NEWS

   1 Bison News
   2 ----------
   3
   4 Changes in version 1.49b, 2002-08-12:
   5
   6 * GLR parsing
   7   The declaration
   8      %glr-parser
   9   causes Bison to produce a Generalized LR (GLR) parser, capable of handling
  10   almost any context-free grammar, ambiguous or not.  The new declarations
  11   %dprec and %merge on grammar rules allow parse-time resolution of
  12   ambiguities.  Contributed by Paul Hilfinger.
  13
  14 * Output Directory
  15   When not in Yacc compatibility mode, when the output file was not
  16   specified, runnning `bison foo/bar.y' created `foo/bar.c'.  It
  17   now creates `bar.c'.
  18
  19 * Undefined token
  20   The undefined token was systematically mapped to 2 which prevented
  21   the use of 2 from the user.  This is no longer the case.
  22
  23 * Unknown token numbers
  24   If yylex returned a code out of range, yyparse could die.  This is
  25   no longer the case.
  26
  27 * Error token
  28   According to POSIX, the error token should be numbered as 256.
  29   Bison extends this requirement by making it a preference: *if* the
  30   user specified that one of her tokens is numbered 256, then error
  31   will be mapped onto another number.
  32
  33 * Verbose error messages
  34   They no longer report `..., expecting error or...' for state where
  35   error recovery is possible.
  36
  37 * End token
  38   Defaults to `$end' instead of `$'.
  39
  40 * Error recovery now conforms to documentation and to POSIX
  41   When a Bison-generated parser encounters a syntax error, it now pops
  42   the stack until it finds a state that allows shifting the error
  43   token.  Formerly, it popped the stack until it found a state that
  44   allowed some non-error action other than a default reduction on the
  45   error token.  The new behavior has long been the documented behavior,
  46   and has long been required by POSIX.  For more details, please see
  47   <http://mail.gnu.org/pipermail/bug-bison/2002-May/001452.html>.
  48
  49 * Traces
  50   Popped tokens and nonterminals are now reported.
  51
  52 * Larger grammars
  53   Larger grammars are now supported (larger token numbers, larger grammar
  54   size (= sum of the LHS and RHS lengths), larger LALR tables).
  55   Formerly, many of these numbers ran afoul of 16-bit limits;
  56   now these limits are 32 bits on most hosts.
  57
  58 * Explicit initial rule
  59   Bison used to play hacks with the initial rule, which the user does
  60   not write.  It is now explicit, and visible in the reports and
  61   graphs as rule 0.
  62
  63 * Useless rules
  64   Before, Bison reported the useless rules, but, although not used,
  65   included them in the parsers.  They are now actually removed.
  66
  67 * Useless rules, useless nonterminals
  68   They are now reported, as a warning, with their locations.
  69
  70 * Rules never reduced
  71   Rules that can never be reduced because of conflicts are now
  72   reported.
  73
  74 * Incorrect `Token not used'
  75   On a grammar such as
  76
  77            %token useless useful
  78            %%
  79            exp: '0' %prec useful;
  80
  81   where a token was used to set the precedence of the last rule,
  82   bison reported both `useful' and `useless' as useless tokens.
  83
  84 * Revert the C++ namespace changes introduced in 1.31
  85   as they caused too many portability hassles.
  86
  87 * Default locations
  88   By an accident of design, the default computation of @$ was
  89   performed after another default computation was performed: @$ = @1.
  90   The latter is now removed: YYLLOC_DEFAULT is fully responsible of
  91   the computation of @$.
  92
  93 * Token end-of-file
  94   The token end of file may be specified by the user, in which case,
  95   the user symbol is used in the reports, the graphs, and the verbose
  96   error messages instead of `$end', which remains being the default.
  97   For instance
  98      %token YYEOF 0
  99   or
 100      %token YYEOF 0 "end of file"
 101
 102 * Semantic parser
 103   This old option, which has been broken for ages, is removed.
 104
 105 * New translations
 106   Brazilian Portuguese, thanks to Alexandre Folle de Menezes.
 107   Croatian, thanks to Denis Lackovic.
 108
 109 * Incorrect token definitions
 110   When fed with `%token 'a' "A"', Bison used to output `#define 'a' 65'.
 111
 112 * Token definitions as enums
 113   Tokens are output both as the traditional #define's, and, provided
 114   the compiler supports ANSI C or is a C++ compiler, as enums.
 115   This helps debuggers producing symbols instead of values.
 116
 117 * Reports
 118   In addition to --verbose, bison supports --report=THINGS, which
 119   produces additional information:
 120   - itemset
 121     complete the core item sets with their closure
 122   - lookahead
 123     explicitly associate lookaheads to items
 124   - solved
 125     describe shift/reduce conflicts solving.
 126     Bison used to systematically output this information on top of
 127     the report.  Solved conflicts are now attached to their states.
 128
 129 * Type clashes
 130   Previous versions don't complain when there is a type clash on
 131   the default action if the rule has a mid-rule action, such as in:
 132
 133       %type <foo> bar
 134       %%
 135       bar: '0' {} '0';
 136
 137   This is fixed.
 138
 139 * GNU M4 is now required when using Bison.
 140 \f
 141 Changes in version 1.35, 2002-03-25:
 142
 143 * C Skeleton
 144   Some projects use Bison's C parser with C++ compilers, and define
 145   YYSTYPE as a class.  The recent adjustment of C parsers for data
 146   alignment and 64 bit architectures made this impossible.
 147
 148   Because for the time being no real solution for C++ parser
 149   generation exists, kludges were implemented in the parser to
 150   maintain this use.  In the future, when Bison has C++ parsers, this
 151   kludge will be disabled.
 152
 153   This kludge also addresses some C++ problems when the stack was
 154   extended.
 155
 156 \f
 157 Changes in version 1.34, 2002-03-12:
 158
 159 * File name clashes are detected
 160   $ bison foo.y -d -o foo.x
 161   fatal error: header and parser would both be named `foo.x'
 162
 163 * A missing `;' at the end of a rule triggers a warning
 164   In accordance with POSIX, and in agreement with other
 165   Yacc implementations, Bison will mandate this semicolon in the near
 166   future.  This eases the implementation of a Bison parser of Bison
 167   grammars by making this grammar LALR(1) instead of LR(2).  To
 168   facilitate the transition, this release introduces a warning.
 169
 170 * Revert the C++ namespace changes introduced in 1.31, as they caused too
 171   many portability hassles.
 172
 173 * DJGPP support added.
 174
 175 * Fix test suite portability problems.
 176 \f
 177 Changes in version 1.33, 2002-02-07:
 178
 179 * Fix C++ issues
 180   Groff could not be compiled for the definition of size_t was lacking
 181   under some conditions.
 182
 183 * Catch invalid @n
 184   As is done with $n.
 185 \f
 186 Changes in version 1.32, 2002-01-23:
 187
 188 * Fix Yacc output file names
 189
 190 * Portability fixes
 191
 192 * Italian, Dutch translations
 193 \f
 194 Changes in version 1.31, 2002-01-14:
 195
 196 * Many Bug Fixes
 197
 198 * GNU Gettext and %expect
 199   GNU Gettext asserts 10 s/r conflicts, but there are 7.  Now that
 200   Bison dies on incorrect %expectations, we fear there will be
 201   too many bug reports for Gettext, so _for the time being_, %expect
 202   does not trigger an error when the input file is named `plural.y'.
 203
 204 * Use of alloca in parsers
 205   If YYSTACK_USE_ALLOCA is defined to 0, then the parsers will use
 206   malloc exclusively.  Since 1.29, but was not NEWS'ed.
 207
 208   alloca is used only when compiled with GCC, to avoid portability
 209   problems as on AIX.
 210
 211 * When the generated parser lacks debugging code, YYDEBUG is now 0
 212   (as POSIX requires) instead of being undefined.
 213
 214 * User Actions
 215   Bison has always permitted actions such as { $$ = $1 }: it adds the
 216   ending semicolon.  Now if in Yacc compatibility mode, the semicolon
 217   is no longer output: one has to write { $$ = $1; }.
 218
 219 * Better C++ compliance
 220   The output parsers try to respect C++ namespaces.
 221   [This turned out to be a failed experiment, and it was reverted later.]
 222
 223 * Reduced Grammars
 224   Fixed bugs when reporting useless nonterminals.
 225
 226 * 64 bit hosts
 227   The parsers work properly on 64 bit hosts.
 228
 229 * Error messages
 230   Some calls to strerror resulted in scrambled or missing error messages.
 231
 232 * %expect
 233   When the number of shift/reduce conflicts is correct, don't issue
 234   any warning.
 235
 236 * The verbose report includes the rule line numbers.
 237
 238 * Rule line numbers are fixed in traces.
 239
 240 * Swedish translation
 241
 242 * Parse errors
 243   Verbose parse error messages from the parsers are better looking.
 244   Before: parse error: unexpected `'/'', expecting `"number"' or `'-'' or `'(''
 245      Now: parse error: unexpected '/', expecting "number" or '-' or '('
 246
 247 * Fixed parser memory leaks.
 248   When the generated parser was using malloc to extend its stacks, the
 249   previous allocations were not freed.
 250
 251 * Fixed verbose output file.
 252   Some newlines were missing.
 253   Some conflicts in state descriptions were missing.
 254
 255 * Fixed conflict report.
 256   Option -v was needed to get the result.
 257
 258 * %expect
 259   Was not used.
 260   Mismatches are errors, not warnings.
 261
 262 * Fixed incorrect processing of some invalid input.
 263
 264 * Fixed CPP guards: 9foo.h uses BISON_9FOO_H instead of 9FOO_H.
 265
 266 * Fixed some typos in the documentation.
 267
 268 * %token MY_EOF 0 is supported.
 269   Before, MY_EOF was silently renumbered as 257.
 270
 271 * doc/refcard.tex is updated.
 272
 273 * %output, %file-prefix, %name-prefix.
 274   New.
 275
 276 * --output
 277   New, aliasing `--output-file'.
 278 \f
 279 Changes in version 1.30, 2001-10-26:
 280
 281 * `--defines' and `--graph' have now an optionnal argument which is the
 282   output file name. `-d' and `-g' do not change, they do not take any
 283   argument.
 284
 285 * `%source_extension' and `%header_extension' are removed, failed
 286   experiment.
 287
 288 * Portability fixes.
 289 \f
 290 Changes in version 1.29, 2001-09-07:
 291
 292 * The output file does not define const, as this caused problems when used
 293   with common autoconfiguration schemes.  If you still use ancient compilers
 294   that lack const, compile with the equivalent of the C compiler option
 295   `-Dconst='.  autoconf's AC_C_CONST macro provides one way to do this.
 296
 297 * Added `-g' and `--graph'.
 298
 299 * The Bison manual is now distributed under the terms of the GNU FDL.
 300
 301 * The input and the output files has automatically a similar extension.
 302
 303 * Russian translation added.
 304
 305 * NLS support updated; should hopefully be less troublesome.
 306
 307 * Added the old Bison reference card.
 308
 309 * Added `--locations' and `%locations'.
 310
 311 * Added `-S' and `--skeleton'.
 312
 313 * `%raw', `-r', `--raw' is disabled.
 314
 315 * Special characters are escaped when output.  This solves the problems
 316   of the #line lines with path names including backslashes.
 317
 318 * New directives.
 319   `%yacc', `%fixed_output_files', `%defines', `%no_parser', `%verbose',
 320   `%debug', `%source_extension' and `%header_extension'.
 321
 322 * @$
 323   Automatic location tracking.
 324 \f
 325 Changes in version 1.28, 1999-07-06:
 326
 327 * Should compile better now with K&R compilers.
 328
 329 * Added NLS.
 330
 331 * Fixed a problem with escaping the double quote character.
 332
 333 * There is now a FAQ.
 334 \f
 335 Changes in version 1.27:
 336
 337 * The make rule which prevented bison.simple from being created on
 338   some systems has been fixed.
 339 \f
 340 Changes in version 1.26:
 341
 342 * Bison now uses automake.
 343
 344 * New mailing lists: <bug-bison@gnu.org> and <help-bison@gnu.org>.
 345
 346 * Token numbers now start at 257 as previously documented, not 258.
 347
 348 * Bison honors the TMPDIR environment variable.
 349
 350 * A couple of buffer overruns have been fixed.
 351
 352 * Problems when closing files should now be reported.
 353
 354 * Generated parsers should now work even on operating systems which do
 355   not provide alloca().
 356 \f
 357 Changes in version 1.25, 1995-10-16:
 358
 359 * Errors in the input grammar are not fatal; Bison keeps reading
 360 the grammar file, and reports all the errors found in it.
 361
 362 * Tokens can now be specified as multiple-character strings: for
 363 example, you could use "<=" for a token which looks like <=, instead
 364 of chosing a name like LESSEQ.
 365
 366 * The %token_table declaration says to write a table of tokens (names
 367 and numbers) into the parser file.  The yylex function can use this
 368 table to recognize multiple-character string tokens, or for other
 369 purposes.
 370
 371 * The %no_lines declaration says not to generate any #line preprocessor
 372 directives in the parser file.
 373
 374 * The %raw declaration says to use internal Bison token numbers, not
 375 Yacc-compatible token numbers, when token names are defined as macros.
 376
 377 * The --no-parser option produces the parser tables without including
 378 the parser engine; a project can now use its own parser engine.
 379 The actions go into a separate file called NAME.act, in the form of
 380 a switch statement body.
 381 \f
 382 Changes in version 1.23:
 383
 384 The user can define YYPARSE_PARAM as the name of an argument to be
 385 passed into yyparse.  The argument should have type void *.  It should
 386 actually point to an object.  Grammar actions can access the variable
 387 by casting it to the proper pointer type.
 388
 389 Line numbers in output file corrected.
 390 \f
 391 Changes in version 1.22:
 392
 393 --help option added.
 394 \f
 395 Changes in version 1.20:
 396
 397 Output file does not redefine const for C++.
 398
 399 Local Variables:
 400 mode: outline
 401 End:
 402
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