NEWS

   1 Bison News
   2 ----------
   3
   4 Changes in version 1.875f:
   5
   6 Changes in version 1.875e, 2004-12-10:
   7
   8 * New directive: %initial-action.
   9   This directive allows the user to run arbitrary code (including
  10   initializing @$) from yyparse before parsing starts.
  11
  12 * The option `--report=lookahead' was changed to `--report=look-ahead'.
  13   The old spelling still works, but is not documented and will be
  14   removed.
  15
  16 * Error token location.
  17   During error recovery, the location of the syntax error is updated
  18   to cover the whole sequence covered by the error token: it includes
  19   the shifted symbols thrown away during the first part of the error
  20   recovery, and the lookahead rejected during the second part.
  21
  22 * Goto numbers are no longer arbitrarily limited to 16-bit counts.
  23
  24 Changes in version 1.875d, 2004-05-21:
  25
  26 * Unescaped newlines are no longer allowed in character constants or
  27   string literals.  They were never portable, and GCC 3.4.0 has
  28   dropped support for them.  Better diagnostics are now generated if
  29   forget a closing quote.
  30
  31 * NUL bytes are no longer allowed in Bison string literals, unfortunately.
  32
  33 * %token numbers can now be hexadecimal integers, e.g., `%token FOO 0x12d'.
  34   This is a GNU extension.
  35
  36 * A new directive "%expect-rr N" specifies the expected number of
  37   reduce/reduce conflicts in GLR parsers.
  38
  39 * Experimental %destructor support has been added to lalr1.cc.
  40
  41 Changes in version 1.875c, 2003-08-25:
  42
  43   (Just bug fixes.)
  44
  45 Changes in version 1.875b, 2003-06-17:
  46
  47 * GLR grammars now support locations.
  48
  49 * Semicolon changes:
  50   - Semicolons are now allowed before "|" in grammar rules, as POSIX requires.
  51   - Stray semicolons are no longer allowed at the start of a grammar.
  52   - Semicolons are now required after in-grammar declarations.
  53
  54 Changes in version 1.875a, 2003-02-01:
  55
  56 * For now, %expect-count violations are now just warnings, not errors.
  57   This is for compatibility with Bison 1.75 and earlier (when there are
  58   reduce/reduce conflicts) and with Bison 1.30 and earlier (when there
  59   are too many or too few shift/reduce conflicts).  However, in future
  60   versions of Bison we plan to improve the %expect machinery so that
  61   these violations will become errors again.
  62
  63 * New configure option --disable-yacc, to disable installation of the
  64   yacc command and -ly library introduced in 1.875 for POSIX conformance.
  65 \f
  66 Changes in version 1.875, 2003-01-01:
  67
  68 * The documentation license has been upgraded to version 1.2
  69   of the GNU Free Documentation License.
  70
  71 * syntax error processing
  72
  73   - In Yacc-style parsers YYLLOC_DEFAULT is now used to compute error
  74     locations too.  This fixes bugs in error-location computation.
  75
  76   - %destructor
  77     It is now possible to reclaim the memory associated to symbols
  78     discarded during error recovery.  This feature is still experimental.
  79
  80   - %error-verbose
  81     This new directive is preferred over YYERROR_VERBOSE.
  82
  83   - #defining yyerror to steal internal variables is discouraged.
  84     It is not guaranteed to work forever.
  85
  86 * POSIX conformance
  87
  88   - Semicolons are once again optional at the end of grammar rules.
  89     This reverts to the behavior of Bison 1.33 and earlier, and improves
  90     compatibility with Yacc.
  91
  92   - `parse error' -> `syntax error'
  93     Bison now uniformly uses the term `syntax error'; formerly, the code
  94     and manual sometimes used the term `parse error' instead.  POSIX
  95     requires `syntax error' in diagnostics, and it was thought better to
  96     be consistent.
  97
  98   - The documentation now emphasizes that yylex and yyerror must be
  99     declared before use.  C99 requires this.
 100
 101   - Bison now parses C99 lexical constructs like UCNs and
 102     backslash-newline within C escape sequences, as POSIX 1003.1-2001 requires.
 103
 104   - File names are properly escaped in C output.  E.g., foo\bar.y is
 105     output as "foo\\bar.y".
 106
 107   - Yacc command and library now available
 108     The Bison distribution now installs a `yacc' command, as POSIX requires.
 109     Also, Bison now installs a small library liby.a containing
 110     implementations of Yacc-compatible yyerror and main functions.
 111     This library is normally not useful, but POSIX requires it.
 112
 113   - Type clashes now generate warnings, not errors.
 114
 115   - If the user does not define YYSTYPE as a macro, Bison now declares it
 116     using typedef instead of defining it as a macro.
 117     For consistency, YYLTYPE is also declared instead of defined.
 118
 119 * Other compatibility issues
 120
 121   - %union directives can now have a tag before the `{', e.g., the
 122     directive `%union foo {...}' now generates the C code
 123     `typedef union foo { ... } YYSTYPE;'; this is for Yacc compatibility.
 124     The default union tag is `YYSTYPE', for compatibility with Solaris 9 Yacc.
 125     For consistency, YYLTYPE's struct tag is now `YYLTYPE' not `yyltype'.
 126     This is for compatibility with both Yacc and Bison 1.35.
 127
 128   - `;' is output before the terminating `}' of an action, for
 129     compatibility with Bison 1.35.
 130
 131   - Bison now uses a Yacc-style format for conflict reports, e.g.,
 132     `conflicts: 2 shift/reduce, 1 reduce/reduce'.
 133
 134   - `yystype' and `yyltype' are now obsolescent macros instead of being
 135     typedefs or tags; they are no longer documented and are planned to be
 136     withdrawn in a future release.
 137
 138 * GLR parser notes
 139
 140   - GLR and inline
 141     Users of Bison have to decide how they handle the portability of the
 142     C keyword `inline'.
 143
 144   - `parsing stack overflow...' -> `parser stack overflow'
 145     GLR parsers now report `parser stack overflow' as per the Bison manual.
 146
 147 * Bison now warns if it detects conflicting outputs to the same file,
 148   e.g., it generates a warning for `bison -d -o foo.h foo.y' since
 149   that command outputs both code and header to foo.h.
 150
 151 * #line in output files
 152   - --no-line works properly.
 153
 154 * Bison can no longer be built by a K&R C compiler; it requires C89 or
 155   later to be built.  This change originally took place a few versions
 156   ago, but nobody noticed until we recently asked someone to try
 157   building Bison with a K&R C compiler.
 158 \f
 159 Changes in version 1.75, 2002-10-14:
 160
 161 * Bison should now work on 64-bit hosts.
 162
 163 * Indonesian translation thanks to Tedi Heriyanto.
 164
 165 * GLR parsers
 166   Fix spurious parse errors.
 167
 168 * Pure parsers
 169   Some people redefine yyerror to steal yyparse' private variables.
 170   Reenable this trick until an official feature replaces it.
 171
 172 * Type Clashes
 173   In agreement with POSIX and with other Yaccs, leaving a default
 174   action is valid when $$ is untyped, and $1 typed:
 175
 176         untyped: ... typed;
 177
 178   but the converse remains an error:
 179
 180         typed: ... untyped;
 181
 182 * Values of mid-rule actions
 183   The following code:
 184
 185         foo: { ... } { $$ = $1; } ...
 186
 187   was incorrectly rejected: $1 is defined in the second mid-rule
 188   action, and is equal to the $$ of the first mid-rule action.
 189 \f
 190 Changes in version 1.50, 2002-10-04:
 191
 192 * GLR parsing
 193   The declaration
 194      %glr-parser
 195   causes Bison to produce a Generalized LR (GLR) parser, capable of handling
 196   almost any context-free grammar, ambiguous or not.  The new declarations
 197   %dprec and %merge on grammar rules allow parse-time resolution of
 198   ambiguities.  Contributed by Paul Hilfinger.
 199
 200   Unfortunately Bison 1.50 does not work properly on 64-bit hosts
 201   like the Alpha, so please stick to 32-bit hosts for now.
 202
 203 * Output Directory
 204   When not in Yacc compatibility mode, when the output file was not
 205   specified, running `bison foo/bar.y' created `foo/bar.c'.  It
 206   now creates `bar.c'.
 207
 208 * Undefined token
 209   The undefined token was systematically mapped to 2 which prevented
 210   the use of 2 by the user.  This is no longer the case.
 211
 212 * Unknown token numbers
 213   If yylex returned an out of range value, yyparse could die.  This is
 214   no longer the case.
 215
 216 * Error token
 217   According to POSIX, the error token must be 256.
 218   Bison extends this requirement by making it a preference: *if* the
 219   user specified that one of her tokens is numbered 256, then error
 220   will be mapped onto another number.
 221
 222 * Verbose error messages
 223   They no longer report `..., expecting error or...' for states where
 224   error recovery is possible.
 225
 226 * End token
 227   Defaults to `$end' instead of `$'.
 228
 229 * Error recovery now conforms to documentation and to POSIX
 230   When a Bison-generated parser encounters a syntax error, it now pops
 231   the stack until it finds a state that allows shifting the error
 232   token.  Formerly, it popped the stack until it found a state that
 233   allowed some non-error action other than a default reduction on the
 234   error token.  The new behavior has long been the documented behavior,
 235   and has long been required by POSIX.  For more details, please see
 236   Paul Eggert, "Reductions during Bison error handling" (2002-05-20)
 237   <http://lists.gnu.org/archive/html/bug-bison/2002-05/msg00038.html>.
 238
 239 * Traces
 240   Popped tokens and nonterminals are now reported.
 241
 242 * Larger grammars
 243   Larger grammars are now supported (larger token numbers, larger grammar
 244   size (= sum of the LHS and RHS lengths), larger LALR tables).
 245   Formerly, many of these numbers ran afoul of 16-bit limits;
 246   now these limits are 32 bits on most hosts.
 247
 248 * Explicit initial rule
 249   Bison used to play hacks with the initial rule, which the user does
 250   not write.  It is now explicit, and visible in the reports and
 251   graphs as rule 0.
 252
 253 * Useless rules
 254   Before, Bison reported the useless rules, but, although not used,
 255   included them in the parsers.  They are now actually removed.
 256
 257 * Useless rules, useless nonterminals
 258   They are now reported, as a warning, with their locations.
 259
 260 * Rules never reduced
 261   Rules that can never be reduced because of conflicts are now
 262   reported.
 263
 264 * Incorrect `Token not used'
 265   On a grammar such as
 266
 267            %token useless useful
 268            %%
 269            exp: '0' %prec useful;
 270
 271   where a token was used to set the precedence of the last rule,
 272   bison reported both `useful' and `useless' as useless tokens.
 273
 274 * Revert the C++ namespace changes introduced in 1.31
 275   as they caused too many portability hassles.
 276
 277 * Default locations
 278   By an accident of design, the default computation of @$ was
 279   performed after another default computation was performed: @$ = @1.
 280   The latter is now removed: YYLLOC_DEFAULT is fully responsible of
 281   the computation of @$.
 282
 283 * Token end-of-file
 284   The token end of file may be specified by the user, in which case,
 285   the user symbol is used in the reports, the graphs, and the verbose
 286   error messages instead of `$end', which remains being the default.
 287   For instance
 288      %token MYEOF 0
 289   or
 290      %token MYEOF 0 "end of file"
 291
 292 * Semantic parser
 293   This old option, which has been broken for ages, is removed.
 294
 295 * New translations
 296   Brazilian Portuguese, thanks to Alexandre Folle de Menezes.
 297   Croatian, thanks to Denis Lackovic.
 298
 299 * Incorrect token definitions
 300   When given `%token 'a' "A"', Bison used to output `#define 'a' 65'.
 301
 302 * Token definitions as enums
 303   Tokens are output both as the traditional #define's, and, provided
 304   the compiler supports ANSI C or is a C++ compiler, as enums.
 305   This lets debuggers display names instead of integers.
 306
 307 * Reports
 308   In addition to --verbose, bison supports --report=THINGS, which
 309   produces additional information:
 310   - itemset
 311     complete the core item sets with their closure
 312   - lookahead [changed to `look-ahead' in 1.875e and later]
 313     explicitly associate look-ahead tokens to items
 314   - solved
 315     describe shift/reduce conflicts solving.
 316     Bison used to systematically output this information on top of
 317     the report.  Solved conflicts are now attached to their states.
 318
 319 * Type clashes
 320   Previous versions don't complain when there is a type clash on
 321   the default action if the rule has a mid-rule action, such as in:
 322
 323       %type <foo> bar
 324       %%
 325       bar: '0' {} '0';
 326
 327   This is fixed.
 328
 329 * GNU M4 is now required when using Bison.
 330 \f
 331 Changes in version 1.35, 2002-03-25:
 332
 333 * C Skeleton
 334   Some projects use Bison's C parser with C++ compilers, and define
 335   YYSTYPE as a class.  The recent adjustment of C parsers for data
 336   alignment and 64 bit architectures made this impossible.
 337
 338   Because for the time being no real solution for C++ parser
 339   generation exists, kludges were implemented in the parser to
 340   maintain this use.  In the future, when Bison has C++ parsers, this
 341   kludge will be disabled.
 342
 343   This kludge also addresses some C++ problems when the stack was
 344   extended.
 345 \f
 346 Changes in version 1.34, 2002-03-12:
 347
 348 * File name clashes are detected
 349   $ bison foo.y -d -o foo.x
 350   fatal error: header and parser would both be named `foo.x'
 351
 352 * A missing `;' at the end of a rule triggers a warning
 353   In accordance with POSIX, and in agreement with other
 354   Yacc implementations, Bison will mandate this semicolon in the near
 355   future.  This eases the implementation of a Bison parser of Bison
 356   grammars by making this grammar LALR(1) instead of LR(2).  To
 357   facilitate the transition, this release introduces a warning.
 358
 359 * Revert the C++ namespace changes introduced in 1.31, as they caused too
 360   many portability hassles.
 361
 362 * DJGPP support added.
 363
 364 * Fix test suite portability problems.
 365 \f
 366 Changes in version 1.33, 2002-02-07:
 367
 368 * Fix C++ issues
 369   Groff could not be compiled for the definition of size_t was lacking
 370   under some conditions.
 371
 372 * Catch invalid @n
 373   As is done with $n.
 374 \f
 375 Changes in version 1.32, 2002-01-23:
 376
 377 * Fix Yacc output file names
 378
 379 * Portability fixes
 380
 381 * Italian, Dutch translations
 382 \f
 383 Changes in version 1.31, 2002-01-14:
 384
 385 * Many Bug Fixes
 386
 387 * GNU Gettext and %expect
 388   GNU Gettext asserts 10 s/r conflicts, but there are 7.  Now that
 389   Bison dies on incorrect %expectations, we fear there will be
 390   too many bug reports for Gettext, so _for the time being_, %expect
 391   does not trigger an error when the input file is named `plural.y'.
 392
 393 * Use of alloca in parsers
 394   If YYSTACK_USE_ALLOCA is defined to 0, then the parsers will use
 395   malloc exclusively.  Since 1.29, but was not NEWS'ed.
 396
 397   alloca is used only when compiled with GCC, to avoid portability
 398   problems as on AIX.
 399
 400 * When the generated parser lacks debugging code, YYDEBUG is now 0
 401   (as POSIX requires) instead of being undefined.
 402
 403 * User Actions
 404   Bison has always permitted actions such as { $$ = $1 }: it adds the
 405   ending semicolon.  Now if in Yacc compatibility mode, the semicolon
 406   is no longer output: one has to write { $$ = $1; }.
 407
 408 * Better C++ compliance
 409   The output parsers try to respect C++ namespaces.
 410   [This turned out to be a failed experiment, and it was reverted later.]
 411
 412 * Reduced Grammars
 413   Fixed bugs when reporting useless nonterminals.
 414
 415 * 64 bit hosts
 416   The parsers work properly on 64 bit hosts.
 417
 418 * Error messages
 419   Some calls to strerror resulted in scrambled or missing error messages.
 420
 421 * %expect
 422   When the number of shift/reduce conflicts is correct, don't issue
 423   any warning.
 424
 425 * The verbose report includes the rule line numbers.
 426
 427 * Rule line numbers are fixed in traces.
 428
 429 * Swedish translation
 430
 431 * Parse errors
 432   Verbose parse error messages from the parsers are better looking.
 433   Before: parse error: unexpected `'/'', expecting `"number"' or `'-'' or `'(''
 434      Now: parse error: unexpected '/', expecting "number" or '-' or '('
 435
 436 * Fixed parser memory leaks.
 437   When the generated parser was using malloc to extend its stacks, the
 438   previous allocations were not freed.
 439
 440 * Fixed verbose output file.
 441   Some newlines were missing.
 442   Some conflicts in state descriptions were missing.
 443
 444 * Fixed conflict report.
 445   Option -v was needed to get the result.
 446
 447 * %expect
 448   Was not used.
 449   Mismatches are errors, not warnings.
 450
 451 * Fixed incorrect processing of some invalid input.
 452
 453 * Fixed CPP guards: 9foo.h uses BISON_9FOO_H instead of 9FOO_H.
 454
 455 * Fixed some typos in the documentation.
 456
 457 * %token MY_EOF 0 is supported.
 458   Before, MY_EOF was silently renumbered as 257.
 459
 460 * doc/refcard.tex is updated.
 461
 462 * %output, %file-prefix, %name-prefix.
 463   New.
 464
 465 * --output
 466   New, aliasing `--output-file'.
 467 \f
 468 Changes in version 1.30, 2001-10-26:
 469
 470 * `--defines' and `--graph' have now an optional argument which is the
 471   output file name. `-d' and `-g' do not change; they do not take any
 472   argument.
 473
 474 * `%source_extension' and `%header_extension' are removed, failed
 475   experiment.
 476
 477 * Portability fixes.
 478 \f
 479 Changes in version 1.29, 2001-09-07:
 480
 481 * The output file does not define const, as this caused problems when used
 482   with common autoconfiguration schemes.  If you still use ancient compilers
 483   that lack const, compile with the equivalent of the C compiler option
 484   `-Dconst='.  autoconf's AC_C_CONST macro provides one way to do this.
 485
 486 * Added `-g' and `--graph'.
 487
 488 * The Bison manual is now distributed under the terms of the GNU FDL.
 489
 490 * The input and the output files has automatically a similar extension.
 491
 492 * Russian translation added.
 493
 494 * NLS support updated; should hopefully be less troublesome.
 495
 496 * Added the old Bison reference card.
 497
 498 * Added `--locations' and `%locations'.
 499
 500 * Added `-S' and `--skeleton'.
 501
 502 * `%raw', `-r', `--raw' is disabled.
 503
 504 * Special characters are escaped when output.  This solves the problems
 505   of the #line lines with path names including backslashes.
 506
 507 * New directives.
 508   `%yacc', `%fixed_output_files', `%defines', `%no_parser', `%verbose',
 509   `%debug', `%source_extension' and `%header_extension'.
 510
 511 * @$
 512   Automatic location tracking.
 513 \f
 514 Changes in version 1.28, 1999-07-06:
 515
 516 * Should compile better now with K&R compilers.
 517
 518 * Added NLS.
 519
 520 * Fixed a problem with escaping the double quote character.
 521
 522 * There is now a FAQ.
 523 \f
 524 Changes in version 1.27:
 525
 526 * The make rule which prevented bison.simple from being created on
 527   some systems has been fixed.
 528 \f
 529 Changes in version 1.26:
 530
 531 * Bison now uses automake.
 532
 533 * New mailing lists: <bug-bison@gnu.org> and <help-bison@gnu.org>.
 534
 535 * Token numbers now start at 257 as previously documented, not 258.
 536
 537 * Bison honors the TMPDIR environment variable.
 538
 539 * A couple of buffer overruns have been fixed.
 540
 541 * Problems when closing files should now be reported.
 542
 543 * Generated parsers should now work even on operating systems which do
 544   not provide alloca().
 545 \f
 546 Changes in version 1.25, 1995-10-16:
 547
 548 * Errors in the input grammar are not fatal; Bison keeps reading
 549 the grammar file, and reports all the errors found in it.
 550
 551 * Tokens can now be specified as multiple-character strings: for
 552 example, you could use "<=" for a token which looks like <=, instead
 553 of chosing a name like LESSEQ.
 554
 555 * The %token_table declaration says to write a table of tokens (names
 556 and numbers) into the parser file.  The yylex function can use this
 557 table to recognize multiple-character string tokens, or for other
 558 purposes.
 559
 560 * The %no_lines declaration says not to generate any #line preprocessor
 561 directives in the parser file.
 562
 563 * The %raw declaration says to use internal Bison token numbers, not
 564 Yacc-compatible token numbers, when token names are defined as macros.
 565
 566 * The --no-parser option produces the parser tables without including
 567 the parser engine; a project can now use its own parser engine.
 568 The actions go into a separate file called NAME.act, in the form of
 569 a switch statement body.
 570 \f
 571 Changes in version 1.23:
 572
 573 The user can define YYPARSE_PARAM as the name of an argument to be
 574 passed into yyparse.  The argument should have type void *.  It should
 575 actually point to an object.  Grammar actions can access the variable
 576 by casting it to the proper pointer type.
 577
 578 Line numbers in output file corrected.
 579 \f
 580 Changes in version 1.22:
 581
 582 --help option added.
 583 \f
 584 Changes in version 1.20:
 585
 586 Output file does not redefine const for C++.
 587
 588 Local Variables:
 589 mode: outline
 590 End:
 591
 592 -----
 593
 594 Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004
 595 Free Software Foundation, Inc.
 596
 597 This file is part of Bison, the GNU Compiler Compiler.
 598
 599 Bison is free software; you can redistribute it and/or modify
 600 it under the terms of the GNU General Public License as published by
 601 the Free Software Foundation; either version 2, or (at your option)
 602 any later version.
 603
 604 Bison is distributed in the hope that it will be useful,
 605 but WITHOUT ANY WARRANTY; without even the implied warranty of
 606 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 607 GNU General Public License for more details.
 608
 609 You should have received a copy of the GNU General Public License
 610 along with autoconf; see the file COPYING.  If not, write to
 611 the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 612 Boston, MA 02111-1307, USA.