NEWS

   1 Bison News
   2 ----------
   3
   4 Changes in version 1.875f:
   5
   6 * Bison-generated parsers no longer default to using the alloca function
   7   (when available) to extend the parser stack, due to widespread
   8   problems in unchecked stack-overflow detection.  You can "#define
   9   YYSTACK_USE_ALLOCA 1" to use alloca anyway, but please read the
  10   manual to determine safe values for YYMAXDEPTH in that case.
  11
  12 Changes in version 1.875e, 2004-12-10:
  13
  14 * New directive: %initial-action.
  15   This directive allows the user to run arbitrary code (including
  16   initializing @$) from yyparse before parsing starts.
  17
  18 * The option `--report=lookahead' was changed to `--report=look-ahead'.
  19   The old spelling still works, but is not documented and will be
  20   removed.
  21
  22 * Error token location.
  23   During error recovery, the location of the syntax error is updated
  24   to cover the whole sequence covered by the error token: it includes
  25   the shifted symbols thrown away during the first part of the error
  26   recovery, and the lookahead rejected during the second part.
  27
  28 * Goto numbers are no longer arbitrarily limited to 16-bit counts.
  29
  30 Changes in version 1.875d, 2004-05-21:
  31
  32 * Unescaped newlines are no longer allowed in character constants or
  33   string literals.  They were never portable, and GCC 3.4.0 has
  34   dropped support for them.  Better diagnostics are now generated if
  35   forget a closing quote.
  36
  37 * NUL bytes are no longer allowed in Bison string literals, unfortunately.
  38
  39 * %token numbers can now be hexadecimal integers, e.g., `%token FOO 0x12d'.
  40   This is a GNU extension.
  41
  42 * A new directive "%expect-rr N" specifies the expected number of
  43   reduce/reduce conflicts in GLR parsers.
  44
  45 * Experimental %destructor support has been added to lalr1.cc.
  46
  47 Changes in version 1.875c, 2003-08-25:
  48
  49   (Just bug fixes.)
  50
  51 Changes in version 1.875b, 2003-06-17:
  52
  53 * GLR grammars now support locations.
  54
  55 * Semicolon changes:
  56   - Semicolons are now allowed before "|" in grammar rules, as POSIX requires.
  57   - Stray semicolons are no longer allowed at the start of a grammar.
  58   - Semicolons are now required after in-grammar declarations.
  59
  60 Changes in version 1.875a, 2003-02-01:
  61
  62 * For now, %expect-count violations are now just warnings, not errors.
  63   This is for compatibility with Bison 1.75 and earlier (when there are
  64   reduce/reduce conflicts) and with Bison 1.30 and earlier (when there
  65   are too many or too few shift/reduce conflicts).  However, in future
  66   versions of Bison we plan to improve the %expect machinery so that
  67   these violations will become errors again.
  68
  69 * New configure option --disable-yacc, to disable installation of the
  70   yacc command and -ly library introduced in 1.875 for POSIX conformance.
  71 \f
  72 Changes in version 1.875, 2003-01-01:
  73
  74 * The documentation license has been upgraded to version 1.2
  75   of the GNU Free Documentation License.
  76
  77 * syntax error processing
  78
  79   - In Yacc-style parsers YYLLOC_DEFAULT is now used to compute error
  80     locations too.  This fixes bugs in error-location computation.
  81
  82   - %destructor
  83     It is now possible to reclaim the memory associated to symbols
  84     discarded during error recovery.  This feature is still experimental.
  85
  86   - %error-verbose
  87     This new directive is preferred over YYERROR_VERBOSE.
  88
  89   - #defining yyerror to steal internal variables is discouraged.
  90     It is not guaranteed to work forever.
  91
  92 * POSIX conformance
  93
  94   - Semicolons are once again optional at the end of grammar rules.
  95     This reverts to the behavior of Bison 1.33 and earlier, and improves
  96     compatibility with Yacc.
  97
  98   - `parse error' -> `syntax error'
  99     Bison now uniformly uses the term `syntax error'; formerly, the code
 100     and manual sometimes used the term `parse error' instead.  POSIX
 101     requires `syntax error' in diagnostics, and it was thought better to
 102     be consistent.
 103
 104   - The documentation now emphasizes that yylex and yyerror must be
 105     declared before use.  C99 requires this.
 106
 107   - Bison now parses C99 lexical constructs like UCNs and
 108     backslash-newline within C escape sequences, as POSIX 1003.1-2001 requires.
 109
 110   - File names are properly escaped in C output.  E.g., foo\bar.y is
 111     output as "foo\\bar.y".
 112
 113   - Yacc command and library now available
 114     The Bison distribution now installs a `yacc' command, as POSIX requires.
 115     Also, Bison now installs a small library liby.a containing
 116     implementations of Yacc-compatible yyerror and main functions.
 117     This library is normally not useful, but POSIX requires it.
 118
 119   - Type clashes now generate warnings, not errors.
 120
 121   - If the user does not define YYSTYPE as a macro, Bison now declares it
 122     using typedef instead of defining it as a macro.
 123     For consistency, YYLTYPE is also declared instead of defined.
 124
 125 * Other compatibility issues
 126
 127   - %union directives can now have a tag before the `{', e.g., the
 128     directive `%union foo {...}' now generates the C code
 129     `typedef union foo { ... } YYSTYPE;'; this is for Yacc compatibility.
 130     The default union tag is `YYSTYPE', for compatibility with Solaris 9 Yacc.
 131     For consistency, YYLTYPE's struct tag is now `YYLTYPE' not `yyltype'.
 132     This is for compatibility with both Yacc and Bison 1.35.
 133
 134   - `;' is output before the terminating `}' of an action, for
 135     compatibility with Bison 1.35.
 136
 137   - Bison now uses a Yacc-style format for conflict reports, e.g.,
 138     `conflicts: 2 shift/reduce, 1 reduce/reduce'.
 139
 140   - `yystype' and `yyltype' are now obsolescent macros instead of being
 141     typedefs or tags; they are no longer documented and are planned to be
 142     withdrawn in a future release.
 143
 144 * GLR parser notes
 145
 146   - GLR and inline
 147     Users of Bison have to decide how they handle the portability of the
 148     C keyword `inline'.
 149
 150   - `parsing stack overflow...' -> `parser stack overflow'
 151     GLR parsers now report `parser stack overflow' as per the Bison manual.
 152
 153 * Bison now warns if it detects conflicting outputs to the same file,
 154   e.g., it generates a warning for `bison -d -o foo.h foo.y' since
 155   that command outputs both code and header to foo.h.
 156
 157 * #line in output files
 158   - --no-line works properly.
 159
 160 * Bison can no longer be built by a K&R C compiler; it requires C89 or
 161   later to be built.  This change originally took place a few versions
 162   ago, but nobody noticed until we recently asked someone to try
 163   building Bison with a K&R C compiler.
 164 \f
 165 Changes in version 1.75, 2002-10-14:
 166
 167 * Bison should now work on 64-bit hosts.
 168
 169 * Indonesian translation thanks to Tedi Heriyanto.
 170
 171 * GLR parsers
 172   Fix spurious parse errors.
 173
 174 * Pure parsers
 175   Some people redefine yyerror to steal yyparse' private variables.
 176   Reenable this trick until an official feature replaces it.
 177
 178 * Type Clashes
 179   In agreement with POSIX and with other Yaccs, leaving a default
 180   action is valid when $$ is untyped, and $1 typed:
 181
 182         untyped: ... typed;
 183
 184   but the converse remains an error:
 185
 186         typed: ... untyped;
 187
 188 * Values of mid-rule actions
 189   The following code:
 190
 191         foo: { ... } { $$ = $1; } ...
 192
 193   was incorrectly rejected: $1 is defined in the second mid-rule
 194   action, and is equal to the $$ of the first mid-rule action.
 195 \f
 196 Changes in version 1.50, 2002-10-04:
 197
 198 * GLR parsing
 199   The declaration
 200      %glr-parser
 201   causes Bison to produce a Generalized LR (GLR) parser, capable of handling
 202   almost any context-free grammar, ambiguous or not.  The new declarations
 203   %dprec and %merge on grammar rules allow parse-time resolution of
 204   ambiguities.  Contributed by Paul Hilfinger.
 205
 206   Unfortunately Bison 1.50 does not work properly on 64-bit hosts
 207   like the Alpha, so please stick to 32-bit hosts for now.
 208
 209 * Output Directory
 210   When not in Yacc compatibility mode, when the output file was not
 211   specified, running `bison foo/bar.y' created `foo/bar.c'.  It
 212   now creates `bar.c'.
 213
 214 * Undefined token
 215   The undefined token was systematically mapped to 2 which prevented
 216   the use of 2 by the user.  This is no longer the case.
 217
 218 * Unknown token numbers
 219   If yylex returned an out of range value, yyparse could die.  This is
 220   no longer the case.
 221
 222 * Error token
 223   According to POSIX, the error token must be 256.
 224   Bison extends this requirement by making it a preference: *if* the
 225   user specified that one of her tokens is numbered 256, then error
 226   will be mapped onto another number.
 227
 228 * Verbose error messages
 229   They no longer report `..., expecting error or...' for states where
 230   error recovery is possible.
 231
 232 * End token
 233   Defaults to `$end' instead of `$'.
 234
 235 * Error recovery now conforms to documentation and to POSIX
 236   When a Bison-generated parser encounters a syntax error, it now pops
 237   the stack until it finds a state that allows shifting the error
 238   token.  Formerly, it popped the stack until it found a state that
 239   allowed some non-error action other than a default reduction on the
 240   error token.  The new behavior has long been the documented behavior,
 241   and has long been required by POSIX.  For more details, please see
 242   Paul Eggert, "Reductions during Bison error handling" (2002-05-20)
 243   <http://lists.gnu.org/archive/html/bug-bison/2002-05/msg00038.html>.
 244
 245 * Traces
 246   Popped tokens and nonterminals are now reported.
 247
 248 * Larger grammars
 249   Larger grammars are now supported (larger token numbers, larger grammar
 250   size (= sum of the LHS and RHS lengths), larger LALR tables).
 251   Formerly, many of these numbers ran afoul of 16-bit limits;
 252   now these limits are 32 bits on most hosts.
 253
 254 * Explicit initial rule
 255   Bison used to play hacks with the initial rule, which the user does
 256   not write.  It is now explicit, and visible in the reports and
 257   graphs as rule 0.
 258
 259 * Useless rules
 260   Before, Bison reported the useless rules, but, although not used,
 261   included them in the parsers.  They are now actually removed.
 262
 263 * Useless rules, useless nonterminals
 264   They are now reported, as a warning, with their locations.
 265
 266 * Rules never reduced
 267   Rules that can never be reduced because of conflicts are now
 268   reported.
 269
 270 * Incorrect `Token not used'
 271   On a grammar such as
 272
 273            %token useless useful
 274            %%
 275            exp: '0' %prec useful;
 276
 277   where a token was used to set the precedence of the last rule,
 278   bison reported both `useful' and `useless' as useless tokens.
 279
 280 * Revert the C++ namespace changes introduced in 1.31
 281   as they caused too many portability hassles.
 282
 283 * Default locations
 284   By an accident of design, the default computation of @$ was
 285   performed after another default computation was performed: @$ = @1.
 286   The latter is now removed: YYLLOC_DEFAULT is fully responsible of
 287   the computation of @$.
 288
 289 * Token end-of-file
 290   The token end of file may be specified by the user, in which case,
 291   the user symbol is used in the reports, the graphs, and the verbose
 292   error messages instead of `$end', which remains being the default.
 293   For instance
 294      %token MYEOF 0
 295   or
 296      %token MYEOF 0 "end of file"
 297
 298 * Semantic parser
 299   This old option, which has been broken for ages, is removed.
 300
 301 * New translations
 302   Brazilian Portuguese, thanks to Alexandre Folle de Menezes.
 303   Croatian, thanks to Denis Lackovic.
 304
 305 * Incorrect token definitions
 306   When given `%token 'a' "A"', Bison used to output `#define 'a' 65'.
 307
 308 * Token definitions as enums
 309   Tokens are output both as the traditional #define's, and, provided
 310   the compiler supports ANSI C or is a C++ compiler, as enums.
 311   This lets debuggers display names instead of integers.
 312
 313 * Reports
 314   In addition to --verbose, bison supports --report=THINGS, which
 315   produces additional information:
 316   - itemset
 317     complete the core item sets with their closure
 318   - lookahead [changed to `look-ahead' in 1.875e and later]
 319     explicitly associate look-ahead tokens to items
 320   - solved
 321     describe shift/reduce conflicts solving.
 322     Bison used to systematically output this information on top of
 323     the report.  Solved conflicts are now attached to their states.
 324
 325 * Type clashes
 326   Previous versions don't complain when there is a type clash on
 327   the default action if the rule has a mid-rule action, such as in:
 328
 329       %type <foo> bar
 330       %%
 331       bar: '0' {} '0';
 332
 333   This is fixed.
 334
 335 * GNU M4 is now required when using Bison.
 336 \f
 337 Changes in version 1.35, 2002-03-25:
 338
 339 * C Skeleton
 340   Some projects use Bison's C parser with C++ compilers, and define
 341   YYSTYPE as a class.  The recent adjustment of C parsers for data
 342   alignment and 64 bit architectures made this impossible.
 343
 344   Because for the time being no real solution for C++ parser
 345   generation exists, kludges were implemented in the parser to
 346   maintain this use.  In the future, when Bison has C++ parsers, this
 347   kludge will be disabled.
 348
 349   This kludge also addresses some C++ problems when the stack was
 350   extended.
 351 \f
 352 Changes in version 1.34, 2002-03-12:
 353
 354 * File name clashes are detected
 355   $ bison foo.y -d -o foo.x
 356   fatal error: header and parser would both be named `foo.x'
 357
 358 * A missing `;' at the end of a rule triggers a warning
 359   In accordance with POSIX, and in agreement with other
 360   Yacc implementations, Bison will mandate this semicolon in the near
 361   future.  This eases the implementation of a Bison parser of Bison
 362   grammars by making this grammar LALR(1) instead of LR(2).  To
 363   facilitate the transition, this release introduces a warning.
 364
 365 * Revert the C++ namespace changes introduced in 1.31, as they caused too
 366   many portability hassles.
 367
 368 * DJGPP support added.
 369
 370 * Fix test suite portability problems.
 371 \f
 372 Changes in version 1.33, 2002-02-07:
 373
 374 * Fix C++ issues
 375   Groff could not be compiled for the definition of size_t was lacking
 376   under some conditions.
 377
 378 * Catch invalid @n
 379   As is done with $n.
 380 \f
 381 Changes in version 1.32, 2002-01-23:
 382
 383 * Fix Yacc output file names
 384
 385 * Portability fixes
 386
 387 * Italian, Dutch translations
 388 \f
 389 Changes in version 1.31, 2002-01-14:
 390
 391 * Many Bug Fixes
 392
 393 * GNU Gettext and %expect
 394   GNU Gettext asserts 10 s/r conflicts, but there are 7.  Now that
 395   Bison dies on incorrect %expectations, we fear there will be
 396   too many bug reports for Gettext, so _for the time being_, %expect
 397   does not trigger an error when the input file is named `plural.y'.
 398
 399 * Use of alloca in parsers
 400   If YYSTACK_USE_ALLOCA is defined to 0, then the parsers will use
 401   malloc exclusively.  Since 1.29, but was not NEWS'ed.
 402
 403   alloca is used only when compiled with GCC, to avoid portability
 404   problems as on AIX.
 405
 406 * When the generated parser lacks debugging code, YYDEBUG is now 0
 407   (as POSIX requires) instead of being undefined.
 408
 409 * User Actions
 410   Bison has always permitted actions such as { $$ = $1 }: it adds the
 411   ending semicolon.  Now if in Yacc compatibility mode, the semicolon
 412   is no longer output: one has to write { $$ = $1; }.
 413
 414 * Better C++ compliance
 415   The output parsers try to respect C++ namespaces.
 416   [This turned out to be a failed experiment, and it was reverted later.]
 417
 418 * Reduced Grammars
 419   Fixed bugs when reporting useless nonterminals.
 420
 421 * 64 bit hosts
 422   The parsers work properly on 64 bit hosts.
 423
 424 * Error messages
 425   Some calls to strerror resulted in scrambled or missing error messages.
 426
 427 * %expect
 428   When the number of shift/reduce conflicts is correct, don't issue
 429   any warning.
 430
 431 * The verbose report includes the rule line numbers.
 432
 433 * Rule line numbers are fixed in traces.
 434
 435 * Swedish translation
 436
 437 * Parse errors
 438   Verbose parse error messages from the parsers are better looking.
 439   Before: parse error: unexpected `'/'', expecting `"number"' or `'-'' or `'(''
 440      Now: parse error: unexpected '/', expecting "number" or '-' or '('
 441
 442 * Fixed parser memory leaks.
 443   When the generated parser was using malloc to extend its stacks, the
 444   previous allocations were not freed.
 445
 446 * Fixed verbose output file.
 447   Some newlines were missing.
 448   Some conflicts in state descriptions were missing.
 449
 450 * Fixed conflict report.
 451   Option -v was needed to get the result.
 452
 453 * %expect
 454   Was not used.
 455   Mismatches are errors, not warnings.
 456
 457 * Fixed incorrect processing of some invalid input.
 458
 459 * Fixed CPP guards: 9foo.h uses BISON_9FOO_H instead of 9FOO_H.
 460
 461 * Fixed some typos in the documentation.
 462
 463 * %token MY_EOF 0 is supported.
 464   Before, MY_EOF was silently renumbered as 257.
 465
 466 * doc/refcard.tex is updated.
 467
 468 * %output, %file-prefix, %name-prefix.
 469   New.
 470
 471 * --output
 472   New, aliasing `--output-file'.
 473 \f
 474 Changes in version 1.30, 2001-10-26:
 475
 476 * `--defines' and `--graph' have now an optional argument which is the
 477   output file name. `-d' and `-g' do not change; they do not take any
 478   argument.
 479
 480 * `%source_extension' and `%header_extension' are removed, failed
 481   experiment.
 482
 483 * Portability fixes.
 484 \f
 485 Changes in version 1.29, 2001-09-07:
 486
 487 * The output file does not define const, as this caused problems when used
 488   with common autoconfiguration schemes.  If you still use ancient compilers
 489   that lack const, compile with the equivalent of the C compiler option
 490   `-Dconst='.  autoconf's AC_C_CONST macro provides one way to do this.
 491
 492 * Added `-g' and `--graph'.
 493
 494 * The Bison manual is now distributed under the terms of the GNU FDL.
 495
 496 * The input and the output files has automatically a similar extension.
 497
 498 * Russian translation added.
 499
 500 * NLS support updated; should hopefully be less troublesome.
 501
 502 * Added the old Bison reference card.
 503
 504 * Added `--locations' and `%locations'.
 505
 506 * Added `-S' and `--skeleton'.
 507
 508 * `%raw', `-r', `--raw' is disabled.
 509
 510 * Special characters are escaped when output.  This solves the problems
 511   of the #line lines with path names including backslashes.
 512
 513 * New directives.
 514   `%yacc', `%fixed_output_files', `%defines', `%no_parser', `%verbose',
 515   `%debug', `%source_extension' and `%header_extension'.
 516
 517 * @$
 518   Automatic location tracking.
 519 \f
 520 Changes in version 1.28, 1999-07-06:
 521
 522 * Should compile better now with K&R compilers.
 523
 524 * Added NLS.
 525
 526 * Fixed a problem with escaping the double quote character.
 527
 528 * There is now a FAQ.
 529 \f
 530 Changes in version 1.27:
 531
 532 * The make rule which prevented bison.simple from being created on
 533   some systems has been fixed.
 534 \f
 535 Changes in version 1.26:
 536
 537 * Bison now uses automake.
 538
 539 * New mailing lists: <bug-bison@gnu.org> and <help-bison@gnu.org>.
 540
 541 * Token numbers now start at 257 as previously documented, not 258.
 542
 543 * Bison honors the TMPDIR environment variable.
 544
 545 * A couple of buffer overruns have been fixed.
 546
 547 * Problems when closing files should now be reported.
 548
 549 * Generated parsers should now work even on operating systems which do
 550   not provide alloca().
 551 \f
 552 Changes in version 1.25, 1995-10-16:
 553
 554 * Errors in the input grammar are not fatal; Bison keeps reading
 555 the grammar file, and reports all the errors found in it.
 556
 557 * Tokens can now be specified as multiple-character strings: for
 558 example, you could use "<=" for a token which looks like <=, instead
 559 of chosing a name like LESSEQ.
 560
 561 * The %token_table declaration says to write a table of tokens (names
 562 and numbers) into the parser file.  The yylex function can use this
 563 table to recognize multiple-character string tokens, or for other
 564 purposes.
 565
 566 * The %no_lines declaration says not to generate any #line preprocessor
 567 directives in the parser file.
 568
 569 * The %raw declaration says to use internal Bison token numbers, not
 570 Yacc-compatible token numbers, when token names are defined as macros.
 571
 572 * The --no-parser option produces the parser tables without including
 573 the parser engine; a project can now use its own parser engine.
 574 The actions go into a separate file called NAME.act, in the form of
 575 a switch statement body.
 576 \f
 577 Changes in version 1.23:
 578
 579 The user can define YYPARSE_PARAM as the name of an argument to be
 580 passed into yyparse.  The argument should have type void *.  It should
 581 actually point to an object.  Grammar actions can access the variable
 582 by casting it to the proper pointer type.
 583
 584 Line numbers in output file corrected.
 585 \f
 586 Changes in version 1.22:
 587
 588 --help option added.
 589 \f
 590 Changes in version 1.20:
 591
 592 Output file does not redefine const for C++.
 593
 594 Local Variables:
 595 mode: outline
 596 End:
 597
 598 -----
 599
 600 Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004
 601 Free Software Foundation, Inc.
 602
 603 This file is part of Bison, the GNU Compiler Compiler.
 604
 605 Bison is free software; you can redistribute it and/or modify
 606 it under the terms of the GNU General Public License as published by
 607 the Free Software Foundation; either version 2, or (at your option)
 608 any later version.
 609
 610 Bison is distributed in the hope that it will be useful,
 611 but WITHOUT ANY WARRANTY; without even the implied warranty of
 612 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 613 GNU General Public License for more details.
 614
 615 You should have received a copy of the GNU General Public License
 616 along with autoconf; see the file COPYING.  If not, write to
 617 the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 618 Boston, MA 02111-1307, USA.