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ed7658fe 1GNU Bison NEWS
3af4feb2 2
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3* Noteworthy changes in release ?.? (????-??-??) [?]
4
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5** Bug fixes
6
a1a77e1f 7 Bugs and portability issues in the test suite have been fixed.
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8
9 Some errors in translations have been addressed, and --help now directs
10 users to the appropriate place to report them.
11
12 Stray Info files shipped by accident are removed.
13
14 Incorrect definitions of YY_, issued by yacc.c when no parser header is
15 generated, are removed.
933ec544 16
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17 All the generated headers are self-contained.
18
5a05f42e 19** Changes in the format of error messages
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20
21 This used to be the format of many error reports:
22
23 foo.y:5.10-24: result type clash on merge function 'merge': <t3> != <t2>
24 foo.y:4.13-27: previous declaration
25
26 It is now:
27
28 foo.y:5.10-25: result type clash on merge function 'merge': <t3> != <t2>
29 foo.y:4.13-27: previous declaration
30
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31** Header guards (yacc.c, glr.c, glr.cc)
32
33 In order to avoid collisions, the header guards are now
34 YY_<PREFIX>_<FILE>_INCLUDED, instead of merely <PREFIX>_<FILE>.
35 For instance the header generated from
36
37 %define api.prefix "calc"
38 %defines "lib/parse.h"
39
40 will use YY_CALC_LIB_PARSE_H_INCLUDED as guard.
41
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42** Exception safety (lalr1.cc)
43
44 The parse function now catches exceptions, uses the %destructors to
45 release memory (the lookahead symbol and the symbols pushed on the stack)
7287be84 46 before re-throwing the exception.
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47
48 This feature is somewhat experimental. User feedback would be
49 appreciated.
50
c12c4c50 51** Fix compiler warnings in the generated parser (yacc.c, glr.c)
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52
53 The compilation of pure parsers (%define api.pure) can trigger GCC
54 warnings such as:
55
56 input.c: In function 'yyparse':
57 input.c:1503:12: warning: 'yylval' may be used uninitialized in this
58 function [-Wmaybe-uninitialized]
59 *++yyvsp = yylval;
60 ^
61
62 This is now fixed; pragmas to avoid these warnings are no longer needed.
63
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64 Warnings from clang ("equality comparison with extraneous parentheses" and
65 "function declared 'noreturn' should not return") have also been
66 addressed.
67
7287be84 68** New %define variable: api.location.type (glr.cc, lalr1.cc, lalr1.java)
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69
70 The %define variable api.location.type defines the name of the type to use
71 for locations. When defined, Bison no longer generates the position.hh
72 and location.hh files, nor does the parser will include them: the user is
73 then responsible to define her type.
74
75 This can be used in programs with several parsers to factor their location
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76 and position files: let one of them generate them, and the others just use
77 them.
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78
79 This feature was actually introduced, but not documented, in Bison 2.5,
80 under the name "location_type" (which is maintained for backward
81 compatibility).
82
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83 For consistency, lalr1.java's %define variables location_type and
84 position_type are deprecated in favor of api.location.type and
85 api.position.type.
86
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87** Graphviz improvements
88
89 The graphical presentation of the states is more readable: their shape is
90 now rectangular, the state number is clearly displayed, and the items are
91 numbered and left-justified.
92
93 The reductions are now explicitly represented as transitions to other
94 diamond shaped nodes.
95
e1eeecd3 96* Noteworthy changes in release 2.6.2 (2012-08-03) [stable]
9c26b8fc 97
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98** Bug fixes
99
100 Buffer overruns, complaints from Flex, and portability issues in the test
101 suite have been fixed.
102
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103** Spaces in %lex- and %parse-param (lalr1.cc, glr.cc)
104
105 Trailing end-of-lines in %parse-param or %lex-param would result in
106 invalid C++. This is fixed.
9c26b8fc 107
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108** Spurious spaces and end-of-lines
109
110 The generated files no longer end (nor start) with empty lines.
111
77b214ef 112* Noteworthy changes in release 2.6.1 (2012-07-30) [stable]
a4107f24 113
cbaea010 114 Bison no longer executes user-specified M4 code when processing a grammar.
8617d87e 115
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116** Future Changes
117
118 In addition to the removal of the features announced in Bison 2.6, the
119 next major release will remove the "Temporary hack for adding a semicolon
120 to the user action", as announced in the release 2.5. Instead of:
121
122 exp: exp "+" exp { $$ = $1 + $3 };
123
124 write:
125
126 exp: exp "+" exp { $$ = $1 + $3; };
127
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128** Bug fixes
129
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130*** Type names are now properly escaped.
131
132*** glr.cc: set_debug_level and debug_level work as expected.
a4107f24 133
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134*** Stray @ or $ in actions
135
136 While Bison used to warn about stray $ or @ in action rules, it did not
137 for other actions such as printers, destructors, or initial actions. It
138 now does.
139
cd735a8c 140** Type names in actions
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141
142 For consistency with rule actions, it is now possible to qualify $$ by a
cd735a8c 143 type-name in destructors, printers, and initial actions. For instance:
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144
145 %printer { fprintf (yyo, "(%d, %f)", $<ival>$, $<fval>$); } <*> <>;
146
147 will display two values for each typed and untyped symbol (provided
cd735a8c 148 that YYSTYPE has both "ival" and "fval" fields).
4982f078 149
1505e8bb 150* Noteworthy changes in release 2.6 (2012-07-19) [stable]
ad6b775f 151
c2425191 152** Future Changes
0f11eec2 153
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154 The next major release of Bison will drop support for the following
155 deprecated features. Please report disagreements to bug-bison@gnu.org.
0f11eec2 156
aaf61036 157*** K&R C parsers
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158
159 Support for generating parsers in K&R C will be removed. Parsers
242cc08e 160 generated for C support ISO C90, and are tested with ISO C99 and ISO C11
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161 compilers.
162
258cddbc 163*** Features deprecated since Bison 1.875
55d1006f 164
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165 The definitions of yystype and yyltype will be removed; use YYSTYPE and
166 YYLTYPE.
55d1006f 167
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168 YYPARSE_PARAM and YYLEX_PARAM, deprecated in favor of %parse-param and
169 %lex-param, will no longer be supported.
170
171 Support for the preprocessor symbol YYERROR_VERBOSE will be removed, use
172 %error-verbose.
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173
174*** The generated header will be included (yacc.c)
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175
176 Instead of duplicating the content of the generated header (definition of
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177 YYSTYPE, yyparse declaration etc.), the generated parser will include it,
178 as is already the case for GLR or C++ parsers. This change is deferred
179 because existing versions of ylwrap (e.g., Automake 1.12.1) do not support
180 it.
0f11eec2 181
c2425191 182** Generated Parser Headers
56ca3d8f 183
258cddbc 184*** Guards (yacc.c, glr.c, glr.cc)
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185
186 The generated headers are now guarded, as is already the case for C++
242cc08e 187 parsers (lalr1.cc). For instance, with --defines=foo.h:
c3e9f08f 188
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189 #ifndef YY_FOO_H
190 # define YY_FOO_H
191 ...
192 #endif /* !YY_FOO_H */
c3e9f08f 193
258cddbc 194*** New declarations (yacc.c, glr.c)
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195
196 The generated header now declares yydebug and yyparse. Both honor
197 --name-prefix=bar_, and yield
198
e29f0771 199 int bar_parse (void);
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200
201 rather than
202
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203 #define yyparse bar_parse
204 int yyparse (void);
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205
206 in order to facilitate the inclusion of several parser headers inside a
207 single compilation unit.
c3e9f08f 208
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209*** Exported symbols in C++
210
211 The symbols YYTOKEN_TABLE and YYERROR_VERBOSE, which were defined in the
212 header, are removed, as they prevent the possibility of including several
213 generated headers from a single compilation unit.
214
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215*** YYLSP_NEEDED
216
217 For the same reasons, the undocumented and unused macro YYLSP_NEEDED is no
218 longer defined.
219
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220** New %define variable: api.prefix
221
222 Now that the generated headers are more complete and properly protected
223 against multiple inclusions, constant names, such as YYSTYPE are a
224 problem. While yyparse and others are properly renamed by %name-prefix,
225 YYSTYPE, YYDEBUG and others have never been affected by it. Because it
226 would introduce backward compatibility issues in projects not expecting
227 YYSTYPE to be renamed, instead of changing the behavior of %name-prefix,
228 it is deprecated in favor of a new %define variable: api.prefix.
229
230 The following examples compares both:
231
232 %name-prefix "bar_" | %define api.prefix "bar_"
233 %token <ival> FOO %token <ival> FOO
234 %union { int ival; } %union { int ival; }
235 %% %%
236 exp: 'a'; exp: 'a';
237
238 bison generates:
239
240 #ifndef BAR_FOO_H #ifndef BAR_FOO_H
241 # define BAR_FOO_H # define BAR_FOO_H
242
243 /* Enabling traces. */ /* Enabling traces. */
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244 # ifndef YYDEBUG | # ifndef BAR_DEBUG
245 > # if defined YYDEBUG
246 > # if YYDEBUG
247 > # define BAR_DEBUG 1
248 > # else
249 > # define BAR_DEBUG 0
250 > # endif
251 > # else
252 # define YYDEBUG 0 | # define BAR_DEBUG 0
253 > # endif
254 # endif | # endif
255
256 # if YYDEBUG | # if BAR_DEBUG
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257 extern int bar_debug; extern int bar_debug;
258 # endif # endif
259
260 /* Tokens. */ /* Tokens. */
261 # ifndef YYTOKENTYPE | # ifndef BAR_TOKENTYPE
262 # define YYTOKENTYPE | # define BAR_TOKENTYPE
263 enum yytokentype { | enum bar_tokentype {
264 FOO = 258 FOO = 258
265 }; };
266 # endif # endif
267
268 #if ! defined YYSTYPE \ | #if ! defined BAR_STYPE \
269 && ! defined YYSTYPE_IS_DECLARED | && ! defined BAR_STYPE_IS_DECLARED
270 typedef union YYSTYPE | typedef union BAR_STYPE
271 { {
272 int ival; int ival;
273 } YYSTYPE; | } BAR_STYPE;
274 # define YYSTYPE_IS_DECLARED 1 | # define BAR_STYPE_IS_DECLARED 1
275 #endif #endif
276
277 extern YYSTYPE bar_lval; | extern BAR_STYPE bar_lval;
278
279 int bar_parse (void); int bar_parse (void);
280
281 #endif /* !BAR_FOO_H */ #endif /* !BAR_FOO_H */
282
dfaac272 283* Noteworthy changes in release 2.5.1 (2012-06-05) [stable]
90dcd415 284
debe2c03 285** Future changes:
041308d0 286
e4ab1254 287 The next major release will drop support for generating parsers in K&R C.
ef51bfa7 288
466b4cf2 289** yacc.c: YYBACKUP works as expected.
94556574 290
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291** glr.c improvements:
292
293*** Location support is eliminated when not requested:
294
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295 GLR parsers used to include location-related code even when locations were
296 not requested, and therefore not even usable.
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297
298*** __attribute__ is preserved:
debe2c03 299
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300 __attribute__ is no longer disabled when __STRICT_ANSI__ is defined (i.e.,
301 when -std is passed to GCC).
debe2c03 302
466b4cf2 303** lalr1.java: several fixes:
041308d0 304
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305 The Java parser no longer throws ArrayIndexOutOfBoundsException if the
306 first token leads to a syntax error. Some minor clean ups.
041308d0 307
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308** Changes for C++:
309
310*** C++11 compatibility:
ef51bfa7 311
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312 C and C++ parsers use "nullptr" instead of "0" when __cplusplus is 201103L
313 or higher.
ef51bfa7 314
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315*** Header guards
316
317 The header files such as "parser.hh", "location.hh", etc. used a constant
318 name for preprocessor guards, for instance:
319
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320 #ifndef BISON_LOCATION_HH
321 # define BISON_LOCATION_HH
322 ...
323 #endif // !BISON_LOCATION_HH
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324
325 The inclusion guard is now computed from "PREFIX/FILE-NAME", where lower
326 case characters are converted to upper case, and series of
327 non-alphanumerical characters are converted to an underscore.
328
329 With "bison -o lang++/parser.cc", "location.hh" would now include:
330
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331 #ifndef YY_LANG_LOCATION_HH
332 # define YY_LANG_LOCATION_HH
333 ...
334 #endif // !YY_LANG_LOCATION_HH
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335
336*** C++ locations:
936c88d1 337
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338 The position and location constructors (and their initialize methods)
339 accept new arguments for line and column. Several issues in the
340 documentation were fixed.
936c88d1 341
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342** liby is no longer asking for "rpl_fprintf" on some platforms.
343
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344** Changes in the manual:
345
346*** %printer is documented
347
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348 The "%printer" directive, supported since at least Bison 1.50, is finally
349 documented. The "mfcalc" example is extended to demonstrate it.
7e508a2b 350
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351 For consistency with the C skeletons, the C++ parsers now also support
352 "yyoutput" (as an alias to "debug_stream ()").
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353
354*** Several improvements have been made:
466b4cf2 355
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356 The layout for grammar excerpts was changed to a more compact scheme.
357 Named references are motivated. The description of the automaton
358 description file (*.output) is updated to the current format. Incorrect
359 index entries were fixed. Some other errors were fixed.
466b4cf2 360
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361** Building bison:
362
363*** Conflicting prototypes with recent/modified Flex.
364
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365 Fixed build problems with the current, unreleased, version of Flex, and
366 some modified versions of 2.5.35, which have modified function prototypes.
466b4cf2 367
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368*** Warnings during the build procedure have been eliminated.
369
370*** Several portability problems in the test suite have been fixed:
466b4cf2 371
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372 This includes warnings with some compilers, unexpected behavior of tools
373 such as diff, warning messages from the test suite itself, etc.
466b4cf2 374
91aadcc7 375*** The install-pdf target works properly:
8ef26c2a 376
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377 Running "make install-pdf" (or -dvi, -html, -info, and -ps) no longer
378 halts in the middle of its course.
8ef26c2a 379
b2bc8a1b 380* Changes in version 2.5 (2011-05-14):
006faedf 381
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382** Grammar symbol names can now contain non-initial dashes:
383
384 Consistently with directives (such as %error-verbose) and with
385 %define variables (e.g. push-pull), grammar symbol names may contain
386 dashes in any position except the beginning. This is a GNU
387 extension over POSIX Yacc. Thus, use of this extension is reported
388 by -Wyacc and rejected in Yacc mode (--yacc).
389
3b1977ea 390** Named references:
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391
392 Historically, Yacc and Bison have supported positional references
393 ($n, $$) to allow access to symbol values from inside of semantic
394 actions code.
395
396 Starting from this version, Bison can also accept named references.
397 When no ambiguity is possible, original symbol names may be used
398 as named references:
399
ac3297d5 400 if_stmt : "if" cond_expr "then" then_stmt ';'
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401 { $if_stmt = mk_if_stmt($cond_expr, $then_stmt); }
402
403 In the more common case, explicit names may be declared:
404
ac3297d5 405 stmt[res] : "if" expr[cond] "then" stmt[then] "else" stmt[else] ';'
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406 { $res = mk_if_stmt($cond, $then, $else); }
407
f840c05a 408 Location information is also accessible using @name syntax. When
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409 accessing symbol names containing dots or dashes, explicit bracketing
410 ($[sym.1]) must be used.
411
f840c05a 412 These features are experimental in this version. More user feedback
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413 will help to stabilize them.
414
3b1977ea 415** IELR(1) and canonical LR(1):
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416
417 IELR(1) is a minimal LR(1) parser table generation algorithm. That
418 is, given any context-free grammar, IELR(1) generates parser tables
723206df 419 with the full language-recognition power of canonical LR(1) but with
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420 nearly the same number of parser states as LALR(1). This reduction
421 in parser states is often an order of magnitude. More importantly,
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422 because canonical LR(1)'s extra parser states may contain duplicate
423 conflicts in the case of non-LR(1) grammars, the number of conflicts
424 for IELR(1) is often an order of magnitude less as well. This can
425 significantly reduce the complexity of developing of a grammar.
426
427 Bison can now generate IELR(1) and canonical LR(1) parser tables in
428 place of its traditional LALR(1) parser tables, which remain the
429 default. You can specify the type of parser tables in the grammar
430 file with these directives:
431
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432 %define lr.type lalr
433 %define lr.type ielr
434 %define lr.type canonical-lr
34a6c2d1 435
6f04ee6c 436 The default-reduction optimization in the parser tables can also be
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437 adjusted using "%define lr.default-reductions". For details on both
438 of these features, see the new section "Tuning LR" in the Bison
6f04ee6c 439 manual.
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440
441 These features are experimental. More user feedback will help to
442 stabilize them.
443
6f04ee6c 444** LAC (Lookahead Correction) for syntax error handling:
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445
446 Canonical LR, IELR, and LALR can suffer from a couple of problems
447 upon encountering a syntax error. First, the parser might perform
448 additional parser stack reductions before discovering the syntax
6f04ee6c 449 error. Such reductions can perform user semantic actions that are
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450 unexpected because they are based on an invalid token, and they
451 cause error recovery to begin in a different syntactic context than
452 the one in which the invalid token was encountered. Second, when
6f04ee6c 453 verbose error messages are enabled (with %error-verbose or the
e4ab1254 454 obsolete "#define YYERROR_VERBOSE"), the expected token list in the
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455 syntax error message can both contain invalid tokens and omit valid
456 tokens.
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457
458 The culprits for the above problems are %nonassoc, default
459 reductions in inconsistent states, and parser state merging. Thus,
460 IELR and LALR suffer the most. Canonical LR can suffer only if
461 %nonassoc is used or if default reductions are enabled for
462 inconsistent states.
463
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464 LAC is a new mechanism within the parsing algorithm that solves
465 these problems for canonical LR, IELR, and LALR without sacrificing
466 %nonassoc, default reductions, or state merging. When LAC is in
467 use, canonical LR and IELR behave almost exactly the same for both
468 syntactically acceptable and syntactically unacceptable input.
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469 While LALR still does not support the full language-recognition
470 power of canonical LR and IELR, LAC at least enables LALR's syntax
471 error handling to correctly reflect LALR's language-recognition
472 power.
473
474 Currently, LAC is only supported for deterministic parsers in C.
475 You can enable LAC with the following directive:
476
477 %define parse.lac full
478
e4ab1254 479 See the new section "LAC" in the Bison manual for additional
6f04ee6c 480 details including a few caveats.
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481
482 LAC is an experimental feature. More user feedback will help to
483 stabilize it.
484
6ee881f6 485** %define improvements:
f37495f6 486
3b1977ea 487*** Can now be invoked via the command line:
4ecd3681 488
34d41938 489 Each of these command-line options
4ecd3681 490
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491 -D NAME[=VALUE]
492 --define=NAME[=VALUE]
493
494 -F NAME[=VALUE]
495 --force-define=NAME[=VALUE]
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496
497 is equivalent to this grammar file declaration
498
34d41938 499 %define NAME ["VALUE"]
4ecd3681 500
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501 except that the manner in which Bison processes multiple definitions
502 for the same NAME differs. Most importantly, -F and --force-define
503 quietly override %define, but -D and --define do not. For further
e4ab1254 504 details, see the section "Bison Options" in the Bison manual.
4ecd3681 505
3b1977ea 506*** Variables renamed:
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507
508 The following %define variables
509
510 api.push_pull
511 lr.keep_unreachable_states
512
513 have been renamed to
514
515 api.push-pull
516 lr.keep-unreachable-states
517
518 The old names are now deprecated but will be maintained indefinitely
519 for backward compatibility.
520
723206df 521*** Values no longer need to be quoted in the grammar file:
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522
523 If a %define value is an identifier, it no longer needs to be placed
524 within quotations marks. For example,
525
526 %define api.push-pull "push"
527
528 can be rewritten as
529
530 %define api.push-pull push
531
6ee881f6 532*** Unrecognized variables are now errors not warnings.
c046698e 533
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534*** Multiple invocations for any variable is now an error not a warning.
535
536** Unrecognized %code qualifiers are now errors not warnings.
537
538** Character literals not of length one:
539
540 Previously, Bison quietly converted all character literals to length
541 one. For example, without warning, Bison interpreted the operators in
542 the following grammar to be the same token:
543
544 exp: exp '++'
545 | exp '+' exp
546 ;
547
548 Bison now warns when a character literal is not of length one. In
549 some future release, Bison will start reporting an error instead.
550
551** Destructor calls fixed for lookaheads altered in semantic actions:
552
553 Previously for deterministic parsers in C, if a user semantic action
554 altered yychar, the parser in some cases used the old yychar value to
555 determine which destructor to call for the lookahead upon a syntax
556 error or upon parser return. This bug has been fixed.
557
558** C++ parsers use YYRHSLOC:
559
560 Similarly to the C parsers, the C++ parsers now define the YYRHSLOC
561 macro and use it in the default YYLLOC_DEFAULT. You are encouraged
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562 to use it. If, for instance, your location structure has "first"
563 and "last" members, instead of
6ee881f6 564
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565 # define YYLLOC_DEFAULT(Current, Rhs, N) \
566 do \
567 if (N) \
568 { \
569 (Current).first = (Rhs)[1].location.first; \
570 (Current).last = (Rhs)[N].location.last; \
571 } \
572 else \
573 { \
574 (Current).first = (Current).last = (Rhs)[0].location.last; \
575 } \
576 while (false)
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577
578 use:
579
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580 # define YYLLOC_DEFAULT(Current, Rhs, N) \
581 do \
582 if (N) \
583 { \
584 (Current).first = YYRHSLOC (Rhs, 1).first; \
585 (Current).last = YYRHSLOC (Rhs, N).last; \
586 } \
587 else \
588 { \
589 (Current).first = (Current).last = YYRHSLOC (Rhs, 0).last; \
590 } \
591 while (false)
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592
593** YYLLOC_DEFAULT in C++:
594
595 The default implementation of YYLLOC_DEFAULT used to be issued in
596 the header file. It is now output in the implementation file, after
597 the user %code sections so that its #ifndef guard does not try to
598 override the user's YYLLOC_DEFAULT if provided.
c046698e 599
3b1977ea 600** YYFAIL now produces warnings and Java parsers no longer implement it:
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601
602 YYFAIL has existed for many years as an undocumented feature of
603 deterministic parsers in C generated by Bison. More recently, it was
604 a documented feature of Bison's experimental Java parsers. As
605 promised in Bison 2.4.2's NEWS entry, any appearance of YYFAIL in a
606 semantic action now produces a deprecation warning, and Java parsers
607 no longer implement YYFAIL at all. For further details, including a
608 discussion of how to suppress C preprocessor warnings about YYFAIL
609 being unused, see the Bison 2.4.2 NEWS entry.
610
3b1977ea 611** Temporary hack for adding a semicolon to the user action:
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612
613 Previously, Bison appended a semicolon to every user action for
614 reductions when the output language defaulted to C (specifically, when
615 neither %yacc, %language, %skeleton, or equivalent command-line
616 options were specified). This allowed actions such as
617
618 exp: exp "+" exp { $$ = $1 + $3 };
619
620 instead of
621
622 exp: exp "+" exp { $$ = $1 + $3; };
623
624 As a first step in removing this misfeature, Bison now issues a
625 warning when it appends a semicolon. Moreover, in cases where Bison
626 cannot easily determine whether a semicolon is needed (for example, an
627 action ending with a cpp directive or a braced compound initializer),
628 it no longer appends one. Thus, the C compiler might now complain
629 about a missing semicolon where it did not before. Future releases of
630 Bison will cease to append semicolons entirely.
631
095a1d11
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632** Verbose syntax error message fixes:
633
e4ab1254 634 When %error-verbose or the obsolete "#define YYERROR_VERBOSE" is
6f04ee6c
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635 specified, syntax error messages produced by the generated parser
636 include the unexpected token as well as a list of expected tokens.
637 The effect of %nonassoc on these verbose messages has been corrected
638 in two ways, but a more complete fix requires LAC, described above:
095a1d11
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639
640*** When %nonassoc is used, there can exist parser states that accept no
641 tokens, and so the parser does not always require a lookahead token
642 in order to detect a syntax error. Because no unexpected token or
643 expected tokens can then be reported, the verbose syntax error
644 message described above is suppressed, and the parser instead
e4ab1254 645 reports the simpler message, "syntax error". Previously, this
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646 suppression was sometimes erroneously triggered by %nonassoc when a
647 lookahead was actually required. Now verbose messages are
648 suppressed only when all previous lookaheads have already been
649 shifted or discarded.
650
651*** Previously, the list of expected tokens erroneously included tokens
652 that would actually induce a syntax error because conflicts for them
653 were resolved with %nonassoc in the current parser state. Such
654 tokens are now properly omitted from the list.
655
656*** Expected token lists are still often wrong due to state merging
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657 (from LALR or IELR) and default reductions, which can both add
658 invalid tokens and subtract valid tokens. Canonical LR almost
659 completely fixes this problem by eliminating state merging and
660 default reductions. However, there is one minor problem left even
661 when using canonical LR and even after the fixes above. That is,
662 if the resolution of a conflict with %nonassoc appears in a later
663 parser state than the one at which some syntax error is
664 discovered, the conflicted token is still erroneously included in
665 the expected token list. Bison's new LAC implementation,
666 described above, eliminates this problem and the need for
667 canonical LR. However, LAC is still experimental and is disabled
668 by default.
1fa30307 669
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670** Java skeleton fixes:
671
672*** A location handling bug has been fixed.
673
674*** The top element of each of the value stack and location stack is now
675 cleared when popped so that it can be garbage collected.
77768165 676
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677*** Parser traces now print the top element of the stack.
678
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679** -W/--warnings fixes:
680
e4ab1254 681*** Bison now properly recognizes the "no-" versions of categories:
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682
683 For example, given the following command line, Bison now enables all
684 warnings except warnings for incompatibilities with POSIX Yacc:
685
686 bison -Wall,no-yacc gram.y
687
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688*** Bison now treats S/R and R/R conflicts like other warnings:
689
690 Previously, conflict reports were independent of Bison's normal
691 warning system. Now, Bison recognizes the warning categories
e4ab1254 692 "conflicts-sr" and "conflicts-rr". This change has important
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693 consequences for the -W and --warnings command-line options. For
694 example:
695
696 bison -Wno-conflicts-sr gram.y # S/R conflicts not reported
697 bison -Wno-conflicts-rr gram.y # R/R conflicts not reported
698 bison -Wnone gram.y # no conflicts are reported
699 bison -Werror gram.y # any conflict is an error
700
701 However, as before, if the %expect or %expect-rr directive is
702 specified, an unexpected number of conflicts is an error, and an
703 expected number of conflicts is not reported, so -W and --warning
704 then have no effect on the conflict report.
705
e4ab1254 706*** The "none" category no longer disables a preceding "error":
dab96632
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707
708 For example, for the following command line, Bison now reports
709 errors instead of warnings for incompatibilities with POSIX Yacc:
710
711 bison -Werror,none,yacc gram.y
712
e4ab1254 713*** The "none" category now disables all Bison warnings:
8ffd7912 714
e4ab1254 715 Previously, the "none" category disabled only Bison warnings for
8ffd7912
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716 which there existed a specific -W/--warning category. However,
717 given the following command line, Bison is now guaranteed to
718 suppress all warnings:
719
720 bison -Wnone gram.y
721
9d6af153
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722** Precedence directives can now assign token number 0:
723
724 Since Bison 2.3b, which restored the ability of precedence
725 directives to assign token numbers, doing so for token number 0 has
726 produced an assertion failure. For example:
727
728 %left END 0
729
730 This bug has been fixed.
731
7527c744 732* Changes in version 2.4.3 (2010-08-05):
7a9c3cb3 733
4631c34f
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734** Bison now obeys -Werror and --warnings=error for warnings about
735 grammar rules that are useless in the parser due to conflicts.
736
7a9c3cb3
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737** Problems with spawning M4 on at least FreeBSD 8 and FreeBSD 9 have
738 been fixed.
739
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740** Failures in the test suite for GCC 4.5 have been fixed.
741
88bb35d6
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742** Failures in the test suite for some versions of Sun Studio C++ have
743 been fixed.
744
43fdc9fd
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745** Contrary to Bison 2.4.2's NEWS entry, it has been decided that
746 warnings about undefined %prec identifiers will not be converted to
747 errors in Bison 2.5. They will remain warnings, which should be
748 sufficient for POSIX while avoiding backward compatibility issues.
749
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750** Minor documentation fixes.
751
ea66d039 752* Changes in version 2.4.2 (2010-03-20):
8defe11b 753
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754** Some portability problems that resulted in failures and livelocks
755 in the test suite on some versions of at least Solaris, AIX, HP-UX,
ea66d039
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756 RHEL4, and Tru64 have been addressed. As a result, fatal Bison
757 errors should no longer cause M4 to report a broken pipe on the
47fa5747
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758 affected platforms.
759
e4ab1254 760** "%prec IDENTIFIER" requires IDENTIFIER to be defined separately.
2c203528
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761
762 POSIX specifies that an error be reported for any identifier that does
763 not appear on the LHS of a grammar rule and that is not defined by
764 %token, %left, %right, or %nonassoc. Bison 2.3b and later lost this
765 error report for the case when an identifier appears only after a
766 %prec directive. It is now restored. However, for backward
767 compatibility with recent Bison releases, it is only a warning for
768 now. In Bison 2.5 and later, it will return to being an error.
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769 [Between the 2.4.2 and 2.4.3 releases, it was decided that this
770 warning will not be converted to an error in Bison 2.5.]
2c203528 771
c5196098
EB
772** Detection of GNU M4 1.4.6 or newer during configure is improved.
773
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774** Warnings from gcc's -Wundef option about undefined YYENABLE_NLS,
775 YYLTYPE_IS_TRIVIAL, and __STRICT_ANSI__ in C/C++ parsers are now
776 avoided.
af2ffe5c 777
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778** %code is now a permanent feature.
779
780 A traditional Yacc prologue directive is written in the form:
781
782 %{CODE%}
783
784 To provide a more flexible alternative, Bison 2.3b introduced the
785 %code directive with the following forms for C/C++:
786
787 %code {CODE}
788 %code requires {CODE}
789 %code provides {CODE}
790 %code top {CODE}
791
792 These forms are now considered permanent features of Bison. See the
793 %code entries in the section "Bison Declaration Summary" in the Bison
794 manual for a summary of their functionality. See the section
795 "Prologue Alternatives" for a detailed discussion including the
796 advantages of %code over the traditional Yacc prologue directive.
797
798 Bison's Java feature as a whole including its current usage of %code
799 is still considered experimental.
800
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801** YYFAIL is deprecated and will eventually be removed.
802
803 YYFAIL has existed for many years as an undocumented feature of
804 deterministic parsers in C generated by Bison. Previously, it was
805 documented for Bison's experimental Java parsers. YYFAIL is no longer
806 documented for Java parsers and is formally deprecated in both cases.
807 Users are strongly encouraged to migrate to YYERROR, which is
808 specified by POSIX.
809
810 Like YYERROR, you can invoke YYFAIL from a semantic action in order to
811 induce a syntax error. The most obvious difference from YYERROR is
812 that YYFAIL will automatically invoke yyerror to report the syntax
813 error so that you don't have to. However, there are several other
814 subtle differences between YYERROR and YYFAIL, and YYFAIL suffers from
e4ab1254 815 inherent flaws when %error-verbose or "#define YYERROR_VERBOSE" is
41d35e54
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816 used. For a more detailed discussion, see:
817
818 http://lists.gnu.org/archive/html/bison-patches/2009-12/msg00024.html
819
820 The upcoming Bison 2.5 will remove YYFAIL from Java parsers, but
821 deterministic parsers in C will continue to implement it. However,
822 because YYFAIL is already flawed, it seems futile to try to make new
823 Bison features compatible with it. Thus, during parser generation,
824 Bison 2.5 will produce a warning whenever it discovers YYFAIL in a
825 rule action. In a later release, YYFAIL will be disabled for
e4ab1254 826 %error-verbose and "#define YYERROR_VERBOSE". Eventually, YYFAIL will
41d35e54
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827 be removed altogether.
828
829 There exists at least one case where Bison 2.5's YYFAIL warning will
830 be a false positive. Some projects add phony uses of YYFAIL and other
831 Bison-defined macros for the sole purpose of suppressing C
832 preprocessor warnings (from GCC cpp's -Wunused-macros, for example).
833 To avoid Bison's future warning, such YYFAIL uses can be moved to the
e4ab1254 834 epilogue (that is, after the second "%%") in the Bison input file. In
41d35e54
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835 this release (2.4.2), Bison already generates its own code to suppress
836 C preprocessor warnings for YYFAIL, so projects can remove their own
837 phony uses of YYFAIL if compatibility with Bison releases prior to
838 2.4.2 is not necessary.
839
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840** Internationalization.
841
842 Fix a regression introduced in Bison 2.4: Under some circumstances,
843 message translations were not installed although supported by the
844 host system.
845
41930e7a 846* Changes in version 2.4.1 (2008-12-11):
c9ba9e59 847
a957d06c
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848** In the GLR defines file, unexpanded M4 macros in the yylval and yylloc
849 declarations have been fixed.
850
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851** Temporary hack for adding a semicolon to the user action.
852
853 Bison used to prepend a trailing semicolon at the end of the user
854 action for reductions. This allowed actions such as
855
856 exp: exp "+" exp { $$ = $1 + $3 };
857
858 instead of
859
860 exp: exp "+" exp { $$ = $1 + $3; };
861
e4ab1254 862 Some grammars still depend on this "feature". Bison 2.4.1 restores
d07932ef
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863 the previous behavior in the case of C output (specifically, when
864 neither %language or %skeleton or equivalent command-line options
865 are used) to leave more time for grammars depending on the old
866 behavior to be adjusted. Future releases of Bison will disable this
867 feature.
a957d06c
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868
869** A few minor improvements to the Bison manual.
c9ba9e59 870
d6fb461d 871* Changes in version 2.4 (2008-11-02):
7bd1665a 872
d6fb461d 873** %language is an experimental feature.
ed4d67dc
JD
874
875 We first introduced this feature in test release 2.3b as a cleaner
876 alternative to %skeleton. Since then, we have discussed the possibility of
877 modifying its effect on Bison's output file names. Thus, in this release,
878 we consider %language to be an experimental feature that will likely evolve
879 in future releases.
7bd1665a 880
d6fb461d 881** Forward compatibility with GNU M4 has been improved.
241fda7a 882
d6fb461d 883** Several bugs in the C++ skeleton and the experimental Java skeleton have been
241fda7a
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884 fixed.
885
d6fb461d 886* Changes in version 2.3b (2008-05-27):
35fe0834 887
d6fb461d 888** The quotes around NAME that used to be required in the following directive
d9df47b6
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889 are now deprecated:
890
891 %define NAME "VALUE"
892
e4ab1254 893** The directive "%pure-parser" is now deprecated in favor of:
d9df47b6
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894
895 %define api.pure
896
897 which has the same effect except that Bison is more careful to warn about
898 unreasonable usage in the latter case.
899
d6fb461d 900** Push Parsing
c373bf8b
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901
902 Bison can now generate an LALR(1) parser in C with a push interface. That
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903 is, instead of invoking "yyparse", which pulls tokens from "yylex", you can
904 push one token at a time to the parser using "yypush_parse", which will
c373bf8b
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905 return to the caller after processing each token. By default, the push
906 interface is disabled. Either of the following directives will enable it:
907
908 %define api.push_pull "push" // Just push; does not require yylex.
909 %define api.push_pull "both" // Push and pull; requires yylex.
910
e4ab1254 911 See the new section "A Push Parser" in the Bison manual for details.
c373bf8b 912
59da312b
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913 The current push parsing interface is experimental and may evolve. More user
914 feedback will help to stabilize it.
915
d6fb461d 916** The -g and --graph options now output graphs in Graphviz DOT format,
8e55b3aa
JD
917 not VCG format. Like --graph, -g now also takes an optional FILE argument
918 and thus cannot be bundled with other short options.
c373bf8b 919
d6fb461d 920** Java
59da312b
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921
922 Bison can now generate an LALR(1) parser in Java. The skeleton is
e4ab1254 923 "data/lalr1.java". Consider using the new %language directive instead of
59da312b
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924 %skeleton to select it.
925
e4ab1254 926 See the new section "Java Parsers" in the Bison manual for details.
59da312b
JD
927
928 The current Java interface is experimental and may evolve. More user
929 feedback will help to stabilize it.
930
d6fb461d 931** %language
59da312b
JD
932
933 This new directive specifies the programming language of the generated
d43f77e7
PB
934 parser, which can be C (the default), C++, or Java. Besides the skeleton
935 that Bison uses, the directive affects the names of the generated files if
936 the grammar file's name ends in ".y".
59da312b 937
d6fb461d 938** XML Automaton Report
59da312b
JD
939
940 Bison can now generate an XML report of the LALR(1) automaton using the new
e4ab1254 941 "--xml" option. The current XML schema is experimental and may evolve. More
59da312b 942 user feedback will help to stabilize it.
c373bf8b 943
d6fb461d 944** The grammar file may now specify the name of the parser header file using
c373bf8b
JD
945 %defines. For example:
946
947 %defines "parser.h"
948
d6fb461d 949** When reporting useless rules, useless nonterminals, and unused terminals,
d80fb37a
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950 Bison now employs the terms "useless in grammar" instead of "useless",
951 "useless in parser" instead of "never reduced", and "unused in grammar"
952 instead of "unused".
cff03fb2 953
d6fb461d 954** Unreachable State Removal
c373bf8b
JD
955
956 Previously, Bison sometimes generated parser tables containing unreachable
31984206
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957 states. A state can become unreachable during conflict resolution if Bison
958 disables a shift action leading to it from a predecessor state. Bison now:
75ad86ee
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959
960 1. Removes unreachable states.
961
962 2. Does not report any conflicts that appeared in unreachable states.
963 WARNING: As a result, you may need to update %expect and %expect-rr
964 directives in existing grammar files.
965
966 3. For any rule used only in such states, Bison now reports the rule as
cff03fb2 967 "useless in parser due to conflicts".
75ad86ee 968
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969 This feature can be disabled with the following directive:
970
971 %define lr.keep_unreachable_states
972
e4ab1254 973 See the %define entry in the "Bison Declaration Summary" in the Bison manual
31984206
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974 for further discussion.
975
e4ab1254 976** Lookahead Set Correction in the ".output" Report
b1cc23c4 977
e4ab1254
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978 When instructed to generate a ".output" file including lookahead sets
979 (using "--report=lookahead", for example), Bison now prints each reduction's
88c78747
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980 lookahead set only next to the associated state's one item that (1) is
981 associated with the same rule as the reduction and (2) has its dot at the end
982 of its RHS. Previously, Bison also erroneously printed the lookahead set
983 next to all of the state's other items associated with the same rule. This
e4ab1254 984 bug affected only the ".output" file and not the generated parser source
88c78747
JD
985 code.
986
e4ab1254 987** --report-file=FILE is a new option to override the default ".output" file
59da312b 988 name.
1bb2bd75 989
e4ab1254 990** The "=" that used to be required in the following directives is now
02975b9a
JD
991 deprecated:
992
993 %file-prefix "parser"
994 %name-prefix "c_"
995 %output "parser.c"
996
e4ab1254 997** An Alternative to "%{...%}" -- "%code QUALIFIER {CODE}"
c373bf8b
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998
999 Bison 2.3a provided a new set of directives as a more flexible alternative to
8e0a5e9e
JD
1000 the traditional Yacc prologue blocks. Those have now been consolidated into
1001 a single %code directive with an optional qualifier field, which identifies
1002 the purpose of the code and thus the location(s) where Bison should generate
1003 it:
1004
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1005 1. "%code {CODE}" replaces "%after-header {CODE}"
1006 2. "%code requires {CODE}" replaces "%start-header {CODE}"
1007 3. "%code provides {CODE}" replaces "%end-header {CODE}"
1008 4. "%code top {CODE}" replaces "%before-header {CODE}"
8e0a5e9e 1009
e4ab1254
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1010 See the %code entries in section "Bison Declaration Summary" in the Bison
1011 manual for a summary of the new functionality. See the new section "Prologue
1012 Alternatives" for a detailed discussion including the advantages of %code
8e0a5e9e
JD
1013 over the traditional Yacc prologues.
1014
1015 The prologue alternatives are experimental. More user feedback will help to
1016 determine whether they should become permanent features.
1017
d6fb461d 1018** Revised warning: unset or unused mid-rule values
17bd8a73
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1019
1020 Since Bison 2.2, Bison has warned about mid-rule values that are set but not
1021 used within any of the actions of the parent rule. For example, Bison warns
1022 about unused $2 in:
1023
1024 exp: '1' { $$ = 1; } '+' exp { $$ = $1 + $4; };
1025
1026 Now, Bison also warns about mid-rule values that are used but not set. For
1027 example, Bison warns about unset $$ in the mid-rule action in:
1028
1029 exp: '1' { $1 = 1; } '+' exp { $$ = $2 + $4; };
1030
1031 However, Bison now disables both of these warnings by default since they
1032 sometimes prove to be false alarms in existing grammars employing the Yacc
1033 constructs $0 or $-N (where N is some positive integer).
1034
e4ab1254
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1035 To enable these warnings, specify the option "--warnings=midrule-values" or
1036 "-W", which is a synonym for "--warnings=all".
17bd8a73 1037
e4ab1254 1038** Default %destructor or %printer with "<*>" or "<>"
c373bf8b
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1039
1040 Bison now recognizes two separate kinds of default %destructor's and
12e35840
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1041 %printer's:
1042
e4ab1254 1043 1. Place "<*>" in a %destructor/%printer symbol list to define a default
12e35840
JD
1044 %destructor/%printer for all grammar symbols for which you have formally
1045 declared semantic type tags.
1046
e4ab1254 1047 2. Place "<>" in a %destructor/%printer symbol list to define a default
12e35840
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1048 %destructor/%printer for all grammar symbols without declared semantic
1049 type tags.
1050
e4ab1254
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1051 Bison no longer supports the "%symbol-default" notation from Bison 2.3a.
1052 "<*>" and "<>" combined achieve the same effect with one exception: Bison no
12e35840
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1053 longer applies any %destructor to a mid-rule value if that mid-rule value is
1054 not actually ever referenced using either $$ or $n in a semantic action.
1055
85894313
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1056 The default %destructor's and %printer's are experimental. More user
1057 feedback will help to determine whether they should become permanent
1058 features.
1059
e4ab1254 1060 See the section "Freeing Discarded Symbols" in the Bison manual for further
12e35840
JD
1061 details.
1062
d6fb461d 1063** %left, %right, and %nonassoc can now declare token numbers. This is required
e4ab1254 1064 by POSIX. However, see the end of section "Operator Precedence" in the Bison
ab7f29f8
JD
1065 manual for a caveat concerning the treatment of literal strings.
1066
d6fb461d 1067** The nonfunctional --no-parser, -n, and %no-parser options have been
b1cc23c4
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1068 completely removed from Bison.
1069
d6fb461d 1070* Changes in version 2.3a, 2006-09-13:
742e4900 1071
d6fb461d 1072** Instead of %union, you can define and use your own union type
ddc8ede1
PE
1073 YYSTYPE if your grammar contains at least one <type> tag.
1074 Your YYSTYPE need not be a macro; it can be a typedef.
1075 This change is for compatibility with other Yacc implementations,
1076 and is required by POSIX.
1077
d6fb461d 1078** Locations columns and lines start at 1.
cd48d21d
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1079 In accordance with the GNU Coding Standards and Emacs.
1080
d6fb461d 1081** You may now declare per-type and default %destructor's and %printer's:
ec5479ce
JD
1082
1083 For example:
1084
b2a0b7ca
JD
1085 %union { char *string; }
1086 %token <string> STRING1
1087 %token <string> STRING2
1088 %type <string> string1
1089 %type <string> string2
1090 %union { char character; }
1091 %token <character> CHR
1092 %type <character> chr
1093 %destructor { free ($$); } %symbol-default
1094 %destructor { free ($$); printf ("%d", @$.first_line); } STRING1 string1
1095 %destructor { } <character>
1096
1097 guarantees that, when the parser discards any user-defined symbol that has a
e4ab1254
AD
1098 semantic type tag other than "<character>", it passes its semantic value to
1099 "free". However, when the parser discards a "STRING1" or a "string1", it
1100 also prints its line number to "stdout". It performs only the second
1101 "%destructor" in this case, so it invokes "free" only once.
ec5479ce 1102
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1103 [Although we failed to mention this here in the 2.3a release, the default
1104 %destructor's and %printer's were experimental, and they were rewritten in
1105 future versions.]
1106
e4ab1254
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1107** Except for LALR(1) parsers in C with POSIX Yacc emulation enabled (with "-y",
1108 "--yacc", or "%yacc"), Bison no longer generates #define statements for
b931235e
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1109 associating token numbers with token names. Removing the #define statements
1110 helps to sanitize the global namespace during preprocessing, but POSIX Yacc
1111 requires them. Bison still generates an enum for token names in all cases.
1112
d6fb461d 1113** Handling of traditional Yacc prologue blocks is now more consistent but
34f98f46 1114 potentially incompatible with previous releases of Bison.
9bc0dd67
JD
1115
1116 As before, you declare prologue blocks in your grammar file with the
e4ab1254 1117 "%{ ... %}" syntax. To generate the pre-prologue, Bison concatenates all
34f98f46
JD
1118 prologue blocks that you've declared before the first %union. To generate
1119 the post-prologue, Bison concatenates all prologue blocks that you've
ddc8ede1 1120 declared after the first %union.
9bc0dd67 1121
34f98f46 1122 Previous releases of Bison inserted the pre-prologue into both the header
9bc0dd67
JD
1123 file and the code file in all cases except for LALR(1) parsers in C. In the
1124 latter case, Bison inserted it only into the code file. For parsers in C++,
1125 the point of insertion was before any token definitions (which associate
1126 token numbers with names). For parsers in C, the point of insertion was
1127 after the token definitions.
1128
1129 Now, Bison never inserts the pre-prologue into the header file. In the code
1130 file, it always inserts it before the token definitions.
1131
d6fb461d 1132** Bison now provides a more flexible alternative to the traditional Yacc
34f98f46
JD
1133 prologue blocks: %before-header, %start-header, %end-header, and
1134 %after-header.
1135
1136 For example, the following declaration order in the grammar file reflects the
1137 order in which Bison will output these code blocks. However, you are free to
1138 declare these code blocks in your grammar file in whatever order is most
1139 convenient for you:
1140
1141 %before-header {
1142 /* Bison treats this block like a pre-prologue block: it inserts it into
1143 * the code file before the contents of the header file. It does *not*
1144 * insert it into the header file. This is a good place to put
1145 * #include's that you want at the top of your code file. A common
e4ab1254 1146 * example is '#include "system.h"'. */
34f98f46
JD
1147 }
1148 %start-header {
1149 /* Bison inserts this block into both the header file and the code file.
1150 * In both files, the point of insertion is before any Bison-generated
1151 * token, semantic type, location type, and class definitions. This is a
1152 * good place to define %union dependencies, for example. */
9bc0dd67
JD
1153 }
1154 %union {
34f98f46
JD
1155 /* Unlike the traditional Yacc prologue blocks, the output order for the
1156 * new %*-header blocks is not affected by their declaration position
1157 * relative to any %union in the grammar file. */
9bc0dd67 1158 }
34f98f46
JD
1159 %end-header {
1160 /* Bison inserts this block into both the header file and the code file.
1161 * In both files, the point of insertion is after the Bison-generated
1162 * definitions. This is a good place to declare or define public
1163 * functions or data structures that depend on the Bison-generated
1164 * definitions. */
9bc0dd67 1165 }
34f98f46
JD
1166 %after-header {
1167 /* Bison treats this block like a post-prologue block: it inserts it into
1168 * the code file after the contents of the header file. It does *not*
1169 * insert it into the header file. This is a good place to declare or
1170 * define internal functions or data structures that depend on the
1171 * Bison-generated definitions. */
1172 }
1173
1174 If you have multiple occurrences of any one of the above declarations, Bison
1175 will concatenate the contents in declaration order.
9bc0dd67 1176
85894313
JD
1177 [Although we failed to mention this here in the 2.3a release, the prologue
1178 alternatives were experimental, and they were rewritten in future versions.]
1179
e4ab1254 1180** The option "--report=look-ahead" has been changed to "--report=lookahead".
9e6e7ed2
PE
1181 The old spelling still works, but is not documented and may be removed
1182 in a future release.
742e4900 1183
d6fb461d 1184* Changes in version 2.3, 2006-06-05:
4ad3ed84 1185
e4ab1254 1186** GLR grammars should now use "YYRECOVERING ()" instead of "YYRECOVERING",
4ad3ed84
PE
1187 for compatibility with LALR(1) grammars.
1188
d6fb461d 1189** It is now documented that any definition of YYSTYPE or YYLTYPE should
4ad3ed84
PE
1190 be to a type name that does not contain parentheses or brackets.
1191
d6fb461d 1192* Changes in version 2.2, 2006-05-19:
193d7c70 1193
d6fb461d 1194** The distribution terms for all Bison-generated parsers now permit
193d7c70
PE
1195 using the parsers in nonfree programs. Previously, this permission
1196 was granted only for Bison-generated LALR(1) parsers in C.
5f4236a0 1197
d6fb461d 1198** %name-prefix changes the namespace name in C++ outputs.
aa08666d 1199
d6fb461d 1200** The C++ parsers export their token_type.
5f4236a0 1201
d6fb461d 1202** Bison now allows multiple %union declarations, and concatenates
d6ca7905
PE
1203 their contents together.
1204
d6fb461d 1205** New warning: unused values
4d7bc38c
PE
1206 Right-hand side symbols whose values are not used are reported,
1207 if the symbols have destructors. For instance:
affac613 1208
8f3596a6 1209 exp: exp "?" exp ":" exp { $1 ? $1 : $3; }
e29f0771
AD
1210 | exp "+" exp
1211 ;
affac613 1212
8f3596a6
AD
1213 will trigger a warning about $$ and $5 in the first rule, and $3 in
1214 the second ($1 is copied to $$ by the default rule). This example
4e26c69e 1215 most likely contains three errors, and could be rewritten as:
affac613 1216
4e26c69e 1217 exp: exp "?" exp ":" exp
e29f0771
AD
1218 { $$ = $1 ? $3 : $5; free ($1 ? $5 : $3); free ($1); }
1219 | exp "+" exp
1220 { $$ = $1 ? $1 : $3; if ($1) free ($3); }
1221 ;
affac613 1222
4e26c69e
PE
1223 However, if the original actions were really intended, memory leaks
1224 and all, the warnings can be suppressed by letting Bison believe the
1225 values are used, e.g.:
721be13c 1226
8f3596a6 1227 exp: exp "?" exp ":" exp { $1 ? $1 : $3; (void) ($$, $5); }
e29f0771
AD
1228 | exp "+" exp { $$ = $1; (void) $3; }
1229 ;
721be13c 1230
84866159
AD
1231 If there are mid-rule actions, the warning is issued if no action
1232 uses it. The following triggers no warning: $1 and $3 are used.
1233
1234 exp: exp { push ($1); } '+' exp { push ($3); sum (); };
1235
721be13c
PE
1236 The warning is intended to help catching lost values and memory leaks.
1237 If a value is ignored, its associated memory typically is not reclaimed.
affac613 1238
d6fb461d 1239** %destructor vs. YYABORT, YYACCEPT, and YYERROR.
9d9b8b70
PE
1240 Destructors are now called when user code invokes YYABORT, YYACCEPT,
1241 and YYERROR, for all objects on the stack, other than objects
1242 corresponding to the right-hand side of the current rule.
a85284cf 1243
d6fb461d 1244** %expect, %expect-rr
035aa4a0
PE
1245 Incorrect numbers of expected conflicts are now actual errors,
1246 instead of warnings.
1247
d6fb461d 1248** GLR, YACC parsers.
4e26c69e
PE
1249 The %parse-params are available in the destructors (and the
1250 experimental printers) as per the documentation.
4b367315 1251
e4ab1254 1252** Bison now warns if it finds a stray "$" or "@" in an action.
ad6a9b97 1253
d6fb461d 1254** %require "VERSION"
4e26c69e
PE
1255 This specifies that the grammar file depends on features implemented
1256 in Bison version VERSION or higher.
b50d2359 1257
d6fb461d 1258** lalr1.cc: The token and value types are now class members.
e14d0ab6
AD
1259 The tokens were defined as free form enums and cpp macros. YYSTYPE
1260 was defined as a free form union. They are now class members:
e4ab1254
AD
1261 tokens are enumerations of the "yy::parser::token" struct, and the
1262 semantic values have the "yy::parser::semantic_type" type.
fb9712a9
AD
1263
1264 If you do not want or can update to this scheme, the directive
e4ab1254 1265 '%define "global_tokens_and_yystype" "1"' triggers the global
b50d2359
AD
1266 definition of tokens and YYSTYPE. This change is suitable both
1267 for previous releases of Bison, and this one.
fb9712a9 1268
b50d2359 1269 If you wish to update, then make sure older version of Bison will
e4ab1254 1270 fail using '%require "2.2"'.
fb9712a9 1271
d6fb461d 1272** DJGPP support added.
193d7c70 1273\f
d6fb461d 1274* Changes in version 2.1, 2005-09-16:
1ce59070 1275
d6fb461d 1276** The C++ lalr1.cc skeleton supports %lex-param.
e14d0ab6 1277
d6fb461d 1278** Bison-generated parsers now support the translation of diagnostics like
baf785db
PE
1279 "syntax error" into languages other than English. The default
1280 language is still English. For details, please see the new
0410a6e0
PE
1281 Internationalization section of the Bison manual. Software
1282 distributors should also see the new PACKAGING file. Thanks to
1283 Bruno Haible for this new feature.
1ce59070 1284
d6fb461d 1285** Wording in the Bison-generated parsers has been changed slightly to
1a059451
PE
1286 simplify translation. In particular, the message "memory exhausted"
1287 has replaced "parser stack overflow", as the old message was not
1288 always accurate for modern Bison-generated parsers.
1289
d6fb461d 1290** Destructors are now called when the parser aborts, for all symbols left
258b75ca
PE
1291 behind on the stack. Also, the start symbol is now destroyed after a
1292 successful parse. In both cases, the behavior was formerly inconsistent.
1293
d6fb461d 1294** When generating verbose diagnostics, Bison-generated parsers no longer
72f000b0
PE
1295 quote the literal strings associated with tokens. For example, for
1296 a syntax error associated with '%token NUM "number"' they might
1297 print 'syntax error, unexpected number' instead of 'syntax error,
1298 unexpected "number"'.
193d7c70 1299\f
d6fb461d 1300* Changes in version 2.0, 2004-12-25:
efeed023 1301
d6fb461d 1302** Possibly-incompatible changes
d7e14fc0 1303
82de6b0d
PE
1304 - Bison-generated parsers no longer default to using the alloca function
1305 (when available) to extend the parser stack, due to widespread
1306 problems in unchecked stack-overflow detection. You can "#define
1307 YYSTACK_USE_ALLOCA 1" to require the use of alloca, but please read
1308 the manual to determine safe values for YYMAXDEPTH in that case.
8dd162d3 1309
82de6b0d
PE
1310 - Error token location.
1311 During error recovery, the location of the syntax error is updated
1312 to cover the whole sequence covered by the error token: it includes
1313 the shifted symbols thrown away during the first part of the error
1314 recovery, and the lookahead rejected during the second part.
18d192f0 1315
82de6b0d
PE
1316 - Semicolon changes:
1317 . Stray semicolons are no longer allowed at the start of a grammar.
1318 . Semicolons are now required after in-grammar declarations.
e342c3be 1319
82de6b0d
PE
1320 - Unescaped newlines are no longer allowed in character constants or
1321 string literals. They were never portable, and GCC 3.4.0 has
1322 dropped support for them. Better diagnostics are now generated if
1323 forget a closing quote.
8dd162d3 1324
82de6b0d 1325 - NUL bytes are no longer allowed in Bison string literals, unfortunately.
f74b6f91 1326
d6fb461d 1327** New features
1452af69 1328
82de6b0d 1329 - GLR grammars now support locations.
4febdd96 1330
82de6b0d
PE
1331 - New directive: %initial-action.
1332 This directive allows the user to run arbitrary code (including
1333 initializing @$) from yyparse before parsing starts.
1452af69 1334
82de6b0d
PE
1335 - A new directive "%expect-rr N" specifies the expected number of
1336 reduce/reduce conflicts in GLR parsers.
1452af69 1337
e4ab1254 1338 - %token numbers can now be hexadecimal integers, e.g., "%token FOO 0x12d".
82de6b0d 1339 This is a GNU extension.
4febdd96 1340
e4ab1254 1341 - The option "--report=lookahead" was changed to "--report=look-ahead".
9e6e7ed2 1342 [However, this was changed back after 2.3.]
1452af69 1343
82de6b0d 1344 - Experimental %destructor support has been added to lalr1.cc.
1452af69 1345
82de6b0d
PE
1346 - New configure option --disable-yacc, to disable installation of the
1347 yacc command and -ly library introduced in 1.875 for POSIX conformance.
6040d338 1348
d6fb461d 1349** Bug fixes
d5a3fe37 1350
82de6b0d
PE
1351 - For now, %expect-count violations are now just warnings, not errors.
1352 This is for compatibility with Bison 1.75 and earlier (when there are
1353 reduce/reduce conflicts) and with Bison 1.30 and earlier (when there
1354 are too many or too few shift/reduce conflicts). However, in future
1355 versions of Bison we plan to improve the %expect machinery so that
1356 these violations will become errors again.
3473d0f8 1357
82de6b0d
PE
1358 - Within Bison itself, numbers (e.g., goto numbers) are no longer
1359 arbitrarily limited to 16-bit counts.
d600ee67 1360
82de6b0d 1361 - Semicolons are now allowed before "|" in grammar rules, as POSIX requires.
d600ee67 1362\f
d6fb461d 1363* Changes in version 1.875, 2003-01-01:
963fcc17 1364
d6fb461d 1365** The documentation license has been upgraded to version 1.2
dc546b0f 1366 of the GNU Free Documentation License.
75eb3bc4 1367
d6fb461d 1368** syntax error processing
75eb3bc4 1369
dc546b0f
PE
1370 - In Yacc-style parsers YYLLOC_DEFAULT is now used to compute error
1371 locations too. This fixes bugs in error-location computation.
75eb3bc4 1372
dc546b0f
PE
1373 - %destructor
1374 It is now possible to reclaim the memory associated to symbols
1375 discarded during error recovery. This feature is still experimental.
20daca06 1376
dc546b0f
PE
1377 - %error-verbose
1378 This new directive is preferred over YYERROR_VERBOSE.
74724a70 1379
dc546b0f
PE
1380 - #defining yyerror to steal internal variables is discouraged.
1381 It is not guaranteed to work forever.
d1de5372 1382
d6fb461d 1383** POSIX conformance
d1de5372 1384
dc546b0f
PE
1385 - Semicolons are once again optional at the end of grammar rules.
1386 This reverts to the behavior of Bison 1.33 and earlier, and improves
1387 compatibility with Yacc.
74724a70 1388
e4ab1254
AD
1389 - "parse error" -> "syntax error"
1390 Bison now uniformly uses the term "syntax error"; formerly, the code
1391 and manual sometimes used the term "parse error" instead. POSIX
1392 requires "syntax error" in diagnostics, and it was thought better to
dc546b0f 1393 be consistent.
74724a70 1394
dc546b0f
PE
1395 - The documentation now emphasizes that yylex and yyerror must be
1396 declared before use. C99 requires this.
d1de5372 1397
dc546b0f
PE
1398 - Bison now parses C99 lexical constructs like UCNs and
1399 backslash-newline within C escape sequences, as POSIX 1003.1-2001 requires.
d1de5372 1400
dc546b0f
PE
1401 - File names are properly escaped in C output. E.g., foo\bar.y is
1402 output as "foo\\bar.y".
6780ca7a 1403
dc546b0f 1404 - Yacc command and library now available
e4ab1254 1405 The Bison distribution now installs a "yacc" command, as POSIX requires.
dc546b0f
PE
1406 Also, Bison now installs a small library liby.a containing
1407 implementations of Yacc-compatible yyerror and main functions.
1408 This library is normally not useful, but POSIX requires it.
6e649e65 1409
dc546b0f 1410 - Type clashes now generate warnings, not errors.
6e649e65 1411
dc546b0f
PE
1412 - If the user does not define YYSTYPE as a macro, Bison now declares it
1413 using typedef instead of defining it as a macro.
1414 For consistency, YYLTYPE is also declared instead of defined.
9501dc6e 1415
d6fb461d 1416** Other compatibility issues
886a425c 1417
e4ab1254
AD
1418 - %union directives can now have a tag before the "{", e.g., the
1419 directive "%union foo {...}" now generates the C code
1420 "typedef union foo { ... } YYSTYPE;"; this is for Yacc compatibility.
1421 The default union tag is "YYSTYPE", for compatibility with Solaris 9 Yacc.
1422 For consistency, YYLTYPE's struct tag is now "YYLTYPE" not "yyltype".
dc546b0f 1423 This is for compatibility with both Yacc and Bison 1.35.
72f889cc 1424
e4ab1254 1425 - ";" is output before the terminating "}" of an action, for
dc546b0f 1426 compatibility with Bison 1.35.
886a425c 1427
dc546b0f 1428 - Bison now uses a Yacc-style format for conflict reports, e.g.,
e4ab1254 1429 "conflicts: 2 shift/reduce, 1 reduce/reduce".
437c2d80 1430
e4ab1254 1431 - "yystype" and "yyltype" are now obsolescent macros instead of being
dc546b0f
PE
1432 typedefs or tags; they are no longer documented and are planned to be
1433 withdrawn in a future release.
2a8d363a 1434
d6fb461d 1435** GLR parser notes
2a8d363a 1436
dc546b0f
PE
1437 - GLR and inline
1438 Users of Bison have to decide how they handle the portability of the
e4ab1254 1439 C keyword "inline".
959e5f51 1440
e4ab1254
AD
1441 - "parsing stack overflow..." -> "parser stack overflow"
1442 GLR parsers now report "parser stack overflow" as per the Bison manual.
900c5db5 1443
18ad57b3
AD
1444** %parse-param and %lex-param
1445 The macros YYPARSE_PARAM and YYLEX_PARAM provide a means to pass
1446 additional context to yyparse and yylex. They suffer from several
1447 shortcomings:
1448
1449 - a single argument only can be added,
1450 - their types are weak (void *),
242cc08e 1451 - this context is not passed to ancillary functions such as yyerror,
18ad57b3
AD
1452 - only yacc.c parsers support them.
1453
1454 The new %parse-param/%lex-param directives provide a more precise control.
1455 For instance:
1456
1457 %parse-param {int *nastiness}
1458 %lex-param {int *nastiness}
1459 %parse-param {int *randomness}
1460
1461 results in the following signatures:
1462
1463 int yylex (int *nastiness);
1464 int yyparse (int *nastiness, int *randomness);
1465
1466 or, if both %pure-parser and %locations are used:
1467
1468 int yylex (YYSTYPE *lvalp, YYLTYPE *llocp, int *nastiness);
1469 int yyparse (int *nastiness, int *randomness);
1470
d6fb461d 1471** Bison now warns if it detects conflicting outputs to the same file,
e4ab1254 1472 e.g., it generates a warning for "bison -d -o foo.h foo.y" since
dc546b0f 1473 that command outputs both code and header to foo.h.
6e40b4eb 1474
d6fb461d 1475** #line in output files
dc546b0f 1476 - --no-line works properly.
6e40b4eb 1477
d6fb461d 1478** Bison can no longer be built by a K&R C compiler; it requires C89 or
6e40b4eb
AD
1479 later to be built. This change originally took place a few versions
1480 ago, but nobody noticed until we recently asked someone to try
1481 building Bison with a K&R C compiler.
d600ee67 1482\f
d6fb461d 1483* Changes in version 1.75, 2002-10-14:
7933f2b5 1484
d6fb461d 1485** Bison should now work on 64-bit hosts.
7933f2b5 1486
d6fb461d 1487** Indonesian translation thanks to Tedi Heriyanto.
7933f2b5 1488
d6fb461d 1489** GLR parsers
f50adbbd
AD
1490 Fix spurious parse errors.
1491
d6fb461d 1492** Pure parsers
f50adbbd
AD
1493 Some people redefine yyerror to steal yyparse' private variables.
1494 Reenable this trick until an official feature replaces it.
1495
d6fb461d 1496** Type Clashes
d90c934c
AD
1497 In agreement with POSIX and with other Yaccs, leaving a default
1498 action is valid when $$ is untyped, and $1 typed:
1499
e29f0771 1500 untyped: ... typed;
d90c934c
AD
1501
1502 but the converse remains an error:
1503
e29f0771 1504 typed: ... untyped;
d90c934c 1505
d6fb461d 1506** Values of mid-rule actions
d90c934c
AD
1507 The following code:
1508
e29f0771 1509 foo: { ... } { $$ = $1; } ...
d90c934c
AD
1510
1511 was incorrectly rejected: $1 is defined in the second mid-rule
1512 action, and is equal to the $$ of the first mid-rule action.
d600ee67 1513\f
d6fb461d 1514* Changes in version 1.50, 2002-10-04:
adc8c848 1515
d6fb461d 1516** GLR parsing
676385e2
PH
1517 The declaration
1518 %glr-parser
1519 causes Bison to produce a Generalized LR (GLR) parser, capable of handling
1520 almost any context-free grammar, ambiguous or not. The new declarations
e8832397 1521 %dprec and %merge on grammar rules allow parse-time resolution of
676385e2
PH
1522 ambiguities. Contributed by Paul Hilfinger.
1523
7933f2b5 1524 Unfortunately Bison 1.50 does not work properly on 64-bit hosts
420f93c8
PE
1525 like the Alpha, so please stick to 32-bit hosts for now.
1526
d6fb461d 1527** Output Directory
8c165d89 1528 When not in Yacc compatibility mode, when the output file was not
e4ab1254
AD
1529 specified, running "bison foo/bar.y" created "foo/bar.c". It
1530 now creates "bar.c".
8c165d89 1531
d6fb461d 1532** Undefined token
007a50a4 1533 The undefined token was systematically mapped to 2 which prevented
e88dbdbf 1534 the use of 2 by the user. This is no longer the case.
007a50a4 1535
d6fb461d 1536** Unknown token numbers
e88dbdbf 1537 If yylex returned an out of range value, yyparse could die. This is
007a50a4
AD
1538 no longer the case.
1539
d6fb461d 1540** Error token
e88dbdbf 1541 According to POSIX, the error token must be 256.
23c5a174
AD
1542 Bison extends this requirement by making it a preference: *if* the
1543 user specified that one of her tokens is numbered 256, then error
1544 will be mapped onto another number.
1545
d6fb461d 1546** Verbose error messages
e4ab1254 1547 They no longer report "..., expecting error or..." for states where
217598da
AD
1548 error recovery is possible.
1549
d6fb461d 1550** End token
e4ab1254 1551 Defaults to "$end" instead of "$".
217598da 1552
d6fb461d 1553** Error recovery now conforms to documentation and to POSIX
68cd8af3
PE
1554 When a Bison-generated parser encounters a syntax error, it now pops
1555 the stack until it finds a state that allows shifting the error
1556 token. Formerly, it popped the stack until it found a state that
1557 allowed some non-error action other than a default reduction on the
1558 error token. The new behavior has long been the documented behavior,
1559 and has long been required by POSIX. For more details, please see
337116ba
PE
1560 Paul Eggert, "Reductions during Bison error handling" (2002-05-20)
1561 <http://lists.gnu.org/archive/html/bug-bison/2002-05/msg00038.html>.
68cd8af3 1562
d6fb461d 1563** Traces
5504898e
AD
1564 Popped tokens and nonterminals are now reported.
1565
d6fb461d 1566** Larger grammars
a861a339
PE
1567 Larger grammars are now supported (larger token numbers, larger grammar
1568 size (= sum of the LHS and RHS lengths), larger LALR tables).
1569 Formerly, many of these numbers ran afoul of 16-bit limits;
1570 now these limits are 32 bits on most hosts.
355e7c1c 1571
d6fb461d 1572** Explicit initial rule
643a5994
AD
1573 Bison used to play hacks with the initial rule, which the user does
1574 not write. It is now explicit, and visible in the reports and
1575 graphs as rule 0.
23c5a174 1576
d6fb461d 1577** Useless rules
643a5994 1578 Before, Bison reported the useless rules, but, although not used,
77714df2 1579 included them in the parsers. They are now actually removed.
23c5a174 1580
d6fb461d 1581** Useless rules, useless nonterminals
6b98e4b5
AD
1582 They are now reported, as a warning, with their locations.
1583
d6fb461d 1584** Rules never reduced
e8832397
AD
1585 Rules that can never be reduced because of conflicts are now
1586 reported.
1587
e4ab1254 1588** Incorrect "Token not used"
11652ab3
AD
1589 On a grammar such as
1590
e29f0771
AD
1591 %token useless useful
1592 %%
1593 exp: '0' %prec useful;
11652ab3
AD
1594
1595 where a token was used to set the precedence of the last rule,
e4ab1254 1596 bison reported both "useful" and "useless" as useless tokens.
11652ab3 1597
d6fb461d 1598** Revert the C++ namespace changes introduced in 1.31
77714df2 1599 as they caused too many portability hassles.
0179dd65 1600
d6fb461d 1601** Default locations
b2d52318
AD
1602 By an accident of design, the default computation of @$ was
1603 performed after another default computation was performed: @$ = @1.
1604 The latter is now removed: YYLLOC_DEFAULT is fully responsible of
1605 the computation of @$.
adc8c848 1606
d6fb461d 1607** Token end-of-file
b7c49edf
AD
1608 The token end of file may be specified by the user, in which case,
1609 the user symbol is used in the reports, the graphs, and the verbose
e4ab1254 1610 error messages instead of "$end", which remains being the default.
b7c49edf 1611 For instance
e29f0771 1612 %token MYEOF 0
b7c49edf 1613 or
e29f0771 1614 %token MYEOF 0 "end of file"
fdbcd8e2 1615
d6fb461d 1616** Semantic parser
fdbcd8e2
AD
1617 This old option, which has been broken for ages, is removed.
1618
d6fb461d 1619** New translations
a861a339 1620 Brazilian Portuguese, thanks to Alexandre Folle de Menezes.
84614e13
AD
1621 Croatian, thanks to Denis Lackovic.
1622
d6fb461d 1623** Incorrect token definitions
e4ab1254
AD
1624 When given
1625 %token 'a' "A"
1626 bison used to output
1627 #define 'a' 65
b87f8b21 1628
d6fb461d 1629** Token definitions as enums
77714df2
AD
1630 Tokens are output both as the traditional #define's, and, provided
1631 the compiler supports ANSI C or is a C++ compiler, as enums.
e88dbdbf 1632 This lets debuggers display names instead of integers.
77714df2 1633
d6fb461d 1634** Reports
ec3bc396
AD
1635 In addition to --verbose, bison supports --report=THINGS, which
1636 produces additional information:
b408954b
AD
1637 - itemset
1638 complete the core item sets with their closure
e4ab1254 1639 - lookahead [changed to "look-ahead" in 1.875e through 2.3, but changed back]
9e6e7ed2 1640 explicitly associate lookahead tokens to items
b408954b
AD
1641 - solved
1642 describe shift/reduce conflicts solving.
1643 Bison used to systematically output this information on top of
1644 the report. Solved conflicts are now attached to their states.
ec3bc396 1645
d6fb461d 1646** Type clashes
9af3fbce
AD
1647 Previous versions don't complain when there is a type clash on
1648 the default action if the rule has a mid-rule action, such as in:
1649
e29f0771
AD
1650 %type <foo> bar
1651 %%
1652 bar: '0' {} '0';
9af3fbce
AD
1653
1654 This is fixed.
a861a339 1655
d6fb461d 1656** GNU M4 is now required when using Bison.
f987e9d2 1657\f
d6fb461d 1658* Changes in version 1.35, 2002-03-25:
76551463 1659
d6fb461d 1660** C Skeleton
76551463
AD
1661 Some projects use Bison's C parser with C++ compilers, and define
1662 YYSTYPE as a class. The recent adjustment of C parsers for data
1663 alignment and 64 bit architectures made this impossible.
1664
1665 Because for the time being no real solution for C++ parser
1666 generation exists, kludges were implemented in the parser to
1667 maintain this use. In the future, when Bison has C++ parsers, this
1668 kludge will be disabled.
1669
1670 This kludge also addresses some C++ problems when the stack was
1671 extended.
76551463 1672\f
d6fb461d 1673* Changes in version 1.34, 2002-03-12:
76551463 1674
d6fb461d 1675** File name clashes are detected
76551463 1676 $ bison foo.y -d -o foo.x
e4ab1254 1677 fatal error: header and parser would both be named "foo.x"
76551463 1678
e4ab1254 1679** A missing ";" at the end of a rule triggers a warning
76551463
AD
1680 In accordance with POSIX, and in agreement with other
1681 Yacc implementations, Bison will mandate this semicolon in the near
1682 future. This eases the implementation of a Bison parser of Bison
1683 grammars by making this grammar LALR(1) instead of LR(2). To
1684 facilitate the transition, this release introduces a warning.
1685
d6fb461d 1686** Revert the C++ namespace changes introduced in 1.31, as they caused too
76551463
AD
1687 many portability hassles.
1688
d6fb461d 1689** DJGPP support added.
76551463 1690
d6fb461d 1691** Fix test suite portability problems.
76551463 1692\f
d6fb461d 1693* Changes in version 1.33, 2002-02-07:
76551463 1694
d6fb461d 1695** Fix C++ issues
76551463
AD
1696 Groff could not be compiled for the definition of size_t was lacking
1697 under some conditions.
1698
d6fb461d 1699** Catch invalid @n
76551463
AD
1700 As is done with $n.
1701\f
d6fb461d 1702* Changes in version 1.32, 2002-01-23:
76551463 1703
d6fb461d 1704** Fix Yacc output file names
76551463 1705
d6fb461d 1706** Portability fixes
76551463 1707
d6fb461d 1708** Italian, Dutch translations
76551463 1709\f
d6fb461d 1710* Changes in version 1.31, 2002-01-14:
52d1aeee 1711
d6fb461d 1712** Many Bug Fixes
52d1aeee 1713
d6fb461d 1714** GNU Gettext and %expect
52d1aeee
MA
1715 GNU Gettext asserts 10 s/r conflicts, but there are 7. Now that
1716 Bison dies on incorrect %expectations, we fear there will be
1717 too many bug reports for Gettext, so _for the time being_, %expect
e4ab1254 1718 does not trigger an error when the input file is named "plural.y".
52d1aeee 1719
d6fb461d 1720** Use of alloca in parsers
52d1aeee
MA
1721 If YYSTACK_USE_ALLOCA is defined to 0, then the parsers will use
1722 malloc exclusively. Since 1.29, but was not NEWS'ed.
1723
1724 alloca is used only when compiled with GCC, to avoid portability
1725 problems as on AIX.
1726
d6fb461d 1727** yyparse now returns 2 if memory is exhausted; formerly it dumped core.
b47dbebe 1728
d6fb461d 1729** When the generated parser lacks debugging code, YYDEBUG is now 0
52d1aeee
MA
1730 (as POSIX requires) instead of being undefined.
1731
d6fb461d 1732** User Actions
52d1aeee
MA
1733 Bison has always permitted actions such as { $$ = $1 }: it adds the
1734 ending semicolon. Now if in Yacc compatibility mode, the semicolon
1735 is no longer output: one has to write { $$ = $1; }.
1736
d6fb461d 1737** Better C++ compliance
52d1aeee 1738 The output parsers try to respect C++ namespaces.
76551463 1739 [This turned out to be a failed experiment, and it was reverted later.]
52d1aeee 1740
d6fb461d 1741** Reduced Grammars
52d1aeee
MA
1742 Fixed bugs when reporting useless nonterminals.
1743
d6fb461d 1744** 64 bit hosts
52d1aeee
MA
1745 The parsers work properly on 64 bit hosts.
1746
d6fb461d 1747** Error messages
52d1aeee
MA
1748 Some calls to strerror resulted in scrambled or missing error messages.
1749
d6fb461d 1750** %expect
52d1aeee
MA
1751 When the number of shift/reduce conflicts is correct, don't issue
1752 any warning.
1753
d6fb461d 1754** The verbose report includes the rule line numbers.
52d1aeee 1755
d6fb461d 1756** Rule line numbers are fixed in traces.
52d1aeee 1757
d6fb461d 1758** Swedish translation
52d1aeee 1759
d6fb461d 1760** Parse errors
52d1aeee
MA
1761 Verbose parse error messages from the parsers are better looking.
1762 Before: parse error: unexpected `'/'', expecting `"number"' or `'-'' or `'(''
1763 Now: parse error: unexpected '/', expecting "number" or '-' or '('
1764
d6fb461d 1765** Fixed parser memory leaks.
52d1aeee
MA
1766 When the generated parser was using malloc to extend its stacks, the
1767 previous allocations were not freed.
1768
d6fb461d 1769** Fixed verbose output file.
52d1aeee
MA
1770 Some newlines were missing.
1771 Some conflicts in state descriptions were missing.
1772
d6fb461d 1773** Fixed conflict report.
52d1aeee
MA
1774 Option -v was needed to get the result.
1775
d6fb461d 1776** %expect
52d1aeee
MA
1777 Was not used.
1778 Mismatches are errors, not warnings.
1779
d6fb461d 1780** Fixed incorrect processing of some invalid input.
52d1aeee 1781
d6fb461d 1782** Fixed CPP guards: 9foo.h uses BISON_9FOO_H instead of 9FOO_H.
52d1aeee 1783
d6fb461d 1784** Fixed some typos in the documentation.
52d1aeee 1785
d6fb461d 1786** %token MY_EOF 0 is supported.
52d1aeee
MA
1787 Before, MY_EOF was silently renumbered as 257.
1788
d6fb461d 1789** doc/refcard.tex is updated.
52d1aeee 1790
d6fb461d 1791** %output, %file-prefix, %name-prefix.
52d1aeee
MA
1792 New.
1793
d6fb461d 1794** --output
e4ab1254 1795 New, aliasing "--output-file".
52d1aeee 1796\f
d6fb461d 1797* Changes in version 1.30, 2001-10-26:
342b8b6e 1798
e4ab1254
AD
1799** "--defines" and "--graph" have now an optional argument which is the
1800 output file name. "-d" and "-g" do not change; they do not take any
342b8b6e
AD
1801 argument.
1802
e4ab1254 1803** "%source_extension" and "%header_extension" are removed, failed
342b8b6e
AD
1804 experiment.
1805
d6fb461d 1806** Portability fixes.
f987e9d2 1807\f
d6fb461d 1808* Changes in version 1.29, 2001-09-07:
342b8b6e 1809
d6fb461d 1810** The output file does not define const, as this caused problems when used
342b8b6e
AD
1811 with common autoconfiguration schemes. If you still use ancient compilers
1812 that lack const, compile with the equivalent of the C compiler option
e4ab1254 1813 "-Dconst=". Autoconf's AC_C_CONST macro provides one way to do this.
342b8b6e 1814
e4ab1254 1815** Added "-g" and "--graph".
f87a2205 1816
d6fb461d 1817** The Bison manual is now distributed under the terms of the GNU FDL.
f2b5126e 1818
d6fb461d 1819** The input and the output files has automatically a similar extension.
234a3be3 1820
d6fb461d 1821** Russian translation added.
f87a2205 1822
d6fb461d 1823** NLS support updated; should hopefully be less troublesome.
f87a2205 1824
d6fb461d 1825** Added the old Bison reference card.
c33638bb 1826
e4ab1254 1827** Added "--locations" and "%locations".
6deb4447 1828
e4ab1254 1829** Added "-S" and "--skeleton".
cd5bd6ac 1830
e4ab1254 1831** "%raw", "-r", "--raw" is disabled.
62ab6972 1832
d6fb461d 1833** Special characters are escaped when output. This solves the problems
cd5bd6ac
AD
1834 of the #line lines with path names including backslashes.
1835
d6fb461d 1836** New directives.
e4ab1254
AD
1837 "%yacc", "%fixed_output_files", "%defines", "%no_parser", "%verbose",
1838 "%debug", "%source_extension" and "%header_extension".
f987e9d2 1839
d6fb461d 1840** @$
f987e9d2 1841 Automatic location tracking.
f87a2205 1842\f
d6fb461d 1843* Changes in version 1.28, 1999-07-06:
d2e00347 1844
d6fb461d 1845** Should compile better now with K&R compilers.
d2e00347 1846
d6fb461d 1847** Added NLS.
d2e00347 1848
d6fb461d 1849** Fixed a problem with escaping the double quote character.
d2e00347 1850
d6fb461d 1851** There is now a FAQ.
d2e00347 1852\f
d6fb461d 1853* Changes in version 1.27:
5c31c3c2 1854
d6fb461d 1855** The make rule which prevented bison.simple from being created on
5c31c3c2
JT
1856 some systems has been fixed.
1857\f
d6fb461d 1858* Changes in version 1.26:
4be07551 1859
7e508a2b 1860** Bison now uses Automake.
4be07551 1861
d6fb461d 1862** New mailing lists: <bug-bison@gnu.org> and <help-bison@gnu.org>.
4be07551 1863
d6fb461d 1864** Token numbers now start at 257 as previously documented, not 258.
4be07551 1865
d6fb461d 1866** Bison honors the TMPDIR environment variable.
4be07551 1867
d6fb461d 1868** A couple of buffer overruns have been fixed.
f51dbca1 1869
d6fb461d 1870** Problems when closing files should now be reported.
f51dbca1 1871
d6fb461d 1872** Generated parsers should now work even on operating systems which do
f51dbca1 1873 not provide alloca().
4be07551 1874\f
d6fb461d 1875* Changes in version 1.25, 1995-10-16:
df8878c5 1876
d6fb461d 1877** Errors in the input grammar are not fatal; Bison keeps reading
df8878c5 1878the grammar file, and reports all the errors found in it.
8c44d3ec 1879
d6fb461d 1880** Tokens can now be specified as multiple-character strings: for
df8878c5 1881example, you could use "<=" for a token which looks like <=, instead
7e508a2b 1882of choosing a name like LESSEQ.
df8878c5 1883
d6fb461d 1884** The %token_table declaration says to write a table of tokens (names
df8878c5
RS
1885and numbers) into the parser file. The yylex function can use this
1886table to recognize multiple-character string tokens, or for other
1887purposes.
1888
d6fb461d 1889** The %no_lines declaration says not to generate any #line preprocessor
df8878c5
RS
1890directives in the parser file.
1891
d6fb461d 1892** The %raw declaration says to use internal Bison token numbers, not
df8878c5
RS
1893Yacc-compatible token numbers, when token names are defined as macros.
1894
d6fb461d 1895** The --no-parser option produces the parser tables without including
df8878c5
RS
1896the parser engine; a project can now use its own parser engine.
1897The actions go into a separate file called NAME.act, in the form of
1898a switch statement body.
1899\f
d6fb461d 1900* Changes in version 1.23:
6780ca7a 1901
4d019228
DM
1902The user can define YYPARSE_PARAM as the name of an argument to be
1903passed into yyparse. The argument should have type void *. It should
1904actually point to an object. Grammar actions can access the variable
1905by casting it to the proper pointer type.
6780ca7a 1906
6780ca7a 1907Line numbers in output file corrected.
6780ca7a 1908\f
d6fb461d 1909* Changes in version 1.22:
6780ca7a
DM
1910
1911--help option added.
6780ca7a 1912\f
d6fb461d 1913* Changes in version 1.20:
6780ca7a
DM
1914
1915Output file does not redefine const for C++.
9f4503d6 1916
76551463
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1917-----
1918
c932d613 1919Copyright (C) 1995-2012 Free Software Foundation, Inc.
76551463 1920
8defe11b 1921This file is part of Bison, the GNU Parser Generator.
76551463 1922
f16b0819 1923This program is free software: you can redistribute it and/or modify
76551463 1924it under the terms of the GNU General Public License as published by
f16b0819
PE
1925the Free Software Foundation, either version 3 of the License, or
1926(at your option) any later version.
76551463 1927
f16b0819 1928This program is distributed in the hope that it will be useful,
76551463
AD
1929but WITHOUT ANY WARRANTY; without even the implied warranty of
1930MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
1931GNU General Public License for more details.
1932
1933You should have received a copy of the GNU General Public License
f16b0819 1934along with this program. If not, see <http://www.gnu.org/licenses/>.
7e508a2b
AD
1935
1936 LocalWords: yacc YYBACKUP glr GCC lalr ArrayIndexOutOfBoundsException nullptr
1937 LocalWords: cplusplus liby rpl fprintf mfcalc Wyacc stmt cond expr mk sym lr
1938 LocalWords: IELR ielr Lookahead YYERROR nonassoc LALR's api lookaheads yychar
1939 LocalWords: destructor lookahead YYRHSLOC YYLLOC Rhs ifndef YYFAIL cpp sr rr
1940 LocalWords: preprocessor initializer Wno Wnone Werror FreeBSD prec livelocks
1941 LocalWords: Solaris AIX UX RHEL Tru LHS gcc's Wundef YYENABLE NLS YYLTYPE VCG
1942 LocalWords: yyerror cpp's Wunused yylval yylloc prepend yyparse yylex yypush
1943 LocalWords: Graphviz xml nonterminals midrule destructor's YYSTYPE typedef ly
1944 LocalWords: CHR chr printf stdout namespace preprocessing enum pre include's
1945 LocalWords: YYRECOVERING nonfree destructors YYABORT YYACCEPT params enums de
1946 LocalWords: struct yystype DJGPP lex param Haible NUM alloca YYSTACK NUL goto
1947 LocalWords: YYMAXDEPTH Unescaped UCNs YYLTYPE's yyltype typedefs inline Yaccs
1948 LocalWords: Heriyanto Reenable dprec Hilfinger Eggert MYEOF Folle Menezes EOF
242cc08e 1949 LocalWords: Lackovic define's itemset Groff Gettext malloc NEWS'ed YYDEBUG YY
7e508a2b 1950 LocalWords: namespaces strerror const autoconfiguration Dconst Autoconf's FDL
242cc08e
AD
1951 LocalWords: Automake TMPDIR LESSEQ ylwrap endif yydebug YYTOKEN YYLSP ival hh
1952 LocalWords: extern YYTOKENTYPE TOKENTYPE yytokentype tokentype STYPE lval pdf
7287be84
AD
1953 LocalWords: lang yyoutput dvi html ps POSIX lvalp llocp calc yyo fval Wmaybe
1954 LocalWords: yyvsp pragmas noreturn java's
7e508a2b
AD
1955
1956Local Variables:
1957mode: outline
e4ab1254 1958fill-column: 76
7e508a2b 1959End: