NEWS

   1 Bison News
   2 ----------
   3
   4 Changes in version 2.3a, 2006-09-13:
   5
   6 * Instead of %union, you can define and use your own union type
   7   YYSTYPE if your grammar contains at least one <type> tag.
   8   Your YYSTYPE need not be a macro; it can be a typedef.
   9   This change is for compatibility with other Yacc implementations,
  10   and is required by POSIX.
  11
  12 * Locations columns and lines start at 1.
  13   In accordance with the GNU Coding Standards and Emacs.
  14
  15 * You may now declare per-type and default %destructor's and %printer's:
  16
  17   For example:
  18
  19     %union { char *string; }
  20     %token <string> STRING1
  21     %token <string> STRING2
  22     %type  <string> string1
  23     %type  <string> string2
  24     %union { char character; }
  25     %token <character> CHR
  26     %type  <character> chr
  27     %destructor { free ($$); } %symbol-default
  28     %destructor { free ($$); printf ("%d", @$.first_line); } STRING1 string1
  29     %destructor { } <character>
  30
  31   guarantees that, when the parser discards any user-defined symbol that has a
  32   semantic type tag other than `<character>', it passes its semantic value to
  33   `free'.  However, when the parser discards a `STRING1' or a `string1', it
  34   also prints its line number to `stdout'.  It performs only the second
  35   `%destructor' in this case, so it invokes `free' only once.
  36
  37 * Except for LALR(1) parsers in C with POSIX Yacc emulation enabled (with `-y',
  38   `--yacc', or `%yacc'), Bison no longer generates #define statements for
  39   associating token numbers with token names.  Removing the #define statements
  40   helps to sanitize the global namespace during preprocessing, but POSIX Yacc
  41   requires them.  Bison still generates an enum for token names in all cases.
  42
  43 * Handling of traditional Yacc prologue blocks is now more consistent but
  44   potentially incompatible with previous releases of Bison.
  45
  46   As before, you declare prologue blocks in your grammar file with the
  47   `%{ ... %}' syntax.  To generate the pre-prologue, Bison concatenates all
  48   prologue blocks that you've declared before the first %union.  To generate
  49   the post-prologue, Bison concatenates all prologue blocks that you've
  50   declared after the first %union.
  51
  52   Previous releases of Bison inserted the pre-prologue into both the header
  53   file and the code file in all cases except for LALR(1) parsers in C.  In the
  54   latter case, Bison inserted it only into the code file.  For parsers in C++,
  55   the point of insertion was before any token definitions (which associate
  56   token numbers with names).  For parsers in C, the point of insertion was
  57   after the token definitions.
  58
  59   Now, Bison never inserts the pre-prologue into the header file.  In the code
  60   file, it always inserts it before the token definitions.
  61
  62 * Bison now provides a more flexible alternative to the traditional Yacc
  63   prologue blocks: %before-header, %start-header, %end-header, and
  64   %after-header.
  65
  66   For example, the following declaration order in the grammar file reflects the
  67   order in which Bison will output these code blocks.  However, you are free to
  68   declare these code blocks in your grammar file in whatever order is most
  69   convenient for you:
  70
  71     %before-header {
  72       /* Bison treats this block like a pre-prologue block: it inserts it into
  73        * the code file before the contents of the header file.  It does *not*
  74        * insert it into the header file.  This is a good place to put
  75        * #include's that you want at the top of your code file.  A common
  76        * example is `#include "system.h"'.  */
  77     }
  78     %start-header {
  79       /* Bison inserts this block into both the header file and the code file.
  80        * In both files, the point of insertion is before any Bison-generated
  81        * token, semantic type, location type, and class definitions.  This is a
  82        * good place to define %union dependencies, for example.  */
  83     }
  84     %union {
  85       /* Unlike the traditional Yacc prologue blocks, the output order for the
  86        * new %*-header blocks is not affected by their declaration position
  87        * relative to any %union in the grammar file.  */
  88     }
  89     %end-header {
  90       /* Bison inserts this block into both the header file and the code file.
  91        * In both files, the point of insertion is after the Bison-generated
  92        * definitions.  This is a good place to declare or define public
  93        * functions or data structures that depend on the Bison-generated
  94        * definitions.  */
  95     }
  96     %after-header {
  97       /* Bison treats this block like a post-prologue block: it inserts it into
  98        * the code file after the contents of the header file.  It does *not*
  99        * insert it into the header file.  This is a good place to declare or
 100        * define internal functions or data structures that depend on the
 101        * Bison-generated definitions.  */
 102     }
 103
 104   If you have multiple occurrences of any one of the above declarations, Bison
 105   will concatenate the contents in declaration order.
 106
 107 * The option `--report=look-ahead' has been changed to `--report=lookahead'.
 108   The old spelling still works, but is not documented and may be removed
 109   in a future release.
 110
 111 Changes in version 2.3, 2006-06-05:
 112
 113 * GLR grammars should now use `YYRECOVERING ()' instead of `YYRECOVERING',
 114   for compatibility with LALR(1) grammars.
 115
 116 * It is now documented that any definition of YYSTYPE or YYLTYPE should
 117   be to a type name that does not contain parentheses or brackets.
 118
 119 Changes in version 2.2, 2006-05-19:
 120
 121 * The distribution terms for all Bison-generated parsers now permit
 122   using the parsers in nonfree programs.  Previously, this permission
 123   was granted only for Bison-generated LALR(1) parsers in C.
 124
 125 * %name-prefix changes the namespace name in C++ outputs.
 126
 127 * The C++ parsers export their token_type.
 128
 129 * Bison now allows multiple %union declarations, and concatenates
 130   their contents together.
 131
 132 * New warning: unused values
 133   Right-hand side symbols whose values are not used are reported,
 134   if the symbols have destructors.  For instance:
 135
 136      exp: exp "?" exp ":" exp { $1 ? $1 : $3; }
 137         | exp "+" exp
 138         ;
 139
 140   will trigger a warning about $$ and $5 in the first rule, and $3 in
 141   the second ($1 is copied to $$ by the default rule).  This example
 142   most likely contains three errors, and could be rewritten as:
 143
 144      exp: exp "?" exp ":" exp
 145             { $$ = $1 ? $3 : $5; free ($1 ? $5 : $3); free ($1); }
 146         | exp "+" exp
 147             { $$ = $1 ? $1 : $3; if ($1) free ($3); }
 148         ;
 149
 150   However, if the original actions were really intended, memory leaks
 151   and all, the warnings can be suppressed by letting Bison believe the
 152   values are used, e.g.:
 153
 154      exp: exp "?" exp ":" exp { $1 ? $1 : $3; (void) ($$, $5); }
 155         | exp "+" exp         { $$ = $1; (void) $3; }
 156         ;
 157
 158   If there are mid-rule actions, the warning is issued if no action
 159   uses it.  The following triggers no warning: $1 and $3 are used.
 160
 161      exp: exp { push ($1); } '+' exp { push ($3); sum (); };
 162
 163   The warning is intended to help catching lost values and memory leaks.
 164   If a value is ignored, its associated memory typically is not reclaimed.
 165
 166 * %destructor vs. YYABORT, YYACCEPT, and YYERROR.
 167   Destructors are now called when user code invokes YYABORT, YYACCEPT,
 168   and YYERROR, for all objects on the stack, other than objects
 169   corresponding to the right-hand side of the current rule.
 170
 171 * %expect, %expect-rr
 172   Incorrect numbers of expected conflicts are now actual errors,
 173   instead of warnings.
 174
 175 * GLR, YACC parsers.
 176   The %parse-params are available in the destructors (and the
 177   experimental printers) as per the documentation.
 178
 179 * Bison now warns if it finds a stray `$' or `@' in an action.
 180
 181 * %require "VERSION"
 182   This specifies that the grammar file depends on features implemented
 183   in Bison version VERSION or higher.
 184
 185 * lalr1.cc: The token and value types are now class members.
 186   The tokens were defined as free form enums and cpp macros.  YYSTYPE
 187   was defined as a free form union.  They are now class members:
 188   tokens are enumerations of the `yy::parser::token' struct, and the
 189   semantic values have the `yy::parser::semantic_type' type.
 190
 191   If you do not want or can update to this scheme, the directive
 192   `%define "global_tokens_and_yystype" "1"' triggers the global
 193   definition of tokens and YYSTYPE.  This change is suitable both
 194   for previous releases of Bison, and this one.
 195
 196   If you wish to update, then make sure older version of Bison will
 197   fail using `%require "2.2"'.
 198
 199 * DJGPP support added.
 200 \f
 201 Changes in version 2.1, 2005-09-16:
 202
 203 * The C++ lalr1.cc skeleton supports %lex-param.
 204
 205 * Bison-generated parsers now support the translation of diagnostics like
 206   "syntax error" into languages other than English.  The default
 207   language is still English.  For details, please see the new
 208   Internationalization section of the Bison manual.  Software
 209   distributors should also see the new PACKAGING file.  Thanks to
 210   Bruno Haible for this new feature.
 211
 212 * Wording in the Bison-generated parsers has been changed slightly to
 213   simplify translation.  In particular, the message "memory exhausted"
 214   has replaced "parser stack overflow", as the old message was not
 215   always accurate for modern Bison-generated parsers.
 216
 217 * Destructors are now called when the parser aborts, for all symbols left
 218   behind on the stack.  Also, the start symbol is now destroyed after a
 219   successful parse.  In both cases, the behavior was formerly inconsistent.
 220
 221 * When generating verbose diagnostics, Bison-generated parsers no longer
 222   quote the literal strings associated with tokens.  For example, for
 223   a syntax error associated with '%token NUM "number"' they might
 224   print 'syntax error, unexpected number' instead of 'syntax error,
 225   unexpected "number"'.
 226 \f
 227 Changes in version 2.0, 2004-12-25:
 228
 229 * Possibly-incompatible changes
 230
 231   - Bison-generated parsers no longer default to using the alloca function
 232     (when available) to extend the parser stack, due to widespread
 233     problems in unchecked stack-overflow detection.  You can "#define
 234     YYSTACK_USE_ALLOCA 1" to require the use of alloca, but please read
 235     the manual to determine safe values for YYMAXDEPTH in that case.
 236
 237   - Error token location.
 238     During error recovery, the location of the syntax error is updated
 239     to cover the whole sequence covered by the error token: it includes
 240     the shifted symbols thrown away during the first part of the error
 241     recovery, and the lookahead rejected during the second part.
 242
 243   - Semicolon changes:
 244     . Stray semicolons are no longer allowed at the start of a grammar.
 245     . Semicolons are now required after in-grammar declarations.
 246
 247   - Unescaped newlines are no longer allowed in character constants or
 248     string literals.  They were never portable, and GCC 3.4.0 has
 249     dropped support for them.  Better diagnostics are now generated if
 250     forget a closing quote.
 251
 252   - NUL bytes are no longer allowed in Bison string literals, unfortunately.
 253
 254 * New features
 255
 256   - GLR grammars now support locations.
 257
 258   - New directive: %initial-action.
 259     This directive allows the user to run arbitrary code (including
 260     initializing @$) from yyparse before parsing starts.
 261
 262   - A new directive "%expect-rr N" specifies the expected number of
 263     reduce/reduce conflicts in GLR parsers.
 264
 265   - %token numbers can now be hexadecimal integers, e.g., `%token FOO 0x12d'.
 266     This is a GNU extension.
 267
 268   - The option `--report=lookahead' was changed to `--report=look-ahead'.
 269     [However, this was changed back after 2.3.]
 270
 271   - Experimental %destructor support has been added to lalr1.cc.
 272
 273   - New configure option --disable-yacc, to disable installation of the
 274     yacc command and -ly library introduced in 1.875 for POSIX conformance.
 275
 276 * Bug fixes
 277
 278   - For now, %expect-count violations are now just warnings, not errors.
 279     This is for compatibility with Bison 1.75 and earlier (when there are
 280     reduce/reduce conflicts) and with Bison 1.30 and earlier (when there
 281     are too many or too few shift/reduce conflicts).  However, in future
 282     versions of Bison we plan to improve the %expect machinery so that
 283     these violations will become errors again.
 284
 285   - Within Bison itself, numbers (e.g., goto numbers) are no longer
 286     arbitrarily limited to 16-bit counts.
 287
 288   - Semicolons are now allowed before "|" in grammar rules, as POSIX requires.
 289 \f
 290 Changes in version 1.875, 2003-01-01:
 291
 292 * The documentation license has been upgraded to version 1.2
 293   of the GNU Free Documentation License.
 294
 295 * syntax error processing
 296
 297   - In Yacc-style parsers YYLLOC_DEFAULT is now used to compute error
 298     locations too.  This fixes bugs in error-location computation.
 299
 300   - %destructor
 301     It is now possible to reclaim the memory associated to symbols
 302     discarded during error recovery.  This feature is still experimental.
 303
 304   - %error-verbose
 305     This new directive is preferred over YYERROR_VERBOSE.
 306
 307   - #defining yyerror to steal internal variables is discouraged.
 308     It is not guaranteed to work forever.
 309
 310 * POSIX conformance
 311
 312   - Semicolons are once again optional at the end of grammar rules.
 313     This reverts to the behavior of Bison 1.33 and earlier, and improves
 314     compatibility with Yacc.
 315
 316   - `parse error' -> `syntax error'
 317     Bison now uniformly uses the term `syntax error'; formerly, the code
 318     and manual sometimes used the term `parse error' instead.  POSIX
 319     requires `syntax error' in diagnostics, and it was thought better to
 320     be consistent.
 321
 322   - The documentation now emphasizes that yylex and yyerror must be
 323     declared before use.  C99 requires this.
 324
 325   - Bison now parses C99 lexical constructs like UCNs and
 326     backslash-newline within C escape sequences, as POSIX 1003.1-2001 requires.
 327
 328   - File names are properly escaped in C output.  E.g., foo\bar.y is
 329     output as "foo\\bar.y".
 330
 331   - Yacc command and library now available
 332     The Bison distribution now installs a `yacc' command, as POSIX requires.
 333     Also, Bison now installs a small library liby.a containing
 334     implementations of Yacc-compatible yyerror and main functions.
 335     This library is normally not useful, but POSIX requires it.
 336
 337   - Type clashes now generate warnings, not errors.
 338
 339   - If the user does not define YYSTYPE as a macro, Bison now declares it
 340     using typedef instead of defining it as a macro.
 341     For consistency, YYLTYPE is also declared instead of defined.
 342
 343 * Other compatibility issues
 344
 345   - %union directives can now have a tag before the `{', e.g., the
 346     directive `%union foo {...}' now generates the C code
 347     `typedef union foo { ... } YYSTYPE;'; this is for Yacc compatibility.
 348     The default union tag is `YYSTYPE', for compatibility with Solaris 9 Yacc.
 349     For consistency, YYLTYPE's struct tag is now `YYLTYPE' not `yyltype'.
 350     This is for compatibility with both Yacc and Bison 1.35.
 351
 352   - `;' is output before the terminating `}' of an action, for
 353     compatibility with Bison 1.35.
 354
 355   - Bison now uses a Yacc-style format for conflict reports, e.g.,
 356     `conflicts: 2 shift/reduce, 1 reduce/reduce'.
 357
 358   - `yystype' and `yyltype' are now obsolescent macros instead of being
 359     typedefs or tags; they are no longer documented and are planned to be
 360     withdrawn in a future release.
 361
 362 * GLR parser notes
 363
 364   - GLR and inline
 365     Users of Bison have to decide how they handle the portability of the
 366     C keyword `inline'.
 367
 368   - `parsing stack overflow...' -> `parser stack overflow'
 369     GLR parsers now report `parser stack overflow' as per the Bison manual.
 370
 371 * Bison now warns if it detects conflicting outputs to the same file,
 372   e.g., it generates a warning for `bison -d -o foo.h foo.y' since
 373   that command outputs both code and header to foo.h.
 374
 375 * #line in output files
 376   - --no-line works properly.
 377
 378 * Bison can no longer be built by a K&R C compiler; it requires C89 or
 379   later to be built.  This change originally took place a few versions
 380   ago, but nobody noticed until we recently asked someone to try
 381   building Bison with a K&R C compiler.
 382 \f
 383 Changes in version 1.75, 2002-10-14:
 384
 385 * Bison should now work on 64-bit hosts.
 386
 387 * Indonesian translation thanks to Tedi Heriyanto.
 388
 389 * GLR parsers
 390   Fix spurious parse errors.
 391
 392 * Pure parsers
 393   Some people redefine yyerror to steal yyparse' private variables.
 394   Reenable this trick until an official feature replaces it.
 395
 396 * Type Clashes
 397   In agreement with POSIX and with other Yaccs, leaving a default
 398   action is valid when $$ is untyped, and $1 typed:
 399
 400         untyped: ... typed;
 401
 402   but the converse remains an error:
 403
 404         typed: ... untyped;
 405
 406 * Values of mid-rule actions
 407   The following code:
 408
 409         foo: { ... } { $$ = $1; } ...
 410
 411   was incorrectly rejected: $1 is defined in the second mid-rule
 412   action, and is equal to the $$ of the first mid-rule action.
 413 \f
 414 Changes in version 1.50, 2002-10-04:
 415
 416 * GLR parsing
 417   The declaration
 418      %glr-parser
 419   causes Bison to produce a Generalized LR (GLR) parser, capable of handling
 420   almost any context-free grammar, ambiguous or not.  The new declarations
 421   %dprec and %merge on grammar rules allow parse-time resolution of
 422   ambiguities.  Contributed by Paul Hilfinger.
 423
 424   Unfortunately Bison 1.50 does not work properly on 64-bit hosts
 425   like the Alpha, so please stick to 32-bit hosts for now.
 426
 427 * Output Directory
 428   When not in Yacc compatibility mode, when the output file was not
 429   specified, running `bison foo/bar.y' created `foo/bar.c'.  It
 430   now creates `bar.c'.
 431
 432 * Undefined token
 433   The undefined token was systematically mapped to 2 which prevented
 434   the use of 2 by the user.  This is no longer the case.
 435
 436 * Unknown token numbers
 437   If yylex returned an out of range value, yyparse could die.  This is
 438   no longer the case.
 439
 440 * Error token
 441   According to POSIX, the error token must be 256.
 442   Bison extends this requirement by making it a preference: *if* the
 443   user specified that one of her tokens is numbered 256, then error
 444   will be mapped onto another number.
 445
 446 * Verbose error messages
 447   They no longer report `..., expecting error or...' for states where
 448   error recovery is possible.
 449
 450 * End token
 451   Defaults to `$end' instead of `$'.
 452
 453 * Error recovery now conforms to documentation and to POSIX
 454   When a Bison-generated parser encounters a syntax error, it now pops
 455   the stack until it finds a state that allows shifting the error
 456   token.  Formerly, it popped the stack until it found a state that
 457   allowed some non-error action other than a default reduction on the
 458   error token.  The new behavior has long been the documented behavior,
 459   and has long been required by POSIX.  For more details, please see
 460   Paul Eggert, "Reductions during Bison error handling" (2002-05-20)
 461   <http://lists.gnu.org/archive/html/bug-bison/2002-05/msg00038.html>.
 462
 463 * Traces
 464   Popped tokens and nonterminals are now reported.
 465
 466 * Larger grammars
 467   Larger grammars are now supported (larger token numbers, larger grammar
 468   size (= sum of the LHS and RHS lengths), larger LALR tables).
 469   Formerly, many of these numbers ran afoul of 16-bit limits;
 470   now these limits are 32 bits on most hosts.
 471
 472 * Explicit initial rule
 473   Bison used to play hacks with the initial rule, which the user does
 474   not write.  It is now explicit, and visible in the reports and
 475   graphs as rule 0.
 476
 477 * Useless rules
 478   Before, Bison reported the useless rules, but, although not used,
 479   included them in the parsers.  They are now actually removed.
 480
 481 * Useless rules, useless nonterminals
 482   They are now reported, as a warning, with their locations.
 483
 484 * Rules never reduced
 485   Rules that can never be reduced because of conflicts are now
 486   reported.
 487
 488 * Incorrect `Token not used'
 489   On a grammar such as
 490
 491            %token useless useful
 492            %%
 493            exp: '0' %prec useful;
 494
 495   where a token was used to set the precedence of the last rule,
 496   bison reported both `useful' and `useless' as useless tokens.
 497
 498 * Revert the C++ namespace changes introduced in 1.31
 499   as they caused too many portability hassles.
 500
 501 * Default locations
 502   By an accident of design, the default computation of @$ was
 503   performed after another default computation was performed: @$ = @1.
 504   The latter is now removed: YYLLOC_DEFAULT is fully responsible of
 505   the computation of @$.
 506
 507 * Token end-of-file
 508   The token end of file may be specified by the user, in which case,
 509   the user symbol is used in the reports, the graphs, and the verbose
 510   error messages instead of `$end', which remains being the default.
 511   For instance
 512      %token MYEOF 0
 513   or
 514      %token MYEOF 0 "end of file"
 515
 516 * Semantic parser
 517   This old option, which has been broken for ages, is removed.
 518
 519 * New translations
 520   Brazilian Portuguese, thanks to Alexandre Folle de Menezes.
 521   Croatian, thanks to Denis Lackovic.
 522
 523 * Incorrect token definitions
 524   When given `%token 'a' "A"', Bison used to output `#define 'a' 65'.
 525
 526 * Token definitions as enums
 527   Tokens are output both as the traditional #define's, and, provided
 528   the compiler supports ANSI C or is a C++ compiler, as enums.
 529   This lets debuggers display names instead of integers.
 530
 531 * Reports
 532   In addition to --verbose, bison supports --report=THINGS, which
 533   produces additional information:
 534   - itemset
 535     complete the core item sets with their closure
 536   - lookahead [changed to `look-ahead' in 1.875e through 2.3, but changed back]
 537     explicitly associate lookahead tokens to items
 538   - solved
 539     describe shift/reduce conflicts solving.
 540     Bison used to systematically output this information on top of
 541     the report.  Solved conflicts are now attached to their states.
 542
 543 * Type clashes
 544   Previous versions don't complain when there is a type clash on
 545   the default action if the rule has a mid-rule action, such as in:
 546
 547       %type <foo> bar
 548       %%
 549       bar: '0' {} '0';
 550
 551   This is fixed.
 552
 553 * GNU M4 is now required when using Bison.
 554 \f
 555 Changes in version 1.35, 2002-03-25:
 556
 557 * C Skeleton
 558   Some projects use Bison's C parser with C++ compilers, and define
 559   YYSTYPE as a class.  The recent adjustment of C parsers for data
 560   alignment and 64 bit architectures made this impossible.
 561
 562   Because for the time being no real solution for C++ parser
 563   generation exists, kludges were implemented in the parser to
 564   maintain this use.  In the future, when Bison has C++ parsers, this
 565   kludge will be disabled.
 566
 567   This kludge also addresses some C++ problems when the stack was
 568   extended.
 569 \f
 570 Changes in version 1.34, 2002-03-12:
 571
 572 * File name clashes are detected
 573   $ bison foo.y -d -o foo.x
 574   fatal error: header and parser would both be named `foo.x'
 575
 576 * A missing `;' at the end of a rule triggers a warning
 577   In accordance with POSIX, and in agreement with other
 578   Yacc implementations, Bison will mandate this semicolon in the near
 579   future.  This eases the implementation of a Bison parser of Bison
 580   grammars by making this grammar LALR(1) instead of LR(2).  To
 581   facilitate the transition, this release introduces a warning.
 582
 583 * Revert the C++ namespace changes introduced in 1.31, as they caused too
 584   many portability hassles.
 585
 586 * DJGPP support added.
 587
 588 * Fix test suite portability problems.
 589 \f
 590 Changes in version 1.33, 2002-02-07:
 591
 592 * Fix C++ issues
 593   Groff could not be compiled for the definition of size_t was lacking
 594   under some conditions.
 595
 596 * Catch invalid @n
 597   As is done with $n.
 598 \f
 599 Changes in version 1.32, 2002-01-23:
 600
 601 * Fix Yacc output file names
 602
 603 * Portability fixes
 604
 605 * Italian, Dutch translations
 606 \f
 607 Changes in version 1.31, 2002-01-14:
 608
 609 * Many Bug Fixes
 610
 611 * GNU Gettext and %expect
 612   GNU Gettext asserts 10 s/r conflicts, but there are 7.  Now that
 613   Bison dies on incorrect %expectations, we fear there will be
 614   too many bug reports for Gettext, so _for the time being_, %expect
 615   does not trigger an error when the input file is named `plural.y'.
 616
 617 * Use of alloca in parsers
 618   If YYSTACK_USE_ALLOCA is defined to 0, then the parsers will use
 619   malloc exclusively.  Since 1.29, but was not NEWS'ed.
 620
 621   alloca is used only when compiled with GCC, to avoid portability
 622   problems as on AIX.
 623
 624 * yyparse now returns 2 if memory is exhausted; formerly it dumped core.
 625
 626 * When the generated parser lacks debugging code, YYDEBUG is now 0
 627   (as POSIX requires) instead of being undefined.
 628
 629 * User Actions
 630   Bison has always permitted actions such as { $$ = $1 }: it adds the
 631   ending semicolon.  Now if in Yacc compatibility mode, the semicolon
 632   is no longer output: one has to write { $$ = $1; }.
 633
 634 * Better C++ compliance
 635   The output parsers try to respect C++ namespaces.
 636   [This turned out to be a failed experiment, and it was reverted later.]
 637
 638 * Reduced Grammars
 639   Fixed bugs when reporting useless nonterminals.
 640
 641 * 64 bit hosts
 642   The parsers work properly on 64 bit hosts.
 643
 644 * Error messages
 645   Some calls to strerror resulted in scrambled or missing error messages.
 646
 647 * %expect
 648   When the number of shift/reduce conflicts is correct, don't issue
 649   any warning.
 650
 651 * The verbose report includes the rule line numbers.
 652
 653 * Rule line numbers are fixed in traces.
 654
 655 * Swedish translation
 656
 657 * Parse errors
 658   Verbose parse error messages from the parsers are better looking.
 659   Before: parse error: unexpected `'/'', expecting `"number"' or `'-'' or `'(''
 660      Now: parse error: unexpected '/', expecting "number" or '-' or '('
 661
 662 * Fixed parser memory leaks.
 663   When the generated parser was using malloc to extend its stacks, the
 664   previous allocations were not freed.
 665
 666 * Fixed verbose output file.
 667   Some newlines were missing.
 668   Some conflicts in state descriptions were missing.
 669
 670 * Fixed conflict report.
 671   Option -v was needed to get the result.
 672
 673 * %expect
 674   Was not used.
 675   Mismatches are errors, not warnings.
 676
 677 * Fixed incorrect processing of some invalid input.
 678
 679 * Fixed CPP guards: 9foo.h uses BISON_9FOO_H instead of 9FOO_H.
 680
 681 * Fixed some typos in the documentation.
 682
 683 * %token MY_EOF 0 is supported.
 684   Before, MY_EOF was silently renumbered as 257.
 685
 686 * doc/refcard.tex is updated.
 687
 688 * %output, %file-prefix, %name-prefix.
 689   New.
 690
 691 * --output
 692   New, aliasing `--output-file'.
 693 \f
 694 Changes in version 1.30, 2001-10-26:
 695
 696 * `--defines' and `--graph' have now an optional argument which is the
 697   output file name. `-d' and `-g' do not change; they do not take any
 698   argument.
 699
 700 * `%source_extension' and `%header_extension' are removed, failed
 701   experiment.
 702
 703 * Portability fixes.
 704 \f
 705 Changes in version 1.29, 2001-09-07:
 706
 707 * The output file does not define const, as this caused problems when used
 708   with common autoconfiguration schemes.  If you still use ancient compilers
 709   that lack const, compile with the equivalent of the C compiler option
 710   `-Dconst='.  autoconf's AC_C_CONST macro provides one way to do this.
 711
 712 * Added `-g' and `--graph'.
 713
 714 * The Bison manual is now distributed under the terms of the GNU FDL.
 715
 716 * The input and the output files has automatically a similar extension.
 717
 718 * Russian translation added.
 719
 720 * NLS support updated; should hopefully be less troublesome.
 721
 722 * Added the old Bison reference card.
 723
 724 * Added `--locations' and `%locations'.
 725
 726 * Added `-S' and `--skeleton'.
 727
 728 * `%raw', `-r', `--raw' is disabled.
 729
 730 * Special characters are escaped when output.  This solves the problems
 731   of the #line lines with path names including backslashes.
 732
 733 * New directives.
 734   `%yacc', `%fixed_output_files', `%defines', `%no_parser', `%verbose',
 735   `%debug', `%source_extension' and `%header_extension'.
 736
 737 * @$
 738   Automatic location tracking.
 739 \f
 740 Changes in version 1.28, 1999-07-06:
 741
 742 * Should compile better now with K&R compilers.
 743
 744 * Added NLS.
 745
 746 * Fixed a problem with escaping the double quote character.
 747
 748 * There is now a FAQ.
 749 \f
 750 Changes in version 1.27:
 751
 752 * The make rule which prevented bison.simple from being created on
 753   some systems has been fixed.
 754 \f
 755 Changes in version 1.26:
 756
 757 * Bison now uses automake.
 758
 759 * New mailing lists: <bug-bison@gnu.org> and <help-bison@gnu.org>.
 760
 761 * Token numbers now start at 257 as previously documented, not 258.
 762
 763 * Bison honors the TMPDIR environment variable.
 764
 765 * A couple of buffer overruns have been fixed.
 766
 767 * Problems when closing files should now be reported.
 768
 769 * Generated parsers should now work even on operating systems which do
 770   not provide alloca().
 771 \f
 772 Changes in version 1.25, 1995-10-16:
 773
 774 * Errors in the input grammar are not fatal; Bison keeps reading
 775 the grammar file, and reports all the errors found in it.
 776
 777 * Tokens can now be specified as multiple-character strings: for
 778 example, you could use "<=" for a token which looks like <=, instead
 779 of chosing a name like LESSEQ.
 780
 781 * The %token_table declaration says to write a table of tokens (names
 782 and numbers) into the parser file.  The yylex function can use this
 783 table to recognize multiple-character string tokens, or for other
 784 purposes.
 785
 786 * The %no_lines declaration says not to generate any #line preprocessor
 787 directives in the parser file.
 788
 789 * The %raw declaration says to use internal Bison token numbers, not
 790 Yacc-compatible token numbers, when token names are defined as macros.
 791
 792 * The --no-parser option produces the parser tables without including
 793 the parser engine; a project can now use its own parser engine.
 794 The actions go into a separate file called NAME.act, in the form of
 795 a switch statement body.
 796 \f
 797 Changes in version 1.23:
 798
 799 The user can define YYPARSE_PARAM as the name of an argument to be
 800 passed into yyparse.  The argument should have type void *.  It should
 801 actually point to an object.  Grammar actions can access the variable
 802 by casting it to the proper pointer type.
 803
 804 Line numbers in output file corrected.
 805 \f
 806 Changes in version 1.22:
 807
 808 --help option added.
 809 \f
 810 Changes in version 1.20:
 811
 812 Output file does not redefine const for C++.
 813
 814 Local Variables:
 815 mode: outline
 816 End:
 817
 818 -----
 819
 820 Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003,
 821 2004, 2005, 2006 Free Software Foundation, Inc.
 822
 823 This file is part of Bison, the GNU Compiler Compiler.
 824
 825 Bison is free software; you can redistribute it and/or modify
 826 it under the terms of the GNU General Public License as published by
 827 the Free Software Foundation; either version 2, or (at your option)
 828 any later version.
 829
 830 Bison is distributed in the hope that it will be useful,
 831 but WITHOUT ANY WARRANTY; without even the implied warranty of
 832 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 833 GNU General Public License for more details.
 834
 835 You should have received a copy of the GNU General Public License
 836 along with autoconf; see the file COPYING.  If not, write to
 837 the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
 838 Boston, MA 02110-1301, USA.