4 Changes in version 2.3a+ (????-??-??):
6 * The -g and --graph options now output graphs in Graphviz DOT format,
9 * An experimental directive %language specifies the language of the
10 generated parser, which can be C (the default) or C++. This
11 directive affects the skeleton used, and the names of the generated
12 files if the grammar file's name ends in ".y".
14 * The grammar file may now specify the name of the parser header file using
15 %defines. For example:
19 * The `=' that used to be required in the following declarations is now
26 * Revised warning: unset or unused mid-rule values
28 Since Bison 2.2, Bison has warned about mid-rule values that are set but not
29 used within any of the actions of the parent rule. For example, Bison warns
32 exp: '1' { $$ = 1; } '+' exp { $$ = $1 + $4; };
34 Now, Bison also warns about mid-rule values that are used but not set. For
35 example, Bison warns about unset $$ in the mid-rule action in:
37 exp: '1' { $1 = 1; } '+' exp { $$ = $2 + $4; };
39 However, Bison now disables both of these warnings by default since they
40 sometimes prove to be false alarms in existing grammars employing the Yacc
41 constructs $0 or $-N (where N is some positive integer).
43 To enable these warnings, specify the flag `--warnings=midrule-values' or
44 `-W', which is a synonym for `--warnings=all'.
46 * Bison now recognizes two separate kinds of default %destructor's and
49 1. Place `<*>' in a %destructor/%printer symbol list to define a default
50 %destructor/%printer for all grammar symbols for which you have formally
51 declared semantic type tags.
53 2. Place `<>' in a %destructor/%printer symbol list to define a default
54 %destructor/%printer for all grammar symbols without declared semantic
57 Bison no longer supports the `%symbol-default' notation from Bison 2.3a.
58 `<*>' and `<>' combined achieve the same effect with one exception: Bison no
59 longer applies any %destructor to a mid-rule value if that mid-rule value is
60 not actually ever referenced using either $$ or $n in a semantic action.
62 The default %destructor's and %printer's are experimental. More user
63 feedback will help to determine whether they should become permanent
66 See the section `Freeing Discarded Symbols' in the Bison manual for further
69 * The Yacc prologue alternatives from Bison 2.3a have been rewritten as the
74 Other than semantic actions, this is probably the most common place you
75 should write verbatim code for the parser implementation. It replaces
76 the traditional Yacc prologue, `%{CODE%}', for most purposes. Compare
79 - `%{CODE%}' appearing after the first `%union {CODE}' in a grammar
80 file. While Bison will continue to support `%{CODE%}' for backward
81 compatibility, `%code {CODE}' is cleaner as its functionality does
82 not depend on its position in the grammar file relative to any
83 `%union {CODE}'. Specifically, `%code {CODE}' always inserts your
84 CODE into the parser code file after the usual contents of the
86 - `%after-header {CODE}', which only Bison 2.3a supported.
90 This is the right place to write dependency code for externally exposed
91 definitions required by Bison. Such exposed definitions are those
92 usually appearing in the parser header file. Thus, this is the right
93 place to define types referenced in `%union {CODE}' directives, and it
94 is the right place to override Bison's default YYSTYPE and YYLTYPE
95 definitions. Compare with:
97 - `%{CODE%}' appearing before the first `%union {CODE}' in a grammar
98 file. Unlike `%{CODE%}', `%requires {CODE}' inserts your CODE both
99 into the parser code file and into the parser header file since
100 Bison's required definitions should depend on it in both places.
101 - `%start-header {CODE}', which only Bison 2.3a supported.
105 This is the right place to write additional definitions you would like
106 Bison to expose externally. That is, this directive inserts your CODE
107 both into the parser header file and into the parser code file after
108 Bison's required definitions. Compare with:
110 - `%end-header {CODE}', which only Bison 2.3a supported.
114 Occasionally it is desirable to insert code near the top of the parser
115 code file. For example:
124 - `%{CODE%}' appearing before the first `%union {CODE}' in a grammar
125 file. `%code-top {CODE}' is cleaner as its functionality does not
126 depend on its position in the grammar file relative to any
128 - `%before-header {CODE}', which only Bison 2.3a supported.
130 If you have multiple occurrences of any one of the above four directives,
131 Bison will concatenate the contents in the order they appear in the grammar
134 The prologue alternatives are experimental. More user feedback will help to
135 determine whether they should become permanent features.
137 Also see the new section `Prologue Alternatives' in the Bison manual.
139 Changes in version 2.3a, 2006-09-13:
141 * Instead of %union, you can define and use your own union type
142 YYSTYPE if your grammar contains at least one <type> tag.
143 Your YYSTYPE need not be a macro; it can be a typedef.
144 This change is for compatibility with other Yacc implementations,
145 and is required by POSIX.
147 * Locations columns and lines start at 1.
148 In accordance with the GNU Coding Standards and Emacs.
150 * You may now declare per-type and default %destructor's and %printer's:
154 %union { char *string; }
155 %token <string> STRING1
156 %token <string> STRING2
157 %type <string> string1
158 %type <string> string2
159 %union { char character; }
160 %token <character> CHR
161 %type <character> chr
162 %destructor { free ($$); } %symbol-default
163 %destructor { free ($$); printf ("%d", @$.first_line); } STRING1 string1
164 %destructor { } <character>
166 guarantees that, when the parser discards any user-defined symbol that has a
167 semantic type tag other than `<character>', it passes its semantic value to
168 `free'. However, when the parser discards a `STRING1' or a `string1', it
169 also prints its line number to `stdout'. It performs only the second
170 `%destructor' in this case, so it invokes `free' only once.
172 [Although we failed to mention this here in the 2.3a release, the default
173 %destructor's and %printer's were experimental, and they were rewritten in
176 * Except for LALR(1) parsers in C with POSIX Yacc emulation enabled (with `-y',
177 `--yacc', or `%yacc'), Bison no longer generates #define statements for
178 associating token numbers with token names. Removing the #define statements
179 helps to sanitize the global namespace during preprocessing, but POSIX Yacc
180 requires them. Bison still generates an enum for token names in all cases.
182 * Handling of traditional Yacc prologue blocks is now more consistent but
183 potentially incompatible with previous releases of Bison.
185 As before, you declare prologue blocks in your grammar file with the
186 `%{ ... %}' syntax. To generate the pre-prologue, Bison concatenates all
187 prologue blocks that you've declared before the first %union. To generate
188 the post-prologue, Bison concatenates all prologue blocks that you've
189 declared after the first %union.
191 Previous releases of Bison inserted the pre-prologue into both the header
192 file and the code file in all cases except for LALR(1) parsers in C. In the
193 latter case, Bison inserted it only into the code file. For parsers in C++,
194 the point of insertion was before any token definitions (which associate
195 token numbers with names). For parsers in C, the point of insertion was
196 after the token definitions.
198 Now, Bison never inserts the pre-prologue into the header file. In the code
199 file, it always inserts it before the token definitions.
201 * Bison now provides a more flexible alternative to the traditional Yacc
202 prologue blocks: %before-header, %start-header, %end-header, and
205 For example, the following declaration order in the grammar file reflects the
206 order in which Bison will output these code blocks. However, you are free to
207 declare these code blocks in your grammar file in whatever order is most
211 /* Bison treats this block like a pre-prologue block: it inserts it into
212 * the code file before the contents of the header file. It does *not*
213 * insert it into the header file. This is a good place to put
214 * #include's that you want at the top of your code file. A common
215 * example is `#include "system.h"'. */
218 /* Bison inserts this block into both the header file and the code file.
219 * In both files, the point of insertion is before any Bison-generated
220 * token, semantic type, location type, and class definitions. This is a
221 * good place to define %union dependencies, for example. */
224 /* Unlike the traditional Yacc prologue blocks, the output order for the
225 * new %*-header blocks is not affected by their declaration position
226 * relative to any %union in the grammar file. */
229 /* Bison inserts this block into both the header file and the code file.
230 * In both files, the point of insertion is after the Bison-generated
231 * definitions. This is a good place to declare or define public
232 * functions or data structures that depend on the Bison-generated
236 /* Bison treats this block like a post-prologue block: it inserts it into
237 * the code file after the contents of the header file. It does *not*
238 * insert it into the header file. This is a good place to declare or
239 * define internal functions or data structures that depend on the
240 * Bison-generated definitions. */
243 If you have multiple occurrences of any one of the above declarations, Bison
244 will concatenate the contents in declaration order.
246 [Although we failed to mention this here in the 2.3a release, the prologue
247 alternatives were experimental, and they were rewritten in future versions.]
249 * The option `--report=look-ahead' has been changed to `--report=lookahead'.
250 The old spelling still works, but is not documented and may be removed
253 Changes in version 2.3, 2006-06-05:
255 * GLR grammars should now use `YYRECOVERING ()' instead of `YYRECOVERING',
256 for compatibility with LALR(1) grammars.
258 * It is now documented that any definition of YYSTYPE or YYLTYPE should
259 be to a type name that does not contain parentheses or brackets.
261 Changes in version 2.2, 2006-05-19:
263 * The distribution terms for all Bison-generated parsers now permit
264 using the parsers in nonfree programs. Previously, this permission
265 was granted only for Bison-generated LALR(1) parsers in C.
267 * %name-prefix changes the namespace name in C++ outputs.
269 * The C++ parsers export their token_type.
271 * Bison now allows multiple %union declarations, and concatenates
272 their contents together.
274 * New warning: unused values
275 Right-hand side symbols whose values are not used are reported,
276 if the symbols have destructors. For instance:
278 exp: exp "?" exp ":" exp { $1 ? $1 : $3; }
282 will trigger a warning about $$ and $5 in the first rule, and $3 in
283 the second ($1 is copied to $$ by the default rule). This example
284 most likely contains three errors, and could be rewritten as:
286 exp: exp "?" exp ":" exp
287 { $$ = $1 ? $3 : $5; free ($1 ? $5 : $3); free ($1); }
289 { $$ = $1 ? $1 : $3; if ($1) free ($3); }
292 However, if the original actions were really intended, memory leaks
293 and all, the warnings can be suppressed by letting Bison believe the
294 values are used, e.g.:
296 exp: exp "?" exp ":" exp { $1 ? $1 : $3; (void) ($$, $5); }
297 | exp "+" exp { $$ = $1; (void) $3; }
300 If there are mid-rule actions, the warning is issued if no action
301 uses it. The following triggers no warning: $1 and $3 are used.
303 exp: exp { push ($1); } '+' exp { push ($3); sum (); };
305 The warning is intended to help catching lost values and memory leaks.
306 If a value is ignored, its associated memory typically is not reclaimed.
308 * %destructor vs. YYABORT, YYACCEPT, and YYERROR.
309 Destructors are now called when user code invokes YYABORT, YYACCEPT,
310 and YYERROR, for all objects on the stack, other than objects
311 corresponding to the right-hand side of the current rule.
313 * %expect, %expect-rr
314 Incorrect numbers of expected conflicts are now actual errors,
318 The %parse-params are available in the destructors (and the
319 experimental printers) as per the documentation.
321 * Bison now warns if it finds a stray `$' or `@' in an action.
324 This specifies that the grammar file depends on features implemented
325 in Bison version VERSION or higher.
327 * lalr1.cc: The token and value types are now class members.
328 The tokens were defined as free form enums and cpp macros. YYSTYPE
329 was defined as a free form union. They are now class members:
330 tokens are enumerations of the `yy::parser::token' struct, and the
331 semantic values have the `yy::parser::semantic_type' type.
333 If you do not want or can update to this scheme, the directive
334 `%define "global_tokens_and_yystype" "1"' triggers the global
335 definition of tokens and YYSTYPE. This change is suitable both
336 for previous releases of Bison, and this one.
338 If you wish to update, then make sure older version of Bison will
339 fail using `%require "2.2"'.
341 * DJGPP support added.
343 Changes in version 2.1, 2005-09-16:
345 * The C++ lalr1.cc skeleton supports %lex-param.
347 * Bison-generated parsers now support the translation of diagnostics like
348 "syntax error" into languages other than English. The default
349 language is still English. For details, please see the new
350 Internationalization section of the Bison manual. Software
351 distributors should also see the new PACKAGING file. Thanks to
352 Bruno Haible for this new feature.
354 * Wording in the Bison-generated parsers has been changed slightly to
355 simplify translation. In particular, the message "memory exhausted"
356 has replaced "parser stack overflow", as the old message was not
357 always accurate for modern Bison-generated parsers.
359 * Destructors are now called when the parser aborts, for all symbols left
360 behind on the stack. Also, the start symbol is now destroyed after a
361 successful parse. In both cases, the behavior was formerly inconsistent.
363 * When generating verbose diagnostics, Bison-generated parsers no longer
364 quote the literal strings associated with tokens. For example, for
365 a syntax error associated with '%token NUM "number"' they might
366 print 'syntax error, unexpected number' instead of 'syntax error,
367 unexpected "number"'.
369 Changes in version 2.0, 2004-12-25:
371 * Possibly-incompatible changes
373 - Bison-generated parsers no longer default to using the alloca function
374 (when available) to extend the parser stack, due to widespread
375 problems in unchecked stack-overflow detection. You can "#define
376 YYSTACK_USE_ALLOCA 1" to require the use of alloca, but please read
377 the manual to determine safe values for YYMAXDEPTH in that case.
379 - Error token location.
380 During error recovery, the location of the syntax error is updated
381 to cover the whole sequence covered by the error token: it includes
382 the shifted symbols thrown away during the first part of the error
383 recovery, and the lookahead rejected during the second part.
386 . Stray semicolons are no longer allowed at the start of a grammar.
387 . Semicolons are now required after in-grammar declarations.
389 - Unescaped newlines are no longer allowed in character constants or
390 string literals. They were never portable, and GCC 3.4.0 has
391 dropped support for them. Better diagnostics are now generated if
392 forget a closing quote.
394 - NUL bytes are no longer allowed in Bison string literals, unfortunately.
398 - GLR grammars now support locations.
400 - New directive: %initial-action.
401 This directive allows the user to run arbitrary code (including
402 initializing @$) from yyparse before parsing starts.
404 - A new directive "%expect-rr N" specifies the expected number of
405 reduce/reduce conflicts in GLR parsers.
407 - %token numbers can now be hexadecimal integers, e.g., `%token FOO 0x12d'.
408 This is a GNU extension.
410 - The option `--report=lookahead' was changed to `--report=look-ahead'.
411 [However, this was changed back after 2.3.]
413 - Experimental %destructor support has been added to lalr1.cc.
415 - New configure option --disable-yacc, to disable installation of the
416 yacc command and -ly library introduced in 1.875 for POSIX conformance.
420 - For now, %expect-count violations are now just warnings, not errors.
421 This is for compatibility with Bison 1.75 and earlier (when there are
422 reduce/reduce conflicts) and with Bison 1.30 and earlier (when there
423 are too many or too few shift/reduce conflicts). However, in future
424 versions of Bison we plan to improve the %expect machinery so that
425 these violations will become errors again.
427 - Within Bison itself, numbers (e.g., goto numbers) are no longer
428 arbitrarily limited to 16-bit counts.
430 - Semicolons are now allowed before "|" in grammar rules, as POSIX requires.
432 Changes in version 1.875, 2003-01-01:
434 * The documentation license has been upgraded to version 1.2
435 of the GNU Free Documentation License.
437 * syntax error processing
439 - In Yacc-style parsers YYLLOC_DEFAULT is now used to compute error
440 locations too. This fixes bugs in error-location computation.
443 It is now possible to reclaim the memory associated to symbols
444 discarded during error recovery. This feature is still experimental.
447 This new directive is preferred over YYERROR_VERBOSE.
449 - #defining yyerror to steal internal variables is discouraged.
450 It is not guaranteed to work forever.
454 - Semicolons are once again optional at the end of grammar rules.
455 This reverts to the behavior of Bison 1.33 and earlier, and improves
456 compatibility with Yacc.
458 - `parse error' -> `syntax error'
459 Bison now uniformly uses the term `syntax error'; formerly, the code
460 and manual sometimes used the term `parse error' instead. POSIX
461 requires `syntax error' in diagnostics, and it was thought better to
464 - The documentation now emphasizes that yylex and yyerror must be
465 declared before use. C99 requires this.
467 - Bison now parses C99 lexical constructs like UCNs and
468 backslash-newline within C escape sequences, as POSIX 1003.1-2001 requires.
470 - File names are properly escaped in C output. E.g., foo\bar.y is
471 output as "foo\\bar.y".
473 - Yacc command and library now available
474 The Bison distribution now installs a `yacc' command, as POSIX requires.
475 Also, Bison now installs a small library liby.a containing
476 implementations of Yacc-compatible yyerror and main functions.
477 This library is normally not useful, but POSIX requires it.
479 - Type clashes now generate warnings, not errors.
481 - If the user does not define YYSTYPE as a macro, Bison now declares it
482 using typedef instead of defining it as a macro.
483 For consistency, YYLTYPE is also declared instead of defined.
485 * Other compatibility issues
487 - %union directives can now have a tag before the `{', e.g., the
488 directive `%union foo {...}' now generates the C code
489 `typedef union foo { ... } YYSTYPE;'; this is for Yacc compatibility.
490 The default union tag is `YYSTYPE', for compatibility with Solaris 9 Yacc.
491 For consistency, YYLTYPE's struct tag is now `YYLTYPE' not `yyltype'.
492 This is for compatibility with both Yacc and Bison 1.35.
494 - `;' is output before the terminating `}' of an action, for
495 compatibility with Bison 1.35.
497 - Bison now uses a Yacc-style format for conflict reports, e.g.,
498 `conflicts: 2 shift/reduce, 1 reduce/reduce'.
500 - `yystype' and `yyltype' are now obsolescent macros instead of being
501 typedefs or tags; they are no longer documented and are planned to be
502 withdrawn in a future release.
507 Users of Bison have to decide how they handle the portability of the
510 - `parsing stack overflow...' -> `parser stack overflow'
511 GLR parsers now report `parser stack overflow' as per the Bison manual.
513 * Bison now warns if it detects conflicting outputs to the same file,
514 e.g., it generates a warning for `bison -d -o foo.h foo.y' since
515 that command outputs both code and header to foo.h.
517 * #line in output files
518 - --no-line works properly.
520 * Bison can no longer be built by a K&R C compiler; it requires C89 or
521 later to be built. This change originally took place a few versions
522 ago, but nobody noticed until we recently asked someone to try
523 building Bison with a K&R C compiler.
525 Changes in version 1.75, 2002-10-14:
527 * Bison should now work on 64-bit hosts.
529 * Indonesian translation thanks to Tedi Heriyanto.
532 Fix spurious parse errors.
535 Some people redefine yyerror to steal yyparse' private variables.
536 Reenable this trick until an official feature replaces it.
539 In agreement with POSIX and with other Yaccs, leaving a default
540 action is valid when $$ is untyped, and $1 typed:
544 but the converse remains an error:
548 * Values of mid-rule actions
551 foo: { ... } { $$ = $1; } ...
553 was incorrectly rejected: $1 is defined in the second mid-rule
554 action, and is equal to the $$ of the first mid-rule action.
556 Changes in version 1.50, 2002-10-04:
561 causes Bison to produce a Generalized LR (GLR) parser, capable of handling
562 almost any context-free grammar, ambiguous or not. The new declarations
563 %dprec and %merge on grammar rules allow parse-time resolution of
564 ambiguities. Contributed by Paul Hilfinger.
566 Unfortunately Bison 1.50 does not work properly on 64-bit hosts
567 like the Alpha, so please stick to 32-bit hosts for now.
570 When not in Yacc compatibility mode, when the output file was not
571 specified, running `bison foo/bar.y' created `foo/bar.c'. It
575 The undefined token was systematically mapped to 2 which prevented
576 the use of 2 by the user. This is no longer the case.
578 * Unknown token numbers
579 If yylex returned an out of range value, yyparse could die. This is
583 According to POSIX, the error token must be 256.
584 Bison extends this requirement by making it a preference: *if* the
585 user specified that one of her tokens is numbered 256, then error
586 will be mapped onto another number.
588 * Verbose error messages
589 They no longer report `..., expecting error or...' for states where
590 error recovery is possible.
593 Defaults to `$end' instead of `$'.
595 * Error recovery now conforms to documentation and to POSIX
596 When a Bison-generated parser encounters a syntax error, it now pops
597 the stack until it finds a state that allows shifting the error
598 token. Formerly, it popped the stack until it found a state that
599 allowed some non-error action other than a default reduction on the
600 error token. The new behavior has long been the documented behavior,
601 and has long been required by POSIX. For more details, please see
602 Paul Eggert, "Reductions during Bison error handling" (2002-05-20)
603 <http://lists.gnu.org/archive/html/bug-bison/2002-05/msg00038.html>.
606 Popped tokens and nonterminals are now reported.
609 Larger grammars are now supported (larger token numbers, larger grammar
610 size (= sum of the LHS and RHS lengths), larger LALR tables).
611 Formerly, many of these numbers ran afoul of 16-bit limits;
612 now these limits are 32 bits on most hosts.
614 * Explicit initial rule
615 Bison used to play hacks with the initial rule, which the user does
616 not write. It is now explicit, and visible in the reports and
620 Before, Bison reported the useless rules, but, although not used,
621 included them in the parsers. They are now actually removed.
623 * Useless rules, useless nonterminals
624 They are now reported, as a warning, with their locations.
626 * Rules never reduced
627 Rules that can never be reduced because of conflicts are now
630 * Incorrect `Token not used'
633 %token useless useful
635 exp: '0' %prec useful;
637 where a token was used to set the precedence of the last rule,
638 bison reported both `useful' and `useless' as useless tokens.
640 * Revert the C++ namespace changes introduced in 1.31
641 as they caused too many portability hassles.
644 By an accident of design, the default computation of @$ was
645 performed after another default computation was performed: @$ = @1.
646 The latter is now removed: YYLLOC_DEFAULT is fully responsible of
647 the computation of @$.
650 The token end of file may be specified by the user, in which case,
651 the user symbol is used in the reports, the graphs, and the verbose
652 error messages instead of `$end', which remains being the default.
656 %token MYEOF 0 "end of file"
659 This old option, which has been broken for ages, is removed.
662 Brazilian Portuguese, thanks to Alexandre Folle de Menezes.
663 Croatian, thanks to Denis Lackovic.
665 * Incorrect token definitions
666 When given `%token 'a' "A"', Bison used to output `#define 'a' 65'.
668 * Token definitions as enums
669 Tokens are output both as the traditional #define's, and, provided
670 the compiler supports ANSI C or is a C++ compiler, as enums.
671 This lets debuggers display names instead of integers.
674 In addition to --verbose, bison supports --report=THINGS, which
675 produces additional information:
677 complete the core item sets with their closure
678 - lookahead [changed to `look-ahead' in 1.875e through 2.3, but changed back]
679 explicitly associate lookahead tokens to items
681 describe shift/reduce conflicts solving.
682 Bison used to systematically output this information on top of
683 the report. Solved conflicts are now attached to their states.
686 Previous versions don't complain when there is a type clash on
687 the default action if the rule has a mid-rule action, such as in:
695 * GNU M4 is now required when using Bison.
697 Changes in version 1.35, 2002-03-25:
700 Some projects use Bison's C parser with C++ compilers, and define
701 YYSTYPE as a class. The recent adjustment of C parsers for data
702 alignment and 64 bit architectures made this impossible.
704 Because for the time being no real solution for C++ parser
705 generation exists, kludges were implemented in the parser to
706 maintain this use. In the future, when Bison has C++ parsers, this
707 kludge will be disabled.
709 This kludge also addresses some C++ problems when the stack was
712 Changes in version 1.34, 2002-03-12:
714 * File name clashes are detected
715 $ bison foo.y -d -o foo.x
716 fatal error: header and parser would both be named `foo.x'
718 * A missing `;' at the end of a rule triggers a warning
719 In accordance with POSIX, and in agreement with other
720 Yacc implementations, Bison will mandate this semicolon in the near
721 future. This eases the implementation of a Bison parser of Bison
722 grammars by making this grammar LALR(1) instead of LR(2). To
723 facilitate the transition, this release introduces a warning.
725 * Revert the C++ namespace changes introduced in 1.31, as they caused too
726 many portability hassles.
728 * DJGPP support added.
730 * Fix test suite portability problems.
732 Changes in version 1.33, 2002-02-07:
735 Groff could not be compiled for the definition of size_t was lacking
736 under some conditions.
741 Changes in version 1.32, 2002-01-23:
743 * Fix Yacc output file names
747 * Italian, Dutch translations
749 Changes in version 1.31, 2002-01-14:
753 * GNU Gettext and %expect
754 GNU Gettext asserts 10 s/r conflicts, but there are 7. Now that
755 Bison dies on incorrect %expectations, we fear there will be
756 too many bug reports for Gettext, so _for the time being_, %expect
757 does not trigger an error when the input file is named `plural.y'.
759 * Use of alloca in parsers
760 If YYSTACK_USE_ALLOCA is defined to 0, then the parsers will use
761 malloc exclusively. Since 1.29, but was not NEWS'ed.
763 alloca is used only when compiled with GCC, to avoid portability
766 * yyparse now returns 2 if memory is exhausted; formerly it dumped core.
768 * When the generated parser lacks debugging code, YYDEBUG is now 0
769 (as POSIX requires) instead of being undefined.
772 Bison has always permitted actions such as { $$ = $1 }: it adds the
773 ending semicolon. Now if in Yacc compatibility mode, the semicolon
774 is no longer output: one has to write { $$ = $1; }.
776 * Better C++ compliance
777 The output parsers try to respect C++ namespaces.
778 [This turned out to be a failed experiment, and it was reverted later.]
781 Fixed bugs when reporting useless nonterminals.
784 The parsers work properly on 64 bit hosts.
787 Some calls to strerror resulted in scrambled or missing error messages.
790 When the number of shift/reduce conflicts is correct, don't issue
793 * The verbose report includes the rule line numbers.
795 * Rule line numbers are fixed in traces.
797 * Swedish translation
800 Verbose parse error messages from the parsers are better looking.
801 Before: parse error: unexpected `'/'', expecting `"number"' or `'-'' or `'(''
802 Now: parse error: unexpected '/', expecting "number" or '-' or '('
804 * Fixed parser memory leaks.
805 When the generated parser was using malloc to extend its stacks, the
806 previous allocations were not freed.
808 * Fixed verbose output file.
809 Some newlines were missing.
810 Some conflicts in state descriptions were missing.
812 * Fixed conflict report.
813 Option -v was needed to get the result.
817 Mismatches are errors, not warnings.
819 * Fixed incorrect processing of some invalid input.
821 * Fixed CPP guards: 9foo.h uses BISON_9FOO_H instead of 9FOO_H.
823 * Fixed some typos in the documentation.
825 * %token MY_EOF 0 is supported.
826 Before, MY_EOF was silently renumbered as 257.
828 * doc/refcard.tex is updated.
830 * %output, %file-prefix, %name-prefix.
834 New, aliasing `--output-file'.
836 Changes in version 1.30, 2001-10-26:
838 * `--defines' and `--graph' have now an optional argument which is the
839 output file name. `-d' and `-g' do not change; they do not take any
842 * `%source_extension' and `%header_extension' are removed, failed
847 Changes in version 1.29, 2001-09-07:
849 * The output file does not define const, as this caused problems when used
850 with common autoconfiguration schemes. If you still use ancient compilers
851 that lack const, compile with the equivalent of the C compiler option
852 `-Dconst='. autoconf's AC_C_CONST macro provides one way to do this.
854 * Added `-g' and `--graph'.
856 * The Bison manual is now distributed under the terms of the GNU FDL.
858 * The input and the output files has automatically a similar extension.
860 * Russian translation added.
862 * NLS support updated; should hopefully be less troublesome.
864 * Added the old Bison reference card.
866 * Added `--locations' and `%locations'.
868 * Added `-S' and `--skeleton'.
870 * `%raw', `-r', `--raw' is disabled.
872 * Special characters are escaped when output. This solves the problems
873 of the #line lines with path names including backslashes.
876 `%yacc', `%fixed_output_files', `%defines', `%no_parser', `%verbose',
877 `%debug', `%source_extension' and `%header_extension'.
880 Automatic location tracking.
882 Changes in version 1.28, 1999-07-06:
884 * Should compile better now with K&R compilers.
888 * Fixed a problem with escaping the double quote character.
890 * There is now a FAQ.
892 Changes in version 1.27:
894 * The make rule which prevented bison.simple from being created on
895 some systems has been fixed.
897 Changes in version 1.26:
899 * Bison now uses automake.
901 * New mailing lists: <bug-bison@gnu.org> and <help-bison@gnu.org>.
903 * Token numbers now start at 257 as previously documented, not 258.
905 * Bison honors the TMPDIR environment variable.
907 * A couple of buffer overruns have been fixed.
909 * Problems when closing files should now be reported.
911 * Generated parsers should now work even on operating systems which do
912 not provide alloca().
914 Changes in version 1.25, 1995-10-16:
916 * Errors in the input grammar are not fatal; Bison keeps reading
917 the grammar file, and reports all the errors found in it.
919 * Tokens can now be specified as multiple-character strings: for
920 example, you could use "<=" for a token which looks like <=, instead
921 of chosing a name like LESSEQ.
923 * The %token_table declaration says to write a table of tokens (names
924 and numbers) into the parser file. The yylex function can use this
925 table to recognize multiple-character string tokens, or for other
928 * The %no_lines declaration says not to generate any #line preprocessor
929 directives in the parser file.
931 * The %raw declaration says to use internal Bison token numbers, not
932 Yacc-compatible token numbers, when token names are defined as macros.
934 * The --no-parser option produces the parser tables without including
935 the parser engine; a project can now use its own parser engine.
936 The actions go into a separate file called NAME.act, in the form of
937 a switch statement body.
939 Changes in version 1.23:
941 The user can define YYPARSE_PARAM as the name of an argument to be
942 passed into yyparse. The argument should have type void *. It should
943 actually point to an object. Grammar actions can access the variable
944 by casting it to the proper pointer type.
946 Line numbers in output file corrected.
948 Changes in version 1.22:
952 Changes in version 1.20:
954 Output file does not redefine const for C++.
962 Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003,
963 2004, 2005, 2006 Free Software Foundation, Inc.
965 This file is part of Bison, the GNU Compiler Compiler.
967 Bison is free software; you can redistribute it and/or modify
968 it under the terms of the GNU General Public License as published by
969 the Free Software Foundation; either version 2, or (at your option)
972 Bison is distributed in the hope that it will be useful,
973 but WITHOUT ANY WARRANTY; without even the implied warranty of
974 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
975 GNU General Public License for more details.
977 You should have received a copy of the GNU General Public License
978 along with autoconf; see the file COPYING. If not, write to
979 the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
980 Boston, MA 02110-1301, USA.