NEWS

   1 Bison News
   2 ----------
   3
   4 Changes in version 2.3a+ (????-??-??):
   5
   6 * Previously, Bison sometimes generated parser tables with states that were
   7   unreachable due to conflicts in predecessor states.  Bison now:
   8
   9     1. Removes unreachable states.
  10
  11     2. Does not report any conflicts that appeared in unreachable states.
  12        WARNING: As a result, you may need to update %expect and %expect-rr
  13        directives in existing grammar files.
  14
  15     3. For any rule used only in such states, Bison now reports the rule as
  16        "never reduced because of conflicts".
  17
  18 * The -g and --graph options now output graphs in Graphviz DOT format,
  19   not VCG format.
  20
  21 * An experimental directive %language specifies the language of the
  22   generated parser, which can be C (the default) or C++.  This
  23   directive affects the skeleton used, and the names of the generated
  24   files if the grammar file's name ends in ".y".
  25
  26 * The grammar file may now specify the name of the parser header file using
  27   %defines.  For example:
  28
  29     %defines "parser.h"
  30
  31 * The `=' that used to be required in the following directives is now
  32   deprecated:
  33
  34     %file-prefix "parser"
  35     %name-prefix "c_"
  36     %output "parser.c"
  37
  38 * The quotes around NAME that used to be required in the following directive
  39   are now deprecated:
  40
  41     %define NAME "VALUE"
  42
  43 * Bison 2.3a provided a new set of directives as a more flexible alternative to
  44   the traditional Yacc prologue blocks.  Those have now been consolidated into
  45   a single %code directive with an optional qualifier field, which identifies
  46   the purpose of the code and thus the location(s) where Bison should generate
  47   it:
  48
  49     1. `%code          {CODE}' replaces `%after-header  {CODE}'
  50     2. `%code requires {CODE}' replaces `%start-header  {CODE}'
  51     3. `%code provides {CODE}' replaces `%end-header    {CODE}'
  52     4. `%code top      {CODE}' replaces `%before-header {CODE}'
  53
  54   See the %code entries in `Appendix A Bison Symbols' in the Bison manual for a
  55   summary of the new functionality.  See the new section `Prologue
  56   Alternatives' for a detailed discussion including the advantages of %code
  57   over the traditional Yacc prologues.
  58
  59   The prologue alternatives are experimental.  More user feedback will help to
  60   determine whether they should become permanent features.
  61
  62 * Revised warning: unset or unused mid-rule values
  63
  64   Since Bison 2.2, Bison has warned about mid-rule values that are set but not
  65   used within any of the actions of the parent rule.  For example, Bison warns
  66   about unused $2 in:
  67
  68     exp: '1' { $$ = 1; } '+' exp { $$ = $1 + $4; };
  69
  70   Now, Bison also warns about mid-rule values that are used but not set.  For
  71   example, Bison warns about unset $$ in the mid-rule action in:
  72
  73     exp: '1' { $1 = 1; } '+' exp { $$ = $2 + $4; };
  74
  75   However, Bison now disables both of these warnings by default since they
  76   sometimes prove to be false alarms in existing grammars employing the Yacc
  77   constructs $0 or $-N (where N is some positive integer).
  78
  79   To enable these warnings, specify the flag `--warnings=midrule-values' or
  80   `-W', which is a synonym for `--warnings=all'.
  81
  82 * Bison now recognizes two separate kinds of default %destructor's and
  83   %printer's:
  84
  85     1. Place `<*>' in a %destructor/%printer symbol list to define a default
  86        %destructor/%printer for all grammar symbols for which you have formally
  87        declared semantic type tags.
  88
  89     2. Place `<>' in a %destructor/%printer symbol list to define a default
  90        %destructor/%printer for all grammar symbols without declared semantic
  91        type tags.
  92
  93   Bison no longer supports the `%symbol-default' notation from Bison 2.3a.
  94   `<*>' and `<>' combined achieve the same effect with one exception: Bison no
  95   longer applies any %destructor to a mid-rule value if that mid-rule value is
  96   not actually ever referenced using either $$ or $n in a semantic action.
  97
  98   The default %destructor's and %printer's are experimental.  More user
  99   feedback will help to determine whether they should become permanent
 100   features.
 101
 102   See the section `Freeing Discarded Symbols' in the Bison manual for further
 103   details.
 104
 105 Changes in version 2.3a, 2006-09-13:
 106
 107 * Instead of %union, you can define and use your own union type
 108   YYSTYPE if your grammar contains at least one <type> tag.
 109   Your YYSTYPE need not be a macro; it can be a typedef.
 110   This change is for compatibility with other Yacc implementations,
 111   and is required by POSIX.
 112
 113 * Locations columns and lines start at 1.
 114   In accordance with the GNU Coding Standards and Emacs.
 115
 116 * You may now declare per-type and default %destructor's and %printer's:
 117
 118   For example:
 119
 120     %union { char *string; }
 121     %token <string> STRING1
 122     %token <string> STRING2
 123     %type  <string> string1
 124     %type  <string> string2
 125     %union { char character; }
 126     %token <character> CHR
 127     %type  <character> chr
 128     %destructor { free ($$); } %symbol-default
 129     %destructor { free ($$); printf ("%d", @$.first_line); } STRING1 string1
 130     %destructor { } <character>
 131
 132   guarantees that, when the parser discards any user-defined symbol that has a
 133   semantic type tag other than `<character>', it passes its semantic value to
 134   `free'.  However, when the parser discards a `STRING1' or a `string1', it
 135   also prints its line number to `stdout'.  It performs only the second
 136   `%destructor' in this case, so it invokes `free' only once.
 137
 138   [Although we failed to mention this here in the 2.3a release, the default
 139   %destructor's and %printer's were experimental, and they were rewritten in
 140   future versions.]
 141
 142 * Except for LALR(1) parsers in C with POSIX Yacc emulation enabled (with `-y',
 143   `--yacc', or `%yacc'), Bison no longer generates #define statements for
 144   associating token numbers with token names.  Removing the #define statements
 145   helps to sanitize the global namespace during preprocessing, but POSIX Yacc
 146   requires them.  Bison still generates an enum for token names in all cases.
 147
 148 * Handling of traditional Yacc prologue blocks is now more consistent but
 149   potentially incompatible with previous releases of Bison.
 150
 151   As before, you declare prologue blocks in your grammar file with the
 152   `%{ ... %}' syntax.  To generate the pre-prologue, Bison concatenates all
 153   prologue blocks that you've declared before the first %union.  To generate
 154   the post-prologue, Bison concatenates all prologue blocks that you've
 155   declared after the first %union.
 156
 157   Previous releases of Bison inserted the pre-prologue into both the header
 158   file and the code file in all cases except for LALR(1) parsers in C.  In the
 159   latter case, Bison inserted it only into the code file.  For parsers in C++,
 160   the point of insertion was before any token definitions (which associate
 161   token numbers with names).  For parsers in C, the point of insertion was
 162   after the token definitions.
 163
 164   Now, Bison never inserts the pre-prologue into the header file.  In the code
 165   file, it always inserts it before the token definitions.
 166
 167 * Bison now provides a more flexible alternative to the traditional Yacc
 168   prologue blocks: %before-header, %start-header, %end-header, and
 169   %after-header.
 170
 171   For example, the following declaration order in the grammar file reflects the
 172   order in which Bison will output these code blocks.  However, you are free to
 173   declare these code blocks in your grammar file in whatever order is most
 174   convenient for you:
 175
 176     %before-header {
 177       /* Bison treats this block like a pre-prologue block: it inserts it into
 178        * the code file before the contents of the header file.  It does *not*
 179        * insert it into the header file.  This is a good place to put
 180        * #include's that you want at the top of your code file.  A common
 181        * example is `#include "system.h"'.  */
 182     }
 183     %start-header {
 184       /* Bison inserts this block into both the header file and the code file.
 185        * In both files, the point of insertion is before any Bison-generated
 186        * token, semantic type, location type, and class definitions.  This is a
 187        * good place to define %union dependencies, for example.  */
 188     }
 189     %union {
 190       /* Unlike the traditional Yacc prologue blocks, the output order for the
 191        * new %*-header blocks is not affected by their declaration position
 192        * relative to any %union in the grammar file.  */
 193     }
 194     %end-header {
 195       /* Bison inserts this block into both the header file and the code file.
 196        * In both files, the point of insertion is after the Bison-generated
 197        * definitions.  This is a good place to declare or define public
 198        * functions or data structures that depend on the Bison-generated
 199        * definitions.  */
 200     }
 201     %after-header {
 202       /* Bison treats this block like a post-prologue block: it inserts it into
 203        * the code file after the contents of the header file.  It does *not*
 204        * insert it into the header file.  This is a good place to declare or
 205        * define internal functions or data structures that depend on the
 206        * Bison-generated definitions.  */
 207     }
 208
 209   If you have multiple occurrences of any one of the above declarations, Bison
 210   will concatenate the contents in declaration order.
 211
 212   [Although we failed to mention this here in the 2.3a release, the prologue
 213   alternatives were experimental, and they were rewritten in future versions.]
 214
 215 * The option `--report=look-ahead' has been changed to `--report=lookahead'.
 216   The old spelling still works, but is not documented and may be removed
 217   in a future release.
 218
 219 Changes in version 2.3, 2006-06-05:
 220
 221 * GLR grammars should now use `YYRECOVERING ()' instead of `YYRECOVERING',
 222   for compatibility with LALR(1) grammars.
 223
 224 * It is now documented that any definition of YYSTYPE or YYLTYPE should
 225   be to a type name that does not contain parentheses or brackets.
 226
 227 Changes in version 2.2, 2006-05-19:
 228
 229 * The distribution terms for all Bison-generated parsers now permit
 230   using the parsers in nonfree programs.  Previously, this permission
 231   was granted only for Bison-generated LALR(1) parsers in C.
 232
 233 * %name-prefix changes the namespace name in C++ outputs.
 234
 235 * The C++ parsers export their token_type.
 236
 237 * Bison now allows multiple %union declarations, and concatenates
 238   their contents together.
 239
 240 * New warning: unused values
 241   Right-hand side symbols whose values are not used are reported,
 242   if the symbols have destructors.  For instance:
 243
 244      exp: exp "?" exp ":" exp { $1 ? $1 : $3; }
 245         | exp "+" exp
 246         ;
 247
 248   will trigger a warning about $$ and $5 in the first rule, and $3 in
 249   the second ($1 is copied to $$ by the default rule).  This example
 250   most likely contains three errors, and could be rewritten as:
 251
 252      exp: exp "?" exp ":" exp
 253             { $$ = $1 ? $3 : $5; free ($1 ? $5 : $3); free ($1); }
 254         | exp "+" exp
 255             { $$ = $1 ? $1 : $3; if ($1) free ($3); }
 256         ;
 257
 258   However, if the original actions were really intended, memory leaks
 259   and all, the warnings can be suppressed by letting Bison believe the
 260   values are used, e.g.:
 261
 262      exp: exp "?" exp ":" exp { $1 ? $1 : $3; (void) ($$, $5); }
 263         | exp "+" exp         { $$ = $1; (void) $3; }
 264         ;
 265
 266   If there are mid-rule actions, the warning is issued if no action
 267   uses it.  The following triggers no warning: $1 and $3 are used.
 268
 269      exp: exp { push ($1); } '+' exp { push ($3); sum (); };
 270
 271   The warning is intended to help catching lost values and memory leaks.
 272   If a value is ignored, its associated memory typically is not reclaimed.
 273
 274 * %destructor vs. YYABORT, YYACCEPT, and YYERROR.
 275   Destructors are now called when user code invokes YYABORT, YYACCEPT,
 276   and YYERROR, for all objects on the stack, other than objects
 277   corresponding to the right-hand side of the current rule.
 278
 279 * %expect, %expect-rr
 280   Incorrect numbers of expected conflicts are now actual errors,
 281   instead of warnings.
 282
 283 * GLR, YACC parsers.
 284   The %parse-params are available in the destructors (and the
 285   experimental printers) as per the documentation.
 286
 287 * Bison now warns if it finds a stray `$' or `@' in an action.
 288
 289 * %require "VERSION"
 290   This specifies that the grammar file depends on features implemented
 291   in Bison version VERSION or higher.
 292
 293 * lalr1.cc: The token and value types are now class members.
 294   The tokens were defined as free form enums and cpp macros.  YYSTYPE
 295   was defined as a free form union.  They are now class members:
 296   tokens are enumerations of the `yy::parser::token' struct, and the
 297   semantic values have the `yy::parser::semantic_type' type.
 298
 299   If you do not want or can update to this scheme, the directive
 300   `%define "global_tokens_and_yystype" "1"' triggers the global
 301   definition of tokens and YYSTYPE.  This change is suitable both
 302   for previous releases of Bison, and this one.
 303
 304   If you wish to update, then make sure older version of Bison will
 305   fail using `%require "2.2"'.
 306
 307 * DJGPP support added.
 308 \f
 309 Changes in version 2.1, 2005-09-16:
 310
 311 * The C++ lalr1.cc skeleton supports %lex-param.
 312
 313 * Bison-generated parsers now support the translation of diagnostics like
 314   "syntax error" into languages other than English.  The default
 315   language is still English.  For details, please see the new
 316   Internationalization section of the Bison manual.  Software
 317   distributors should also see the new PACKAGING file.  Thanks to
 318   Bruno Haible for this new feature.
 319
 320 * Wording in the Bison-generated parsers has been changed slightly to
 321   simplify translation.  In particular, the message "memory exhausted"
 322   has replaced "parser stack overflow", as the old message was not
 323   always accurate for modern Bison-generated parsers.
 324
 325 * Destructors are now called when the parser aborts, for all symbols left
 326   behind on the stack.  Also, the start symbol is now destroyed after a
 327   successful parse.  In both cases, the behavior was formerly inconsistent.
 328
 329 * When generating verbose diagnostics, Bison-generated parsers no longer
 330   quote the literal strings associated with tokens.  For example, for
 331   a syntax error associated with '%token NUM "number"' they might
 332   print 'syntax error, unexpected number' instead of 'syntax error,
 333   unexpected "number"'.
 334 \f
 335 Changes in version 2.0, 2004-12-25:
 336
 337 * Possibly-incompatible changes
 338
 339   - Bison-generated parsers no longer default to using the alloca function
 340     (when available) to extend the parser stack, due to widespread
 341     problems in unchecked stack-overflow detection.  You can "#define
 342     YYSTACK_USE_ALLOCA 1" to require the use of alloca, but please read
 343     the manual to determine safe values for YYMAXDEPTH in that case.
 344
 345   - Error token location.
 346     During error recovery, the location of the syntax error is updated
 347     to cover the whole sequence covered by the error token: it includes
 348     the shifted symbols thrown away during the first part of the error
 349     recovery, and the lookahead rejected during the second part.
 350
 351   - Semicolon changes:
 352     . Stray semicolons are no longer allowed at the start of a grammar.
 353     . Semicolons are now required after in-grammar declarations.
 354
 355   - Unescaped newlines are no longer allowed in character constants or
 356     string literals.  They were never portable, and GCC 3.4.0 has
 357     dropped support for them.  Better diagnostics are now generated if
 358     forget a closing quote.
 359
 360   - NUL bytes are no longer allowed in Bison string literals, unfortunately.
 361
 362 * New features
 363
 364   - GLR grammars now support locations.
 365
 366   - New directive: %initial-action.
 367     This directive allows the user to run arbitrary code (including
 368     initializing @$) from yyparse before parsing starts.
 369
 370   - A new directive "%expect-rr N" specifies the expected number of
 371     reduce/reduce conflicts in GLR parsers.
 372
 373   - %token numbers can now be hexadecimal integers, e.g., `%token FOO 0x12d'.
 374     This is a GNU extension.
 375
 376   - The option `--report=lookahead' was changed to `--report=look-ahead'.
 377     [However, this was changed back after 2.3.]
 378
 379   - Experimental %destructor support has been added to lalr1.cc.
 380
 381   - New configure option --disable-yacc, to disable installation of the
 382     yacc command and -ly library introduced in 1.875 for POSIX conformance.
 383
 384 * Bug fixes
 385
 386   - For now, %expect-count violations are now just warnings, not errors.
 387     This is for compatibility with Bison 1.75 and earlier (when there are
 388     reduce/reduce conflicts) and with Bison 1.30 and earlier (when there
 389     are too many or too few shift/reduce conflicts).  However, in future
 390     versions of Bison we plan to improve the %expect machinery so that
 391     these violations will become errors again.
 392
 393   - Within Bison itself, numbers (e.g., goto numbers) are no longer
 394     arbitrarily limited to 16-bit counts.
 395
 396   - Semicolons are now allowed before "|" in grammar rules, as POSIX requires.
 397 \f
 398 Changes in version 1.875, 2003-01-01:
 399
 400 * The documentation license has been upgraded to version 1.2
 401   of the GNU Free Documentation License.
 402
 403 * syntax error processing
 404
 405   - In Yacc-style parsers YYLLOC_DEFAULT is now used to compute error
 406     locations too.  This fixes bugs in error-location computation.
 407
 408   - %destructor
 409     It is now possible to reclaim the memory associated to symbols
 410     discarded during error recovery.  This feature is still experimental.
 411
 412   - %error-verbose
 413     This new directive is preferred over YYERROR_VERBOSE.
 414
 415   - #defining yyerror to steal internal variables is discouraged.
 416     It is not guaranteed to work forever.
 417
 418 * POSIX conformance
 419
 420   - Semicolons are once again optional at the end of grammar rules.
 421     This reverts to the behavior of Bison 1.33 and earlier, and improves
 422     compatibility with Yacc.
 423
 424   - `parse error' -> `syntax error'
 425     Bison now uniformly uses the term `syntax error'; formerly, the code
 426     and manual sometimes used the term `parse error' instead.  POSIX
 427     requires `syntax error' in diagnostics, and it was thought better to
 428     be consistent.
 429
 430   - The documentation now emphasizes that yylex and yyerror must be
 431     declared before use.  C99 requires this.
 432
 433   - Bison now parses C99 lexical constructs like UCNs and
 434     backslash-newline within C escape sequences, as POSIX 1003.1-2001 requires.
 435
 436   - File names are properly escaped in C output.  E.g., foo\bar.y is
 437     output as "foo\\bar.y".
 438
 439   - Yacc command and library now available
 440     The Bison distribution now installs a `yacc' command, as POSIX requires.
 441     Also, Bison now installs a small library liby.a containing
 442     implementations of Yacc-compatible yyerror and main functions.
 443     This library is normally not useful, but POSIX requires it.
 444
 445   - Type clashes now generate warnings, not errors.
 446
 447   - If the user does not define YYSTYPE as a macro, Bison now declares it
 448     using typedef instead of defining it as a macro.
 449     For consistency, YYLTYPE is also declared instead of defined.
 450
 451 * Other compatibility issues
 452
 453   - %union directives can now have a tag before the `{', e.g., the
 454     directive `%union foo {...}' now generates the C code
 455     `typedef union foo { ... } YYSTYPE;'; this is for Yacc compatibility.
 456     The default union tag is `YYSTYPE', for compatibility with Solaris 9 Yacc.
 457     For consistency, YYLTYPE's struct tag is now `YYLTYPE' not `yyltype'.
 458     This is for compatibility with both Yacc and Bison 1.35.
 459
 460   - `;' is output before the terminating `}' of an action, for
 461     compatibility with Bison 1.35.
 462
 463   - Bison now uses a Yacc-style format for conflict reports, e.g.,
 464     `conflicts: 2 shift/reduce, 1 reduce/reduce'.
 465
 466   - `yystype' and `yyltype' are now obsolescent macros instead of being
 467     typedefs or tags; they are no longer documented and are planned to be
 468     withdrawn in a future release.
 469
 470 * GLR parser notes
 471
 472   - GLR and inline
 473     Users of Bison have to decide how they handle the portability of the
 474     C keyword `inline'.
 475
 476   - `parsing stack overflow...' -> `parser stack overflow'
 477     GLR parsers now report `parser stack overflow' as per the Bison manual.
 478
 479 * Bison now warns if it detects conflicting outputs to the same file,
 480   e.g., it generates a warning for `bison -d -o foo.h foo.y' since
 481   that command outputs both code and header to foo.h.
 482
 483 * #line in output files
 484   - --no-line works properly.
 485
 486 * Bison can no longer be built by a K&R C compiler; it requires C89 or
 487   later to be built.  This change originally took place a few versions
 488   ago, but nobody noticed until we recently asked someone to try
 489   building Bison with a K&R C compiler.
 490 \f
 491 Changes in version 1.75, 2002-10-14:
 492
 493 * Bison should now work on 64-bit hosts.
 494
 495 * Indonesian translation thanks to Tedi Heriyanto.
 496
 497 * GLR parsers
 498   Fix spurious parse errors.
 499
 500 * Pure parsers
 501   Some people redefine yyerror to steal yyparse' private variables.
 502   Reenable this trick until an official feature replaces it.
 503
 504 * Type Clashes
 505   In agreement with POSIX and with other Yaccs, leaving a default
 506   action is valid when $$ is untyped, and $1 typed:
 507
 508         untyped: ... typed;
 509
 510   but the converse remains an error:
 511
 512         typed: ... untyped;
 513
 514 * Values of mid-rule actions
 515   The following code:
 516
 517         foo: { ... } { $$ = $1; } ...
 518
 519   was incorrectly rejected: $1 is defined in the second mid-rule
 520   action, and is equal to the $$ of the first mid-rule action.
 521 \f
 522 Changes in version 1.50, 2002-10-04:
 523
 524 * GLR parsing
 525   The declaration
 526      %glr-parser
 527   causes Bison to produce a Generalized LR (GLR) parser, capable of handling
 528   almost any context-free grammar, ambiguous or not.  The new declarations
 529   %dprec and %merge on grammar rules allow parse-time resolution of
 530   ambiguities.  Contributed by Paul Hilfinger.
 531
 532   Unfortunately Bison 1.50 does not work properly on 64-bit hosts
 533   like the Alpha, so please stick to 32-bit hosts for now.
 534
 535 * Output Directory
 536   When not in Yacc compatibility mode, when the output file was not
 537   specified, running `bison foo/bar.y' created `foo/bar.c'.  It
 538   now creates `bar.c'.
 539
 540 * Undefined token
 541   The undefined token was systematically mapped to 2 which prevented
 542   the use of 2 by the user.  This is no longer the case.
 543
 544 * Unknown token numbers
 545   If yylex returned an out of range value, yyparse could die.  This is
 546   no longer the case.
 547
 548 * Error token
 549   According to POSIX, the error token must be 256.
 550   Bison extends this requirement by making it a preference: *if* the
 551   user specified that one of her tokens is numbered 256, then error
 552   will be mapped onto another number.
 553
 554 * Verbose error messages
 555   They no longer report `..., expecting error or...' for states where
 556   error recovery is possible.
 557
 558 * End token
 559   Defaults to `$end' instead of `$'.
 560
 561 * Error recovery now conforms to documentation and to POSIX
 562   When a Bison-generated parser encounters a syntax error, it now pops
 563   the stack until it finds a state that allows shifting the error
 564   token.  Formerly, it popped the stack until it found a state that
 565   allowed some non-error action other than a default reduction on the
 566   error token.  The new behavior has long been the documented behavior,
 567   and has long been required by POSIX.  For more details, please see
 568   Paul Eggert, "Reductions during Bison error handling" (2002-05-20)
 569   <http://lists.gnu.org/archive/html/bug-bison/2002-05/msg00038.html>.
 570
 571 * Traces
 572   Popped tokens and nonterminals are now reported.
 573
 574 * Larger grammars
 575   Larger grammars are now supported (larger token numbers, larger grammar
 576   size (= sum of the LHS and RHS lengths), larger LALR tables).
 577   Formerly, many of these numbers ran afoul of 16-bit limits;
 578   now these limits are 32 bits on most hosts.
 579
 580 * Explicit initial rule
 581   Bison used to play hacks with the initial rule, which the user does
 582   not write.  It is now explicit, and visible in the reports and
 583   graphs as rule 0.
 584
 585 * Useless rules
 586   Before, Bison reported the useless rules, but, although not used,
 587   included them in the parsers.  They are now actually removed.
 588
 589 * Useless rules, useless nonterminals
 590   They are now reported, as a warning, with their locations.
 591
 592 * Rules never reduced
 593   Rules that can never be reduced because of conflicts are now
 594   reported.
 595
 596 * Incorrect `Token not used'
 597   On a grammar such as
 598
 599            %token useless useful
 600            %%
 601            exp: '0' %prec useful;
 602
 603   where a token was used to set the precedence of the last rule,
 604   bison reported both `useful' and `useless' as useless tokens.
 605
 606 * Revert the C++ namespace changes introduced in 1.31
 607   as they caused too many portability hassles.
 608
 609 * Default locations
 610   By an accident of design, the default computation of @$ was
 611   performed after another default computation was performed: @$ = @1.
 612   The latter is now removed: YYLLOC_DEFAULT is fully responsible of
 613   the computation of @$.
 614
 615 * Token end-of-file
 616   The token end of file may be specified by the user, in which case,
 617   the user symbol is used in the reports, the graphs, and the verbose
 618   error messages instead of `$end', which remains being the default.
 619   For instance
 620      %token MYEOF 0
 621   or
 622      %token MYEOF 0 "end of file"
 623
 624 * Semantic parser
 625   This old option, which has been broken for ages, is removed.
 626
 627 * New translations
 628   Brazilian Portuguese, thanks to Alexandre Folle de Menezes.
 629   Croatian, thanks to Denis Lackovic.
 630
 631 * Incorrect token definitions
 632   When given `%token 'a' "A"', Bison used to output `#define 'a' 65'.
 633
 634 * Token definitions as enums
 635   Tokens are output both as the traditional #define's, and, provided
 636   the compiler supports ANSI C or is a C++ compiler, as enums.
 637   This lets debuggers display names instead of integers.
 638
 639 * Reports
 640   In addition to --verbose, bison supports --report=THINGS, which
 641   produces additional information:
 642   - itemset
 643     complete the core item sets with their closure
 644   - lookahead [changed to `look-ahead' in 1.875e through 2.3, but changed back]
 645     explicitly associate lookahead tokens to items
 646   - solved
 647     describe shift/reduce conflicts solving.
 648     Bison used to systematically output this information on top of
 649     the report.  Solved conflicts are now attached to their states.
 650
 651 * Type clashes
 652   Previous versions don't complain when there is a type clash on
 653   the default action if the rule has a mid-rule action, such as in:
 654
 655       %type <foo> bar
 656       %%
 657       bar: '0' {} '0';
 658
 659   This is fixed.
 660
 661 * GNU M4 is now required when using Bison.
 662 \f
 663 Changes in version 1.35, 2002-03-25:
 664
 665 * C Skeleton
 666   Some projects use Bison's C parser with C++ compilers, and define
 667   YYSTYPE as a class.  The recent adjustment of C parsers for data
 668   alignment and 64 bit architectures made this impossible.
 669
 670   Because for the time being no real solution for C++ parser
 671   generation exists, kludges were implemented in the parser to
 672   maintain this use.  In the future, when Bison has C++ parsers, this
 673   kludge will be disabled.
 674
 675   This kludge also addresses some C++ problems when the stack was
 676   extended.
 677 \f
 678 Changes in version 1.34, 2002-03-12:
 679
 680 * File name clashes are detected
 681   $ bison foo.y -d -o foo.x
 682   fatal error: header and parser would both be named `foo.x'
 683
 684 * A missing `;' at the end of a rule triggers a warning
 685   In accordance with POSIX, and in agreement with other
 686   Yacc implementations, Bison will mandate this semicolon in the near
 687   future.  This eases the implementation of a Bison parser of Bison
 688   grammars by making this grammar LALR(1) instead of LR(2).  To
 689   facilitate the transition, this release introduces a warning.
 690
 691 * Revert the C++ namespace changes introduced in 1.31, as they caused too
 692   many portability hassles.
 693
 694 * DJGPP support added.
 695
 696 * Fix test suite portability problems.
 697 \f
 698 Changes in version 1.33, 2002-02-07:
 699
 700 * Fix C++ issues
 701   Groff could not be compiled for the definition of size_t was lacking
 702   under some conditions.
 703
 704 * Catch invalid @n
 705   As is done with $n.
 706 \f
 707 Changes in version 1.32, 2002-01-23:
 708
 709 * Fix Yacc output file names
 710
 711 * Portability fixes
 712
 713 * Italian, Dutch translations
 714 \f
 715 Changes in version 1.31, 2002-01-14:
 716
 717 * Many Bug Fixes
 718
 719 * GNU Gettext and %expect
 720   GNU Gettext asserts 10 s/r conflicts, but there are 7.  Now that
 721   Bison dies on incorrect %expectations, we fear there will be
 722   too many bug reports for Gettext, so _for the time being_, %expect
 723   does not trigger an error when the input file is named `plural.y'.
 724
 725 * Use of alloca in parsers
 726   If YYSTACK_USE_ALLOCA is defined to 0, then the parsers will use
 727   malloc exclusively.  Since 1.29, but was not NEWS'ed.
 728
 729   alloca is used only when compiled with GCC, to avoid portability
 730   problems as on AIX.
 731
 732 * yyparse now returns 2 if memory is exhausted; formerly it dumped core.
 733
 734 * When the generated parser lacks debugging code, YYDEBUG is now 0
 735   (as POSIX requires) instead of being undefined.
 736
 737 * User Actions
 738   Bison has always permitted actions such as { $$ = $1 }: it adds the
 739   ending semicolon.  Now if in Yacc compatibility mode, the semicolon
 740   is no longer output: one has to write { $$ = $1; }.
 741
 742 * Better C++ compliance
 743   The output parsers try to respect C++ namespaces.
 744   [This turned out to be a failed experiment, and it was reverted later.]
 745
 746 * Reduced Grammars
 747   Fixed bugs when reporting useless nonterminals.
 748
 749 * 64 bit hosts
 750   The parsers work properly on 64 bit hosts.
 751
 752 * Error messages
 753   Some calls to strerror resulted in scrambled or missing error messages.
 754
 755 * %expect
 756   When the number of shift/reduce conflicts is correct, don't issue
 757   any warning.
 758
 759 * The verbose report includes the rule line numbers.
 760
 761 * Rule line numbers are fixed in traces.
 762
 763 * Swedish translation
 764
 765 * Parse errors
 766   Verbose parse error messages from the parsers are better looking.
 767   Before: parse error: unexpected `'/'', expecting `"number"' or `'-'' or `'(''
 768      Now: parse error: unexpected '/', expecting "number" or '-' or '('
 769
 770 * Fixed parser memory leaks.
 771   When the generated parser was using malloc to extend its stacks, the
 772   previous allocations were not freed.
 773
 774 * Fixed verbose output file.
 775   Some newlines were missing.
 776   Some conflicts in state descriptions were missing.
 777
 778 * Fixed conflict report.
 779   Option -v was needed to get the result.
 780
 781 * %expect
 782   Was not used.
 783   Mismatches are errors, not warnings.
 784
 785 * Fixed incorrect processing of some invalid input.
 786
 787 * Fixed CPP guards: 9foo.h uses BISON_9FOO_H instead of 9FOO_H.
 788
 789 * Fixed some typos in the documentation.
 790
 791 * %token MY_EOF 0 is supported.
 792   Before, MY_EOF was silently renumbered as 257.
 793
 794 * doc/refcard.tex is updated.
 795
 796 * %output, %file-prefix, %name-prefix.
 797   New.
 798
 799 * --output
 800   New, aliasing `--output-file'.
 801 \f
 802 Changes in version 1.30, 2001-10-26:
 803
 804 * `--defines' and `--graph' have now an optional argument which is the
 805   output file name. `-d' and `-g' do not change; they do not take any
 806   argument.
 807
 808 * `%source_extension' and `%header_extension' are removed, failed
 809   experiment.
 810
 811 * Portability fixes.
 812 \f
 813 Changes in version 1.29, 2001-09-07:
 814
 815 * The output file does not define const, as this caused problems when used
 816   with common autoconfiguration schemes.  If you still use ancient compilers
 817   that lack const, compile with the equivalent of the C compiler option
 818   `-Dconst='.  autoconf's AC_C_CONST macro provides one way to do this.
 819
 820 * Added `-g' and `--graph'.
 821
 822 * The Bison manual is now distributed under the terms of the GNU FDL.
 823
 824 * The input and the output files has automatically a similar extension.
 825
 826 * Russian translation added.
 827
 828 * NLS support updated; should hopefully be less troublesome.
 829
 830 * Added the old Bison reference card.
 831
 832 * Added `--locations' and `%locations'.
 833
 834 * Added `-S' and `--skeleton'.
 835
 836 * `%raw', `-r', `--raw' is disabled.
 837
 838 * Special characters are escaped when output.  This solves the problems
 839   of the #line lines with path names including backslashes.
 840
 841 * New directives.
 842   `%yacc', `%fixed_output_files', `%defines', `%no_parser', `%verbose',
 843   `%debug', `%source_extension' and `%header_extension'.
 844
 845 * @$
 846   Automatic location tracking.
 847 \f
 848 Changes in version 1.28, 1999-07-06:
 849
 850 * Should compile better now with K&R compilers.
 851
 852 * Added NLS.
 853
 854 * Fixed a problem with escaping the double quote character.
 855
 856 * There is now a FAQ.
 857 \f
 858 Changes in version 1.27:
 859
 860 * The make rule which prevented bison.simple from being created on
 861   some systems has been fixed.
 862 \f
 863 Changes in version 1.26:
 864
 865 * Bison now uses automake.
 866
 867 * New mailing lists: <bug-bison@gnu.org> and <help-bison@gnu.org>.
 868
 869 * Token numbers now start at 257 as previously documented, not 258.
 870
 871 * Bison honors the TMPDIR environment variable.
 872
 873 * A couple of buffer overruns have been fixed.
 874
 875 * Problems when closing files should now be reported.
 876
 877 * Generated parsers should now work even on operating systems which do
 878   not provide alloca().
 879 \f
 880 Changes in version 1.25, 1995-10-16:
 881
 882 * Errors in the input grammar are not fatal; Bison keeps reading
 883 the grammar file, and reports all the errors found in it.
 884
 885 * Tokens can now be specified as multiple-character strings: for
 886 example, you could use "<=" for a token which looks like <=, instead
 887 of chosing a name like LESSEQ.
 888
 889 * The %token_table declaration says to write a table of tokens (names
 890 and numbers) into the parser file.  The yylex function can use this
 891 table to recognize multiple-character string tokens, or for other
 892 purposes.
 893
 894 * The %no_lines declaration says not to generate any #line preprocessor
 895 directives in the parser file.
 896
 897 * The %raw declaration says to use internal Bison token numbers, not
 898 Yacc-compatible token numbers, when token names are defined as macros.
 899
 900 * The --no-parser option produces the parser tables without including
 901 the parser engine; a project can now use its own parser engine.
 902 The actions go into a separate file called NAME.act, in the form of
 903 a switch statement body.
 904 \f
 905 Changes in version 1.23:
 906
 907 The user can define YYPARSE_PARAM as the name of an argument to be
 908 passed into yyparse.  The argument should have type void *.  It should
 909 actually point to an object.  Grammar actions can access the variable
 910 by casting it to the proper pointer type.
 911
 912 Line numbers in output file corrected.
 913 \f
 914 Changes in version 1.22:
 915
 916 --help option added.
 917 \f
 918 Changes in version 1.20:
 919
 920 Output file does not redefine const for C++.
 921
 922 Local Variables:
 923 mode: outline
 924 End:
 925
 926 -----
 927
 928 Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003,
 929 2004, 2005, 2006, 2007 Free Software Foundation, Inc.
 930
 931 This file is part of Bison, the GNU Compiler Compiler.
 932
 933 Bison is free software; you can redistribute it and/or modify
 934 it under the terms of the GNU General Public License as published by
 935 the Free Software Foundation; either version 2, or (at your option)
 936 any later version.
 937
 938 Bison is distributed in the hope that it will be useful,
 939 but WITHOUT ANY WARRANTY; without even the implied warranty of
 940 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 941 GNU General Public License for more details.
 942
 943 You should have received a copy of the GNU General Public License
 944 along with autoconf; see the file COPYING.  If not, write to
 945 the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
 946 Boston, MA 02110-1301, USA.