NEWS

   1 Bison News
   2 ----------
   3
   4 Changes in version 1.875b, 2003-06-17:
   5
   6 * GLR grammars now support locations.
   7
   8 * Semicolon changes:
   9   - Semicolons are now allowed before "|" in grammar rules, as POSIX requires.
  10   - Stray semicolons are no longer allowed at the start of a grammar.
  11   - Semicolons are now required after in-grammar declarations.
  12
  13 Changes in version 1.875a, 2003-02-01:
  14
  15 * For now, %expect-count violations are now just warnings, not errors.
  16   This is for compatibility with Bison 1.75 and earlier (when there are
  17   reduce/reduce conflicts) and with Bison 1.30 and earlier (when there
  18   are too many or too few shift/reduce conflicts).  However, in future
  19   versions of Bison we plan to improve the %expect machinery so that
  20   these violations will become errors again.
  21
  22 * New configure option --disable-yacc, to disable installation of the
  23   yacc command and -ly library introduced in 1.875 for POSIX conformance.
  24 \f
  25 Changes in version 1.875, 2003-01-01:
  26
  27 * The documentation license has been upgraded to version 1.2
  28   of the GNU Free Documentation License.
  29
  30 * syntax error processing
  31
  32   - In Yacc-style parsers YYLLOC_DEFAULT is now used to compute error
  33     locations too.  This fixes bugs in error-location computation.
  34
  35   - %destructor
  36     It is now possible to reclaim the memory associated to symbols
  37     discarded during error recovery.  This feature is still experimental.
  38
  39   - %error-verbose
  40     This new directive is preferred over YYERROR_VERBOSE.
  41
  42   - #defining yyerror to steal internal variables is discouraged.
  43     It is not guaranteed to work forever.
  44
  45 * POSIX conformance
  46
  47   - Semicolons are once again optional at the end of grammar rules.
  48     This reverts to the behavior of Bison 1.33 and earlier, and improves
  49     compatibility with Yacc.
  50
  51   - `parse error' -> `syntax error'
  52     Bison now uniformly uses the term `syntax error'; formerly, the code
  53     and manual sometimes used the term `parse error' instead.  POSIX
  54     requires `syntax error' in diagnostics, and it was thought better to
  55     be consistent.
  56
  57   - The documentation now emphasizes that yylex and yyerror must be
  58     declared before use.  C99 requires this.
  59
  60   - Bison now parses C99 lexical constructs like UCNs and
  61     backslash-newline within C escape sequences, as POSIX 1003.1-2001 requires.
  62
  63   - File names are properly escaped in C output.  E.g., foo\bar.y is
  64     output as "foo\\bar.y".
  65
  66   - Yacc command and library now available
  67     The Bison distribution now installs a `yacc' command, as POSIX requires.
  68     Also, Bison now installs a small library liby.a containing
  69     implementations of Yacc-compatible yyerror and main functions.
  70     This library is normally not useful, but POSIX requires it.
  71
  72   - Type clashes now generate warnings, not errors.
  73
  74   - If the user does not define YYSTYPE as a macro, Bison now declares it
  75     using typedef instead of defining it as a macro.
  76     For consistency, YYLTYPE is also declared instead of defined.
  77
  78 * Other compatibility issues
  79
  80   - %union directives can now have a tag before the `{', e.g., the
  81     directive `%union foo {...}' now generates the C code
  82     `typedef union foo { ... } YYSTYPE;'; this is for Yacc compatibility.
  83     The default union tag is `YYSTYPE', for compatibility with Solaris 9 Yacc.
  84     For consistency, YYLTYPE's struct tag is now `YYLTYPE' not `yyltype'.
  85     This is for compatibility with both Yacc and Bison 1.35.
  86
  87   - `;' is output before the terminating `}' of an action, for
  88     compatibility with Bison 1.35.
  89
  90   - Bison now uses a Yacc-style format for conflict reports, e.g.,
  91     `conflicts: 2 shift/reduce, 1 reduce/reduce'.
  92
  93   - `yystype' and `yyltype' are now obsolescent macros instead of being
  94     typedefs or tags; they are no longer documented and are planned to be
  95     withdrawn in a future release.
  96
  97 * GLR parser notes
  98
  99   - GLR and inline
 100     Users of Bison have to decide how they handle the portability of the
 101     C keyword `inline'.
 102
 103   - `parsing stack overflow...' -> `parser stack overflow'
 104     GLR parsers now report `parser stack overflow' as per the Bison manual.
 105
 106 * Bison now warns if it detects conflicting outputs to the same file,
 107   e.g., it generates a warning for `bison -d -o foo.h foo.y' since
 108   that command outputs both code and header to foo.h.
 109
 110 * #line in output files
 111   - --no-line works properly.
 112
 113 * Bison can no longer be built by a K&R C compiler; it requires C89 or
 114   later to be built.  This change originally took place a few versions
 115   ago, but nobody noticed until we recently asked someone to try
 116   building Bison with a K&R C compiler.
 117 \f
 118 Changes in version 1.75, 2002-10-14:
 119
 120 * Bison should now work on 64-bit hosts.
 121
 122 * Indonesian translation thanks to Tedi Heriyanto.
 123
 124 * GLR parsers
 125   Fix spurious parse errors.
 126
 127 * Pure parsers
 128   Some people redefine yyerror to steal yyparse' private variables.
 129   Reenable this trick until an official feature replaces it.
 130
 131 * Type Clashes
 132   In agreement with POSIX and with other Yaccs, leaving a default
 133   action is valid when $$ is untyped, and $1 typed:
 134
 135         untyped: ... typed;
 136
 137   but the converse remains an error:
 138
 139         typed: ... untyped;
 140
 141 * Values of mid-rule actions
 142   The following code:
 143
 144         foo: { ... } { $$ = $1; } ...
 145
 146   was incorrectly rejected: $1 is defined in the second mid-rule
 147   action, and is equal to the $$ of the first mid-rule action.
 148 \f
 149 Changes in version 1.50, 2002-10-04:
 150
 151 * GLR parsing
 152   The declaration
 153      %glr-parser
 154   causes Bison to produce a Generalized LR (GLR) parser, capable of handling
 155   almost any context-free grammar, ambiguous or not.  The new declarations
 156   %dprec and %merge on grammar rules allow parse-time resolution of
 157   ambiguities.  Contributed by Paul Hilfinger.
 158
 159   Unfortunately Bison 1.50 does not work properly on 64-bit hosts
 160   like the Alpha, so please stick to 32-bit hosts for now.
 161
 162 * Output Directory
 163   When not in Yacc compatibility mode, when the output file was not
 164   specified, running `bison foo/bar.y' created `foo/bar.c'.  It
 165   now creates `bar.c'.
 166
 167 * Undefined token
 168   The undefined token was systematically mapped to 2 which prevented
 169   the use of 2 by the user.  This is no longer the case.
 170
 171 * Unknown token numbers
 172   If yylex returned an out of range value, yyparse could die.  This is
 173   no longer the case.
 174
 175 * Error token
 176   According to POSIX, the error token must be 256.
 177   Bison extends this requirement by making it a preference: *if* the
 178   user specified that one of her tokens is numbered 256, then error
 179   will be mapped onto another number.
 180
 181 * Verbose error messages
 182   They no longer report `..., expecting error or...' for states where
 183   error recovery is possible.
 184
 185 * End token
 186   Defaults to `$end' instead of `$'.
 187
 188 * Error recovery now conforms to documentation and to POSIX
 189   When a Bison-generated parser encounters a syntax error, it now pops
 190   the stack until it finds a state that allows shifting the error
 191   token.  Formerly, it popped the stack until it found a state that
 192   allowed some non-error action other than a default reduction on the
 193   error token.  The new behavior has long been the documented behavior,
 194   and has long been required by POSIX.  For more details, please see
 195   <http://mail.gnu.org/pipermail/bug-bison/2002-May/001452.html>.
 196
 197 * Traces
 198   Popped tokens and nonterminals are now reported.
 199
 200 * Larger grammars
 201   Larger grammars are now supported (larger token numbers, larger grammar
 202   size (= sum of the LHS and RHS lengths), larger LALR tables).
 203   Formerly, many of these numbers ran afoul of 16-bit limits;
 204   now these limits are 32 bits on most hosts.
 205
 206 * Explicit initial rule
 207   Bison used to play hacks with the initial rule, which the user does
 208   not write.  It is now explicit, and visible in the reports and
 209   graphs as rule 0.
 210
 211 * Useless rules
 212   Before, Bison reported the useless rules, but, although not used,
 213   included them in the parsers.  They are now actually removed.
 214
 215 * Useless rules, useless nonterminals
 216   They are now reported, as a warning, with their locations.
 217
 218 * Rules never reduced
 219   Rules that can never be reduced because of conflicts are now
 220   reported.
 221
 222 * Incorrect `Token not used'
 223   On a grammar such as
 224
 225            %token useless useful
 226            %%
 227            exp: '0' %prec useful;
 228
 229   where a token was used to set the precedence of the last rule,
 230   bison reported both `useful' and `useless' as useless tokens.
 231
 232 * Revert the C++ namespace changes introduced in 1.31
 233   as they caused too many portability hassles.
 234
 235 * Default locations
 236   By an accident of design, the default computation of @$ was
 237   performed after another default computation was performed: @$ = @1.
 238   The latter is now removed: YYLLOC_DEFAULT is fully responsible of
 239   the computation of @$.
 240
 241 * Token end-of-file
 242   The token end of file may be specified by the user, in which case,
 243   the user symbol is used in the reports, the graphs, and the verbose
 244   error messages instead of `$end', which remains being the default.
 245   For instance
 246      %token MYEOF 0
 247   or
 248      %token MYEOF 0 "end of file"
 249
 250 * Semantic parser
 251   This old option, which has been broken for ages, is removed.
 252
 253 * New translations
 254   Brazilian Portuguese, thanks to Alexandre Folle de Menezes.
 255   Croatian, thanks to Denis Lackovic.
 256
 257 * Incorrect token definitions
 258   When given `%token 'a' "A"', Bison used to output `#define 'a' 65'.
 259
 260 * Token definitions as enums
 261   Tokens are output both as the traditional #define's, and, provided
 262   the compiler supports ANSI C or is a C++ compiler, as enums.
 263   This lets debuggers display names instead of integers.
 264
 265 * Reports
 266   In addition to --verbose, bison supports --report=THINGS, which
 267   produces additional information:
 268   - itemset
 269     complete the core item sets with their closure
 270   - lookahead
 271     explicitly associate lookaheads to items
 272   - solved
 273     describe shift/reduce conflicts solving.
 274     Bison used to systematically output this information on top of
 275     the report.  Solved conflicts are now attached to their states.
 276
 277 * Type clashes
 278   Previous versions don't complain when there is a type clash on
 279   the default action if the rule has a mid-rule action, such as in:
 280
 281       %type <foo> bar
 282       %%
 283       bar: '0' {} '0';
 284
 285   This is fixed.
 286
 287 * GNU M4 is now required when using Bison.
 288 \f
 289 Changes in version 1.35, 2002-03-25:
 290
 291 * C Skeleton
 292   Some projects use Bison's C parser with C++ compilers, and define
 293   YYSTYPE as a class.  The recent adjustment of C parsers for data
 294   alignment and 64 bit architectures made this impossible.
 295
 296   Because for the time being no real solution for C++ parser
 297   generation exists, kludges were implemented in the parser to
 298   maintain this use.  In the future, when Bison has C++ parsers, this
 299   kludge will be disabled.
 300
 301   This kludge also addresses some C++ problems when the stack was
 302   extended.
 303 \f
 304 Changes in version 1.34, 2002-03-12:
 305
 306 * File name clashes are detected
 307   $ bison foo.y -d -o foo.x
 308   fatal error: header and parser would both be named `foo.x'
 309
 310 * A missing `;' at the end of a rule triggers a warning
 311   In accordance with POSIX, and in agreement with other
 312   Yacc implementations, Bison will mandate this semicolon in the near
 313   future.  This eases the implementation of a Bison parser of Bison
 314   grammars by making this grammar LALR(1) instead of LR(2).  To
 315   facilitate the transition, this release introduces a warning.
 316
 317 * Revert the C++ namespace changes introduced in 1.31, as they caused too
 318   many portability hassles.
 319
 320 * DJGPP support added.
 321
 322 * Fix test suite portability problems.
 323 \f
 324 Changes in version 1.33, 2002-02-07:
 325
 326 * Fix C++ issues
 327   Groff could not be compiled for the definition of size_t was lacking
 328   under some conditions.
 329
 330 * Catch invalid @n
 331   As is done with $n.
 332 \f
 333 Changes in version 1.32, 2002-01-23:
 334
 335 * Fix Yacc output file names
 336
 337 * Portability fixes
 338
 339 * Italian, Dutch translations
 340 \f
 341 Changes in version 1.31, 2002-01-14:
 342
 343 * Many Bug Fixes
 344
 345 * GNU Gettext and %expect
 346   GNU Gettext asserts 10 s/r conflicts, but there are 7.  Now that
 347   Bison dies on incorrect %expectations, we fear there will be
 348   too many bug reports for Gettext, so _for the time being_, %expect
 349   does not trigger an error when the input file is named `plural.y'.
 350
 351 * Use of alloca in parsers
 352   If YYSTACK_USE_ALLOCA is defined to 0, then the parsers will use
 353   malloc exclusively.  Since 1.29, but was not NEWS'ed.
 354
 355   alloca is used only when compiled with GCC, to avoid portability
 356   problems as on AIX.
 357
 358 * When the generated parser lacks debugging code, YYDEBUG is now 0
 359   (as POSIX requires) instead of being undefined.
 360
 361 * User Actions
 362   Bison has always permitted actions such as { $$ = $1 }: it adds the
 363   ending semicolon.  Now if in Yacc compatibility mode, the semicolon
 364   is no longer output: one has to write { $$ = $1; }.
 365
 366 * Better C++ compliance
 367   The output parsers try to respect C++ namespaces.
 368   [This turned out to be a failed experiment, and it was reverted later.]
 369
 370 * Reduced Grammars
 371   Fixed bugs when reporting useless nonterminals.
 372
 373 * 64 bit hosts
 374   The parsers work properly on 64 bit hosts.
 375
 376 * Error messages
 377   Some calls to strerror resulted in scrambled or missing error messages.
 378
 379 * %expect
 380   When the number of shift/reduce conflicts is correct, don't issue
 381   any warning.
 382
 383 * The verbose report includes the rule line numbers.
 384
 385 * Rule line numbers are fixed in traces.
 386
 387 * Swedish translation
 388
 389 * Parse errors
 390   Verbose parse error messages from the parsers are better looking.
 391   Before: parse error: unexpected `'/'', expecting `"number"' or `'-'' or `'(''
 392      Now: parse error: unexpected '/', expecting "number" or '-' or '('
 393
 394 * Fixed parser memory leaks.
 395   When the generated parser was using malloc to extend its stacks, the
 396   previous allocations were not freed.
 397
 398 * Fixed verbose output file.
 399   Some newlines were missing.
 400   Some conflicts in state descriptions were missing.
 401
 402 * Fixed conflict report.
 403   Option -v was needed to get the result.
 404
 405 * %expect
 406   Was not used.
 407   Mismatches are errors, not warnings.
 408
 409 * Fixed incorrect processing of some invalid input.
 410
 411 * Fixed CPP guards: 9foo.h uses BISON_9FOO_H instead of 9FOO_H.
 412
 413 * Fixed some typos in the documentation.
 414
 415 * %token MY_EOF 0 is supported.
 416   Before, MY_EOF was silently renumbered as 257.
 417
 418 * doc/refcard.tex is updated.
 419
 420 * %output, %file-prefix, %name-prefix.
 421   New.
 422
 423 * --output
 424   New, aliasing `--output-file'.
 425 \f
 426 Changes in version 1.30, 2001-10-26:
 427
 428 * `--defines' and `--graph' have now an optional argument which is the
 429   output file name. `-d' and `-g' do not change; they do not take any
 430   argument.
 431
 432 * `%source_extension' and `%header_extension' are removed, failed
 433   experiment.
 434
 435 * Portability fixes.
 436 \f
 437 Changes in version 1.29, 2001-09-07:
 438
 439 * The output file does not define const, as this caused problems when used
 440   with common autoconfiguration schemes.  If you still use ancient compilers
 441   that lack const, compile with the equivalent of the C compiler option
 442   `-Dconst='.  autoconf's AC_C_CONST macro provides one way to do this.
 443
 444 * Added `-g' and `--graph'.
 445
 446 * The Bison manual is now distributed under the terms of the GNU FDL.
 447
 448 * The input and the output files has automatically a similar extension.
 449
 450 * Russian translation added.
 451
 452 * NLS support updated; should hopefully be less troublesome.
 453
 454 * Added the old Bison reference card.
 455
 456 * Added `--locations' and `%locations'.
 457
 458 * Added `-S' and `--skeleton'.
 459
 460 * `%raw', `-r', `--raw' is disabled.
 461
 462 * Special characters are escaped when output.  This solves the problems
 463   of the #line lines with path names including backslashes.
 464
 465 * New directives.
 466   `%yacc', `%fixed_output_files', `%defines', `%no_parser', `%verbose',
 467   `%debug', `%source_extension' and `%header_extension'.
 468
 469 * @$
 470   Automatic location tracking.
 471 \f
 472 Changes in version 1.28, 1999-07-06:
 473
 474 * Should compile better now with K&R compilers.
 475
 476 * Added NLS.
 477
 478 * Fixed a problem with escaping the double quote character.
 479
 480 * There is now a FAQ.
 481 \f
 482 Changes in version 1.27:
 483
 484 * The make rule which prevented bison.simple from being created on
 485   some systems has been fixed.
 486 \f
 487 Changes in version 1.26:
 488
 489 * Bison now uses automake.
 490
 491 * New mailing lists: <bug-bison@gnu.org> and <help-bison@gnu.org>.
 492
 493 * Token numbers now start at 257 as previously documented, not 258.
 494
 495 * Bison honors the TMPDIR environment variable.
 496
 497 * A couple of buffer overruns have been fixed.
 498
 499 * Problems when closing files should now be reported.
 500
 501 * Generated parsers should now work even on operating systems which do
 502   not provide alloca().
 503 \f
 504 Changes in version 1.25, 1995-10-16:
 505
 506 * Errors in the input grammar are not fatal; Bison keeps reading
 507 the grammar file, and reports all the errors found in it.
 508
 509 * Tokens can now be specified as multiple-character strings: for
 510 example, you could use "<=" for a token which looks like <=, instead
 511 of chosing a name like LESSEQ.
 512
 513 * The %token_table declaration says to write a table of tokens (names
 514 and numbers) into the parser file.  The yylex function can use this
 515 table to recognize multiple-character string tokens, or for other
 516 purposes.
 517
 518 * The %no_lines declaration says not to generate any #line preprocessor
 519 directives in the parser file.
 520
 521 * The %raw declaration says to use internal Bison token numbers, not
 522 Yacc-compatible token numbers, when token names are defined as macros.
 523
 524 * The --no-parser option produces the parser tables without including
 525 the parser engine; a project can now use its own parser engine.
 526 The actions go into a separate file called NAME.act, in the form of
 527 a switch statement body.
 528 \f
 529 Changes in version 1.23:
 530
 531 The user can define YYPARSE_PARAM as the name of an argument to be
 532 passed into yyparse.  The argument should have type void *.  It should
 533 actually point to an object.  Grammar actions can access the variable
 534 by casting it to the proper pointer type.
 535
 536 Line numbers in output file corrected.
 537 \f
 538 Changes in version 1.22:
 539
 540 --help option added.
 541 \f
 542 Changes in version 1.20:
 543
 544 Output file does not redefine const for C++.
 545
 546 Local Variables:
 547 mode: outline
 548 End:
 549
 550 -----
 551
 552 Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003
 553 Free Software Foundation, Inc.
 554
 555 This file is part of Bison, the GNU Compiler Compiler.
 556
 557 Bison is free software; you can redistribute it and/or modify
 558 it under the terms of the GNU General Public License as published by
 559 the Free Software Foundation; either version 2, or (at your option)
 560 any later version.
 561
 562 Bison is distributed in the hope that it will be useful,
 563 but WITHOUT ANY WARRANTY; without even the implied warranty of
 564 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 565 GNU General Public License for more details.
 566
 567 You should have received a copy of the GNU General Public License
 568 along with autoconf; see the file COPYING.  If not, write to
 569 the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 570 Boston, MA 02111-1307, USA.