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 * When instructed to generate a `.output' file including lookahead sets
  19   (using `--report=lookahead', for example), Bison now prints each reduction's
  20   lookahead set only next to the associated state's one item that (1) is
  21   associated with the same rule as the reduction and (2) has its dot at the end
  22   of its RHS.  Previously, Bison also erroneously printed the lookahead set
  23   next to all of the state's other items associated with the same rule.  This
  24   bug affected only the `.output' file and not the generated parser source
  25   code.
  26
  27 * The -g and --graph options now output graphs in Graphviz DOT format,
  28   not VCG format.
  29
  30 * An experimental directive %language specifies the language of the
  31   generated parser, which can be C (the default) or C++.  This
  32   directive affects the skeleton used, and the names of the generated
  33   files if the grammar file's name ends in ".y".
  34
  35 * The grammar file may now specify the name of the parser header file using
  36   %defines.  For example:
  37
  38     %defines "parser.h"
  39
  40 * The `=' that used to be required in the following directives is now
  41   deprecated:
  42
  43     %file-prefix "parser"
  44     %name-prefix "c_"
  45     %output "parser.c"
  46
  47 * The quotes around NAME that used to be required in the following directive
  48   are now deprecated:
  49
  50     %define NAME "VALUE"
  51
  52 * Bison 2.3a provided a new set of directives as a more flexible alternative to
  53   the traditional Yacc prologue blocks.  Those have now been consolidated into
  54   a single %code directive with an optional qualifier field, which identifies
  55   the purpose of the code and thus the location(s) where Bison should generate
  56   it:
  57
  58     1. `%code          {CODE}' replaces `%after-header  {CODE}'
  59     2. `%code requires {CODE}' replaces `%start-header  {CODE}'
  60     3. `%code provides {CODE}' replaces `%end-header    {CODE}'
  61     4. `%code top      {CODE}' replaces `%before-header {CODE}'
  62
  63   See the %code entries in section `Bison Declaration Summary' in the Bison
  64   manual for a summary of the new functionality.  See the new section `Prologue
  65   Alternatives' for a detailed discussion including the advantages of %code
  66   over the traditional Yacc prologues.
  67
  68   The prologue alternatives are experimental.  More user feedback will help to
  69   determine whether they should become permanent features.
  70
  71 * Revised warning: unset or unused mid-rule values
  72
  73   Since Bison 2.2, Bison has warned about mid-rule values that are set but not
  74   used within any of the actions of the parent rule.  For example, Bison warns
  75   about unused $2 in:
  76
  77     exp: '1' { $$ = 1; } '+' exp { $$ = $1 + $4; };
  78
  79   Now, Bison also warns about mid-rule values that are used but not set.  For
  80   example, Bison warns about unset $$ in the mid-rule action in:
  81
  82     exp: '1' { $1 = 1; } '+' exp { $$ = $2 + $4; };
  83
  84   However, Bison now disables both of these warnings by default since they
  85   sometimes prove to be false alarms in existing grammars employing the Yacc
  86   constructs $0 or $-N (where N is some positive integer).
  87
  88   To enable these warnings, specify the flag `--warnings=midrule-values' or
  89   `-W', which is a synonym for `--warnings=all'.
  90
  91 * Bison now recognizes two separate kinds of default %destructor's and
  92   %printer's:
  93
  94     1. Place `<*>' in a %destructor/%printer symbol list to define a default
  95        %destructor/%printer for all grammar symbols for which you have formally
  96        declared semantic type tags.
  97
  98     2. Place `<>' in a %destructor/%printer symbol list to define a default
  99        %destructor/%printer for all grammar symbols without declared semantic
 100        type tags.
 101
 102   Bison no longer supports the `%symbol-default' notation from Bison 2.3a.
 103   `<*>' and `<>' combined achieve the same effect with one exception: Bison no
 104   longer applies any %destructor to a mid-rule value if that mid-rule value is
 105   not actually ever referenced using either $$ or $n in a semantic action.
 106
 107   The default %destructor's and %printer's are experimental.  More user
 108   feedback will help to determine whether they should become permanent
 109   features.
 110
 111   See the section `Freeing Discarded Symbols' in the Bison manual for further
 112   details.
 113
 114 Changes in version 2.3a, 2006-09-13:
 115
 116 * Instead of %union, you can define and use your own union type
 117   YYSTYPE if your grammar contains at least one <type> tag.
 118   Your YYSTYPE need not be a macro; it can be a typedef.
 119   This change is for compatibility with other Yacc implementations,
 120   and is required by POSIX.
 121
 122 * Locations columns and lines start at 1.
 123   In accordance with the GNU Coding Standards and Emacs.
 124
 125 * You may now declare per-type and default %destructor's and %printer's:
 126
 127   For example:
 128
 129     %union { char *string; }
 130     %token <string> STRING1
 131     %token <string> STRING2
 132     %type  <string> string1
 133     %type  <string> string2
 134     %union { char character; }
 135     %token <character> CHR
 136     %type  <character> chr
 137     %destructor { free ($$); } %symbol-default
 138     %destructor { free ($$); printf ("%d", @$.first_line); } STRING1 string1
 139     %destructor { } <character>
 140
 141   guarantees that, when the parser discards any user-defined symbol that has a
 142   semantic type tag other than `<character>', it passes its semantic value to
 143   `free'.  However, when the parser discards a `STRING1' or a `string1', it
 144   also prints its line number to `stdout'.  It performs only the second
 145   `%destructor' in this case, so it invokes `free' only once.
 146
 147   [Although we failed to mention this here in the 2.3a release, the default
 148   %destructor's and %printer's were experimental, and they were rewritten in
 149   future versions.]
 150
 151 * Except for LALR(1) parsers in C with POSIX Yacc emulation enabled (with `-y',
 152   `--yacc', or `%yacc'), Bison no longer generates #define statements for
 153   associating token numbers with token names.  Removing the #define statements
 154   helps to sanitize the global namespace during preprocessing, but POSIX Yacc
 155   requires them.  Bison still generates an enum for token names in all cases.
 156
 157 * Handling of traditional Yacc prologue blocks is now more consistent but
 158   potentially incompatible with previous releases of Bison.
 159
 160   As before, you declare prologue blocks in your grammar file with the
 161   `%{ ... %}' syntax.  To generate the pre-prologue, Bison concatenates all
 162   prologue blocks that you've declared before the first %union.  To generate
 163   the post-prologue, Bison concatenates all prologue blocks that you've
 164   declared after the first %union.
 165
 166   Previous releases of Bison inserted the pre-prologue into both the header
 167   file and the code file in all cases except for LALR(1) parsers in C.  In the
 168   latter case, Bison inserted it only into the code file.  For parsers in C++,
 169   the point of insertion was before any token definitions (which associate
 170   token numbers with names).  For parsers in C, the point of insertion was
 171   after the token definitions.
 172
 173   Now, Bison never inserts the pre-prologue into the header file.  In the code
 174   file, it always inserts it before the token definitions.
 175
 176 * Bison now provides a more flexible alternative to the traditional Yacc
 177   prologue blocks: %before-header, %start-header, %end-header, and
 178   %after-header.
 179
 180   For example, the following declaration order in the grammar file reflects the
 181   order in which Bison will output these code blocks.  However, you are free to
 182   declare these code blocks in your grammar file in whatever order is most
 183   convenient for you:
 184
 185     %before-header {
 186       /* Bison treats this block like a pre-prologue block: it inserts it into
 187        * the code file before the contents of the header file.  It does *not*
 188        * insert it into the header file.  This is a good place to put
 189        * #include's that you want at the top of your code file.  A common
 190        * example is `#include "system.h"'.  */
 191     }
 192     %start-header {
 193       /* Bison inserts this block into both the header file and the code file.
 194        * In both files, the point of insertion is before any Bison-generated
 195        * token, semantic type, location type, and class definitions.  This is a
 196        * good place to define %union dependencies, for example.  */
 197     }
 198     %union {
 199       /* Unlike the traditional Yacc prologue blocks, the output order for the
 200        * new %*-header blocks is not affected by their declaration position
 201        * relative to any %union in the grammar file.  */
 202     }
 203     %end-header {
 204       /* Bison inserts this block into both the header file and the code file.
 205        * In both files, the point of insertion is after the Bison-generated
 206        * definitions.  This is a good place to declare or define public
 207        * functions or data structures that depend on the Bison-generated
 208        * definitions.  */
 209     }
 210     %after-header {
 211       /* Bison treats this block like a post-prologue block: it inserts it into
 212        * the code file after the contents of the header file.  It does *not*
 213        * insert it into the header file.  This is a good place to declare or
 214        * define internal functions or data structures that depend on the
 215        * Bison-generated definitions.  */
 216     }
 217
 218   If you have multiple occurrences of any one of the above declarations, Bison
 219   will concatenate the contents in declaration order.
 220
 221   [Although we failed to mention this here in the 2.3a release, the prologue
 222   alternatives were experimental, and they were rewritten in future versions.]
 223
 224 * The option `--report=look-ahead' has been changed to `--report=lookahead'.
 225   The old spelling still works, but is not documented and may be removed
 226   in a future release.
 227
 228 Changes in version 2.3, 2006-06-05:
 229
 230 * GLR grammars should now use `YYRECOVERING ()' instead of `YYRECOVERING',
 231   for compatibility with LALR(1) grammars.
 232
 233 * It is now documented that any definition of YYSTYPE or YYLTYPE should
 234   be to a type name that does not contain parentheses or brackets.
 235
 236 Changes in version 2.2, 2006-05-19:
 237
 238 * The distribution terms for all Bison-generated parsers now permit
 239   using the parsers in nonfree programs.  Previously, this permission
 240   was granted only for Bison-generated LALR(1) parsers in C.
 241
 242 * %name-prefix changes the namespace name in C++ outputs.
 243
 244 * The C++ parsers export their token_type.
 245
 246 * Bison now allows multiple %union declarations, and concatenates
 247   their contents together.
 248
 249 * New warning: unused values
 250   Right-hand side symbols whose values are not used are reported,
 251   if the symbols have destructors.  For instance:
 252
 253      exp: exp "?" exp ":" exp { $1 ? $1 : $3; }
 254         | exp "+" exp
 255         ;
 256
 257   will trigger a warning about $$ and $5 in the first rule, and $3 in
 258   the second ($1 is copied to $$ by the default rule).  This example
 259   most likely contains three errors, and could be rewritten as:
 260
 261      exp: exp "?" exp ":" exp
 262             { $$ = $1 ? $3 : $5; free ($1 ? $5 : $3); free ($1); }
 263         | exp "+" exp
 264             { $$ = $1 ? $1 : $3; if ($1) free ($3); }
 265         ;
 266
 267   However, if the original actions were really intended, memory leaks
 268   and all, the warnings can be suppressed by letting Bison believe the
 269   values are used, e.g.:
 270
 271      exp: exp "?" exp ":" exp { $1 ? $1 : $3; (void) ($$, $5); }
 272         | exp "+" exp         { $$ = $1; (void) $3; }
 273         ;
 274
 275   If there are mid-rule actions, the warning is issued if no action
 276   uses it.  The following triggers no warning: $1 and $3 are used.
 277
 278      exp: exp { push ($1); } '+' exp { push ($3); sum (); };
 279
 280   The warning is intended to help catching lost values and memory leaks.
 281   If a value is ignored, its associated memory typically is not reclaimed.
 282
 283 * %destructor vs. YYABORT, YYACCEPT, and YYERROR.
 284   Destructors are now called when user code invokes YYABORT, YYACCEPT,
 285   and YYERROR, for all objects on the stack, other than objects
 286   corresponding to the right-hand side of the current rule.
 287
 288 * %expect, %expect-rr
 289   Incorrect numbers of expected conflicts are now actual errors,
 290   instead of warnings.
 291
 292 * GLR, YACC parsers.
 293   The %parse-params are available in the destructors (and the
 294   experimental printers) as per the documentation.
 295
 296 * Bison now warns if it finds a stray `$' or `@' in an action.
 297
 298 * %require "VERSION"
 299   This specifies that the grammar file depends on features implemented
 300   in Bison version VERSION or higher.
 301
 302 * lalr1.cc: The token and value types are now class members.
 303   The tokens were defined as free form enums and cpp macros.  YYSTYPE
 304   was defined as a free form union.  They are now class members:
 305   tokens are enumerations of the `yy::parser::token' struct, and the
 306   semantic values have the `yy::parser::semantic_type' type.
 307
 308   If you do not want or can update to this scheme, the directive
 309   `%define "global_tokens_and_yystype" "1"' triggers the global
 310   definition of tokens and YYSTYPE.  This change is suitable both
 311   for previous releases of Bison, and this one.
 312
 313   If you wish to update, then make sure older version of Bison will
 314   fail using `%require "2.2"'.
 315
 316 * DJGPP support added.
 317 \f
 318 Changes in version 2.1, 2005-09-16:
 319
 320 * The C++ lalr1.cc skeleton supports %lex-param.
 321
 322 * Bison-generated parsers now support the translation of diagnostics like
 323   "syntax error" into languages other than English.  The default
 324   language is still English.  For details, please see the new
 325   Internationalization section of the Bison manual.  Software
 326   distributors should also see the new PACKAGING file.  Thanks to
 327   Bruno Haible for this new feature.
 328
 329 * Wording in the Bison-generated parsers has been changed slightly to
 330   simplify translation.  In particular, the message "memory exhausted"
 331   has replaced "parser stack overflow", as the old message was not
 332   always accurate for modern Bison-generated parsers.
 333
 334 * Destructors are now called when the parser aborts, for all symbols left
 335   behind on the stack.  Also, the start symbol is now destroyed after a
 336   successful parse.  In both cases, the behavior was formerly inconsistent.
 337
 338 * When generating verbose diagnostics, Bison-generated parsers no longer
 339   quote the literal strings associated with tokens.  For example, for
 340   a syntax error associated with '%token NUM "number"' they might
 341   print 'syntax error, unexpected number' instead of 'syntax error,
 342   unexpected "number"'.
 343 \f
 344 Changes in version 2.0, 2004-12-25:
 345
 346 * Possibly-incompatible changes
 347
 348   - Bison-generated parsers no longer default to using the alloca function
 349     (when available) to extend the parser stack, due to widespread
 350     problems in unchecked stack-overflow detection.  You can "#define
 351     YYSTACK_USE_ALLOCA 1" to require the use of alloca, but please read
 352     the manual to determine safe values for YYMAXDEPTH in that case.
 353
 354   - Error token location.
 355     During error recovery, the location of the syntax error is updated
 356     to cover the whole sequence covered by the error token: it includes
 357     the shifted symbols thrown away during the first part of the error
 358     recovery, and the lookahead rejected during the second part.
 359
 360   - Semicolon changes:
 361     . Stray semicolons are no longer allowed at the start of a grammar.
 362     . Semicolons are now required after in-grammar declarations.
 363
 364   - Unescaped newlines are no longer allowed in character constants or
 365     string literals.  They were never portable, and GCC 3.4.0 has
 366     dropped support for them.  Better diagnostics are now generated if
 367     forget a closing quote.
 368
 369   - NUL bytes are no longer allowed in Bison string literals, unfortunately.
 370
 371 * New features
 372
 373   - GLR grammars now support locations.
 374
 375   - New directive: %initial-action.
 376     This directive allows the user to run arbitrary code (including
 377     initializing @$) from yyparse before parsing starts.
 378
 379   - A new directive "%expect-rr N" specifies the expected number of
 380     reduce/reduce conflicts in GLR parsers.
 381
 382   - %token numbers can now be hexadecimal integers, e.g., `%token FOO 0x12d'.
 383     This is a GNU extension.
 384
 385   - The option `--report=lookahead' was changed to `--report=look-ahead'.
 386     [However, this was changed back after 2.3.]
 387
 388   - Experimental %destructor support has been added to lalr1.cc.
 389
 390   - New configure option --disable-yacc, to disable installation of the
 391     yacc command and -ly library introduced in 1.875 for POSIX conformance.
 392
 393 * Bug fixes
 394
 395   - For now, %expect-count violations are now just warnings, not errors.
 396     This is for compatibility with Bison 1.75 and earlier (when there are
 397     reduce/reduce conflicts) and with Bison 1.30 and earlier (when there
 398     are too many or too few shift/reduce conflicts).  However, in future
 399     versions of Bison we plan to improve the %expect machinery so that
 400     these violations will become errors again.
 401
 402   - Within Bison itself, numbers (e.g., goto numbers) are no longer
 403     arbitrarily limited to 16-bit counts.
 404
 405   - Semicolons are now allowed before "|" in grammar rules, as POSIX requires.
 406 \f
 407 Changes in version 1.875, 2003-01-01:
 408
 409 * The documentation license has been upgraded to version 1.2
 410   of the GNU Free Documentation License.
 411
 412 * syntax error processing
 413
 414   - In Yacc-style parsers YYLLOC_DEFAULT is now used to compute error
 415     locations too.  This fixes bugs in error-location computation.
 416
 417   - %destructor
 418     It is now possible to reclaim the memory associated to symbols
 419     discarded during error recovery.  This feature is still experimental.
 420
 421   - %error-verbose
 422     This new directive is preferred over YYERROR_VERBOSE.
 423
 424   - #defining yyerror to steal internal variables is discouraged.
 425     It is not guaranteed to work forever.
 426
 427 * POSIX conformance
 428
 429   - Semicolons are once again optional at the end of grammar rules.
 430     This reverts to the behavior of Bison 1.33 and earlier, and improves
 431     compatibility with Yacc.
 432
 433   - `parse error' -> `syntax error'
 434     Bison now uniformly uses the term `syntax error'; formerly, the code
 435     and manual sometimes used the term `parse error' instead.  POSIX
 436     requires `syntax error' in diagnostics, and it was thought better to
 437     be consistent.
 438
 439   - The documentation now emphasizes that yylex and yyerror must be
 440     declared before use.  C99 requires this.
 441
 442   - Bison now parses C99 lexical constructs like UCNs and
 443     backslash-newline within C escape sequences, as POSIX 1003.1-2001 requires.
 444
 445   - File names are properly escaped in C output.  E.g., foo\bar.y is
 446     output as "foo\\bar.y".
 447
 448   - Yacc command and library now available
 449     The Bison distribution now installs a `yacc' command, as POSIX requires.
 450     Also, Bison now installs a small library liby.a containing
 451     implementations of Yacc-compatible yyerror and main functions.
 452     This library is normally not useful, but POSIX requires it.
 453
 454   - Type clashes now generate warnings, not errors.
 455
 456   - If the user does not define YYSTYPE as a macro, Bison now declares it
 457     using typedef instead of defining it as a macro.
 458     For consistency, YYLTYPE is also declared instead of defined.
 459
 460 * Other compatibility issues
 461
 462   - %union directives can now have a tag before the `{', e.g., the
 463     directive `%union foo {...}' now generates the C code
 464     `typedef union foo { ... } YYSTYPE;'; this is for Yacc compatibility.
 465     The default union tag is `YYSTYPE', for compatibility with Solaris 9 Yacc.
 466     For consistency, YYLTYPE's struct tag is now `YYLTYPE' not `yyltype'.
 467     This is for compatibility with both Yacc and Bison 1.35.
 468
 469   - `;' is output before the terminating `}' of an action, for
 470     compatibility with Bison 1.35.
 471
 472   - Bison now uses a Yacc-style format for conflict reports, e.g.,
 473     `conflicts: 2 shift/reduce, 1 reduce/reduce'.
 474
 475   - `yystype' and `yyltype' are now obsolescent macros instead of being
 476     typedefs or tags; they are no longer documented and are planned to be
 477     withdrawn in a future release.
 478
 479 * GLR parser notes
 480
 481   - GLR and inline
 482     Users of Bison have to decide how they handle the portability of the
 483     C keyword `inline'.
 484
 485   - `parsing stack overflow...' -> `parser stack overflow'
 486     GLR parsers now report `parser stack overflow' as per the Bison manual.
 487
 488 * Bison now warns if it detects conflicting outputs to the same file,
 489   e.g., it generates a warning for `bison -d -o foo.h foo.y' since
 490   that command outputs both code and header to foo.h.
 491
 492 * #line in output files
 493   - --no-line works properly.
 494
 495 * Bison can no longer be built by a K&R C compiler; it requires C89 or
 496   later to be built.  This change originally took place a few versions
 497   ago, but nobody noticed until we recently asked someone to try
 498   building Bison with a K&R C compiler.
 499 \f
 500 Changes in version 1.75, 2002-10-14:
 501
 502 * Bison should now work on 64-bit hosts.
 503
 504 * Indonesian translation thanks to Tedi Heriyanto.
 505
 506 * GLR parsers
 507   Fix spurious parse errors.
 508
 509 * Pure parsers
 510   Some people redefine yyerror to steal yyparse' private variables.
 511   Reenable this trick until an official feature replaces it.
 512
 513 * Type Clashes
 514   In agreement with POSIX and with other Yaccs, leaving a default
 515   action is valid when $$ is untyped, and $1 typed:
 516
 517         untyped: ... typed;
 518
 519   but the converse remains an error:
 520
 521         typed: ... untyped;
 522
 523 * Values of mid-rule actions
 524   The following code:
 525
 526         foo: { ... } { $$ = $1; } ...
 527
 528   was incorrectly rejected: $1 is defined in the second mid-rule
 529   action, and is equal to the $$ of the first mid-rule action.
 530 \f
 531 Changes in version 1.50, 2002-10-04:
 532
 533 * GLR parsing
 534   The declaration
 535      %glr-parser
 536   causes Bison to produce a Generalized LR (GLR) parser, capable of handling
 537   almost any context-free grammar, ambiguous or not.  The new declarations
 538   %dprec and %merge on grammar rules allow parse-time resolution of
 539   ambiguities.  Contributed by Paul Hilfinger.
 540
 541   Unfortunately Bison 1.50 does not work properly on 64-bit hosts
 542   like the Alpha, so please stick to 32-bit hosts for now.
 543
 544 * Output Directory
 545   When not in Yacc compatibility mode, when the output file was not
 546   specified, running `bison foo/bar.y' created `foo/bar.c'.  It
 547   now creates `bar.c'.
 548
 549 * Undefined token
 550   The undefined token was systematically mapped to 2 which prevented
 551   the use of 2 by the user.  This is no longer the case.
 552
 553 * Unknown token numbers
 554   If yylex returned an out of range value, yyparse could die.  This is
 555   no longer the case.
 556
 557 * Error token
 558   According to POSIX, the error token must be 256.
 559   Bison extends this requirement by making it a preference: *if* the
 560   user specified that one of her tokens is numbered 256, then error
 561   will be mapped onto another number.
 562
 563 * Verbose error messages
 564   They no longer report `..., expecting error or...' for states where
 565   error recovery is possible.
 566
 567 * End token
 568   Defaults to `$end' instead of `$'.
 569
 570 * Error recovery now conforms to documentation and to POSIX
 571   When a Bison-generated parser encounters a syntax error, it now pops
 572   the stack until it finds a state that allows shifting the error
 573   token.  Formerly, it popped the stack until it found a state that
 574   allowed some non-error action other than a default reduction on the
 575   error token.  The new behavior has long been the documented behavior,
 576   and has long been required by POSIX.  For more details, please see
 577   Paul Eggert, "Reductions during Bison error handling" (2002-05-20)
 578   <http://lists.gnu.org/archive/html/bug-bison/2002-05/msg00038.html>.
 579
 580 * Traces
 581   Popped tokens and nonterminals are now reported.
 582
 583 * Larger grammars
 584   Larger grammars are now supported (larger token numbers, larger grammar
 585   size (= sum of the LHS and RHS lengths), larger LALR tables).
 586   Formerly, many of these numbers ran afoul of 16-bit limits;
 587   now these limits are 32 bits on most hosts.
 588
 589 * Explicit initial rule
 590   Bison used to play hacks with the initial rule, which the user does
 591   not write.  It is now explicit, and visible in the reports and
 592   graphs as rule 0.
 593
 594 * Useless rules
 595   Before, Bison reported the useless rules, but, although not used,
 596   included them in the parsers.  They are now actually removed.
 597
 598 * Useless rules, useless nonterminals
 599   They are now reported, as a warning, with their locations.
 600
 601 * Rules never reduced
 602   Rules that can never be reduced because of conflicts are now
 603   reported.
 604
 605 * Incorrect `Token not used'
 606   On a grammar such as
 607
 608            %token useless useful
 609            %%
 610            exp: '0' %prec useful;
 611
 612   where a token was used to set the precedence of the last rule,
 613   bison reported both `useful' and `useless' as useless tokens.
 614
 615 * Revert the C++ namespace changes introduced in 1.31
 616   as they caused too many portability hassles.
 617
 618 * Default locations
 619   By an accident of design, the default computation of @$ was
 620   performed after another default computation was performed: @$ = @1.
 621   The latter is now removed: YYLLOC_DEFAULT is fully responsible of
 622   the computation of @$.
 623
 624 * Token end-of-file
 625   The token end of file may be specified by the user, in which case,
 626   the user symbol is used in the reports, the graphs, and the verbose
 627   error messages instead of `$end', which remains being the default.
 628   For instance
 629      %token MYEOF 0
 630   or
 631      %token MYEOF 0 "end of file"
 632
 633 * Semantic parser
 634   This old option, which has been broken for ages, is removed.
 635
 636 * New translations
 637   Brazilian Portuguese, thanks to Alexandre Folle de Menezes.
 638   Croatian, thanks to Denis Lackovic.
 639
 640 * Incorrect token definitions
 641   When given `%token 'a' "A"', Bison used to output `#define 'a' 65'.
 642
 643 * Token definitions as enums
 644   Tokens are output both as the traditional #define's, and, provided
 645   the compiler supports ANSI C or is a C++ compiler, as enums.
 646   This lets debuggers display names instead of integers.
 647
 648 * Reports
 649   In addition to --verbose, bison supports --report=THINGS, which
 650   produces additional information:
 651   - itemset
 652     complete the core item sets with their closure
 653   - lookahead [changed to `look-ahead' in 1.875e through 2.3, but changed back]
 654     explicitly associate lookahead tokens to items
 655   - solved
 656     describe shift/reduce conflicts solving.
 657     Bison used to systematically output this information on top of
 658     the report.  Solved conflicts are now attached to their states.
 659
 660 * Type clashes
 661   Previous versions don't complain when there is a type clash on
 662   the default action if the rule has a mid-rule action, such as in:
 663
 664       %type <foo> bar
 665       %%
 666       bar: '0' {} '0';
 667
 668   This is fixed.
 669
 670 * GNU M4 is now required when using Bison.
 671 \f
 672 Changes in version 1.35, 2002-03-25:
 673
 674 * C Skeleton
 675   Some projects use Bison's C parser with C++ compilers, and define
 676   YYSTYPE as a class.  The recent adjustment of C parsers for data
 677   alignment and 64 bit architectures made this impossible.
 678
 679   Because for the time being no real solution for C++ parser
 680   generation exists, kludges were implemented in the parser to
 681   maintain this use.  In the future, when Bison has C++ parsers, this
 682   kludge will be disabled.
 683
 684   This kludge also addresses some C++ problems when the stack was
 685   extended.
 686 \f
 687 Changes in version 1.34, 2002-03-12:
 688
 689 * File name clashes are detected
 690   $ bison foo.y -d -o foo.x
 691   fatal error: header and parser would both be named `foo.x'
 692
 693 * A missing `;' at the end of a rule triggers a warning
 694   In accordance with POSIX, and in agreement with other
 695   Yacc implementations, Bison will mandate this semicolon in the near
 696   future.  This eases the implementation of a Bison parser of Bison
 697   grammars by making this grammar LALR(1) instead of LR(2).  To
 698   facilitate the transition, this release introduces a warning.
 699
 700 * Revert the C++ namespace changes introduced in 1.31, as they caused too
 701   many portability hassles.
 702
 703 * DJGPP support added.
 704
 705 * Fix test suite portability problems.
 706 \f
 707 Changes in version 1.33, 2002-02-07:
 708
 709 * Fix C++ issues
 710   Groff could not be compiled for the definition of size_t was lacking
 711   under some conditions.
 712
 713 * Catch invalid @n
 714   As is done with $n.
 715 \f
 716 Changes in version 1.32, 2002-01-23:
 717
 718 * Fix Yacc output file names
 719
 720 * Portability fixes
 721
 722 * Italian, Dutch translations
 723 \f
 724 Changes in version 1.31, 2002-01-14:
 725
 726 * Many Bug Fixes
 727
 728 * GNU Gettext and %expect
 729   GNU Gettext asserts 10 s/r conflicts, but there are 7.  Now that
 730   Bison dies on incorrect %expectations, we fear there will be
 731   too many bug reports for Gettext, so _for the time being_, %expect
 732   does not trigger an error when the input file is named `plural.y'.
 733
 734 * Use of alloca in parsers
 735   If YYSTACK_USE_ALLOCA is defined to 0, then the parsers will use
 736   malloc exclusively.  Since 1.29, but was not NEWS'ed.
 737
 738   alloca is used only when compiled with GCC, to avoid portability
 739   problems as on AIX.
 740
 741 * yyparse now returns 2 if memory is exhausted; formerly it dumped core.
 742
 743 * When the generated parser lacks debugging code, YYDEBUG is now 0
 744   (as POSIX requires) instead of being undefined.
 745
 746 * User Actions
 747   Bison has always permitted actions such as { $$ = $1 }: it adds the
 748   ending semicolon.  Now if in Yacc compatibility mode, the semicolon
 749   is no longer output: one has to write { $$ = $1; }.
 750
 751 * Better C++ compliance
 752   The output parsers try to respect C++ namespaces.
 753   [This turned out to be a failed experiment, and it was reverted later.]
 754
 755 * Reduced Grammars
 756   Fixed bugs when reporting useless nonterminals.
 757
 758 * 64 bit hosts
 759   The parsers work properly on 64 bit hosts.
 760
 761 * Error messages
 762   Some calls to strerror resulted in scrambled or missing error messages.
 763
 764 * %expect
 765   When the number of shift/reduce conflicts is correct, don't issue
 766   any warning.
 767
 768 * The verbose report includes the rule line numbers.
 769
 770 * Rule line numbers are fixed in traces.
 771
 772 * Swedish translation
 773
 774 * Parse errors
 775   Verbose parse error messages from the parsers are better looking.
 776   Before: parse error: unexpected `'/'', expecting `"number"' or `'-'' or `'(''
 777      Now: parse error: unexpected '/', expecting "number" or '-' or '('
 778
 779 * Fixed parser memory leaks.
 780   When the generated parser was using malloc to extend its stacks, the
 781   previous allocations were not freed.
 782
 783 * Fixed verbose output file.
 784   Some newlines were missing.
 785   Some conflicts in state descriptions were missing.
 786
 787 * Fixed conflict report.
 788   Option -v was needed to get the result.
 789
 790 * %expect
 791   Was not used.
 792   Mismatches are errors, not warnings.
 793
 794 * Fixed incorrect processing of some invalid input.
 795
 796 * Fixed CPP guards: 9foo.h uses BISON_9FOO_H instead of 9FOO_H.
 797
 798 * Fixed some typos in the documentation.
 799
 800 * %token MY_EOF 0 is supported.
 801   Before, MY_EOF was silently renumbered as 257.
 802
 803 * doc/refcard.tex is updated.
 804
 805 * %output, %file-prefix, %name-prefix.
 806   New.
 807
 808 * --output
 809   New, aliasing `--output-file'.
 810 \f
 811 Changes in version 1.30, 2001-10-26:
 812
 813 * `--defines' and `--graph' have now an optional argument which is the
 814   output file name. `-d' and `-g' do not change; they do not take any
 815   argument.
 816
 817 * `%source_extension' and `%header_extension' are removed, failed
 818   experiment.
 819
 820 * Portability fixes.
 821 \f
 822 Changes in version 1.29, 2001-09-07:
 823
 824 * The output file does not define const, as this caused problems when used
 825   with common autoconfiguration schemes.  If you still use ancient compilers
 826   that lack const, compile with the equivalent of the C compiler option
 827   `-Dconst='.  autoconf's AC_C_CONST macro provides one way to do this.
 828
 829 * Added `-g' and `--graph'.
 830
 831 * The Bison manual is now distributed under the terms of the GNU FDL.
 832
 833 * The input and the output files has automatically a similar extension.
 834
 835 * Russian translation added.
 836
 837 * NLS support updated; should hopefully be less troublesome.
 838
 839 * Added the old Bison reference card.
 840
 841 * Added `--locations' and `%locations'.
 842
 843 * Added `-S' and `--skeleton'.
 844
 845 * `%raw', `-r', `--raw' is disabled.
 846
 847 * Special characters are escaped when output.  This solves the problems
 848   of the #line lines with path names including backslashes.
 849
 850 * New directives.
 851   `%yacc', `%fixed_output_files', `%defines', `%no_parser', `%verbose',
 852   `%debug', `%source_extension' and `%header_extension'.
 853
 854 * @$
 855   Automatic location tracking.
 856 \f
 857 Changes in version 1.28, 1999-07-06:
 858
 859 * Should compile better now with K&R compilers.
 860
 861 * Added NLS.
 862
 863 * Fixed a problem with escaping the double quote character.
 864
 865 * There is now a FAQ.
 866 \f
 867 Changes in version 1.27:
 868
 869 * The make rule which prevented bison.simple from being created on
 870   some systems has been fixed.
 871 \f
 872 Changes in version 1.26:
 873
 874 * Bison now uses automake.
 875
 876 * New mailing lists: <bug-bison@gnu.org> and <help-bison@gnu.org>.
 877
 878 * Token numbers now start at 257 as previously documented, not 258.
 879
 880 * Bison honors the TMPDIR environment variable.
 881
 882 * A couple of buffer overruns have been fixed.
 883
 884 * Problems when closing files should now be reported.
 885
 886 * Generated parsers should now work even on operating systems which do
 887   not provide alloca().
 888 \f
 889 Changes in version 1.25, 1995-10-16:
 890
 891 * Errors in the input grammar are not fatal; Bison keeps reading
 892 the grammar file, and reports all the errors found in it.
 893
 894 * Tokens can now be specified as multiple-character strings: for
 895 example, you could use "<=" for a token which looks like <=, instead
 896 of chosing a name like LESSEQ.
 897
 898 * The %token_table declaration says to write a table of tokens (names
 899 and numbers) into the parser file.  The yylex function can use this
 900 table to recognize multiple-character string tokens, or for other
 901 purposes.
 902
 903 * The %no_lines declaration says not to generate any #line preprocessor
 904 directives in the parser file.
 905
 906 * The %raw declaration says to use internal Bison token numbers, not
 907 Yacc-compatible token numbers, when token names are defined as macros.
 908
 909 * The --no-parser option produces the parser tables without including
 910 the parser engine; a project can now use its own parser engine.
 911 The actions go into a separate file called NAME.act, in the form of
 912 a switch statement body.
 913 \f
 914 Changes in version 1.23:
 915
 916 The user can define YYPARSE_PARAM as the name of an argument to be
 917 passed into yyparse.  The argument should have type void *.  It should
 918 actually point to an object.  Grammar actions can access the variable
 919 by casting it to the proper pointer type.
 920
 921 Line numbers in output file corrected.
 922 \f
 923 Changes in version 1.22:
 924
 925 --help option added.
 926 \f
 927 Changes in version 1.20:
 928
 929 Output file does not redefine const for C++.
 930
 931 Local Variables:
 932 mode: outline
 933 End:
 934
 935 -----
 936
 937 Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003,
 938 2004, 2005, 2006, 2007 Free Software Foundation, Inc.
 939
 940 This file is part of Bison, the GNU Compiler Compiler.
 941
 942 This program is free software: you can redistribute it and/or modify
 943 it under the terms of the GNU General Public License as published by
 944 the Free Software Foundation, either version 3 of the License, or
 945 (at your option) any later version.
 946
 947 This program is distributed in the hope that it will be useful,
 948 but WITHOUT ANY WARRANTY; without even the implied warranty of
 949 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 950 GNU General Public License for more details.
 951
 952 You should have received a copy of the GNU General Public License
 953 along with this program.  If not, see <http://www.gnu.org/licenses/>.