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