NEWS

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