NEWS

   1 Bison News
   2 ----------
   3
   4 Changes in version 2.0a, 2005-05-22:
   5
   6 * Bison-generated C parsers use the _ macro to translate strings from
   7   English to the user's language, e.g., _("syntax error").  By default,
   8   _ is defined to be a no-op macro so the strings are not translated.
   9
  10 * When generating verbose diagnostics, Bison-generated C parsers no longer
  11   quote the literal strings associated with tokens.  For example, for
  12   a syntax error associated with '%token NUM "number"' they might
  13   print 'syntax error, unexpected number' instead of 'syntax error,
  14   unexpected "number"'.
  15
  16 Changes in version 2.0, 2004-12-25:
  17
  18 * Possibly-incompatible changes
  19
  20   - Bison-generated parsers no longer default to using the alloca function
  21     (when available) to extend the parser stack, due to widespread
  22     problems in unchecked stack-overflow detection.  You can "#define
  23     YYSTACK_USE_ALLOCA 1" to require the use of alloca, but please read
  24     the manual to determine safe values for YYMAXDEPTH in that case.
  25
  26   - Error token location.
  27     During error recovery, the location of the syntax error is updated
  28     to cover the whole sequence covered by the error token: it includes
  29     the shifted symbols thrown away during the first part of the error
  30     recovery, and the lookahead rejected during the second part.
  31
  32   - Semicolon changes:
  33     . Stray semicolons are no longer allowed at the start of a grammar.
  34     . Semicolons are now required after in-grammar declarations.
  35
  36   - Unescaped newlines are no longer allowed in character constants or
  37     string literals.  They were never portable, and GCC 3.4.0 has
  38     dropped support for them.  Better diagnostics are now generated if
  39     forget a closing quote.
  40
  41   - NUL bytes are no longer allowed in Bison string literals, unfortunately.
  42
  43 * New features
  44
  45   - GLR grammars now support locations.
  46
  47   - New directive: %initial-action.
  48     This directive allows the user to run arbitrary code (including
  49     initializing @$) from yyparse before parsing starts.
  50
  51   - A new directive "%expect-rr N" specifies the expected number of
  52     reduce/reduce conflicts in GLR parsers.
  53
  54   - %token numbers can now be hexadecimal integers, e.g., `%token FOO 0x12d'.
  55     This is a GNU extension.
  56
  57   - The option `--report=lookahead' was changed to `--report=look-ahead'.
  58     The old spelling still works, but is not documented and will be
  59     removed.
  60
  61   - Experimental %destructor support has been added to lalr1.cc.
  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
  66 * Bug fixes
  67
  68   - For now, %expect-count violations are now just warnings, not errors.
  69     This is for compatibility with Bison 1.75 and earlier (when there are
  70     reduce/reduce conflicts) and with Bison 1.30 and earlier (when there
  71     are too many or too few shift/reduce conflicts).  However, in future
  72     versions of Bison we plan to improve the %expect machinery so that
  73     these violations will become errors again.
  74
  75   - Within Bison itself, numbers (e.g., goto numbers) are no longer
  76     arbitrarily limited to 16-bit counts.
  77
  78   - Semicolons are now allowed before "|" in grammar rules, as POSIX requires.
  79 \f
  80 Changes in version 1.875, 2003-01-01:
  81
  82 * The documentation license has been upgraded to version 1.2
  83   of the GNU Free Documentation License.
  84
  85 * syntax error processing
  86
  87   - In Yacc-style parsers YYLLOC_DEFAULT is now used to compute error
  88     locations too.  This fixes bugs in error-location computation.
  89
  90   - %destructor
  91     It is now possible to reclaim the memory associated to symbols
  92     discarded during error recovery.  This feature is still experimental.
  93
  94   - %error-verbose
  95     This new directive is preferred over YYERROR_VERBOSE.
  96
  97   - #defining yyerror to steal internal variables is discouraged.
  98     It is not guaranteed to work forever.
  99
 100 * POSIX conformance
 101
 102   - Semicolons are once again optional at the end of grammar rules.
 103     This reverts to the behavior of Bison 1.33 and earlier, and improves
 104     compatibility with Yacc.
 105
 106   - `parse error' -> `syntax error'
 107     Bison now uniformly uses the term `syntax error'; formerly, the code
 108     and manual sometimes used the term `parse error' instead.  POSIX
 109     requires `syntax error' in diagnostics, and it was thought better to
 110     be consistent.
 111
 112   - The documentation now emphasizes that yylex and yyerror must be
 113     declared before use.  C99 requires this.
 114
 115   - Bison now parses C99 lexical constructs like UCNs and
 116     backslash-newline within C escape sequences, as POSIX 1003.1-2001 requires.
 117
 118   - File names are properly escaped in C output.  E.g., foo\bar.y is
 119     output as "foo\\bar.y".
 120
 121   - Yacc command and library now available
 122     The Bison distribution now installs a `yacc' command, as POSIX requires.
 123     Also, Bison now installs a small library liby.a containing
 124     implementations of Yacc-compatible yyerror and main functions.
 125     This library is normally not useful, but POSIX requires it.
 126
 127   - Type clashes now generate warnings, not errors.
 128
 129   - If the user does not define YYSTYPE as a macro, Bison now declares it
 130     using typedef instead of defining it as a macro.
 131     For consistency, YYLTYPE is also declared instead of defined.
 132
 133 * Other compatibility issues
 134
 135   - %union directives can now have a tag before the `{', e.g., the
 136     directive `%union foo {...}' now generates the C code
 137     `typedef union foo { ... } YYSTYPE;'; this is for Yacc compatibility.
 138     The default union tag is `YYSTYPE', for compatibility with Solaris 9 Yacc.
 139     For consistency, YYLTYPE's struct tag is now `YYLTYPE' not `yyltype'.
 140     This is for compatibility with both Yacc and Bison 1.35.
 141
 142   - `;' is output before the terminating `}' of an action, for
 143     compatibility with Bison 1.35.
 144
 145   - Bison now uses a Yacc-style format for conflict reports, e.g.,
 146     `conflicts: 2 shift/reduce, 1 reduce/reduce'.
 147
 148   - `yystype' and `yyltype' are now obsolescent macros instead of being
 149     typedefs or tags; they are no longer documented and are planned to be
 150     withdrawn in a future release.
 151
 152 * GLR parser notes
 153
 154   - GLR and inline
 155     Users of Bison have to decide how they handle the portability of the
 156     C keyword `inline'.
 157
 158   - `parsing stack overflow...' -> `parser stack overflow'
 159     GLR parsers now report `parser stack overflow' as per the Bison manual.
 160
 161 * Bison now warns if it detects conflicting outputs to the same file,
 162   e.g., it generates a warning for `bison -d -o foo.h foo.y' since
 163   that command outputs both code and header to foo.h.
 164
 165 * #line in output files
 166   - --no-line works properly.
 167
 168 * Bison can no longer be built by a K&R C compiler; it requires C89 or
 169   later to be built.  This change originally took place a few versions
 170   ago, but nobody noticed until we recently asked someone to try
 171   building Bison with a K&R C compiler.
 172 \f
 173 Changes in version 1.75, 2002-10-14:
 174
 175 * Bison should now work on 64-bit hosts.
 176
 177 * Indonesian translation thanks to Tedi Heriyanto.
 178
 179 * GLR parsers
 180   Fix spurious parse errors.
 181
 182 * Pure parsers
 183   Some people redefine yyerror to steal yyparse' private variables.
 184   Reenable this trick until an official feature replaces it.
 185
 186 * Type Clashes
 187   In agreement with POSIX and with other Yaccs, leaving a default
 188   action is valid when $$ is untyped, and $1 typed:
 189
 190         untyped: ... typed;
 191
 192   but the converse remains an error:
 193
 194         typed: ... untyped;
 195
 196 * Values of mid-rule actions
 197   The following code:
 198
 199         foo: { ... } { $$ = $1; } ...
 200
 201   was incorrectly rejected: $1 is defined in the second mid-rule
 202   action, and is equal to the $$ of the first mid-rule action.
 203 \f
 204 Changes in version 1.50, 2002-10-04:
 205
 206 * GLR parsing
 207   The declaration
 208      %glr-parser
 209   causes Bison to produce a Generalized LR (GLR) parser, capable of handling
 210   almost any context-free grammar, ambiguous or not.  The new declarations
 211   %dprec and %merge on grammar rules allow parse-time resolution of
 212   ambiguities.  Contributed by Paul Hilfinger.
 213
 214   Unfortunately Bison 1.50 does not work properly on 64-bit hosts
 215   like the Alpha, so please stick to 32-bit hosts for now.
 216
 217 * Output Directory
 218   When not in Yacc compatibility mode, when the output file was not
 219   specified, running `bison foo/bar.y' created `foo/bar.c'.  It
 220   now creates `bar.c'.
 221
 222 * Undefined token
 223   The undefined token was systematically mapped to 2 which prevented
 224   the use of 2 by the user.  This is no longer the case.
 225
 226 * Unknown token numbers
 227   If yylex returned an out of range value, yyparse could die.  This is
 228   no longer the case.
 229
 230 * Error token
 231   According to POSIX, the error token must be 256.
 232   Bison extends this requirement by making it a preference: *if* the
 233   user specified that one of her tokens is numbered 256, then error
 234   will be mapped onto another number.
 235
 236 * Verbose error messages
 237   They no longer report `..., expecting error or...' for states where
 238   error recovery is possible.
 239
 240 * End token
 241   Defaults to `$end' instead of `$'.
 242
 243 * Error recovery now conforms to documentation and to POSIX
 244   When a Bison-generated parser encounters a syntax error, it now pops
 245   the stack until it finds a state that allows shifting the error
 246   token.  Formerly, it popped the stack until it found a state that
 247   allowed some non-error action other than a default reduction on the
 248   error token.  The new behavior has long been the documented behavior,
 249   and has long been required by POSIX.  For more details, please see
 250   Paul Eggert, "Reductions during Bison error handling" (2002-05-20)
 251   <http://lists.gnu.org/archive/html/bug-bison/2002-05/msg00038.html>.
 252
 253 * Traces
 254   Popped tokens and nonterminals are now reported.
 255
 256 * Larger grammars
 257   Larger grammars are now supported (larger token numbers, larger grammar
 258   size (= sum of the LHS and RHS lengths), larger LALR tables).
 259   Formerly, many of these numbers ran afoul of 16-bit limits;
 260   now these limits are 32 bits on most hosts.
 261
 262 * Explicit initial rule
 263   Bison used to play hacks with the initial rule, which the user does
 264   not write.  It is now explicit, and visible in the reports and
 265   graphs as rule 0.
 266
 267 * Useless rules
 268   Before, Bison reported the useless rules, but, although not used,
 269   included them in the parsers.  They are now actually removed.
 270
 271 * Useless rules, useless nonterminals
 272   They are now reported, as a warning, with their locations.
 273
 274 * Rules never reduced
 275   Rules that can never be reduced because of conflicts are now
 276   reported.
 277
 278 * Incorrect `Token not used'
 279   On a grammar such as
 280
 281            %token useless useful
 282            %%
 283            exp: '0' %prec useful;
 284
 285   where a token was used to set the precedence of the last rule,
 286   bison reported both `useful' and `useless' as useless tokens.
 287
 288 * Revert the C++ namespace changes introduced in 1.31
 289   as they caused too many portability hassles.
 290
 291 * Default locations
 292   By an accident of design, the default computation of @$ was
 293   performed after another default computation was performed: @$ = @1.
 294   The latter is now removed: YYLLOC_DEFAULT is fully responsible of
 295   the computation of @$.
 296
 297 * Token end-of-file
 298   The token end of file may be specified by the user, in which case,
 299   the user symbol is used in the reports, the graphs, and the verbose
 300   error messages instead of `$end', which remains being the default.
 301   For instance
 302      %token MYEOF 0
 303   or
 304      %token MYEOF 0 "end of file"
 305
 306 * Semantic parser
 307   This old option, which has been broken for ages, is removed.
 308
 309 * New translations
 310   Brazilian Portuguese, thanks to Alexandre Folle de Menezes.
 311   Croatian, thanks to Denis Lackovic.
 312
 313 * Incorrect token definitions
 314   When given `%token 'a' "A"', Bison used to output `#define 'a' 65'.
 315
 316 * Token definitions as enums
 317   Tokens are output both as the traditional #define's, and, provided
 318   the compiler supports ANSI C or is a C++ compiler, as enums.
 319   This lets debuggers display names instead of integers.
 320
 321 * Reports
 322   In addition to --verbose, bison supports --report=THINGS, which
 323   produces additional information:
 324   - itemset
 325     complete the core item sets with their closure
 326   - lookahead [changed to `look-ahead' in 1.875e and later]
 327     explicitly associate look-ahead tokens to items
 328   - solved
 329     describe shift/reduce conflicts solving.
 330     Bison used to systematically output this information on top of
 331     the report.  Solved conflicts are now attached to their states.
 332
 333 * Type clashes
 334   Previous versions don't complain when there is a type clash on
 335   the default action if the rule has a mid-rule action, such as in:
 336
 337       %type <foo> bar
 338       %%
 339       bar: '0' {} '0';
 340
 341   This is fixed.
 342
 343 * GNU M4 is now required when using Bison.
 344 \f
 345 Changes in version 1.35, 2002-03-25:
 346
 347 * C Skeleton
 348   Some projects use Bison's C parser with C++ compilers, and define
 349   YYSTYPE as a class.  The recent adjustment of C parsers for data
 350   alignment and 64 bit architectures made this impossible.
 351
 352   Because for the time being no real solution for C++ parser
 353   generation exists, kludges were implemented in the parser to
 354   maintain this use.  In the future, when Bison has C++ parsers, this
 355   kludge will be disabled.
 356
 357   This kludge also addresses some C++ problems when the stack was
 358   extended.
 359 \f
 360 Changes in version 1.34, 2002-03-12:
 361
 362 * File name clashes are detected
 363   $ bison foo.y -d -o foo.x
 364   fatal error: header and parser would both be named `foo.x'
 365
 366 * A missing `;' at the end of a rule triggers a warning
 367   In accordance with POSIX, and in agreement with other
 368   Yacc implementations, Bison will mandate this semicolon in the near
 369   future.  This eases the implementation of a Bison parser of Bison
 370   grammars by making this grammar LALR(1) instead of LR(2).  To
 371   facilitate the transition, this release introduces a warning.
 372
 373 * Revert the C++ namespace changes introduced in 1.31, as they caused too
 374   many portability hassles.
 375
 376 * DJGPP support added.
 377
 378 * Fix test suite portability problems.
 379 \f
 380 Changes in version 1.33, 2002-02-07:
 381
 382 * Fix C++ issues
 383   Groff could not be compiled for the definition of size_t was lacking
 384   under some conditions.
 385
 386 * Catch invalid @n
 387   As is done with $n.
 388 \f
 389 Changes in version 1.32, 2002-01-23:
 390
 391 * Fix Yacc output file names
 392
 393 * Portability fixes
 394
 395 * Italian, Dutch translations
 396 \f
 397 Changes in version 1.31, 2002-01-14:
 398
 399 * Many Bug Fixes
 400
 401 * GNU Gettext and %expect
 402   GNU Gettext asserts 10 s/r conflicts, but there are 7.  Now that
 403   Bison dies on incorrect %expectations, we fear there will be
 404   too many bug reports for Gettext, so _for the time being_, %expect
 405   does not trigger an error when the input file is named `plural.y'.
 406
 407 * Use of alloca in parsers
 408   If YYSTACK_USE_ALLOCA is defined to 0, then the parsers will use
 409   malloc exclusively.  Since 1.29, but was not NEWS'ed.
 410
 411   alloca is used only when compiled with GCC, to avoid portability
 412   problems as on AIX.
 413
 414 * When the generated parser lacks debugging code, YYDEBUG is now 0
 415   (as POSIX requires) instead of being undefined.
 416
 417 * User Actions
 418   Bison has always permitted actions such as { $$ = $1 }: it adds the
 419   ending semicolon.  Now if in Yacc compatibility mode, the semicolon
 420   is no longer output: one has to write { $$ = $1; }.
 421
 422 * Better C++ compliance
 423   The output parsers try to respect C++ namespaces.
 424   [This turned out to be a failed experiment, and it was reverted later.]
 425
 426 * Reduced Grammars
 427   Fixed bugs when reporting useless nonterminals.
 428
 429 * 64 bit hosts
 430   The parsers work properly on 64 bit hosts.
 431
 432 * Error messages
 433   Some calls to strerror resulted in scrambled or missing error messages.
 434
 435 * %expect
 436   When the number of shift/reduce conflicts is correct, don't issue
 437   any warning.
 438
 439 * The verbose report includes the rule line numbers.
 440
 441 * Rule line numbers are fixed in traces.
 442
 443 * Swedish translation
 444
 445 * Parse errors
 446   Verbose parse error messages from the parsers are better looking.
 447   Before: parse error: unexpected `'/'', expecting `"number"' or `'-'' or `'(''
 448      Now: parse error: unexpected '/', expecting "number" or '-' or '('
 449
 450 * Fixed parser memory leaks.
 451   When the generated parser was using malloc to extend its stacks, the
 452   previous allocations were not freed.
 453
 454 * Fixed verbose output file.
 455   Some newlines were missing.
 456   Some conflicts in state descriptions were missing.
 457
 458 * Fixed conflict report.
 459   Option -v was needed to get the result.
 460
 461 * %expect
 462   Was not used.
 463   Mismatches are errors, not warnings.
 464
 465 * Fixed incorrect processing of some invalid input.
 466
 467 * Fixed CPP guards: 9foo.h uses BISON_9FOO_H instead of 9FOO_H.
 468
 469 * Fixed some typos in the documentation.
 470
 471 * %token MY_EOF 0 is supported.
 472   Before, MY_EOF was silently renumbered as 257.
 473
 474 * doc/refcard.tex is updated.
 475
 476 * %output, %file-prefix, %name-prefix.
 477   New.
 478
 479 * --output
 480   New, aliasing `--output-file'.
 481 \f
 482 Changes in version 1.30, 2001-10-26:
 483
 484 * `--defines' and `--graph' have now an optional argument which is the
 485   output file name. `-d' and `-g' do not change; they do not take any
 486   argument.
 487
 488 * `%source_extension' and `%header_extension' are removed, failed
 489   experiment.
 490
 491 * Portability fixes.
 492 \f
 493 Changes in version 1.29, 2001-09-07:
 494
 495 * The output file does not define const, as this caused problems when used
 496   with common autoconfiguration schemes.  If you still use ancient compilers
 497   that lack const, compile with the equivalent of the C compiler option
 498   `-Dconst='.  autoconf's AC_C_CONST macro provides one way to do this.
 499
 500 * Added `-g' and `--graph'.
 501
 502 * The Bison manual is now distributed under the terms of the GNU FDL.
 503
 504 * The input and the output files has automatically a similar extension.
 505
 506 * Russian translation added.
 507
 508 * NLS support updated; should hopefully be less troublesome.
 509
 510 * Added the old Bison reference card.
 511
 512 * Added `--locations' and `%locations'.
 513
 514 * Added `-S' and `--skeleton'.
 515
 516 * `%raw', `-r', `--raw' is disabled.
 517
 518 * Special characters are escaped when output.  This solves the problems
 519   of the #line lines with path names including backslashes.
 520
 521 * New directives.
 522   `%yacc', `%fixed_output_files', `%defines', `%no_parser', `%verbose',
 523   `%debug', `%source_extension' and `%header_extension'.
 524
 525 * @$
 526   Automatic location tracking.
 527 \f
 528 Changes in version 1.28, 1999-07-06:
 529
 530 * Should compile better now with K&R compilers.
 531
 532 * Added NLS.
 533
 534 * Fixed a problem with escaping the double quote character.
 535
 536 * There is now a FAQ.
 537 \f
 538 Changes in version 1.27:
 539
 540 * The make rule which prevented bison.simple from being created on
 541   some systems has been fixed.
 542 \f
 543 Changes in version 1.26:
 544
 545 * Bison now uses automake.
 546
 547 * New mailing lists: <bug-bison@gnu.org> and <help-bison@gnu.org>.
 548
 549 * Token numbers now start at 257 as previously documented, not 258.
 550
 551 * Bison honors the TMPDIR environment variable.
 552
 553 * A couple of buffer overruns have been fixed.
 554
 555 * Problems when closing files should now be reported.
 556
 557 * Generated parsers should now work even on operating systems which do
 558   not provide alloca().
 559 \f
 560 Changes in version 1.25, 1995-10-16:
 561
 562 * Errors in the input grammar are not fatal; Bison keeps reading
 563 the grammar file, and reports all the errors found in it.
 564
 565 * Tokens can now be specified as multiple-character strings: for
 566 example, you could use "<=" for a token which looks like <=, instead
 567 of chosing a name like LESSEQ.
 568
 569 * The %token_table declaration says to write a table of tokens (names
 570 and numbers) into the parser file.  The yylex function can use this
 571 table to recognize multiple-character string tokens, or for other
 572 purposes.
 573
 574 * The %no_lines declaration says not to generate any #line preprocessor
 575 directives in the parser file.
 576
 577 * The %raw declaration says to use internal Bison token numbers, not
 578 Yacc-compatible token numbers, when token names are defined as macros.
 579
 580 * The --no-parser option produces the parser tables without including
 581 the parser engine; a project can now use its own parser engine.
 582 The actions go into a separate file called NAME.act, in the form of
 583 a switch statement body.
 584 \f
 585 Changes in version 1.23:
 586
 587 The user can define YYPARSE_PARAM as the name of an argument to be
 588 passed into yyparse.  The argument should have type void *.  It should
 589 actually point to an object.  Grammar actions can access the variable
 590 by casting it to the proper pointer type.
 591
 592 Line numbers in output file corrected.
 593 \f
 594 Changes in version 1.22:
 595
 596 --help option added.
 597 \f
 598 Changes in version 1.20:
 599
 600 Output file does not redefine const for C++.
 601
 602 Local Variables:
 603 mode: outline
 604 End:
 605
 606 -----
 607
 608 Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005
 609 Free Software Foundation, Inc.
 610
 611 This file is part of Bison, the GNU Compiler Compiler.
 612
 613 Bison is free software; you can redistribute it and/or modify
 614 it under the terms of the GNU General Public License as published by
 615 the Free Software Foundation; either version 2, or (at your option)
 616 any later version.
 617
 618 Bison is distributed in the hope that it will be useful,
 619 but WITHOUT ANY WARRANTY; without even the implied warranty of
 620 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 621 GNU General Public License for more details.
 622
 623 You should have received a copy of the GNU General Public License
 624 along with autoconf; see the file COPYING.  If not, write to
 625 the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
 626 Boston, MA 02110-1301, USA.