NEWS

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