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1 Bison News
2 ----------
3
4 * Changes in version 2.4.3 (????-??-??):
5
6 ** Problems with spawning M4 on at least FreeBSD 8 and FreeBSD 9 have
7 been fixed.
8
9 * Changes in version 2.4.2 (2010-03-20):
10
11 ** Some portability problems that resulted in failures and livelocks
12 in the test suite on some versions of at least Solaris, AIX, HP-UX,
13 RHEL4, and Tru64 have been addressed. As a result, fatal Bison
14 errors should no longer cause M4 to report a broken pipe on the
15 affected platforms.
16
17 ** `%prec IDENTIFIER' requires IDENTIFIER to be defined separately.
18
19 POSIX specifies that an error be reported for any identifier that does
20 not appear on the LHS of a grammar rule and that is not defined by
21 %token, %left, %right, or %nonassoc. Bison 2.3b and later lost this
22 error report for the case when an identifier appears only after a
23 %prec directive. It is now restored. However, for backward
24 compatibility with recent Bison releases, it is only a warning for
25 now. In Bison 2.5 and later, it will return to being an error.
26
27 ** Detection of GNU M4 1.4.6 or newer during configure is improved.
28
29 ** Warnings from gcc's -Wundef option about undefined YYENABLE_NLS,
30 YYLTYPE_IS_TRIVIAL, and __STRICT_ANSI__ in C/C++ parsers are now
31 avoided.
32
33 ** %code is now a permanent feature.
34
35 A traditional Yacc prologue directive is written in the form:
36
37 %{CODE%}
38
39 To provide a more flexible alternative, Bison 2.3b introduced the
40 %code directive with the following forms for C/C++:
41
42 %code {CODE}
43 %code requires {CODE}
44 %code provides {CODE}
45 %code top {CODE}
46
47 These forms are now considered permanent features of Bison. See the
48 %code entries in the section "Bison Declaration Summary" in the Bison
49 manual for a summary of their functionality. See the section
50 "Prologue Alternatives" for a detailed discussion including the
51 advantages of %code over the traditional Yacc prologue directive.
52
53 Bison's Java feature as a whole including its current usage of %code
54 is still considered experimental.
55
56 ** YYFAIL is deprecated and will eventually be removed.
57
58 YYFAIL has existed for many years as an undocumented feature of
59 deterministic parsers in C generated by Bison. Previously, it was
60 documented for Bison's experimental Java parsers. YYFAIL is no longer
61 documented for Java parsers and is formally deprecated in both cases.
62 Users are strongly encouraged to migrate to YYERROR, which is
63 specified by POSIX.
64
65 Like YYERROR, you can invoke YYFAIL from a semantic action in order to
66 induce a syntax error. The most obvious difference from YYERROR is
67 that YYFAIL will automatically invoke yyerror to report the syntax
68 error so that you don't have to. However, there are several other
69 subtle differences between YYERROR and YYFAIL, and YYFAIL suffers from
70 inherent flaws when %error-verbose or `#define YYERROR_VERBOSE' is
71 used. For a more detailed discussion, see:
72
73 http://lists.gnu.org/archive/html/bison-patches/2009-12/msg00024.html
74
75 The upcoming Bison 2.5 will remove YYFAIL from Java parsers, but
76 deterministic parsers in C will continue to implement it. However,
77 because YYFAIL is already flawed, it seems futile to try to make new
78 Bison features compatible with it. Thus, during parser generation,
79 Bison 2.5 will produce a warning whenever it discovers YYFAIL in a
80 rule action. In a later release, YYFAIL will be disabled for
81 %error-verbose and `#define YYERROR_VERBOSE'. Eventually, YYFAIL will
82 be removed altogether.
83
84 There exists at least one case where Bison 2.5's YYFAIL warning will
85 be a false positive. Some projects add phony uses of YYFAIL and other
86 Bison-defined macros for the sole purpose of suppressing C
87 preprocessor warnings (from GCC cpp's -Wunused-macros, for example).
88 To avoid Bison's future warning, such YYFAIL uses can be moved to the
89 epilogue (that is, after the second `%%') in the Bison input file. In
90 this release (2.4.2), Bison already generates its own code to suppress
91 C preprocessor warnings for YYFAIL, so projects can remove their own
92 phony uses of YYFAIL if compatibility with Bison releases prior to
93 2.4.2 is not necessary.
94
95 ** Internationalization.
96
97 Fix a regression introduced in Bison 2.4: Under some circumstances,
98 message translations were not installed although supported by the
99 host system.
100
101 * Changes in version 2.4.1 (2008-12-11):
102
103 ** In the GLR defines file, unexpanded M4 macros in the yylval and yylloc
104 declarations have been fixed.
105
106 ** Temporary hack for adding a semicolon to the user action.
107
108 Bison used to prepend a trailing semicolon at the end of the user
109 action for reductions. This allowed actions such as
110
111 exp: exp "+" exp { $$ = $1 + $3 };
112
113 instead of
114
115 exp: exp "+" exp { $$ = $1 + $3; };
116
117 Some grammars still depend on this `feature'. Bison 2.4.1 restores
118 the previous behavior in the case of C output (specifically, when
119 neither %language or %skeleton or equivalent command-line options
120 are used) to leave more time for grammars depending on the old
121 behavior to be adjusted. Future releases of Bison will disable this
122 feature.
123
124 ** A few minor improvements to the Bison manual.
125
126 * Changes in version 2.4 (2008-11-02):
127
128 ** %language is an experimental feature.
129
130 We first introduced this feature in test release 2.3b as a cleaner
131 alternative to %skeleton. Since then, we have discussed the possibility of
132 modifying its effect on Bison's output file names. Thus, in this release,
133 we consider %language to be an experimental feature that will likely evolve
134 in future releases.
135
136 ** Forward compatibility with GNU M4 has been improved.
137
138 ** Several bugs in the C++ skeleton and the experimental Java skeleton have been
139 fixed.
140
141 * Changes in version 2.3b (2008-05-27):
142
143 ** The quotes around NAME that used to be required in the following directive
144 are now deprecated:
145
146 %define NAME "VALUE"
147
148 ** The directive `%pure-parser' is now deprecated in favor of:
149
150 %define api.pure
151
152 which has the same effect except that Bison is more careful to warn about
153 unreasonable usage in the latter case.
154
155 ** Push Parsing
156
157 Bison can now generate an LALR(1) parser in C with a push interface. That
158 is, instead of invoking `yyparse', which pulls tokens from `yylex', you can
159 push one token at a time to the parser using `yypush_parse', which will
160 return to the caller after processing each token. By default, the push
161 interface is disabled. Either of the following directives will enable it:
162
163 %define api.push_pull "push" // Just push; does not require yylex.
164 %define api.push_pull "both" // Push and pull; requires yylex.
165
166 See the new section `A Push Parser' in the Bison manual for details.
167
168 The current push parsing interface is experimental and may evolve. More user
169 feedback will help to stabilize it.
170
171 ** The -g and --graph options now output graphs in Graphviz DOT format,
172 not VCG format. Like --graph, -g now also takes an optional FILE argument
173 and thus cannot be bundled with other short options.
174
175 ** Java
176
177 Bison can now generate an LALR(1) parser in Java. The skeleton is
178 `data/lalr1.java'. Consider using the new %language directive instead of
179 %skeleton to select it.
180
181 See the new section `Java Parsers' in the Bison manual for details.
182
183 The current Java interface is experimental and may evolve. More user
184 feedback will help to stabilize it.
185
186 ** %language
187
188 This new directive specifies the programming language of the generated
189 parser, which can be C (the default), C++, or Java. Besides the skeleton
190 that Bison uses, the directive affects the names of the generated files if
191 the grammar file's name ends in ".y".
192
193 ** XML Automaton Report
194
195 Bison can now generate an XML report of the LALR(1) automaton using the new
196 `--xml' option. The current XML schema is experimental and may evolve. More
197 user feedback will help to stabilize it.
198
199 ** The grammar file may now specify the name of the parser header file using
200 %defines. For example:
201
202 %defines "parser.h"
203
204 ** When reporting useless rules, useless nonterminals, and unused terminals,
205 Bison now employs the terms "useless in grammar" instead of "useless",
206 "useless in parser" instead of "never reduced", and "unused in grammar"
207 instead of "unused".
208
209 ** Unreachable State Removal
210
211 Previously, Bison sometimes generated parser tables containing unreachable
212 states. A state can become unreachable during conflict resolution if Bison
213 disables a shift action leading to it from a predecessor state. Bison now:
214
215 1. Removes unreachable states.
216
217 2. Does not report any conflicts that appeared in unreachable states.
218 WARNING: As a result, you may need to update %expect and %expect-rr
219 directives in existing grammar files.
220
221 3. For any rule used only in such states, Bison now reports the rule as
222 "useless in parser due to conflicts".
223
224 This feature can be disabled with the following directive:
225
226 %define lr.keep_unreachable_states
227
228 See the %define entry in the `Bison Declaration Summary' in the Bison manual
229 for further discussion.
230
231 ** Lookahead Set Correction in the `.output' Report
232
233 When instructed to generate a `.output' file including lookahead sets
234 (using `--report=lookahead', for example), Bison now prints each reduction's
235 lookahead set only next to the associated state's one item that (1) is
236 associated with the same rule as the reduction and (2) has its dot at the end
237 of its RHS. Previously, Bison also erroneously printed the lookahead set
238 next to all of the state's other items associated with the same rule. This
239 bug affected only the `.output' file and not the generated parser source
240 code.
241
242 ** --report-file=FILE is a new option to override the default `.output' file
243 name.
244
245 ** The `=' that used to be required in the following directives is now
246 deprecated:
247
248 %file-prefix "parser"
249 %name-prefix "c_"
250 %output "parser.c"
251
252 ** An Alternative to `%{...%}' -- `%code QUALIFIER {CODE}'
253
254 Bison 2.3a provided a new set of directives as a more flexible alternative to
255 the traditional Yacc prologue blocks. Those have now been consolidated into
256 a single %code directive with an optional qualifier field, which identifies
257 the purpose of the code and thus the location(s) where Bison should generate
258 it:
259
260 1. `%code {CODE}' replaces `%after-header {CODE}'
261 2. `%code requires {CODE}' replaces `%start-header {CODE}'
262 3. `%code provides {CODE}' replaces `%end-header {CODE}'
263 4. `%code top {CODE}' replaces `%before-header {CODE}'
264
265 See the %code entries in section `Bison Declaration Summary' in the Bison
266 manual for a summary of the new functionality. See the new section `Prologue
267 Alternatives' for a detailed discussion including the advantages of %code
268 over the traditional Yacc prologues.
269
270 The prologue alternatives are experimental. More user feedback will help to
271 determine whether they should become permanent features.
272
273 ** Revised warning: unset or unused mid-rule values
274
275 Since Bison 2.2, Bison has warned about mid-rule values that are set but not
276 used within any of the actions of the parent rule. For example, Bison warns
277 about unused $2 in:
278
279 exp: '1' { $$ = 1; } '+' exp { $$ = $1 + $4; };
280
281 Now, Bison also warns about mid-rule values that are used but not set. For
282 example, Bison warns about unset $$ in the mid-rule action in:
283
284 exp: '1' { $1 = 1; } '+' exp { $$ = $2 + $4; };
285
286 However, Bison now disables both of these warnings by default since they
287 sometimes prove to be false alarms in existing grammars employing the Yacc
288 constructs $0 or $-N (where N is some positive integer).
289
290 To enable these warnings, specify the option `--warnings=midrule-values' or
291 `-W', which is a synonym for `--warnings=all'.
292
293 ** Default %destructor or %printer with `<*>' or `<>'
294
295 Bison now recognizes two separate kinds of default %destructor's and
296 %printer's:
297
298 1. Place `<*>' in a %destructor/%printer symbol list to define a default
299 %destructor/%printer for all grammar symbols for which you have formally
300 declared semantic type tags.
301
302 2. Place `<>' in a %destructor/%printer symbol list to define a default
303 %destructor/%printer for all grammar symbols without declared semantic
304 type tags.
305
306 Bison no longer supports the `%symbol-default' notation from Bison 2.3a.
307 `<*>' and `<>' combined achieve the same effect with one exception: Bison no
308 longer applies any %destructor to a mid-rule value if that mid-rule value is
309 not actually ever referenced using either $$ or $n in a semantic action.
310
311 The default %destructor's and %printer's are experimental. More user
312 feedback will help to determine whether they should become permanent
313 features.
314
315 See the section `Freeing Discarded Symbols' in the Bison manual for further
316 details.
317
318 ** %left, %right, and %nonassoc can now declare token numbers. This is required
319 by POSIX. However, see the end of section `Operator Precedence' in the Bison
320 manual for a caveat concerning the treatment of literal strings.
321
322 ** The nonfunctional --no-parser, -n, and %no-parser options have been
323 completely removed from Bison.
324
325 * Changes in version 2.3a, 2006-09-13:
326
327 ** Instead of %union, you can define and use your own union type
328 YYSTYPE if your grammar contains at least one <type> tag.
329 Your YYSTYPE need not be a macro; it can be a typedef.
330 This change is for compatibility with other Yacc implementations,
331 and is required by POSIX.
332
333 ** Locations columns and lines start at 1.
334 In accordance with the GNU Coding Standards and Emacs.
335
336 ** You may now declare per-type and default %destructor's and %printer's:
337
338 For example:
339
340 %union { char *string; }
341 %token <string> STRING1
342 %token <string> STRING2
343 %type <string> string1
344 %type <string> string2
345 %union { char character; }
346 %token <character> CHR
347 %type <character> chr
348 %destructor { free ($$); } %symbol-default
349 %destructor { free ($$); printf ("%d", @$.first_line); } STRING1 string1
350 %destructor { } <character>
351
352 guarantees that, when the parser discards any user-defined symbol that has a
353 semantic type tag other than `<character>', it passes its semantic value to
354 `free'. However, when the parser discards a `STRING1' or a `string1', it
355 also prints its line number to `stdout'. It performs only the second
356 `%destructor' in this case, so it invokes `free' only once.
357
358 [Although we failed to mention this here in the 2.3a release, the default
359 %destructor's and %printer's were experimental, and they were rewritten in
360 future versions.]
361
362 ** Except for LALR(1) parsers in C with POSIX Yacc emulation enabled (with `-y',
363 `--yacc', or `%yacc'), Bison no longer generates #define statements for
364 associating token numbers with token names. Removing the #define statements
365 helps to sanitize the global namespace during preprocessing, but POSIX Yacc
366 requires them. Bison still generates an enum for token names in all cases.
367
368 ** Handling of traditional Yacc prologue blocks is now more consistent but
369 potentially incompatible with previous releases of Bison.
370
371 As before, you declare prologue blocks in your grammar file with the
372 `%{ ... %}' syntax. To generate the pre-prologue, Bison concatenates all
373 prologue blocks that you've declared before the first %union. To generate
374 the post-prologue, Bison concatenates all prologue blocks that you've
375 declared after the first %union.
376
377 Previous releases of Bison inserted the pre-prologue into both the header
378 file and the code file in all cases except for LALR(1) parsers in C. In the
379 latter case, Bison inserted it only into the code file. For parsers in C++,
380 the point of insertion was before any token definitions (which associate
381 token numbers with names). For parsers in C, the point of insertion was
382 after the token definitions.
383
384 Now, Bison never inserts the pre-prologue into the header file. In the code
385 file, it always inserts it before the token definitions.
386
387 ** Bison now provides a more flexible alternative to the traditional Yacc
388 prologue blocks: %before-header, %start-header, %end-header, and
389 %after-header.
390
391 For example, the following declaration order in the grammar file reflects the
392 order in which Bison will output these code blocks. However, you are free to
393 declare these code blocks in your grammar file in whatever order is most
394 convenient for you:
395
396 %before-header {
397 /* Bison treats this block like a pre-prologue block: it inserts it into
398 * the code file before the contents of the header file. It does *not*
399 * insert it into the header file. This is a good place to put
400 * #include's that you want at the top of your code file. A common
401 * example is `#include "system.h"'. */
402 }
403 %start-header {
404 /* Bison inserts this block into both the header file and the code file.
405 * In both files, the point of insertion is before any Bison-generated
406 * token, semantic type, location type, and class definitions. This is a
407 * good place to define %union dependencies, for example. */
408 }
409 %union {
410 /* Unlike the traditional Yacc prologue blocks, the output order for the
411 * new %*-header blocks is not affected by their declaration position
412 * relative to any %union in the grammar file. */
413 }
414 %end-header {
415 /* Bison inserts this block into both the header file and the code file.
416 * In both files, the point of insertion is after the Bison-generated
417 * definitions. This is a good place to declare or define public
418 * functions or data structures that depend on the Bison-generated
419 * definitions. */
420 }
421 %after-header {
422 /* Bison treats this block like a post-prologue block: it inserts it into
423 * the code file after the contents of the header file. It does *not*
424 * insert it into the header file. This is a good place to declare or
425 * define internal functions or data structures that depend on the
426 * Bison-generated definitions. */
427 }
428
429 If you have multiple occurrences of any one of the above declarations, Bison
430 will concatenate the contents in declaration order.
431
432 [Although we failed to mention this here in the 2.3a release, the prologue
433 alternatives were experimental, and they were rewritten in future versions.]
434
435 ** The option `--report=look-ahead' has been changed to `--report=lookahead'.
436 The old spelling still works, but is not documented and may be removed
437 in a future release.
438
439 * Changes in version 2.3, 2006-06-05:
440
441 ** GLR grammars should now use `YYRECOVERING ()' instead of `YYRECOVERING',
442 for compatibility with LALR(1) grammars.
443
444 ** It is now documented that any definition of YYSTYPE or YYLTYPE should
445 be to a type name that does not contain parentheses or brackets.
446
447 * Changes in version 2.2, 2006-05-19:
448
449 ** The distribution terms for all Bison-generated parsers now permit
450 using the parsers in nonfree programs. Previously, this permission
451 was granted only for Bison-generated LALR(1) parsers in C.
452
453 ** %name-prefix changes the namespace name in C++ outputs.
454
455 ** The C++ parsers export their token_type.
456
457 ** Bison now allows multiple %union declarations, and concatenates
458 their contents together.
459
460 ** New warning: unused values
461 Right-hand side symbols whose values are not used are reported,
462 if the symbols have destructors. For instance:
463
464 exp: exp "?" exp ":" exp { $1 ? $1 : $3; }
465 | exp "+" exp
466 ;
467
468 will trigger a warning about $$ and $5 in the first rule, and $3 in
469 the second ($1 is copied to $$ by the default rule). This example
470 most likely contains three errors, and could be rewritten as:
471
472 exp: exp "?" exp ":" exp
473 { $$ = $1 ? $3 : $5; free ($1 ? $5 : $3); free ($1); }
474 | exp "+" exp
475 { $$ = $1 ? $1 : $3; if ($1) free ($3); }
476 ;
477
478 However, if the original actions were really intended, memory leaks
479 and all, the warnings can be suppressed by letting Bison believe the
480 values are used, e.g.:
481
482 exp: exp "?" exp ":" exp { $1 ? $1 : $3; (void) ($$, $5); }
483 | exp "+" exp { $$ = $1; (void) $3; }
484 ;
485
486 If there are mid-rule actions, the warning is issued if no action
487 uses it. The following triggers no warning: $1 and $3 are used.
488
489 exp: exp { push ($1); } '+' exp { push ($3); sum (); };
490
491 The warning is intended to help catching lost values and memory leaks.
492 If a value is ignored, its associated memory typically is not reclaimed.
493
494 ** %destructor vs. YYABORT, YYACCEPT, and YYERROR.
495 Destructors are now called when user code invokes YYABORT, YYACCEPT,
496 and YYERROR, for all objects on the stack, other than objects
497 corresponding to the right-hand side of the current rule.
498
499 ** %expect, %expect-rr
500 Incorrect numbers of expected conflicts are now actual errors,
501 instead of warnings.
502
503 ** GLR, YACC parsers.
504 The %parse-params are available in the destructors (and the
505 experimental printers) as per the documentation.
506
507 ** Bison now warns if it finds a stray `$' or `@' in an action.
508
509 ** %require "VERSION"
510 This specifies that the grammar file depends on features implemented
511 in Bison version VERSION or higher.
512
513 ** lalr1.cc: The token and value types are now class members.
514 The tokens were defined as free form enums and cpp macros. YYSTYPE
515 was defined as a free form union. They are now class members:
516 tokens are enumerations of the `yy::parser::token' struct, and the
517 semantic values have the `yy::parser::semantic_type' type.
518
519 If you do not want or can update to this scheme, the directive
520 `%define "global_tokens_and_yystype" "1"' triggers the global
521 definition of tokens and YYSTYPE. This change is suitable both
522 for previous releases of Bison, and this one.
523
524 If you wish to update, then make sure older version of Bison will
525 fail using `%require "2.2"'.
526
527 ** DJGPP support added.
528 \f
529 * Changes in version 2.1, 2005-09-16:
530
531 ** The C++ lalr1.cc skeleton supports %lex-param.
532
533 ** Bison-generated parsers now support the translation of diagnostics like
534 "syntax error" into languages other than English. The default
535 language is still English. For details, please see the new
536 Internationalization section of the Bison manual. Software
537 distributors should also see the new PACKAGING file. Thanks to
538 Bruno Haible for this new feature.
539
540 ** Wording in the Bison-generated parsers has been changed slightly to
541 simplify translation. In particular, the message "memory exhausted"
542 has replaced "parser stack overflow", as the old message was not
543 always accurate for modern Bison-generated parsers.
544
545 ** Destructors are now called when the parser aborts, for all symbols left
546 behind on the stack. Also, the start symbol is now destroyed after a
547 successful parse. In both cases, the behavior was formerly inconsistent.
548
549 ** When generating verbose diagnostics, Bison-generated parsers no longer
550 quote the literal strings associated with tokens. For example, for
551 a syntax error associated with '%token NUM "number"' they might
552 print 'syntax error, unexpected number' instead of 'syntax error,
553 unexpected "number"'.
554 \f
555 * Changes in version 2.0, 2004-12-25:
556
557 ** Possibly-incompatible changes
558
559 - Bison-generated parsers no longer default to using the alloca function
560 (when available) to extend the parser stack, due to widespread
561 problems in unchecked stack-overflow detection. You can "#define
562 YYSTACK_USE_ALLOCA 1" to require the use of alloca, but please read
563 the manual to determine safe values for YYMAXDEPTH in that case.
564
565 - Error token location.
566 During error recovery, the location of the syntax error is updated
567 to cover the whole sequence covered by the error token: it includes
568 the shifted symbols thrown away during the first part of the error
569 recovery, and the lookahead rejected during the second part.
570
571 - Semicolon changes:
572 . Stray semicolons are no longer allowed at the start of a grammar.
573 . Semicolons are now required after in-grammar declarations.
574
575 - Unescaped newlines are no longer allowed in character constants or
576 string literals. They were never portable, and GCC 3.4.0 has
577 dropped support for them. Better diagnostics are now generated if
578 forget a closing quote.
579
580 - NUL bytes are no longer allowed in Bison string literals, unfortunately.
581
582 ** New features
583
584 - GLR grammars now support locations.
585
586 - New directive: %initial-action.
587 This directive allows the user to run arbitrary code (including
588 initializing @$) from yyparse before parsing starts.
589
590 - A new directive "%expect-rr N" specifies the expected number of
591 reduce/reduce conflicts in GLR parsers.
592
593 - %token numbers can now be hexadecimal integers, e.g., `%token FOO 0x12d'.
594 This is a GNU extension.
595
596 - The option `--report=lookahead' was changed to `--report=look-ahead'.
597 [However, this was changed back after 2.3.]
598
599 - Experimental %destructor support has been added to lalr1.cc.
600
601 - New configure option --disable-yacc, to disable installation of the
602 yacc command and -ly library introduced in 1.875 for POSIX conformance.
603
604 ** Bug fixes
605
606 - For now, %expect-count violations are now just warnings, not errors.
607 This is for compatibility with Bison 1.75 and earlier (when there are
608 reduce/reduce conflicts) and with Bison 1.30 and earlier (when there
609 are too many or too few shift/reduce conflicts). However, in future
610 versions of Bison we plan to improve the %expect machinery so that
611 these violations will become errors again.
612
613 - Within Bison itself, numbers (e.g., goto numbers) are no longer
614 arbitrarily limited to 16-bit counts.
615
616 - Semicolons are now allowed before "|" in grammar rules, as POSIX requires.
617 \f
618 * Changes in version 1.875, 2003-01-01:
619
620 ** The documentation license has been upgraded to version 1.2
621 of the GNU Free Documentation License.
622
623 ** syntax error processing
624
625 - In Yacc-style parsers YYLLOC_DEFAULT is now used to compute error
626 locations too. This fixes bugs in error-location computation.
627
628 - %destructor
629 It is now possible to reclaim the memory associated to symbols
630 discarded during error recovery. This feature is still experimental.
631
632 - %error-verbose
633 This new directive is preferred over YYERROR_VERBOSE.
634
635 - #defining yyerror to steal internal variables is discouraged.
636 It is not guaranteed to work forever.
637
638 ** POSIX conformance
639
640 - Semicolons are once again optional at the end of grammar rules.
641 This reverts to the behavior of Bison 1.33 and earlier, and improves
642 compatibility with Yacc.
643
644 - `parse error' -> `syntax error'
645 Bison now uniformly uses the term `syntax error'; formerly, the code
646 and manual sometimes used the term `parse error' instead. POSIX
647 requires `syntax error' in diagnostics, and it was thought better to
648 be consistent.
649
650 - The documentation now emphasizes that yylex and yyerror must be
651 declared before use. C99 requires this.
652
653 - Bison now parses C99 lexical constructs like UCNs and
654 backslash-newline within C escape sequences, as POSIX 1003.1-2001 requires.
655
656 - File names are properly escaped in C output. E.g., foo\bar.y is
657 output as "foo\\bar.y".
658
659 - Yacc command and library now available
660 The Bison distribution now installs a `yacc' command, as POSIX requires.
661 Also, Bison now installs a small library liby.a containing
662 implementations of Yacc-compatible yyerror and main functions.
663 This library is normally not useful, but POSIX requires it.
664
665 - Type clashes now generate warnings, not errors.
666
667 - If the user does not define YYSTYPE as a macro, Bison now declares it
668 using typedef instead of defining it as a macro.
669 For consistency, YYLTYPE is also declared instead of defined.
670
671 ** Other compatibility issues
672
673 - %union directives can now have a tag before the `{', e.g., the
674 directive `%union foo {...}' now generates the C code
675 `typedef union foo { ... } YYSTYPE;'; this is for Yacc compatibility.
676 The default union tag is `YYSTYPE', for compatibility with Solaris 9 Yacc.
677 For consistency, YYLTYPE's struct tag is now `YYLTYPE' not `yyltype'.
678 This is for compatibility with both Yacc and Bison 1.35.
679
680 - `;' is output before the terminating `}' of an action, for
681 compatibility with Bison 1.35.
682
683 - Bison now uses a Yacc-style format for conflict reports, e.g.,
684 `conflicts: 2 shift/reduce, 1 reduce/reduce'.
685
686 - `yystype' and `yyltype' are now obsolescent macros instead of being
687 typedefs or tags; they are no longer documented and are planned to be
688 withdrawn in a future release.
689
690 ** GLR parser notes
691
692 - GLR and inline
693 Users of Bison have to decide how they handle the portability of the
694 C keyword `inline'.
695
696 - `parsing stack overflow...' -> `parser stack overflow'
697 GLR parsers now report `parser stack overflow' as per the Bison manual.
698
699 ** Bison now warns if it detects conflicting outputs to the same file,
700 e.g., it generates a warning for `bison -d -o foo.h foo.y' since
701 that command outputs both code and header to foo.h.
702
703 ** #line in output files
704 - --no-line works properly.
705
706 ** Bison can no longer be built by a K&R C compiler; it requires C89 or
707 later to be built. This change originally took place a few versions
708 ago, but nobody noticed until we recently asked someone to try
709 building Bison with a K&R C compiler.
710 \f
711 * Changes in version 1.75, 2002-10-14:
712
713 ** Bison should now work on 64-bit hosts.
714
715 ** Indonesian translation thanks to Tedi Heriyanto.
716
717 ** GLR parsers
718 Fix spurious parse errors.
719
720 ** Pure parsers
721 Some people redefine yyerror to steal yyparse' private variables.
722 Reenable this trick until an official feature replaces it.
723
724 ** Type Clashes
725 In agreement with POSIX and with other Yaccs, leaving a default
726 action is valid when $$ is untyped, and $1 typed:
727
728 untyped: ... typed;
729
730 but the converse remains an error:
731
732 typed: ... untyped;
733
734 ** Values of mid-rule actions
735 The following code:
736
737 foo: { ... } { $$ = $1; } ...
738
739 was incorrectly rejected: $1 is defined in the second mid-rule
740 action, and is equal to the $$ of the first mid-rule action.
741 \f
742 * Changes in version 1.50, 2002-10-04:
743
744 ** GLR parsing
745 The declaration
746 %glr-parser
747 causes Bison to produce a Generalized LR (GLR) parser, capable of handling
748 almost any context-free grammar, ambiguous or not. The new declarations
749 %dprec and %merge on grammar rules allow parse-time resolution of
750 ambiguities. Contributed by Paul Hilfinger.
751
752 Unfortunately Bison 1.50 does not work properly on 64-bit hosts
753 like the Alpha, so please stick to 32-bit hosts for now.
754
755 ** Output Directory
756 When not in Yacc compatibility mode, when the output file was not
757 specified, running `bison foo/bar.y' created `foo/bar.c'. It
758 now creates `bar.c'.
759
760 ** Undefined token
761 The undefined token was systematically mapped to 2 which prevented
762 the use of 2 by the user. This is no longer the case.
763
764 ** Unknown token numbers
765 If yylex returned an out of range value, yyparse could die. This is
766 no longer the case.
767
768 ** Error token
769 According to POSIX, the error token must be 256.
770 Bison extends this requirement by making it a preference: *if* the
771 user specified that one of her tokens is numbered 256, then error
772 will be mapped onto another number.
773
774 ** Verbose error messages
775 They no longer report `..., expecting error or...' for states where
776 error recovery is possible.
777
778 ** End token
779 Defaults to `$end' instead of `$'.
780
781 ** Error recovery now conforms to documentation and to POSIX
782 When a Bison-generated parser encounters a syntax error, it now pops
783 the stack until it finds a state that allows shifting the error
784 token. Formerly, it popped the stack until it found a state that
785 allowed some non-error action other than a default reduction on the
786 error token. The new behavior has long been the documented behavior,
787 and has long been required by POSIX. For more details, please see
788 Paul Eggert, "Reductions during Bison error handling" (2002-05-20)
789 <http://lists.gnu.org/archive/html/bug-bison/2002-05/msg00038.html>.
790
791 ** Traces
792 Popped tokens and nonterminals are now reported.
793
794 ** Larger grammars
795 Larger grammars are now supported (larger token numbers, larger grammar
796 size (= sum of the LHS and RHS lengths), larger LALR tables).
797 Formerly, many of these numbers ran afoul of 16-bit limits;
798 now these limits are 32 bits on most hosts.
799
800 ** Explicit initial rule
801 Bison used to play hacks with the initial rule, which the user does
802 not write. It is now explicit, and visible in the reports and
803 graphs as rule 0.
804
805 ** Useless rules
806 Before, Bison reported the useless rules, but, although not used,
807 included them in the parsers. They are now actually removed.
808
809 ** Useless rules, useless nonterminals
810 They are now reported, as a warning, with their locations.
811
812 ** Rules never reduced
813 Rules that can never be reduced because of conflicts are now
814 reported.
815
816 ** Incorrect `Token not used'
817 On a grammar such as
818
819 %token useless useful
820 %%
821 exp: '0' %prec useful;
822
823 where a token was used to set the precedence of the last rule,
824 bison reported both `useful' and `useless' as useless tokens.
825
826 ** Revert the C++ namespace changes introduced in 1.31
827 as they caused too many portability hassles.
828
829 ** Default locations
830 By an accident of design, the default computation of @$ was
831 performed after another default computation was performed: @$ = @1.
832 The latter is now removed: YYLLOC_DEFAULT is fully responsible of
833 the computation of @$.
834
835 ** Token end-of-file
836 The token end of file may be specified by the user, in which case,
837 the user symbol is used in the reports, the graphs, and the verbose
838 error messages instead of `$end', which remains being the default.
839 For instance
840 %token MYEOF 0
841 or
842 %token MYEOF 0 "end of file"
843
844 ** Semantic parser
845 This old option, which has been broken for ages, is removed.
846
847 ** New translations
848 Brazilian Portuguese, thanks to Alexandre Folle de Menezes.
849 Croatian, thanks to Denis Lackovic.
850
851 ** Incorrect token definitions
852 When given `%token 'a' "A"', Bison used to output `#define 'a' 65'.
853
854 ** Token definitions as enums
855 Tokens are output both as the traditional #define's, and, provided
856 the compiler supports ANSI C or is a C++ compiler, as enums.
857 This lets debuggers display names instead of integers.
858
859 ** Reports
860 In addition to --verbose, bison supports --report=THINGS, which
861 produces additional information:
862 - itemset
863 complete the core item sets with their closure
864 - lookahead [changed to `look-ahead' in 1.875e through 2.3, but changed back]
865 explicitly associate lookahead tokens to items
866 - solved
867 describe shift/reduce conflicts solving.
868 Bison used to systematically output this information on top of
869 the report. Solved conflicts are now attached to their states.
870
871 ** Type clashes
872 Previous versions don't complain when there is a type clash on
873 the default action if the rule has a mid-rule action, such as in:
874
875 %type <foo> bar
876 %%
877 bar: '0' {} '0';
878
879 This is fixed.
880
881 ** GNU M4 is now required when using Bison.
882 \f
883 * Changes in version 1.35, 2002-03-25:
884
885 ** C Skeleton
886 Some projects use Bison's C parser with C++ compilers, and define
887 YYSTYPE as a class. The recent adjustment of C parsers for data
888 alignment and 64 bit architectures made this impossible.
889
890 Because for the time being no real solution for C++ parser
891 generation exists, kludges were implemented in the parser to
892 maintain this use. In the future, when Bison has C++ parsers, this
893 kludge will be disabled.
894
895 This kludge also addresses some C++ problems when the stack was
896 extended.
897 \f
898 * Changes in version 1.34, 2002-03-12:
899
900 ** File name clashes are detected
901 $ bison foo.y -d -o foo.x
902 fatal error: header and parser would both be named `foo.x'
903
904 ** A missing `;' at the end of a rule triggers a warning
905 In accordance with POSIX, and in agreement with other
906 Yacc implementations, Bison will mandate this semicolon in the near
907 future. This eases the implementation of a Bison parser of Bison
908 grammars by making this grammar LALR(1) instead of LR(2). To
909 facilitate the transition, this release introduces a warning.
910
911 ** Revert the C++ namespace changes introduced in 1.31, as they caused too
912 many portability hassles.
913
914 ** DJGPP support added.
915
916 ** Fix test suite portability problems.
917 \f
918 * Changes in version 1.33, 2002-02-07:
919
920 ** Fix C++ issues
921 Groff could not be compiled for the definition of size_t was lacking
922 under some conditions.
923
924 ** Catch invalid @n
925 As is done with $n.
926 \f
927 * Changes in version 1.32, 2002-01-23:
928
929 ** Fix Yacc output file names
930
931 ** Portability fixes
932
933 ** Italian, Dutch translations
934 \f
935 * Changes in version 1.31, 2002-01-14:
936
937 ** Many Bug Fixes
938
939 ** GNU Gettext and %expect
940 GNU Gettext asserts 10 s/r conflicts, but there are 7. Now that
941 Bison dies on incorrect %expectations, we fear there will be
942 too many bug reports for Gettext, so _for the time being_, %expect
943 does not trigger an error when the input file is named `plural.y'.
944
945 ** Use of alloca in parsers
946 If YYSTACK_USE_ALLOCA is defined to 0, then the parsers will use
947 malloc exclusively. Since 1.29, but was not NEWS'ed.
948
949 alloca is used only when compiled with GCC, to avoid portability
950 problems as on AIX.
951
952 ** yyparse now returns 2 if memory is exhausted; formerly it dumped core.
953
954 ** When the generated parser lacks debugging code, YYDEBUG is now 0
955 (as POSIX requires) instead of being undefined.
956
957 ** User Actions
958 Bison has always permitted actions such as { $$ = $1 }: it adds the
959 ending semicolon. Now if in Yacc compatibility mode, the semicolon
960 is no longer output: one has to write { $$ = $1; }.
961
962 ** Better C++ compliance
963 The output parsers try to respect C++ namespaces.
964 [This turned out to be a failed experiment, and it was reverted later.]
965
966 ** Reduced Grammars
967 Fixed bugs when reporting useless nonterminals.
968
969 ** 64 bit hosts
970 The parsers work properly on 64 bit hosts.
971
972 ** Error messages
973 Some calls to strerror resulted in scrambled or missing error messages.
974
975 ** %expect
976 When the number of shift/reduce conflicts is correct, don't issue
977 any warning.
978
979 ** The verbose report includes the rule line numbers.
980
981 ** Rule line numbers are fixed in traces.
982
983 ** Swedish translation
984
985 ** Parse errors
986 Verbose parse error messages from the parsers are better looking.
987 Before: parse error: unexpected `'/'', expecting `"number"' or `'-'' or `'(''
988 Now: parse error: unexpected '/', expecting "number" or '-' or '('
989
990 ** Fixed parser memory leaks.
991 When the generated parser was using malloc to extend its stacks, the
992 previous allocations were not freed.
993
994 ** Fixed verbose output file.
995 Some newlines were missing.
996 Some conflicts in state descriptions were missing.
997
998 ** Fixed conflict report.
999 Option -v was needed to get the result.
1000
1001 ** %expect
1002 Was not used.
1003 Mismatches are errors, not warnings.
1004
1005 ** Fixed incorrect processing of some invalid input.
1006
1007 ** Fixed CPP guards: 9foo.h uses BISON_9FOO_H instead of 9FOO_H.
1008
1009 ** Fixed some typos in the documentation.
1010
1011 ** %token MY_EOF 0 is supported.
1012 Before, MY_EOF was silently renumbered as 257.
1013
1014 ** doc/refcard.tex is updated.
1015
1016 ** %output, %file-prefix, %name-prefix.
1017 New.
1018
1019 ** --output
1020 New, aliasing `--output-file'.
1021 \f
1022 * Changes in version 1.30, 2001-10-26:
1023
1024 ** `--defines' and `--graph' have now an optional argument which is the
1025 output file name. `-d' and `-g' do not change; they do not take any
1026 argument.
1027
1028 ** `%source_extension' and `%header_extension' are removed, failed
1029 experiment.
1030
1031 ** Portability fixes.
1032 \f
1033 * Changes in version 1.29, 2001-09-07:
1034
1035 ** The output file does not define const, as this caused problems when used
1036 with common autoconfiguration schemes. If you still use ancient compilers
1037 that lack const, compile with the equivalent of the C compiler option
1038 `-Dconst='. autoconf's AC_C_CONST macro provides one way to do this.
1039
1040 ** Added `-g' and `--graph'.
1041
1042 ** The Bison manual is now distributed under the terms of the GNU FDL.
1043
1044 ** The input and the output files has automatically a similar extension.
1045
1046 ** Russian translation added.
1047
1048 ** NLS support updated; should hopefully be less troublesome.
1049
1050 ** Added the old Bison reference card.
1051
1052 ** Added `--locations' and `%locations'.
1053
1054 ** Added `-S' and `--skeleton'.
1055
1056 ** `%raw', `-r', `--raw' is disabled.
1057
1058 ** Special characters are escaped when output. This solves the problems
1059 of the #line lines with path names including backslashes.
1060
1061 ** New directives.
1062 `%yacc', `%fixed_output_files', `%defines', `%no_parser', `%verbose',
1063 `%debug', `%source_extension' and `%header_extension'.
1064
1065 ** @$
1066 Automatic location tracking.
1067 \f
1068 * Changes in version 1.28, 1999-07-06:
1069
1070 ** Should compile better now with K&R compilers.
1071
1072 ** Added NLS.
1073
1074 ** Fixed a problem with escaping the double quote character.
1075
1076 ** There is now a FAQ.
1077 \f
1078 * Changes in version 1.27:
1079
1080 ** The make rule which prevented bison.simple from being created on
1081 some systems has been fixed.
1082 \f
1083 * Changes in version 1.26:
1084
1085 ** Bison now uses automake.
1086
1087 ** New mailing lists: <bug-bison@gnu.org> and <help-bison@gnu.org>.
1088
1089 ** Token numbers now start at 257 as previously documented, not 258.
1090
1091 ** Bison honors the TMPDIR environment variable.
1092
1093 ** A couple of buffer overruns have been fixed.
1094
1095 ** Problems when closing files should now be reported.
1096
1097 ** Generated parsers should now work even on operating systems which do
1098 not provide alloca().
1099 \f
1100 * Changes in version 1.25, 1995-10-16:
1101
1102 ** Errors in the input grammar are not fatal; Bison keeps reading
1103 the grammar file, and reports all the errors found in it.
1104
1105 ** Tokens can now be specified as multiple-character strings: for
1106 example, you could use "<=" for a token which looks like <=, instead
1107 of chosing a name like LESSEQ.
1108
1109 ** The %token_table declaration says to write a table of tokens (names
1110 and numbers) into the parser file. The yylex function can use this
1111 table to recognize multiple-character string tokens, or for other
1112 purposes.
1113
1114 ** The %no_lines declaration says not to generate any #line preprocessor
1115 directives in the parser file.
1116
1117 ** The %raw declaration says to use internal Bison token numbers, not
1118 Yacc-compatible token numbers, when token names are defined as macros.
1119
1120 ** The --no-parser option produces the parser tables without including
1121 the parser engine; a project can now use its own parser engine.
1122 The actions go into a separate file called NAME.act, in the form of
1123 a switch statement body.
1124 \f
1125 * Changes in version 1.23:
1126
1127 The user can define YYPARSE_PARAM as the name of an argument to be
1128 passed into yyparse. The argument should have type void *. It should
1129 actually point to an object. Grammar actions can access the variable
1130 by casting it to the proper pointer type.
1131
1132 Line numbers in output file corrected.
1133 \f
1134 * Changes in version 1.22:
1135
1136 --help option added.
1137 \f
1138 * Changes in version 1.20:
1139
1140 Output file does not redefine const for C++.
1141
1142 Local Variables:
1143 mode: outline
1144 End:
1145
1146 -----
1147
1148 Copyright (C) 1995-2010 Free Software Foundation, Inc.
1149
1150 This file is part of Bison, the GNU Parser Generator.
1151
1152 This program is free software: you can redistribute it and/or modify
1153 it under the terms of the GNU General Public License as published by
1154 the Free Software Foundation, either version 3 of the License, or
1155 (at your option) any later version.
1156
1157 This program is distributed in the hope that it will be useful,
1158 but WITHOUT ANY WARRANTY; without even the implied warranty of
1159 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
1160 GNU General Public License for more details.
1161
1162 You should have received a copy of the GNU General Public License
1163 along with this program. If not, see <http://www.gnu.org/licenses/>.