NEWS

   1 Bison News
   2 ----------
   3
   4 Changes in version 1.50, 2002-10-04:
   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   Unfortunately GLR parsing does not yet work properly on 64-bit hosts
  15   like the Alpha, so please stick to 32-bit hosts for now.
  16
  17 * Output Directory
  18   When not in Yacc compatibility mode, when the output file was not
  19   specified, running `bison foo/bar.y' created `foo/bar.c'.  It
  20   now creates `bar.c'.
  21
  22 * Undefined token
  23   The undefined token was systematically mapped to 2 which prevented
  24   the use of 2 by the user.  This is no longer the case.
  25
  26 * Unknown token numbers
  27   If yylex returned an out of range value, yyparse could die.  This is
  28   no longer the case.
  29
  30 * Error token
  31   According to POSIX, the error token must be 256.
  32   Bison extends this requirement by making it a preference: *if* the
  33   user specified that one of her tokens is numbered 256, then error
  34   will be mapped onto another number.
  35
  36 * Verbose error messages
  37   They no longer report `..., expecting error or...' for states where
  38   error recovery is possible.
  39
  40 * End token
  41   Defaults to `$end' instead of `$'.
  42
  43 * Error recovery now conforms to documentation and to POSIX
  44   When a Bison-generated parser encounters a syntax error, it now pops
  45   the stack until it finds a state that allows shifting the error
  46   token.  Formerly, it popped the stack until it found a state that
  47   allowed some non-error action other than a default reduction on the
  48   error token.  The new behavior has long been the documented behavior,
  49   and has long been required by POSIX.  For more details, please see
  50   <http://mail.gnu.org/pipermail/bug-bison/2002-May/001452.html>.
  51
  52 * Traces
  53   Popped tokens and nonterminals are now reported.
  54
  55 * Larger grammars
  56   Larger grammars are now supported (larger token numbers, larger grammar
  57   size (= sum of the LHS and RHS lengths), larger LALR tables).
  58   Formerly, many of these numbers ran afoul of 16-bit limits;
  59   now these limits are 32 bits on most hosts.
  60
  61 * Explicit initial rule
  62   Bison used to play hacks with the initial rule, which the user does
  63   not write.  It is now explicit, and visible in the reports and
  64   graphs as rule 0.
  65
  66 * Useless rules
  67   Before, Bison reported the useless rules, but, although not used,
  68   included them in the parsers.  They are now actually removed.
  69
  70 * Useless rules, useless nonterminals
  71   They are now reported, as a warning, with their locations.
  72
  73 * Rules never reduced
  74   Rules that can never be reduced because of conflicts are now
  75   reported.
  76
  77 * Incorrect `Token not used'
  78   On a grammar such as
  79
  80            %token useless useful
  81            %%
  82            exp: '0' %prec useful;
  83
  84   where a token was used to set the precedence of the last rule,
  85   bison reported both `useful' and `useless' as useless tokens.
  86
  87 * Revert the C++ namespace changes introduced in 1.31
  88   as they caused too many portability hassles.
  89
  90 * Default locations
  91   By an accident of design, the default computation of @$ was
  92   performed after another default computation was performed: @$ = @1.
  93   The latter is now removed: YYLLOC_DEFAULT is fully responsible of
  94   the computation of @$.
  95
  96 * Token end-of-file
  97   The token end of file may be specified by the user, in which case,
  98   the user symbol is used in the reports, the graphs, and the verbose
  99   error messages instead of `$end', which remains being the default.
 100   For instance
 101      %token YYEOF 0
 102   or
 103      %token YYEOF 0 "end of file"
 104
 105 * Semantic parser
 106   This old option, which has been broken for ages, is removed.
 107
 108 * New translations
 109   Brazilian Portuguese, thanks to Alexandre Folle de Menezes.
 110   Croatian, thanks to Denis Lackovic.
 111
 112 * Incorrect token definitions
 113   When given `%token 'a' "A"', Bison used to output `#define 'a' 65'.
 114
 115 * Token definitions as enums
 116   Tokens are output both as the traditional #define's, and, provided
 117   the compiler supports ANSI C or is a C++ compiler, as enums.
 118   This lets debuggers display names instead of integers.
 119
 120 * Reports
 121   In addition to --verbose, bison supports --report=THINGS, which
 122   produces additional information:
 123   - itemset
 124     complete the core item sets with their closure
 125   - lookahead
 126     explicitly associate lookaheads to items
 127   - solved
 128     describe shift/reduce conflicts solving.
 129     Bison used to systematically output this information on top of
 130     the report.  Solved conflicts are now attached to their states.
 131
 132 * Type clashes
 133   Previous versions don't complain when there is a type clash on
 134   the default action if the rule has a mid-rule action, such as in:
 135
 136       %type <foo> bar
 137       %%
 138       bar: '0' {} '0';
 139
 140   This is fixed.
 141
 142 * GNU M4 is now required when using Bison.
 143 \f
 144 Changes in version 1.35, 2002-03-25:
 145
 146 * C Skeleton
 147   Some projects use Bison's C parser with C++ compilers, and define
 148   YYSTYPE as a class.  The recent adjustment of C parsers for data
 149   alignment and 64 bit architectures made this impossible.
 150
 151   Because for the time being no real solution for C++ parser
 152   generation exists, kludges were implemented in the parser to
 153   maintain this use.  In the future, when Bison has C++ parsers, this
 154   kludge will be disabled.
 155
 156   This kludge also addresses some C++ problems when the stack was
 157   extended.
 158 \f
 159 Changes in version 1.34, 2002-03-12:
 160
 161 * File name clashes are detected
 162   $ bison foo.y -d -o foo.x
 163   fatal error: header and parser would both be named `foo.x'
 164
 165 * A missing `;' at the end of a rule triggers a warning
 166   In accordance with POSIX, and in agreement with other
 167   Yacc implementations, Bison will mandate this semicolon in the near
 168   future.  This eases the implementation of a Bison parser of Bison
 169   grammars by making this grammar LALR(1) instead of LR(2).  To
 170   facilitate the transition, this release introduces a warning.
 171
 172 * Revert the C++ namespace changes introduced in 1.31, as they caused too
 173   many portability hassles.
 174
 175 * DJGPP support added.
 176
 177 * Fix test suite portability problems.
 178 \f
 179 Changes in version 1.33, 2002-02-07:
 180
 181 * Fix C++ issues
 182   Groff could not be compiled for the definition of size_t was lacking
 183   under some conditions.
 184
 185 * Catch invalid @n
 186   As is done with $n.
 187 \f
 188 Changes in version 1.32, 2002-01-23:
 189
 190 * Fix Yacc output file names
 191
 192 * Portability fixes
 193
 194 * Italian, Dutch translations
 195 \f
 196 Changes in version 1.31, 2002-01-14:
 197
 198 * Many Bug Fixes
 199
 200 * GNU Gettext and %expect
 201   GNU Gettext asserts 10 s/r conflicts, but there are 7.  Now that
 202   Bison dies on incorrect %expectations, we fear there will be
 203   too many bug reports for Gettext, so _for the time being_, %expect
 204   does not trigger an error when the input file is named `plural.y'.
 205
 206 * Use of alloca in parsers
 207   If YYSTACK_USE_ALLOCA is defined to 0, then the parsers will use
 208   malloc exclusively.  Since 1.29, but was not NEWS'ed.
 209
 210   alloca is used only when compiled with GCC, to avoid portability
 211   problems as on AIX.
 212
 213 * When the generated parser lacks debugging code, YYDEBUG is now 0
 214   (as POSIX requires) instead of being undefined.
 215
 216 * User Actions
 217   Bison has always permitted actions such as { $$ = $1 }: it adds the
 218   ending semicolon.  Now if in Yacc compatibility mode, the semicolon
 219   is no longer output: one has to write { $$ = $1; }.
 220
 221 * Better C++ compliance
 222   The output parsers try to respect C++ namespaces.
 223   [This turned out to be a failed experiment, and it was reverted later.]
 224
 225 * Reduced Grammars
 226   Fixed bugs when reporting useless nonterminals.
 227
 228 * 64 bit hosts
 229   The parsers work properly on 64 bit hosts.
 230
 231 * Error messages
 232   Some calls to strerror resulted in scrambled or missing error messages.
 233
 234 * %expect
 235   When the number of shift/reduce conflicts is correct, don't issue
 236   any warning.
 237
 238 * The verbose report includes the rule line numbers.
 239
 240 * Rule line numbers are fixed in traces.
 241
 242 * Swedish translation
 243
 244 * Parse errors
 245   Verbose parse error messages from the parsers are better looking.
 246   Before: parse error: unexpected `'/'', expecting `"number"' or `'-'' or `'(''
 247      Now: parse error: unexpected '/', expecting "number" or '-' or '('
 248
 249 * Fixed parser memory leaks.
 250   When the generated parser was using malloc to extend its stacks, the
 251   previous allocations were not freed.
 252
 253 * Fixed verbose output file.
 254   Some newlines were missing.
 255   Some conflicts in state descriptions were missing.
 256
 257 * Fixed conflict report.
 258   Option -v was needed to get the result.
 259
 260 * %expect
 261   Was not used.
 262   Mismatches are errors, not warnings.
 263
 264 * Fixed incorrect processing of some invalid input.
 265
 266 * Fixed CPP guards: 9foo.h uses BISON_9FOO_H instead of 9FOO_H.
 267
 268 * Fixed some typos in the documentation.
 269
 270 * %token MY_EOF 0 is supported.
 271   Before, MY_EOF was silently renumbered as 257.
 272
 273 * doc/refcard.tex is updated.
 274
 275 * %output, %file-prefix, %name-prefix.
 276   New.
 277
 278 * --output
 279   New, aliasing `--output-file'.
 280 \f
 281 Changes in version 1.30, 2001-10-26:
 282
 283 * `--defines' and `--graph' have now an optionnal argument which is the
 284   output file name. `-d' and `-g' do not change, they do not take any
 285   argument.
 286
 287 * `%source_extension' and `%header_extension' are removed, failed
 288   experiment.
 289
 290 * Portability fixes.
 291 \f
 292 Changes in version 1.29, 2001-09-07:
 293
 294 * The output file does not define const, as this caused problems when used
 295   with common autoconfiguration schemes.  If you still use ancient compilers
 296   that lack const, compile with the equivalent of the C compiler option
 297   `-Dconst='.  autoconf's AC_C_CONST macro provides one way to do this.
 298
 299 * Added `-g' and `--graph'.
 300
 301 * The Bison manual is now distributed under the terms of the GNU FDL.
 302
 303 * The input and the output files has automatically a similar extension.
 304
 305 * Russian translation added.
 306
 307 * NLS support updated; should hopefully be less troublesome.
 308
 309 * Added the old Bison reference card.
 310
 311 * Added `--locations' and `%locations'.
 312
 313 * Added `-S' and `--skeleton'.
 314
 315 * `%raw', `-r', `--raw' is disabled.
 316
 317 * Special characters are escaped when output.  This solves the problems
 318   of the #line lines with path names including backslashes.
 319
 320 * New directives.
 321   `%yacc', `%fixed_output_files', `%defines', `%no_parser', `%verbose',
 322   `%debug', `%source_extension' and `%header_extension'.
 323
 324 * @$
 325   Automatic location tracking.
 326 \f
 327 Changes in version 1.28, 1999-07-06:
 328
 329 * Should compile better now with K&R compilers.
 330
 331 * Added NLS.
 332
 333 * Fixed a problem with escaping the double quote character.
 334
 335 * There is now a FAQ.
 336 \f
 337 Changes in version 1.27:
 338
 339 * The make rule which prevented bison.simple from being created on
 340   some systems has been fixed.
 341 \f
 342 Changes in version 1.26:
 343
 344 * Bison now uses automake.
 345
 346 * New mailing lists: <bug-bison@gnu.org> and <help-bison@gnu.org>.
 347
 348 * Token numbers now start at 257 as previously documented, not 258.
 349
 350 * Bison honors the TMPDIR environment variable.
 351
 352 * A couple of buffer overruns have been fixed.
 353
 354 * Problems when closing files should now be reported.
 355
 356 * Generated parsers should now work even on operating systems which do
 357   not provide alloca().
 358 \f
 359 Changes in version 1.25, 1995-10-16:
 360
 361 * Errors in the input grammar are not fatal; Bison keeps reading
 362 the grammar file, and reports all the errors found in it.
 363
 364 * Tokens can now be specified as multiple-character strings: for
 365 example, you could use "<=" for a token which looks like <=, instead
 366 of chosing a name like LESSEQ.
 367
 368 * The %token_table declaration says to write a table of tokens (names
 369 and numbers) into the parser file.  The yylex function can use this
 370 table to recognize multiple-character string tokens, or for other
 371 purposes.
 372
 373 * The %no_lines declaration says not to generate any #line preprocessor
 374 directives in the parser file.
 375
 376 * The %raw declaration says to use internal Bison token numbers, not
 377 Yacc-compatible token numbers, when token names are defined as macros.
 378
 379 * The --no-parser option produces the parser tables without including
 380 the parser engine; a project can now use its own parser engine.
 381 The actions go into a separate file called NAME.act, in the form of
 382 a switch statement body.
 383 \f
 384 Changes in version 1.23:
 385
 386 The user can define YYPARSE_PARAM as the name of an argument to be
 387 passed into yyparse.  The argument should have type void *.  It should
 388 actually point to an object.  Grammar actions can access the variable
 389 by casting it to the proper pointer type.
 390
 391 Line numbers in output file corrected.
 392 \f
 393 Changes in version 1.22:
 394
 395 --help option added.
 396 \f
 397 Changes in version 1.20:
 398
 399 Output file does not redefine const for C++.
 400
 401 Local Variables:
 402 mode: outline
 403 End:
 404
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