double quote character.
 519
 520 * There is now a FAQ.
 521 \f
 522 Changes in version 1.27:
 523
 524 * The make rule which prevented bison.simple from being created on
 525   some systems has been fixed.
 526 \f
 527 Changes in version 1.26:
 528
 529 * Bison now uses automake.
 530
 531 * New mailing lists: <bug-bison@gnu.org> and <help-bison@gnu.org>.
 532
 533 * Token numbers now start at 257 as previously documented, not 258.
 534
 535 * Bison honors the TMPDIR environment variable.
 536
 537 * A couple of buffer overruns have been fixed.
 538
 539 * Problems when closing files should now be reported.
 540
 541 * Generated parsers should now work even on operating systems which do
 542   not provide alloca().
 543 \f
 544 Changes in version 1.25, 1995-10-16:
 545
 546 * Errors in the input grammar are not fatal; Bison keeps reading
 547 the grammar file, and reports all the errors found in it.
 548
 549 * Tokens can now be specified as multiple-character strings: for
 550 example, you could use "<=" for a token which looks like <=, instead
 551 of chosing a name like LESSEQ.
 552
 553 * The %token_table declaration says to write a table of tokens (names
 554 and numbers) into the parser file.  The yylex function can use this
 555 table to recognize multiple-character string tokens, or for other
 556 purposes.
 557
 558 * The %no_lines declaration says not to generate any #line preprocessor
 559 directives in the parser file.
 560
 561 * The %raw declaration says to use internal Bison token numbers, not
 562 Yacc-compatible token numbers, when token names are defined as macros.
 563
 564 * The --no-parser option produces the parser tables without including
 565 the parser engine; a project can now use its own parser engine.
 566 The actions go into a separate file called NAME.act, in the form of
 567 a switch statement body.
 568 \f
 569 Changes in version 1.23:
 570
 571 The user can define YYPARSE_PARAM as the name of an argument to be
 572 passed into yyparse.  The argument should have type void *.  It should
 573 actually point to an object.  Grammar actions can access the variable
 574 by casting it to the proper pointer type.
 575
 576 Line numbers in output file corrected.
 577 \f
 578 Changes in version 1.22:
 579
 580 --help option added.
 581 \f
 582 Changes in version 1.20:
 583
 584 Output file does not redefine const for C++.
 585
 586 Local Variables:
 587 mode: outline
 588 End:
 589
 590 -----
 591
 592 Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004
 593 Free Software Foundation, Inc.
 594
 595 This file is part of Bison, the GNU Compiler Compiler.
 596
 597 Bison is free software; you can redistribute it and/or modify
 598 it under the terms of the GNU General Public License as published by
 599 the Free Software Foundation; either version 2, or (at your option)
 600 any later version.
 601
 602 Bison is distributed in the hope that it will be useful,
 603 but WITHOUT ANY WARRANTY; without even the implied warranty of
 604 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 605 GNU General Public License for more details.
 606
 607 You should have received a copy of the GNU General Public License
 608 along with autoconf; see the file COPYING.  If not, write to
 609 the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 610 Boston, MA 02111-1307, USA.