4 Changes in version 2.1a:
6 * New warning: unused values
7 Typed right-hand side symbols whose value are not used are reported.
10 exp: exp "?" exp ":" exp { $1 ? $1 : $3; }
14 will trigger a warning about $$ and $5 in the first rule, and $3 in
15 the second ($1 is copied to $$ by the default rule). This example
16 most likely contains three errors, and should be rewritten as:
18 exp: exp "?" exp ":" exp { $$ = $1 ? $3 : $5; }
19 | exp "+" exp { $$ = $1 + $3; }
22 However, if the original actions were really intended, the warnings
23 can be suppressed by letting Bison believe the values are used, e.g.:
25 exp: exp "?" exp ":" exp { $1 ? $1 : $3; (void) ($$, $5); }
26 | exp "+" exp { $$ = $1; (void) $3; }
29 The warning is intended to help catching lost values and memory leaks.
30 If a value is ignored, its associated memory typically is not reclaimed.
32 * %destructor vs. YYABORT, YYACCEPT, and YYERROR.
33 Destructors are now called when user code invokes YYABORT, YYACCEPT,
34 and YYERROR, for all objects on the stack, other than objects
35 corresponding to the right-hand side of the current rule.
38 Incorrect numbers of expected conflicts are now actual errors,
42 The %parse-params are available in the %destructor's (and the
43 experimental %printer's) as per the documentation.
45 * Bison now warns if it finds a stray `$' or `@' in an action.
48 To specify that the grammar file depends on features implemented in
49 Bison version VERSION or higher.
51 * lalr1.cc: The token and value types are now class members.
52 The tokens were defined as free form enums and cpp macros. YYSTYPE
53 was defined as a free form union. They are now class members:
54 tokens are enumerations of the `yy::parser::token' struct, and the
55 semantic values have the `yy::parser::semantic_type' type.
57 If you do not want or can update to this scheme, the directive
58 `%define "global_tokens_and_yystype" "1"' triggers the global
59 definition of tokens and YYSTYPE. This change is suitable both
60 for previous releases of Bison, and this one.
62 If you wish to update, then make sure older version of Bison will
63 fail using `%require "2.1a"'.
65 * DJGPP support added.
67 Changes in version 2.1, 2005-09-16:
69 * The C++ lalr1.cc skeleton supports %lex-param.
71 * Bison-generated parsers now support the translation of diagnostics like
72 "syntax error" into languages other than English. The default
73 language is still English. For details, please see the new
74 Internationalization section of the Bison manual. Software
75 distributors should also see the new PACKAGING file. Thanks to
76 Bruno Haible for this new feature.
78 * Wording in the Bison-generated parsers has been changed slightly to
79 simplify translation. In particular, the message "memory exhausted"
80 has replaced "parser stack overflow", as the old message was not
81 always accurate for modern Bison-generated parsers.
83 * Destructors are now called when the parser aborts, for all symbols left
84 behind on the stack. Also, the start symbol is now destroyed after a
85 successful parse. In both cases, the behavior was formerly inconsistent.
87 * When generating verbose diagnostics, Bison-generated parsers no longer
88 quote the literal strings associated with tokens. For example, for
89 a syntax error associated with '%token NUM "number"' they might
90 print 'syntax error, unexpected number' instead of 'syntax error,
93 Changes in version 2.0, 2004-12-25:
95 * Possibly-incompatible changes
97 - Bison-generated parsers no longer default to using the alloca function
98 (when available) to extend the parser stack, due to widespread
99 problems in unchecked stack-overflow detection. You can "#define
100 YYSTACK_USE_ALLOCA 1" to require the use of alloca, but please read
101 the manual to determine safe values for YYMAXDEPTH in that case.
103 - Error token location.
104 During error recovery, the location of the syntax error is updated
105 to cover the whole sequence covered by the error token: it includes
106 the shifted symbols thrown away during the first part of the error
107 recovery, and the lookahead rejected during the second part.
110 . Stray semicolons are no longer allowed at the start of a grammar.
111 . Semicolons are now required after in-grammar declarations.
113 - Unescaped newlines are no longer allowed in character constants or
114 string literals. They were never portable, and GCC 3.4.0 has
115 dropped support for them. Better diagnostics are now generated if
116 forget a closing quote.
118 - NUL bytes are no longer allowed in Bison string literals, unfortunately.
122 - GLR grammars now support locations.
124 - New directive: %initial-action.
125 This directive allows the user to run arbitrary code (including
126 initializing @$) from yyparse before parsing starts.
128 - A new directive "%expect-rr N" specifies the expected number of
129 reduce/reduce conflicts in GLR parsers.
131 - %token numbers can now be hexadecimal integers, e.g., `%token FOO 0x12d'.
132 This is a GNU extension.
134 - The option `--report=lookahead' was changed to `--report=look-ahead'.
135 The old spelling still works, but is not documented and will be
138 - Experimental %destructor support has been added to lalr1.cc.
140 - New configure option --disable-yacc, to disable installation of the
141 yacc command and -ly library introduced in 1.875 for POSIX conformance.
145 - For now, %expect-count violations are now just warnings, not errors.
146 This is for compatibility with Bison 1.75 and earlier (when there are
147 reduce/reduce conflicts) and with Bison 1.30 and earlier (when there
148 are too many or too few shift/reduce conflicts). However, in future
149 versions of Bison we plan to improve the %expect machinery so that
150 these violations will become errors again.
152 - Within Bison itself, numbers (e.g., goto numbers) are no longer
153 arbitrarily limited to 16-bit counts.
155 - Semicolons are now allowed before "|" in grammar rules, as POSIX requires.
157 Changes in version 1.875, 2003-01-01:
159 * The documentation license has been upgraded to version 1.2
160 of the GNU Free Documentation License.
162 * syntax error processing
164 - In Yacc-style parsers YYLLOC_DEFAULT is now used to compute error
165 locations too. This fixes bugs in error-location computation.
168 It is now possible to reclaim the memory associated to symbols
169 discarded during error recovery. This feature is still experimental.
172 This new directive is preferred over YYERROR_VERBOSE.
174 - #defining yyerror to steal internal variables is discouraged.
175 It is not guaranteed to work forever.
179 - Semicolons are once again optional at the end of grammar rules.
180 This reverts to the behavior of Bison 1.33 and earlier, and improves
181 compatibility with Yacc.
183 - `parse error' -> `syntax error'
184 Bison now uniformly uses the term `syntax error'; formerly, the code
185 and manual sometimes used the term `parse error' instead. POSIX
186 requires `syntax error' in diagnostics, and it was thought better to
189 - The documentation now emphasizes that yylex and yyerror must be
190 declared before use. C99 requires this.
192 - Bison now parses C99 lexical constructs like UCNs and
193 backslash-newline within C escape sequences, as POSIX 1003.1-2001 requires.
195 - File names are properly escaped in C output. E.g., foo\bar.y is
196 output as "foo\\bar.y".
198 - Yacc command and library now available
199 The Bison distribution now installs a `yacc' command, as POSIX requires.
200 Also, Bison now installs a small library liby.a containing
201 implementations of Yacc-compatible yyerror and main functions.
202 This library is normally not useful, but POSIX requires it.
204 - Type clashes now generate warnings, not errors.
206 - If the user does not define YYSTYPE as a macro, Bison now declares it
207 using typedef instead of defining it as a macro.
208 For consistency, YYLTYPE is also declared instead of defined.
210 * Other compatibility issues
212 - %union directives can now have a tag before the `{', e.g., the
213 directive `%union foo {...}' now generates the C code
214 `typedef union foo { ... } YYSTYPE;'; this is for Yacc compatibility.
215 The default union tag is `YYSTYPE', for compatibility with Solaris 9 Yacc.
216 For consistency, YYLTYPE's struct tag is now `YYLTYPE' not `yyltype'.
217 This is for compatibility with both Yacc and Bison 1.35.
219 - `;' is output before the terminating `}' of an action, for
220 compatibility with Bison 1.35.
222 - Bison now uses a Yacc-style format for conflict reports, e.g.,
223 `conflicts: 2 shift/reduce, 1 reduce/reduce'.
225 - `yystype' and `yyltype' are now obsolescent macros instead of being
226 typedefs or tags; they are no longer documented and are planned to be
227 withdrawn in a future release.
232 Users of Bison have to decide how they handle the portability of the
235 - `parsing stack overflow...' -> `parser stack overflow'
236 GLR parsers now report `parser stack overflow' as per the Bison manual.
238 * Bison now warns if it detects conflicting outputs to the same file,
239 e.g., it generates a warning for `bison -d -o foo.h foo.y' since
240 that command outputs both code and header to foo.h.
242 * #line in output files
243 - --no-line works properly.
245 * Bison can no longer be built by a K&R C compiler; it requires C89 or
246 later to be built. This change originally took place a few versions
247 ago, but nobody noticed until we recently asked someone to try
248 building Bison with a K&R C compiler.
250 Changes in version 1.75, 2002-10-14:
252 * Bison should now work on 64-bit hosts.
254 * Indonesian translation thanks to Tedi Heriyanto.
257 Fix spurious parse errors.
260 Some people redefine yyerror to steal yyparse' private variables.
261 Reenable this trick until an official feature replaces it.
264 In agreement with POSIX and with other Yaccs, leaving a default
265 action is valid when $$ is untyped, and $1 typed:
269 but the converse remains an error:
273 * Values of mid-rule actions
276 foo: { ... } { $$ = $1; } ...
278 was incorrectly rejected: $1 is defined in the second mid-rule
279 action, and is equal to the $$ of the first mid-rule action.
281 Changes in version 1.50, 2002-10-04:
286 causes Bison to produce a Generalized LR (GLR) parser, capable of handling
287 almost any context-free grammar, ambiguous or not. The new declarations
288 %dprec and %merge on grammar rules allow parse-time resolution of
289 ambiguities. Contributed by Paul Hilfinger.
291 Unfortunately Bison 1.50 does not work properly on 64-bit hosts
292 like the Alpha, so please stick to 32-bit hosts for now.
295 When not in Yacc compatibility mode, when the output file was not
296 specified, running `bison foo/bar.y' created `foo/bar.c'. It
300 The undefined token was systematically mapped to 2 which prevented
301 the use of 2 by the user. This is no longer the case.
303 * Unknown token numbers
304 If yylex returned an out of range value, yyparse could die. This is
308 According to POSIX, the error token must be 256.
309 Bison extends this requirement by making it a preference: *if* the
310 user specified that one of her tokens is numbered 256, then error
311 will be mapped onto another number.
313 * Verbose error messages
314 They no longer report `..., expecting error or...' for states where
315 error recovery is possible.
318 Defaults to `$end' instead of `$'.
320 * Error recovery now conforms to documentation and to POSIX
321 When a Bison-generated parser encounters a syntax error, it now pops
322 the stack until it finds a state that allows shifting the error
323 token. Formerly, it popped the stack until it found a state that
324 allowed some non-error action other than a default reduction on the
325 error token. The new behavior has long been the documented behavior,
326 and has long been required by POSIX. For more details, please see
327 Paul Eggert, "Reductions during Bison error handling" (2002-05-20)
328 <http://lists.gnu.org/archive/html/bug-bison/2002-05/msg00038.html>.
331 Popped tokens and nonterminals are now reported.
334 Larger grammars are now supported (larger token numbers, larger grammar
335 size (= sum of the LHS and RHS lengths), larger LALR tables).
336 Formerly, many of these numbers ran afoul of 16-bit limits;
337 now these limits are 32 bits on most hosts.
339 * Explicit initial rule
340 Bison used to play hacks with the initial rule, which the user does
341 not write. It is now explicit, and visible in the reports and
345 Before, Bison reported the useless rules, but, although not used,
346 included them in the parsers. They are now actually removed.
348 * Useless rules, useless nonterminals
349 They are now reported, as a warning, with their locations.
351 * Rules never reduced
352 Rules that can never be reduced because of conflicts are now
355 * Incorrect `Token not used'
358 %token useless useful
360 exp: '0' %prec useful;
362 where a token was used to set the precedence of the last rule,
363 bison reported both `useful' and `useless' as useless tokens.
365 * Revert the C++ namespace changes introduced in 1.31
366 as they caused too many portability hassles.
369 By an accident of design, the default computation of @$ was
370 performed after another default computation was performed: @$ = @1.
371 The latter is now removed: YYLLOC_DEFAULT is fully responsible of
372 the computation of @$.
375 The token end of file may be specified by the user, in which case,
376 the user symbol is used in the reports, the graphs, and the verbose
377 error messages instead of `$end', which remains being the default.
381 %token MYEOF 0 "end of file"
384 This old option, which has been broken for ages, is removed.
387 Brazilian Portuguese, thanks to Alexandre Folle de Menezes.
388 Croatian, thanks to Denis Lackovic.
390 * Incorrect token definitions
391 When given `%token 'a' "A"', Bison used to output `#define 'a' 65'.
393 * Token definitions as enums
394 Tokens are output both as the traditional #define's, and, provided
395 the compiler supports ANSI C or is a C++ compiler, as enums.
396 This lets debuggers display names instead of integers.
399 In addition to --verbose, bison supports --report=THINGS, which
400 produces additional information:
402 complete the core item sets with their closure
403 - lookahead [changed to `look-ahead' in 1.875e and later]
404 explicitly associate look-ahead tokens to items
406 describe shift/reduce conflicts solving.
407 Bison used to systematically output this information on top of
408 the report. Solved conflicts are now attached to their states.
411 Previous versions don't complain when there is a type clash on
412 the default action if the rule has a mid-rule action, such as in:
420 * GNU M4 is now required when using Bison.
422 Changes in version 1.35, 2002-03-25:
425 Some projects use Bison's C parser with C++ compilers, and define
426 YYSTYPE as a class. The recent adjustment of C parsers for data
427 alignment and 64 bit architectures made this impossible.
429 Because for the time being no real solution for C++ parser
430 generation exists, kludges were implemented in the parser to
431 maintain this use. In the future, when Bison has C++ parsers, this
432 kludge will be disabled.
434 This kludge also addresses some C++ problems when the stack was
437 Changes in version 1.34, 2002-03-12:
439 * File name clashes are detected
440 $ bison foo.y -d -o foo.x
441 fatal error: header and parser would both be named `foo.x'
443 * A missing `;' at the end of a rule triggers a warning
444 In accordance with POSIX, and in agreement with other
445 Yacc implementations, Bison will mandate this semicolon in the near
446 future. This eases the implementation of a Bison parser of Bison
447 grammars by making this grammar LALR(1) instead of LR(2). To
448 facilitate the transition, this release introduces a warning.
450 * Revert the C++ namespace changes introduced in 1.31, as they caused too
451 many portability hassles.
453 * DJGPP support added.
455 * Fix test suite portability problems.
457 Changes in version 1.33, 2002-02-07:
460 Groff could not be compiled for the definition of size_t was lacking
461 under some conditions.
466 Changes in version 1.32, 2002-01-23:
468 * Fix Yacc output file names
472 * Italian, Dutch translations
474 Changes in version 1.31, 2002-01-14:
478 * GNU Gettext and %expect
479 GNU Gettext asserts 10 s/r conflicts, but there are 7. Now that
480 Bison dies on incorrect %expectations, we fear there will be
481 too many bug reports for Gettext, so _for the time being_, %expect
482 does not trigger an error when the input file is named `plural.y'.
484 * Use of alloca in parsers
485 If YYSTACK_USE_ALLOCA is defined to 0, then the parsers will use
486 malloc exclusively. Since 1.29, but was not NEWS'ed.
488 alloca is used only when compiled with GCC, to avoid portability
491 * yyparse now returns 2 if memory is exhausted; formerly it dumped core.
493 * When the generated parser lacks debugging code, YYDEBUG is now 0
494 (as POSIX requires) instead of being undefined.
497 Bison has always permitted actions such as { $$ = $1 }: it adds the
498 ending semicolon. Now if in Yacc compatibility mode, the semicolon
499 is no longer output: one has to write { $$ = $1; }.
501 * Better C++ compliance
502 The output parsers try to respect C++ namespaces.
503 [This turned out to be a failed experiment, and it was reverted later.]
506 Fixed bugs when reporting useless nonterminals.
509 The parsers work properly on 64 bit hosts.
512 Some calls to strerror resulted in scrambled or missing error messages.
515 When the number of shift/reduce conflicts is correct, don't issue
518 * The verbose report includes the rule line numbers.
520 * Rule line numbers are fixed in traces.
522 * Swedish translation
525 Verbose parse error messages from the parsers are better looking.
526 Before: parse error: unexpected `'/'', expecting `"number"' or `'-'' or `'(''
527 Now: parse error: unexpected '/', expecting "number" or '-' or '('
529 * Fixed parser memory leaks.
530 When the generated parser was using malloc to extend its stacks, the
531 previous allocations were not freed.
533 * Fixed verbose output file.
534 Some newlines were missing.
535 Some conflicts in state descriptions were missing.
537 * Fixed conflict report.
538 Option -v was needed to get the result.
542 Mismatches are errors, not warnings.
544 * Fixed incorrect processing of some invalid input.
546 * Fixed CPP guards: 9foo.h uses BISON_9FOO_H instead of 9FOO_H.
548 * Fixed some typos in the documentation.
550 * %token MY_EOF 0 is supported.
551 Before, MY_EOF was silently renumbered as 257.
553 * doc/refcard.tex is updated.
555 * %output, %file-prefix, %name-prefix.
559 New, aliasing `--output-file'.
561 Changes in version 1.30, 2001-10-26:
563 * `--defines' and `--graph' have now an optional argument which is the
564 output file name. `-d' and `-g' do not change; they do not take any
567 * `%source_extension' and `%header_extension' are removed, failed
572 Changes in version 1.29, 2001-09-07:
574 * The output file does not define const, as this caused problems when used
575 with common autoconfiguration schemes. If you still use ancient compilers
576 that lack const, compile with the equivalent of the C compiler option
577 `-Dconst='. autoconf's AC_C_CONST macro provides one way to do this.
579 * Added `-g' and `--graph'.
581 * The Bison manual is now distributed under the terms of the GNU FDL.
583 * The input and the output files has automatically a similar extension.
585 * Russian translation added.
587 * NLS support updated; should hopefully be less troublesome.
589 * Added the old Bison reference card.
591 * Added `--locations' and `%locations'.
593 * Added `-S' and `--skeleton'.
595 * `%raw', `-r', `--raw' is disabled.
597 * Special characters are escaped when output. This solves the problems
598 of the #line lines with path names including backslashes.
601 `%yacc', `%fixed_output_files', `%defines', `%no_parser', `%verbose',
602 `%debug', `%source_extension' and `%header_extension'.
605 Automatic location tracking.
607 Changes in version 1.28, 1999-07-06:
609 * Should compile better now with K&R compilers.
613 * Fixed a problem with escaping the double quote character.
615 * There is now a FAQ.
617 Changes in version 1.27:
619 * The make rule which prevented bison.simple from being created on
620 some systems has been fixed.
622 Changes in version 1.26:
624 * Bison now uses automake.
626 * New mailing lists: <bug-bison@gnu.org> and <help-bison@gnu.org>.
628 * Token numbers now start at 257 as previously documented, not 258.
630 * Bison honors the TMPDIR environment variable.
632 * A couple of buffer overruns have been fixed.
634 * Problems when closing files should now be reported.
636 * Generated parsers should now work even on operating systems which do
637 not provide alloca().
639 Changes in version 1.25, 1995-10-16:
641 * Errors in the input grammar are not fatal; Bison keeps reading
642 the grammar file, and reports all the errors found in it.
644 * Tokens can now be specified as multiple-character strings: for
645 example, you could use "<=" for a token which looks like <=, instead
646 of chosing a name like LESSEQ.
648 * The %token_table declaration says to write a table of tokens (names
649 and numbers) into the parser file. The yylex function can use this
650 table to recognize multiple-character string tokens, or for other
653 * The %no_lines declaration says not to generate any #line preprocessor
654 directives in the parser file.
656 * The %raw declaration says to use internal Bison token numbers, not
657 Yacc-compatible token numbers, when token names are defined as macros.
659 * The --no-parser option produces the parser tables without including
660 the parser engine; a project can now use its own parser engine.
661 The actions go into a separate file called NAME.act, in the form of
662 a switch statement body.
664 Changes in version 1.23:
666 The user can define YYPARSE_PARAM as the name of an argument to be
667 passed into yyparse. The argument should have type void *. It should
668 actually point to an object. Grammar actions can access the variable
669 by casting it to the proper pointer type.
671 Line numbers in output file corrected.
673 Changes in version 1.22:
677 Changes in version 1.20:
679 Output file does not redefine const for C++.
687 Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005
688 Free Software Foundation, Inc.
690 This file is part of Bison, the GNU Compiler Compiler.
692 Bison is free software; you can redistribute it and/or modify
693 it under the terms of the GNU General Public License as published by
694 the Free Software Foundation; either version 2, or (at your option)
697 Bison is distributed in the hope that it will be useful,
698 but WITHOUT ANY WARRANTY; without even the implied warranty of
699 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
700 GNU General Public License for more details.
702 You should have received a copy of the GNU General Public License
703 along with autoconf; see the file COPYING. If not, write to
704 the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
705 Boston, MA 02110-1301, USA.