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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** %language is no longer an experimental feature.
6
7 The introduction of this feature, in 2.4, was four years ago. The --language
8 option and the %language directive are no longer experimental.
9
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10** New format for error reports: carets
11
12 Caret errors have been added to Bison, for example (taken from the
13 documentation):
14
15 input.y:3.20-23: error: ambiguous reference: '$exp'
16 exp: exp '+' exp { $exp = $1 + $2; };
17 ^^^^
18
19 The default behaviour for now is still not to display these unless explictly
20 asked with -fall of -fcaret. However, in a later release, it will be made the
21 default behavior (but may still be deactivated with -fno-caret).
22
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23** New value for %define variable: api.pure full
24
25 The %define variable api.pure requests a pure (reentrant) parser. However,
26 for historical reasons, using it in a location-tracking Yacc parser resulted
27 in an yyerror function that did not take a location as a parameter. With this
28 new value, the user may request a better pure parser, where yyerror does take
29 a location as a parameter (in location-tracking parsers).
30
31 The use of "%define api.pure true" is deprecated in favor of this new
32 "%define api.pure full".
33
5a05f42e 34** Changes in the format of error messages
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35
36 This used to be the format of many error reports:
37
38 foo.y:5.10-24: result type clash on merge function 'merge': <t3> != <t2>
39 foo.y:4.13-27: previous declaration
40
41 It is now:
42
43 foo.y:5.10-25: result type clash on merge function 'merge': <t3> != <t2>
44 foo.y:4.13-27: previous declaration
45
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46** Exception safety (lalr1.cc)
47
48 The parse function now catches exceptions, uses the %destructors to
49 release memory (the lookahead symbol and the symbols pushed on the stack)
7287be84 50 before re-throwing the exception.
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51
52 This feature is somewhat experimental. User feedback would be
53 appreciated.
54
7287be84 55** New %define variable: api.location.type (glr.cc, lalr1.cc, lalr1.java)
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56
57 The %define variable api.location.type defines the name of the type to use
58 for locations. When defined, Bison no longer generates the position.hh
59 and location.hh files, nor does the parser will include them: the user is
60 then responsible to define her type.
61
62 This can be used in programs with several parsers to factor their location
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63 and position files: let one of them generate them, and the others just use
64 them.
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65
66 This feature was actually introduced, but not documented, in Bison 2.5,
67 under the name "location_type" (which is maintained for backward
68 compatibility).
69
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70 For consistency, lalr1.java's %define variables location_type and
71 position_type are deprecated in favor of api.location.type and
72 api.position.type.
73
9c16d399 74** Graph improvements in DOT and XSLT
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75
76 The graphical presentation of the states is more readable: their shape is
77 now rectangular, the state number is clearly displayed, and the items are
78 numbered and left-justified.
79
80 The reductions are now explicitly represented as transitions to other
81 diamond shaped nodes.
82
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83 These changes are present in both --graph output and xml2dot.xsl XSLT
84 processing, with minor (documented) differences.
85
86 Two nodes were added to the documentation: Xml and Graphviz.
87
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88* Noteworthy changes in release ?.? (????-??-??) [?]
89
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90** Bug fixes
91
92 Warnings about uninitialized yylloc in yyparse have been fixed.
93
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94** Documentation
95
96 The sections about shift/reduce and reduce/reduce conflicts resolution
97 have been fixed and extended.
9d2423f5 98
9d3f7eaf 99* Noteworthy changes in release 2.6.5 (2012-11-07) [stable]
6f1360bd 100
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101 We consider compiler warnings about Bison generated parsers to be bugs.
102 Rather than working around them in your own project, please consider
103 reporting them to us.
104
105** Bug fixes
106
107 Warnings about uninitialized yylval and/or yylloc for push parsers with a
108 pure interface have been fixed for GCC 4.0 up to 4.8, and Clang 2.9 to
109 3.2.
110
111 Other issues in the test suite have been addressed.
6f1360bd 112
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113 Nul characters are correctly displayed in error messages.
114
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115 When possible, yylloc is correctly initialized before calling yylex. It
116 is no longer necessary to initialize it in the %initial-action.
117
0ac15849 118* Noteworthy changes in release 2.6.4 (2012-10-23) [stable]
a4eb820f 119
468455e1 120 Bison 2.6.3's --version was incorrect. This release fixes this issue.
a4eb820f 121
6eb8f74f 122* Noteworthy changes in release 2.6.3 (2012-10-22) [stable]
933ec544 123
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124** Bug fixes
125
9a50c55a 126 Bugs and portability issues in the test suite have been fixed.
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127
128 Some errors in translations have been addressed, and --help now directs
129 users to the appropriate place to report them.
130
131 Stray Info files shipped by accident are removed.
132
133 Incorrect definitions of YY_, issued by yacc.c when no parser header is
134 generated, are removed.
933ec544 135
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136 All the generated headers are self-contained.
137
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138** Header guards (yacc.c, glr.c, glr.cc)
139
140 In order to avoid collisions, the header guards are now
141 YY_<PREFIX>_<FILE>_INCLUDED, instead of merely <PREFIX>_<FILE>.
142 For instance the header generated from
143
144 %define api.prefix "calc"
145 %defines "lib/parse.h"
146
147 will use YY_CALC_LIB_PARSE_H_INCLUDED as guard.
148
7b70847e 149** Fix compiler warnings in the generated parser (yacc.c, glr.c)
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150
151 The compilation of pure parsers (%define api.pure) can trigger GCC
152 warnings such as:
153
154 input.c: In function 'yyparse':
155 input.c:1503:12: warning: 'yylval' may be used uninitialized in this
156 function [-Wmaybe-uninitialized]
157 *++yyvsp = yylval;
158 ^
159
160 This is now fixed; pragmas to avoid these warnings are no longer needed.
161
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162 Warnings from clang ("equality comparison with extraneous parentheses" and
163 "function declared 'noreturn' should not return") have also been
164 addressed.
165
e1eeecd3 166* Noteworthy changes in release 2.6.2 (2012-08-03) [stable]
9c26b8fc 167
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168** Bug fixes
169
170 Buffer overruns, complaints from Flex, and portability issues in the test
171 suite have been fixed.
172
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173** Spaces in %lex- and %parse-param (lalr1.cc, glr.cc)
174
175 Trailing end-of-lines in %parse-param or %lex-param would result in
176 invalid C++. This is fixed.
9c26b8fc 177
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178** Spurious spaces and end-of-lines
179
180 The generated files no longer end (nor start) with empty lines.
181
77b214ef 182* Noteworthy changes in release 2.6.1 (2012-07-30) [stable]
a4107f24 183
cbaea010 184 Bison no longer executes user-specified M4 code when processing a grammar.
8617d87e 185
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186** Future Changes
187
188 In addition to the removal of the features announced in Bison 2.6, the
189 next major release will remove the "Temporary hack for adding a semicolon
190 to the user action", as announced in the release 2.5. Instead of:
191
192 exp: exp "+" exp { $$ = $1 + $3 };
193
194 write:
195
196 exp: exp "+" exp { $$ = $1 + $3; };
197
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198** Bug fixes
199
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200*** Type names are now properly escaped.
201
202*** glr.cc: set_debug_level and debug_level work as expected.
a4107f24 203
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204*** Stray @ or $ in actions
205
206 While Bison used to warn about stray $ or @ in action rules, it did not
207 for other actions such as printers, destructors, or initial actions. It
208 now does.
209
cd735a8c 210** Type names in actions
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211
212 For consistency with rule actions, it is now possible to qualify $$ by a
cd735a8c 213 type-name in destructors, printers, and initial actions. For instance:
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214
215 %printer { fprintf (yyo, "(%d, %f)", $<ival>$, $<fval>$); } <*> <>;
216
217 will display two values for each typed and untyped symbol (provided
cd735a8c 218 that YYSTYPE has both "ival" and "fval" fields).
4982f078 219
1505e8bb 220* Noteworthy changes in release 2.6 (2012-07-19) [stable]
ad6b775f 221
c2425191 222** Future Changes
0f11eec2 223
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224 The next major release of Bison will drop support for the following
225 deprecated features. Please report disagreements to bug-bison@gnu.org.
0f11eec2 226
aaf61036 227*** K&R C parsers
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228
229 Support for generating parsers in K&R C will be removed. Parsers
242cc08e 230 generated for C support ISO C90, and are tested with ISO C99 and ISO C11
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231 compilers.
232
258cddbc 233*** Features deprecated since Bison 1.875
55d1006f 234
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235 The definitions of yystype and yyltype will be removed; use YYSTYPE and
236 YYLTYPE.
55d1006f 237
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238 YYPARSE_PARAM and YYLEX_PARAM, deprecated in favor of %parse-param and
239 %lex-param, will no longer be supported.
240
241 Support for the preprocessor symbol YYERROR_VERBOSE will be removed, use
242 %error-verbose.
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243
244*** The generated header will be included (yacc.c)
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245
246 Instead of duplicating the content of the generated header (definition of
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247 YYSTYPE, yyparse declaration etc.), the generated parser will include it,
248 as is already the case for GLR or C++ parsers. This change is deferred
249 because existing versions of ylwrap (e.g., Automake 1.12.1) do not support
250 it.
0f11eec2 251
c2425191 252** Generated Parser Headers
56ca3d8f 253
258cddbc 254*** Guards (yacc.c, glr.c, glr.cc)
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255
256 The generated headers are now guarded, as is already the case for C++
242cc08e 257 parsers (lalr1.cc). For instance, with --defines=foo.h:
c3e9f08f 258
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259 #ifndef YY_FOO_H
260 # define YY_FOO_H
261 ...
262 #endif /* !YY_FOO_H */
c3e9f08f 263
258cddbc 264*** New declarations (yacc.c, glr.c)
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265
266 The generated header now declares yydebug and yyparse. Both honor
267 --name-prefix=bar_, and yield
268
e29f0771 269 int bar_parse (void);
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270
271 rather than
272
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273 #define yyparse bar_parse
274 int yyparse (void);
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275
276 in order to facilitate the inclusion of several parser headers inside a
277 single compilation unit.
c3e9f08f 278
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279*** Exported symbols in C++
280
281 The symbols YYTOKEN_TABLE and YYERROR_VERBOSE, which were defined in the
282 header, are removed, as they prevent the possibility of including several
283 generated headers from a single compilation unit.
284
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285*** YYLSP_NEEDED
286
287 For the same reasons, the undocumented and unused macro YYLSP_NEEDED is no
288 longer defined.
289
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290** New %define variable: api.prefix
291
292 Now that the generated headers are more complete and properly protected
293 against multiple inclusions, constant names, such as YYSTYPE are a
294 problem. While yyparse and others are properly renamed by %name-prefix,
295 YYSTYPE, YYDEBUG and others have never been affected by it. Because it
296 would introduce backward compatibility issues in projects not expecting
297 YYSTYPE to be renamed, instead of changing the behavior of %name-prefix,
298 it is deprecated in favor of a new %define variable: api.prefix.
299
300 The following examples compares both:
301
302 %name-prefix "bar_" | %define api.prefix "bar_"
303 %token <ival> FOO %token <ival> FOO
304 %union { int ival; } %union { int ival; }
305 %% %%
306 exp: 'a'; exp: 'a';
307
308 bison generates:
309
310 #ifndef BAR_FOO_H #ifndef BAR_FOO_H
311 # define BAR_FOO_H # define BAR_FOO_H
312
313 /* Enabling traces. */ /* Enabling traces. */
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314 # ifndef YYDEBUG | # ifndef BAR_DEBUG
315 > # if defined YYDEBUG
316 > # if YYDEBUG
317 > # define BAR_DEBUG 1
318 > # else
319 > # define BAR_DEBUG 0
320 > # endif
321 > # else
322 # define YYDEBUG 0 | # define BAR_DEBUG 0
323 > # endif
324 # endif | # endif
325
326 # if YYDEBUG | # if BAR_DEBUG
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327 extern int bar_debug; extern int bar_debug;
328 # endif # endif
329
330 /* Tokens. */ /* Tokens. */
331 # ifndef YYTOKENTYPE | # ifndef BAR_TOKENTYPE
332 # define YYTOKENTYPE | # define BAR_TOKENTYPE
333 enum yytokentype { | enum bar_tokentype {
334 FOO = 258 FOO = 258
335 }; };
336 # endif # endif
337
338 #if ! defined YYSTYPE \ | #if ! defined BAR_STYPE \
339 && ! defined YYSTYPE_IS_DECLARED | && ! defined BAR_STYPE_IS_DECLARED
340 typedef union YYSTYPE | typedef union BAR_STYPE
341 { {
342 int ival; int ival;
343 } YYSTYPE; | } BAR_STYPE;
344 # define YYSTYPE_IS_DECLARED 1 | # define BAR_STYPE_IS_DECLARED 1
345 #endif #endif
346
347 extern YYSTYPE bar_lval; | extern BAR_STYPE bar_lval;
348
349 int bar_parse (void); int bar_parse (void);
350
351 #endif /* !BAR_FOO_H */ #endif /* !BAR_FOO_H */
352
dfaac272 353* Noteworthy changes in release 2.5.1 (2012-06-05) [stable]
90dcd415 354
debe2c03 355** Future changes:
041308d0 356
e4ab1254 357 The next major release will drop support for generating parsers in K&R C.
ef51bfa7 358
466b4cf2 359** yacc.c: YYBACKUP works as expected.
94556574 360
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361** glr.c improvements:
362
363*** Location support is eliminated when not requested:
364
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365 GLR parsers used to include location-related code even when locations were
366 not requested, and therefore not even usable.
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367
368*** __attribute__ is preserved:
debe2c03 369
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370 __attribute__ is no longer disabled when __STRICT_ANSI__ is defined (i.e.,
371 when -std is passed to GCC).
debe2c03 372
466b4cf2 373** lalr1.java: several fixes:
041308d0 374
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375 The Java parser no longer throws ArrayIndexOutOfBoundsException if the
376 first token leads to a syntax error. Some minor clean ups.
041308d0 377
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378** Changes for C++:
379
380*** C++11 compatibility:
ef51bfa7 381
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382 C and C++ parsers use "nullptr" instead of "0" when __cplusplus is 201103L
383 or higher.
ef51bfa7 384
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385*** Header guards
386
387 The header files such as "parser.hh", "location.hh", etc. used a constant
388 name for preprocessor guards, for instance:
389
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390 #ifndef BISON_LOCATION_HH
391 # define BISON_LOCATION_HH
392 ...
393 #endif // !BISON_LOCATION_HH
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394
395 The inclusion guard is now computed from "PREFIX/FILE-NAME", where lower
396 case characters are converted to upper case, and series of
397 non-alphanumerical characters are converted to an underscore.
398
399 With "bison -o lang++/parser.cc", "location.hh" would now include:
400
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401 #ifndef YY_LANG_LOCATION_HH
402 # define YY_LANG_LOCATION_HH
403 ...
404 #endif // !YY_LANG_LOCATION_HH
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405
406*** C++ locations:
936c88d1 407
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408 The position and location constructors (and their initialize methods)
409 accept new arguments for line and column. Several issues in the
410 documentation were fixed.
936c88d1 411
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412** liby is no longer asking for "rpl_fprintf" on some platforms.
413
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414** Changes in the manual:
415
416*** %printer is documented
417
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418 The "%printer" directive, supported since at least Bison 1.50, is finally
419 documented. The "mfcalc" example is extended to demonstrate it.
7e508a2b 420
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421 For consistency with the C skeletons, the C++ parsers now also support
422 "yyoutput" (as an alias to "debug_stream ()").
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423
424*** Several improvements have been made:
466b4cf2 425
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426 The layout for grammar excerpts was changed to a more compact scheme.
427 Named references are motivated. The description of the automaton
428 description file (*.output) is updated to the current format. Incorrect
429 index entries were fixed. Some other errors were fixed.
466b4cf2 430
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431** Building bison:
432
433*** Conflicting prototypes with recent/modified Flex.
434
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435 Fixed build problems with the current, unreleased, version of Flex, and
436 some modified versions of 2.5.35, which have modified function prototypes.
466b4cf2 437
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438*** Warnings during the build procedure have been eliminated.
439
440*** Several portability problems in the test suite have been fixed:
466b4cf2 441
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442 This includes warnings with some compilers, unexpected behavior of tools
443 such as diff, warning messages from the test suite itself, etc.
466b4cf2 444
91aadcc7 445*** The install-pdf target works properly:
8ef26c2a 446
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447 Running "make install-pdf" (or -dvi, -html, -info, and -ps) no longer
448 halts in the middle of its course.
8ef26c2a 449
b2bc8a1b 450* Changes in version 2.5 (2011-05-14):
006faedf 451
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452** Grammar symbol names can now contain non-initial dashes:
453
454 Consistently with directives (such as %error-verbose) and with
455 %define variables (e.g. push-pull), grammar symbol names may contain
456 dashes in any position except the beginning. This is a GNU
457 extension over POSIX Yacc. Thus, use of this extension is reported
458 by -Wyacc and rejected in Yacc mode (--yacc).
459
3b1977ea 460** Named references:
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461
462 Historically, Yacc and Bison have supported positional references
463 ($n, $$) to allow access to symbol values from inside of semantic
464 actions code.
465
466 Starting from this version, Bison can also accept named references.
467 When no ambiguity is possible, original symbol names may be used
468 as named references:
469
ac3297d5 470 if_stmt : "if" cond_expr "then" then_stmt ';'
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471 { $if_stmt = mk_if_stmt($cond_expr, $then_stmt); }
472
473 In the more common case, explicit names may be declared:
474
ac3297d5 475 stmt[res] : "if" expr[cond] "then" stmt[then] "else" stmt[else] ';'
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476 { $res = mk_if_stmt($cond, $then, $else); }
477
f840c05a 478 Location information is also accessible using @name syntax. When
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479 accessing symbol names containing dots or dashes, explicit bracketing
480 ($[sym.1]) must be used.
481
f840c05a 482 These features are experimental in this version. More user feedback
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483 will help to stabilize them.
484
3b1977ea 485** IELR(1) and canonical LR(1):
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486
487 IELR(1) is a minimal LR(1) parser table generation algorithm. That
488 is, given any context-free grammar, IELR(1) generates parser tables
723206df 489 with the full language-recognition power of canonical LR(1) but with
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490 nearly the same number of parser states as LALR(1). This reduction
491 in parser states is often an order of magnitude. More importantly,
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492 because canonical LR(1)'s extra parser states may contain duplicate
493 conflicts in the case of non-LR(1) grammars, the number of conflicts
494 for IELR(1) is often an order of magnitude less as well. This can
495 significantly reduce the complexity of developing of a grammar.
496
497 Bison can now generate IELR(1) and canonical LR(1) parser tables in
498 place of its traditional LALR(1) parser tables, which remain the
499 default. You can specify the type of parser tables in the grammar
500 file with these directives:
501
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502 %define lr.type lalr
503 %define lr.type ielr
504 %define lr.type canonical-lr
34a6c2d1 505
6f04ee6c 506 The default-reduction optimization in the parser tables can also be
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507 adjusted using "%define lr.default-reductions". For details on both
508 of these features, see the new section "Tuning LR" in the Bison
6f04ee6c 509 manual.
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510
511 These features are experimental. More user feedback will help to
512 stabilize them.
513
6f04ee6c 514** LAC (Lookahead Correction) for syntax error handling:
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515
516 Canonical LR, IELR, and LALR can suffer from a couple of problems
517 upon encountering a syntax error. First, the parser might perform
518 additional parser stack reductions before discovering the syntax
6f04ee6c 519 error. Such reductions can perform user semantic actions that are
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520 unexpected because they are based on an invalid token, and they
521 cause error recovery to begin in a different syntactic context than
522 the one in which the invalid token was encountered. Second, when
6f04ee6c 523 verbose error messages are enabled (with %error-verbose or the
e4ab1254 524 obsolete "#define YYERROR_VERBOSE"), the expected token list in the
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525 syntax error message can both contain invalid tokens and omit valid
526 tokens.
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527
528 The culprits for the above problems are %nonassoc, default
529 reductions in inconsistent states, and parser state merging. Thus,
530 IELR and LALR suffer the most. Canonical LR can suffer only if
531 %nonassoc is used or if default reductions are enabled for
532 inconsistent states.
533
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534 LAC is a new mechanism within the parsing algorithm that solves
535 these problems for canonical LR, IELR, and LALR without sacrificing
536 %nonassoc, default reductions, or state merging. When LAC is in
537 use, canonical LR and IELR behave almost exactly the same for both
538 syntactically acceptable and syntactically unacceptable input.
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539 While LALR still does not support the full language-recognition
540 power of canonical LR and IELR, LAC at least enables LALR's syntax
541 error handling to correctly reflect LALR's language-recognition
542 power.
543
544 Currently, LAC is only supported for deterministic parsers in C.
545 You can enable LAC with the following directive:
546
547 %define parse.lac full
548
e4ab1254 549 See the new section "LAC" in the Bison manual for additional
6f04ee6c 550 details including a few caveats.
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551
552 LAC is an experimental feature. More user feedback will help to
553 stabilize it.
554
6ee881f6 555** %define improvements:
f37495f6 556
3b1977ea 557*** Can now be invoked via the command line:
4ecd3681 558
34d41938 559 Each of these command-line options
4ecd3681 560
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561 -D NAME[=VALUE]
562 --define=NAME[=VALUE]
563
564 -F NAME[=VALUE]
565 --force-define=NAME[=VALUE]
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566
567 is equivalent to this grammar file declaration
568
34d41938 569 %define NAME ["VALUE"]
4ecd3681 570
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571 except that the manner in which Bison processes multiple definitions
572 for the same NAME differs. Most importantly, -F and --force-define
573 quietly override %define, but -D and --define do not. For further
e4ab1254 574 details, see the section "Bison Options" in the Bison manual.
4ecd3681 575
3b1977ea 576*** Variables renamed:
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577
578 The following %define variables
579
580 api.push_pull
581 lr.keep_unreachable_states
582
583 have been renamed to
584
585 api.push-pull
586 lr.keep-unreachable-states
587
588 The old names are now deprecated but will be maintained indefinitely
589 for backward compatibility.
590
723206df 591*** Values no longer need to be quoted in the grammar file:
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592
593 If a %define value is an identifier, it no longer needs to be placed
594 within quotations marks. For example,
595
596 %define api.push-pull "push"
597
598 can be rewritten as
599
600 %define api.push-pull push
601
6ee881f6 602*** Unrecognized variables are now errors not warnings.
c046698e 603
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604*** Multiple invocations for any variable is now an error not a warning.
605
606** Unrecognized %code qualifiers are now errors not warnings.
607
608** Character literals not of length one:
609
610 Previously, Bison quietly converted all character literals to length
611 one. For example, without warning, Bison interpreted the operators in
612 the following grammar to be the same token:
613
614 exp: exp '++'
615 | exp '+' exp
616 ;
617
618 Bison now warns when a character literal is not of length one. In
619 some future release, Bison will start reporting an error instead.
620
621** Destructor calls fixed for lookaheads altered in semantic actions:
622
623 Previously for deterministic parsers in C, if a user semantic action
624 altered yychar, the parser in some cases used the old yychar value to
625 determine which destructor to call for the lookahead upon a syntax
626 error or upon parser return. This bug has been fixed.
627
628** C++ parsers use YYRHSLOC:
629
630 Similarly to the C parsers, the C++ parsers now define the YYRHSLOC
631 macro and use it in the default YYLLOC_DEFAULT. You are encouraged
e4ab1254
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632 to use it. If, for instance, your location structure has "first"
633 and "last" members, instead of
6ee881f6 634
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635 # define YYLLOC_DEFAULT(Current, Rhs, N) \
636 do \
637 if (N) \
638 { \
639 (Current).first = (Rhs)[1].location.first; \
640 (Current).last = (Rhs)[N].location.last; \
641 } \
642 else \
643 { \
644 (Current).first = (Current).last = (Rhs)[0].location.last; \
645 } \
646 while (false)
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647
648 use:
649
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650 # define YYLLOC_DEFAULT(Current, Rhs, N) \
651 do \
652 if (N) \
653 { \
654 (Current).first = YYRHSLOC (Rhs, 1).first; \
655 (Current).last = YYRHSLOC (Rhs, N).last; \
656 } \
657 else \
658 { \
659 (Current).first = (Current).last = YYRHSLOC (Rhs, 0).last; \
660 } \
661 while (false)
6ee881f6
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662
663** YYLLOC_DEFAULT in C++:
664
665 The default implementation of YYLLOC_DEFAULT used to be issued in
666 the header file. It is now output in the implementation file, after
667 the user %code sections so that its #ifndef guard does not try to
668 override the user's YYLLOC_DEFAULT if provided.
c046698e 669
3b1977ea 670** YYFAIL now produces warnings and Java parsers no longer implement it:
62efdd2a
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671
672 YYFAIL has existed for many years as an undocumented feature of
673 deterministic parsers in C generated by Bison. More recently, it was
674 a documented feature of Bison's experimental Java parsers. As
675 promised in Bison 2.4.2's NEWS entry, any appearance of YYFAIL in a
676 semantic action now produces a deprecation warning, and Java parsers
677 no longer implement YYFAIL at all. For further details, including a
678 discussion of how to suppress C preprocessor warnings about YYFAIL
679 being unused, see the Bison 2.4.2 NEWS entry.
680
3b1977ea 681** Temporary hack for adding a semicolon to the user action:
a2d05674
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682
683 Previously, Bison appended a semicolon to every user action for
684 reductions when the output language defaulted to C (specifically, when
685 neither %yacc, %language, %skeleton, or equivalent command-line
686 options were specified). This allowed actions such as
687
688 exp: exp "+" exp { $$ = $1 + $3 };
689
690 instead of
691
692 exp: exp "+" exp { $$ = $1 + $3; };
693
694 As a first step in removing this misfeature, Bison now issues a
695 warning when it appends a semicolon. Moreover, in cases where Bison
696 cannot easily determine whether a semicolon is needed (for example, an
697 action ending with a cpp directive or a braced compound initializer),
698 it no longer appends one. Thus, the C compiler might now complain
699 about a missing semicolon where it did not before. Future releases of
700 Bison will cease to append semicolons entirely.
701
095a1d11
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702** Verbose syntax error message fixes:
703
e4ab1254 704 When %error-verbose or the obsolete "#define YYERROR_VERBOSE" is
6f04ee6c
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705 specified, syntax error messages produced by the generated parser
706 include the unexpected token as well as a list of expected tokens.
707 The effect of %nonassoc on these verbose messages has been corrected
708 in two ways, but a more complete fix requires LAC, described above:
095a1d11
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709
710*** When %nonassoc is used, there can exist parser states that accept no
711 tokens, and so the parser does not always require a lookahead token
712 in order to detect a syntax error. Because no unexpected token or
713 expected tokens can then be reported, the verbose syntax error
714 message described above is suppressed, and the parser instead
e4ab1254 715 reports the simpler message, "syntax error". Previously, this
095a1d11
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716 suppression was sometimes erroneously triggered by %nonassoc when a
717 lookahead was actually required. Now verbose messages are
718 suppressed only when all previous lookaheads have already been
719 shifted or discarded.
720
721*** Previously, the list of expected tokens erroneously included tokens
722 that would actually induce a syntax error because conflicts for them
723 were resolved with %nonassoc in the current parser state. Such
724 tokens are now properly omitted from the list.
725
726*** Expected token lists are still often wrong due to state merging
4c38b19e
JD
727 (from LALR or IELR) and default reductions, which can both add
728 invalid tokens and subtract valid tokens. Canonical LR almost
729 completely fixes this problem by eliminating state merging and
730 default reductions. However, there is one minor problem left even
731 when using canonical LR and even after the fixes above. That is,
732 if the resolution of a conflict with %nonassoc appears in a later
733 parser state than the one at which some syntax error is
734 discovered, the conflicted token is still erroneously included in
735 the expected token list. Bison's new LAC implementation,
736 described above, eliminates this problem and the need for
737 canonical LR. However, LAC is still experimental and is disabled
738 by default.
1fa30307 739
4c2a6e42
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740** Java skeleton fixes:
741
742*** A location handling bug has been fixed.
743
744*** The top element of each of the value stack and location stack is now
745 cleared when popped so that it can be garbage collected.
77768165 746
f0e2c228
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747*** Parser traces now print the top element of the stack.
748
248dba53
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749** -W/--warnings fixes:
750
e4ab1254 751*** Bison now properly recognizes the "no-" versions of categories:
248dba53
JD
752
753 For example, given the following command line, Bison now enables all
754 warnings except warnings for incompatibilities with POSIX Yacc:
755
756 bison -Wall,no-yacc gram.y
757
6f8bdce2
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758*** Bison now treats S/R and R/R conflicts like other warnings:
759
760 Previously, conflict reports were independent of Bison's normal
761 warning system. Now, Bison recognizes the warning categories
e4ab1254 762 "conflicts-sr" and "conflicts-rr". This change has important
6f8bdce2
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763 consequences for the -W and --warnings command-line options. For
764 example:
765
766 bison -Wno-conflicts-sr gram.y # S/R conflicts not reported
767 bison -Wno-conflicts-rr gram.y # R/R conflicts not reported
768 bison -Wnone gram.y # no conflicts are reported
769 bison -Werror gram.y # any conflict is an error
770
771 However, as before, if the %expect or %expect-rr directive is
772 specified, an unexpected number of conflicts is an error, and an
773 expected number of conflicts is not reported, so -W and --warning
774 then have no effect on the conflict report.
775
e4ab1254 776*** The "none" category no longer disables a preceding "error":
dab96632
JD
777
778 For example, for the following command line, Bison now reports
779 errors instead of warnings for incompatibilities with POSIX Yacc:
780
781 bison -Werror,none,yacc gram.y
782
e4ab1254 783*** The "none" category now disables all Bison warnings:
8ffd7912 784
e4ab1254 785 Previously, the "none" category disabled only Bison warnings for
8ffd7912
JD
786 which there existed a specific -W/--warning category. However,
787 given the following command line, Bison is now guaranteed to
788 suppress all warnings:
789
790 bison -Wnone gram.y
791
9d6af153
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792** Precedence directives can now assign token number 0:
793
794 Since Bison 2.3b, which restored the ability of precedence
795 directives to assign token numbers, doing so for token number 0 has
796 produced an assertion failure. For example:
797
798 %left END 0
799
800 This bug has been fixed.
801
7527c744 802* Changes in version 2.4.3 (2010-08-05):
7a9c3cb3 803
4631c34f
JD
804** Bison now obeys -Werror and --warnings=error for warnings about
805 grammar rules that are useless in the parser due to conflicts.
806
7a9c3cb3
JD
807** Problems with spawning M4 on at least FreeBSD 8 and FreeBSD 9 have
808 been fixed.
809
132247cd
JD
810** Failures in the test suite for GCC 4.5 have been fixed.
811
88bb35d6
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812** Failures in the test suite for some versions of Sun Studio C++ have
813 been fixed.
814
43fdc9fd
JD
815** Contrary to Bison 2.4.2's NEWS entry, it has been decided that
816 warnings about undefined %prec identifiers will not be converted to
817 errors in Bison 2.5. They will remain warnings, which should be
818 sufficient for POSIX while avoiding backward compatibility issues.
819
cf22447c
JD
820** Minor documentation fixes.
821
ea66d039 822* Changes in version 2.4.2 (2010-03-20):
8defe11b 823
47fa5747
JD
824** Some portability problems that resulted in failures and livelocks
825 in the test suite on some versions of at least Solaris, AIX, HP-UX,
ea66d039
JD
826 RHEL4, and Tru64 have been addressed. As a result, fatal Bison
827 errors should no longer cause M4 to report a broken pipe on the
47fa5747
JD
828 affected platforms.
829
e4ab1254 830** "%prec IDENTIFIER" requires IDENTIFIER to be defined separately.
2c203528
JD
831
832 POSIX specifies that an error be reported for any identifier that does
833 not appear on the LHS of a grammar rule and that is not defined by
834 %token, %left, %right, or %nonassoc. Bison 2.3b and later lost this
835 error report for the case when an identifier appears only after a
836 %prec directive. It is now restored. However, for backward
837 compatibility with recent Bison releases, it is only a warning for
838 now. In Bison 2.5 and later, it will return to being an error.
43fdc9fd
JD
839 [Between the 2.4.2 and 2.4.3 releases, it was decided that this
840 warning will not be converted to an error in Bison 2.5.]
2c203528 841
c5196098
EB
842** Detection of GNU M4 1.4.6 or newer during configure is improved.
843
34731471
JD
844** Warnings from gcc's -Wundef option about undefined YYENABLE_NLS,
845 YYLTYPE_IS_TRIVIAL, and __STRICT_ANSI__ in C/C++ parsers are now
846 avoided.
af2ffe5c 847
966aba65
JD
848** %code is now a permanent feature.
849
850 A traditional Yacc prologue directive is written in the form:
851
852 %{CODE%}
853
854 To provide a more flexible alternative, Bison 2.3b introduced the
855 %code directive with the following forms for C/C++:
856
857 %code {CODE}
858 %code requires {CODE}
859 %code provides {CODE}
860 %code top {CODE}
861
862 These forms are now considered permanent features of Bison. See the
863 %code entries in the section "Bison Declaration Summary" in the Bison
864 manual for a summary of their functionality. See the section
865 "Prologue Alternatives" for a detailed discussion including the
866 advantages of %code over the traditional Yacc prologue directive.
867
868 Bison's Java feature as a whole including its current usage of %code
869 is still considered experimental.
870
41d35e54
JD
871** YYFAIL is deprecated and will eventually be removed.
872
873 YYFAIL has existed for many years as an undocumented feature of
874 deterministic parsers in C generated by Bison. Previously, it was
875 documented for Bison's experimental Java parsers. YYFAIL is no longer
876 documented for Java parsers and is formally deprecated in both cases.
877 Users are strongly encouraged to migrate to YYERROR, which is
878 specified by POSIX.
879
880 Like YYERROR, you can invoke YYFAIL from a semantic action in order to
881 induce a syntax error. The most obvious difference from YYERROR is
882 that YYFAIL will automatically invoke yyerror to report the syntax
883 error so that you don't have to. However, there are several other
884 subtle differences between YYERROR and YYFAIL, and YYFAIL suffers from
e4ab1254 885 inherent flaws when %error-verbose or "#define YYERROR_VERBOSE" is
41d35e54
JD
886 used. For a more detailed discussion, see:
887
888 http://lists.gnu.org/archive/html/bison-patches/2009-12/msg00024.html
889
890 The upcoming Bison 2.5 will remove YYFAIL from Java parsers, but
891 deterministic parsers in C will continue to implement it. However,
892 because YYFAIL is already flawed, it seems futile to try to make new
893 Bison features compatible with it. Thus, during parser generation,
894 Bison 2.5 will produce a warning whenever it discovers YYFAIL in a
895 rule action. In a later release, YYFAIL will be disabled for
e4ab1254 896 %error-verbose and "#define YYERROR_VERBOSE". Eventually, YYFAIL will
41d35e54
JD
897 be removed altogether.
898
899 There exists at least one case where Bison 2.5's YYFAIL warning will
900 be a false positive. Some projects add phony uses of YYFAIL and other
901 Bison-defined macros for the sole purpose of suppressing C
902 preprocessor warnings (from GCC cpp's -Wunused-macros, for example).
903 To avoid Bison's future warning, such YYFAIL uses can be moved to the
e4ab1254 904 epilogue (that is, after the second "%%") in the Bison input file. In
41d35e54
JD
905 this release (2.4.2), Bison already generates its own code to suppress
906 C preprocessor warnings for YYFAIL, so projects can remove their own
907 phony uses of YYFAIL if compatibility with Bison releases prior to
908 2.4.2 is not necessary.
909
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AD
910** Internationalization.
911
912 Fix a regression introduced in Bison 2.4: Under some circumstances,
913 message translations were not installed although supported by the
914 host system.
915
41930e7a 916* Changes in version 2.4.1 (2008-12-11):
c9ba9e59 917
a957d06c
JD
918** In the GLR defines file, unexpanded M4 macros in the yylval and yylloc
919 declarations have been fixed.
920
738cde3e
AD
921** Temporary hack for adding a semicolon to the user action.
922
923 Bison used to prepend a trailing semicolon at the end of the user
924 action for reductions. This allowed actions such as
925
926 exp: exp "+" exp { $$ = $1 + $3 };
927
928 instead of
929
930 exp: exp "+" exp { $$ = $1 + $3; };
931
e4ab1254 932 Some grammars still depend on this "feature". Bison 2.4.1 restores
d07932ef
JD
933 the previous behavior in the case of C output (specifically, when
934 neither %language or %skeleton or equivalent command-line options
935 are used) to leave more time for grammars depending on the old
936 behavior to be adjusted. Future releases of Bison will disable this
937 feature.
a957d06c
JD
938
939** A few minor improvements to the Bison manual.
c9ba9e59 940
d6fb461d 941* Changes in version 2.4 (2008-11-02):
7bd1665a 942
d6fb461d 943** %language is an experimental feature.
ed4d67dc
JD
944
945 We first introduced this feature in test release 2.3b as a cleaner
946 alternative to %skeleton. Since then, we have discussed the possibility of
947 modifying its effect on Bison's output file names. Thus, in this release,
948 we consider %language to be an experimental feature that will likely evolve
949 in future releases.
7bd1665a 950
d6fb461d 951** Forward compatibility with GNU M4 has been improved.
241fda7a 952
d6fb461d 953** Several bugs in the C++ skeleton and the experimental Java skeleton have been
241fda7a
JD
954 fixed.
955
d6fb461d 956* Changes in version 2.3b (2008-05-27):
35fe0834 957
d6fb461d 958** The quotes around NAME that used to be required in the following directive
d9df47b6
JD
959 are now deprecated:
960
961 %define NAME "VALUE"
962
e4ab1254 963** The directive "%pure-parser" is now deprecated in favor of:
d9df47b6
JD
964
965 %define api.pure
966
967 which has the same effect except that Bison is more careful to warn about
968 unreasonable usage in the latter case.
969
d6fb461d 970** Push Parsing
c373bf8b
JD
971
972 Bison can now generate an LALR(1) parser in C with a push interface. That
e4ab1254
AD
973 is, instead of invoking "yyparse", which pulls tokens from "yylex", you can
974 push one token at a time to the parser using "yypush_parse", which will
c373bf8b
JD
975 return to the caller after processing each token. By default, the push
976 interface is disabled. Either of the following directives will enable it:
977
978 %define api.push_pull "push" // Just push; does not require yylex.
979 %define api.push_pull "both" // Push and pull; requires yylex.
980
e4ab1254 981 See the new section "A Push Parser" in the Bison manual for details.
c373bf8b 982
59da312b
JD
983 The current push parsing interface is experimental and may evolve. More user
984 feedback will help to stabilize it.
985
d6fb461d 986** The -g and --graph options now output graphs in Graphviz DOT format,
8e55b3aa
JD
987 not VCG format. Like --graph, -g now also takes an optional FILE argument
988 and thus cannot be bundled with other short options.
c373bf8b 989
d6fb461d 990** Java
59da312b
JD
991
992 Bison can now generate an LALR(1) parser in Java. The skeleton is
e4ab1254 993 "data/lalr1.java". Consider using the new %language directive instead of
59da312b
JD
994 %skeleton to select it.
995
e4ab1254 996 See the new section "Java Parsers" in the Bison manual for details.
59da312b
JD
997
998 The current Java interface is experimental and may evolve. More user
999 feedback will help to stabilize it.
1000
d6fb461d 1001** %language
59da312b
JD
1002
1003 This new directive specifies the programming language of the generated
d43f77e7
PB
1004 parser, which can be C (the default), C++, or Java. Besides the skeleton
1005 that Bison uses, the directive affects the names of the generated files if
1006 the grammar file's name ends in ".y".
59da312b 1007
d6fb461d 1008** XML Automaton Report
59da312b
JD
1009
1010 Bison can now generate an XML report of the LALR(1) automaton using the new
e4ab1254 1011 "--xml" option. The current XML schema is experimental and may evolve. More
59da312b 1012 user feedback will help to stabilize it.
c373bf8b 1013
d6fb461d 1014** The grammar file may now specify the name of the parser header file using
c373bf8b
JD
1015 %defines. For example:
1016
1017 %defines "parser.h"
1018
d6fb461d 1019** When reporting useless rules, useless nonterminals, and unused terminals,
d80fb37a
JD
1020 Bison now employs the terms "useless in grammar" instead of "useless",
1021 "useless in parser" instead of "never reduced", and "unused in grammar"
1022 instead of "unused".
cff03fb2 1023
d6fb461d 1024** Unreachable State Removal
c373bf8b
JD
1025
1026 Previously, Bison sometimes generated parser tables containing unreachable
31984206
JD
1027 states. A state can become unreachable during conflict resolution if Bison
1028 disables a shift action leading to it from a predecessor state. Bison now:
75ad86ee
JD
1029
1030 1. Removes unreachable states.
1031
1032 2. Does not report any conflicts that appeared in unreachable states.
1033 WARNING: As a result, you may need to update %expect and %expect-rr
1034 directives in existing grammar files.
1035
1036 3. For any rule used only in such states, Bison now reports the rule as
cff03fb2 1037 "useless in parser due to conflicts".
75ad86ee 1038
31984206
JD
1039 This feature can be disabled with the following directive:
1040
1041 %define lr.keep_unreachable_states
1042
e4ab1254 1043 See the %define entry in the "Bison Declaration Summary" in the Bison manual
31984206
JD
1044 for further discussion.
1045
e4ab1254 1046** Lookahead Set Correction in the ".output" Report
b1cc23c4 1047
e4ab1254
AD
1048 When instructed to generate a ".output" file including lookahead sets
1049 (using "--report=lookahead", for example), Bison now prints each reduction's
88c78747
JD
1050 lookahead set only next to the associated state's one item that (1) is
1051 associated with the same rule as the reduction and (2) has its dot at the end
1052 of its RHS. Previously, Bison also erroneously printed the lookahead set
1053 next to all of the state's other items associated with the same rule. This
e4ab1254 1054 bug affected only the ".output" file and not the generated parser source
88c78747
JD
1055 code.
1056
e4ab1254 1057** --report-file=FILE is a new option to override the default ".output" file
59da312b 1058 name.
1bb2bd75 1059
e4ab1254 1060** The "=" that used to be required in the following directives is now
02975b9a
JD
1061 deprecated:
1062
1063 %file-prefix "parser"
1064 %name-prefix "c_"
1065 %output "parser.c"
1066
e4ab1254 1067** An Alternative to "%{...%}" -- "%code QUALIFIER {CODE}"
c373bf8b
JD
1068
1069 Bison 2.3a provided a new set of directives as a more flexible alternative to
8e0a5e9e
JD
1070 the traditional Yacc prologue blocks. Those have now been consolidated into
1071 a single %code directive with an optional qualifier field, which identifies
1072 the purpose of the code and thus the location(s) where Bison should generate
1073 it:
1074
e4ab1254
AD
1075 1. "%code {CODE}" replaces "%after-header {CODE}"
1076 2. "%code requires {CODE}" replaces "%start-header {CODE}"
1077 3. "%code provides {CODE}" replaces "%end-header {CODE}"
1078 4. "%code top {CODE}" replaces "%before-header {CODE}"
8e0a5e9e 1079
e4ab1254
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1080 See the %code entries in section "Bison Declaration Summary" in the Bison
1081 manual for a summary of the new functionality. See the new section "Prologue
1082 Alternatives" for a detailed discussion including the advantages of %code
8e0a5e9e
JD
1083 over the traditional Yacc prologues.
1084
1085 The prologue alternatives are experimental. More user feedback will help to
1086 determine whether they should become permanent features.
1087
d6fb461d 1088** Revised warning: unset or unused mid-rule values
17bd8a73
JD
1089
1090 Since Bison 2.2, Bison has warned about mid-rule values that are set but not
1091 used within any of the actions of the parent rule. For example, Bison warns
1092 about unused $2 in:
1093
1094 exp: '1' { $$ = 1; } '+' exp { $$ = $1 + $4; };
1095
1096 Now, Bison also warns about mid-rule values that are used but not set. For
1097 example, Bison warns about unset $$ in the mid-rule action in:
1098
1099 exp: '1' { $1 = 1; } '+' exp { $$ = $2 + $4; };
1100
1101 However, Bison now disables both of these warnings by default since they
1102 sometimes prove to be false alarms in existing grammars employing the Yacc
1103 constructs $0 or $-N (where N is some positive integer).
1104
e4ab1254
AD
1105 To enable these warnings, specify the option "--warnings=midrule-values" or
1106 "-W", which is a synonym for "--warnings=all".
17bd8a73 1107
e4ab1254 1108** Default %destructor or %printer with "<*>" or "<>"
c373bf8b
JD
1109
1110 Bison now recognizes two separate kinds of default %destructor's and
12e35840
JD
1111 %printer's:
1112
e4ab1254 1113 1. Place "<*>" in a %destructor/%printer symbol list to define a default
12e35840
JD
1114 %destructor/%printer for all grammar symbols for which you have formally
1115 declared semantic type tags.
1116
e4ab1254 1117 2. Place "<>" in a %destructor/%printer symbol list to define a default
12e35840
JD
1118 %destructor/%printer for all grammar symbols without declared semantic
1119 type tags.
1120
e4ab1254
AD
1121 Bison no longer supports the "%symbol-default" notation from Bison 2.3a.
1122 "<*>" and "<>" combined achieve the same effect with one exception: Bison no
12e35840
JD
1123 longer applies any %destructor to a mid-rule value if that mid-rule value is
1124 not actually ever referenced using either $$ or $n in a semantic action.
1125
85894313
JD
1126 The default %destructor's and %printer's are experimental. More user
1127 feedback will help to determine whether they should become permanent
1128 features.
1129
e4ab1254 1130 See the section "Freeing Discarded Symbols" in the Bison manual for further
12e35840
JD
1131 details.
1132
d6fb461d 1133** %left, %right, and %nonassoc can now declare token numbers. This is required
e4ab1254 1134 by POSIX. However, see the end of section "Operator Precedence" in the Bison
ab7f29f8
JD
1135 manual for a caveat concerning the treatment of literal strings.
1136
d6fb461d 1137** The nonfunctional --no-parser, -n, and %no-parser options have been
b1cc23c4
JD
1138 completely removed from Bison.
1139
d6fb461d 1140* Changes in version 2.3a, 2006-09-13:
742e4900 1141
d6fb461d 1142** Instead of %union, you can define and use your own union type
ddc8ede1
PE
1143 YYSTYPE if your grammar contains at least one <type> tag.
1144 Your YYSTYPE need not be a macro; it can be a typedef.
1145 This change is for compatibility with other Yacc implementations,
1146 and is required by POSIX.
1147
d6fb461d 1148** Locations columns and lines start at 1.
cd48d21d
AD
1149 In accordance with the GNU Coding Standards and Emacs.
1150
d6fb461d 1151** You may now declare per-type and default %destructor's and %printer's:
ec5479ce
JD
1152
1153 For example:
1154
b2a0b7ca
JD
1155 %union { char *string; }
1156 %token <string> STRING1
1157 %token <string> STRING2
1158 %type <string> string1
1159 %type <string> string2
1160 %union { char character; }
1161 %token <character> CHR
1162 %type <character> chr
1163 %destructor { free ($$); } %symbol-default
1164 %destructor { free ($$); printf ("%d", @$.first_line); } STRING1 string1
1165 %destructor { } <character>
1166
1167 guarantees that, when the parser discards any user-defined symbol that has a
e4ab1254
AD
1168 semantic type tag other than "<character>", it passes its semantic value to
1169 "free". However, when the parser discards a "STRING1" or a "string1", it
1170 also prints its line number to "stdout". It performs only the second
1171 "%destructor" in this case, so it invokes "free" only once.
ec5479ce 1172
85894313
JD
1173 [Although we failed to mention this here in the 2.3a release, the default
1174 %destructor's and %printer's were experimental, and they were rewritten in
1175 future versions.]
1176
e4ab1254
AD
1177** Except for LALR(1) parsers in C with POSIX Yacc emulation enabled (with "-y",
1178 "--yacc", or "%yacc"), Bison no longer generates #define statements for
b931235e
JD
1179 associating token numbers with token names. Removing the #define statements
1180 helps to sanitize the global namespace during preprocessing, but POSIX Yacc
1181 requires them. Bison still generates an enum for token names in all cases.
1182
d6fb461d 1183** Handling of traditional Yacc prologue blocks is now more consistent but
34f98f46 1184 potentially incompatible with previous releases of Bison.
9bc0dd67
JD
1185
1186 As before, you declare prologue blocks in your grammar file with the
e4ab1254 1187 "%{ ... %}" syntax. To generate the pre-prologue, Bison concatenates all
34f98f46
JD
1188 prologue blocks that you've declared before the first %union. To generate
1189 the post-prologue, Bison concatenates all prologue blocks that you've
ddc8ede1 1190 declared after the first %union.
9bc0dd67 1191
34f98f46 1192 Previous releases of Bison inserted the pre-prologue into both the header
9bc0dd67
JD
1193 file and the code file in all cases except for LALR(1) parsers in C. In the
1194 latter case, Bison inserted it only into the code file. For parsers in C++,
1195 the point of insertion was before any token definitions (which associate
1196 token numbers with names). For parsers in C, the point of insertion was
1197 after the token definitions.
1198
1199 Now, Bison never inserts the pre-prologue into the header file. In the code
1200 file, it always inserts it before the token definitions.
1201
d6fb461d 1202** Bison now provides a more flexible alternative to the traditional Yacc
34f98f46
JD
1203 prologue blocks: %before-header, %start-header, %end-header, and
1204 %after-header.
1205
1206 For example, the following declaration order in the grammar file reflects the
1207 order in which Bison will output these code blocks. However, you are free to
1208 declare these code blocks in your grammar file in whatever order is most
1209 convenient for you:
1210
1211 %before-header {
1212 /* Bison treats this block like a pre-prologue block: it inserts it into
1213 * the code file before the contents of the header file. It does *not*
1214 * insert it into the header file. This is a good place to put
1215 * #include's that you want at the top of your code file. A common
e4ab1254 1216 * example is '#include "system.h"'. */
34f98f46
JD
1217 }
1218 %start-header {
1219 /* Bison inserts this block into both the header file and the code file.
1220 * In both files, the point of insertion is before any Bison-generated
1221 * token, semantic type, location type, and class definitions. This is a
1222 * good place to define %union dependencies, for example. */
9bc0dd67
JD
1223 }
1224 %union {
34f98f46
JD
1225 /* Unlike the traditional Yacc prologue blocks, the output order for the
1226 * new %*-header blocks is not affected by their declaration position
1227 * relative to any %union in the grammar file. */
9bc0dd67 1228 }
34f98f46
JD
1229 %end-header {
1230 /* Bison inserts this block into both the header file and the code file.
1231 * In both files, the point of insertion is after the Bison-generated
1232 * definitions. This is a good place to declare or define public
1233 * functions or data structures that depend on the Bison-generated
1234 * definitions. */
9bc0dd67 1235 }
34f98f46
JD
1236 %after-header {
1237 /* Bison treats this block like a post-prologue block: it inserts it into
1238 * the code file after the contents of the header file. It does *not*
1239 * insert it into the header file. This is a good place to declare or
1240 * define internal functions or data structures that depend on the
1241 * Bison-generated definitions. */
1242 }
1243
1244 If you have multiple occurrences of any one of the above declarations, Bison
1245 will concatenate the contents in declaration order.
9bc0dd67 1246
85894313
JD
1247 [Although we failed to mention this here in the 2.3a release, the prologue
1248 alternatives were experimental, and they were rewritten in future versions.]
1249
e4ab1254 1250** The option "--report=look-ahead" has been changed to "--report=lookahead".
9e6e7ed2
PE
1251 The old spelling still works, but is not documented and may be removed
1252 in a future release.
742e4900 1253
d6fb461d 1254* Changes in version 2.3, 2006-06-05:
4ad3ed84 1255
e4ab1254 1256** GLR grammars should now use "YYRECOVERING ()" instead of "YYRECOVERING",
4ad3ed84
PE
1257 for compatibility with LALR(1) grammars.
1258
d6fb461d 1259** It is now documented that any definition of YYSTYPE or YYLTYPE should
4ad3ed84
PE
1260 be to a type name that does not contain parentheses or brackets.
1261
d6fb461d 1262* Changes in version 2.2, 2006-05-19:
193d7c70 1263
d6fb461d 1264** The distribution terms for all Bison-generated parsers now permit
193d7c70
PE
1265 using the parsers in nonfree programs. Previously, this permission
1266 was granted only for Bison-generated LALR(1) parsers in C.
5f4236a0 1267
d6fb461d 1268** %name-prefix changes the namespace name in C++ outputs.
aa08666d 1269
d6fb461d 1270** The C++ parsers export their token_type.
5f4236a0 1271
d6fb461d 1272** Bison now allows multiple %union declarations, and concatenates
d6ca7905
PE
1273 their contents together.
1274
d6fb461d 1275** New warning: unused values
4d7bc38c
PE
1276 Right-hand side symbols whose values are not used are reported,
1277 if the symbols have destructors. For instance:
affac613 1278
8f3596a6 1279 exp: exp "?" exp ":" exp { $1 ? $1 : $3; }
e29f0771
AD
1280 | exp "+" exp
1281 ;
affac613 1282
8f3596a6
AD
1283 will trigger a warning about $$ and $5 in the first rule, and $3 in
1284 the second ($1 is copied to $$ by the default rule). This example
4e26c69e 1285 most likely contains three errors, and could be rewritten as:
affac613 1286
4e26c69e 1287 exp: exp "?" exp ":" exp
e29f0771
AD
1288 { $$ = $1 ? $3 : $5; free ($1 ? $5 : $3); free ($1); }
1289 | exp "+" exp
1290 { $$ = $1 ? $1 : $3; if ($1) free ($3); }
1291 ;
affac613 1292
4e26c69e
PE
1293 However, if the original actions were really intended, memory leaks
1294 and all, the warnings can be suppressed by letting Bison believe the
1295 values are used, e.g.:
721be13c 1296
8f3596a6 1297 exp: exp "?" exp ":" exp { $1 ? $1 : $3; (void) ($$, $5); }
e29f0771
AD
1298 | exp "+" exp { $$ = $1; (void) $3; }
1299 ;
721be13c 1300
84866159
AD
1301 If there are mid-rule actions, the warning is issued if no action
1302 uses it. The following triggers no warning: $1 and $3 are used.
1303
1304 exp: exp { push ($1); } '+' exp { push ($3); sum (); };
1305
721be13c
PE
1306 The warning is intended to help catching lost values and memory leaks.
1307 If a value is ignored, its associated memory typically is not reclaimed.
affac613 1308
d6fb461d 1309** %destructor vs. YYABORT, YYACCEPT, and YYERROR.
9d9b8b70
PE
1310 Destructors are now called when user code invokes YYABORT, YYACCEPT,
1311 and YYERROR, for all objects on the stack, other than objects
1312 corresponding to the right-hand side of the current rule.
a85284cf 1313
d6fb461d 1314** %expect, %expect-rr
035aa4a0
PE
1315 Incorrect numbers of expected conflicts are now actual errors,
1316 instead of warnings.
1317
d6fb461d 1318** GLR, YACC parsers.
4e26c69e
PE
1319 The %parse-params are available in the destructors (and the
1320 experimental printers) as per the documentation.
4b367315 1321
e4ab1254 1322** Bison now warns if it finds a stray "$" or "@" in an action.
ad6a9b97 1323
d6fb461d 1324** %require "VERSION"
4e26c69e
PE
1325 This specifies that the grammar file depends on features implemented
1326 in Bison version VERSION or higher.
b50d2359 1327
d6fb461d 1328** lalr1.cc: The token and value types are now class members.
e14d0ab6
AD
1329 The tokens were defined as free form enums and cpp macros. YYSTYPE
1330 was defined as a free form union. They are now class members:
e4ab1254
AD
1331 tokens are enumerations of the "yy::parser::token" struct, and the
1332 semantic values have the "yy::parser::semantic_type" type.
fb9712a9
AD
1333
1334 If you do not want or can update to this scheme, the directive
e4ab1254 1335 '%define "global_tokens_and_yystype" "1"' triggers the global
b50d2359
AD
1336 definition of tokens and YYSTYPE. This change is suitable both
1337 for previous releases of Bison, and this one.
fb9712a9 1338
b50d2359 1339 If you wish to update, then make sure older version of Bison will
e4ab1254 1340 fail using '%require "2.2"'.
fb9712a9 1341
d6fb461d 1342** DJGPP support added.
193d7c70 1343\f
d6fb461d 1344* Changes in version 2.1, 2005-09-16:
1ce59070 1345
d6fb461d 1346** The C++ lalr1.cc skeleton supports %lex-param.
e14d0ab6 1347
d6fb461d 1348** Bison-generated parsers now support the translation of diagnostics like
baf785db
PE
1349 "syntax error" into languages other than English. The default
1350 language is still English. For details, please see the new
0410a6e0
PE
1351 Internationalization section of the Bison manual. Software
1352 distributors should also see the new PACKAGING file. Thanks to
1353 Bruno Haible for this new feature.
1ce59070 1354
d6fb461d 1355** Wording in the Bison-generated parsers has been changed slightly to
1a059451
PE
1356 simplify translation. In particular, the message "memory exhausted"
1357 has replaced "parser stack overflow", as the old message was not
1358 always accurate for modern Bison-generated parsers.
1359
d6fb461d 1360** Destructors are now called when the parser aborts, for all symbols left
258b75ca
PE
1361 behind on the stack. Also, the start symbol is now destroyed after a
1362 successful parse. In both cases, the behavior was formerly inconsistent.
1363
d6fb461d 1364** When generating verbose diagnostics, Bison-generated parsers no longer
72f000b0
PE
1365 quote the literal strings associated with tokens. For example, for
1366 a syntax error associated with '%token NUM "number"' they might
1367 print 'syntax error, unexpected number' instead of 'syntax error,
1368 unexpected "number"'.
193d7c70 1369\f
d6fb461d 1370* Changes in version 2.0, 2004-12-25:
efeed023 1371
d6fb461d 1372** Possibly-incompatible changes
d7e14fc0 1373
82de6b0d
PE
1374 - Bison-generated parsers no longer default to using the alloca function
1375 (when available) to extend the parser stack, due to widespread
1376 problems in unchecked stack-overflow detection. You can "#define
1377 YYSTACK_USE_ALLOCA 1" to require the use of alloca, but please read
1378 the manual to determine safe values for YYMAXDEPTH in that case.
8dd162d3 1379
82de6b0d
PE
1380 - Error token location.
1381 During error recovery, the location of the syntax error is updated
1382 to cover the whole sequence covered by the error token: it includes
1383 the shifted symbols thrown away during the first part of the error
1384 recovery, and the lookahead rejected during the second part.
18d192f0 1385
82de6b0d
PE
1386 - Semicolon changes:
1387 . Stray semicolons are no longer allowed at the start of a grammar.
1388 . Semicolons are now required after in-grammar declarations.
e342c3be 1389
82de6b0d
PE
1390 - Unescaped newlines are no longer allowed in character constants or
1391 string literals. They were never portable, and GCC 3.4.0 has
1392 dropped support for them. Better diagnostics are now generated if
1393 forget a closing quote.
8dd162d3 1394
82de6b0d 1395 - NUL bytes are no longer allowed in Bison string literals, unfortunately.
f74b6f91 1396
d6fb461d 1397** New features
1452af69 1398
82de6b0d 1399 - GLR grammars now support locations.
4febdd96 1400
82de6b0d
PE
1401 - New directive: %initial-action.
1402 This directive allows the user to run arbitrary code (including
1403 initializing @$) from yyparse before parsing starts.
1452af69 1404
82de6b0d
PE
1405 - A new directive "%expect-rr N" specifies the expected number of
1406 reduce/reduce conflicts in GLR parsers.
1452af69 1407
e4ab1254 1408 - %token numbers can now be hexadecimal integers, e.g., "%token FOO 0x12d".
82de6b0d 1409 This is a GNU extension.
4febdd96 1410
e4ab1254 1411 - The option "--report=lookahead" was changed to "--report=look-ahead".
9e6e7ed2 1412 [However, this was changed back after 2.3.]
1452af69 1413
82de6b0d 1414 - Experimental %destructor support has been added to lalr1.cc.
1452af69 1415
82de6b0d
PE
1416 - New configure option --disable-yacc, to disable installation of the
1417 yacc command and -ly library introduced in 1.875 for POSIX conformance.
6040d338 1418
d6fb461d 1419** Bug fixes
d5a3fe37 1420
82de6b0d
PE
1421 - For now, %expect-count violations are now just warnings, not errors.
1422 This is for compatibility with Bison 1.75 and earlier (when there are
1423 reduce/reduce conflicts) and with Bison 1.30 and earlier (when there
1424 are too many or too few shift/reduce conflicts). However, in future
1425 versions of Bison we plan to improve the %expect machinery so that
1426 these violations will become errors again.
3473d0f8 1427
82de6b0d
PE
1428 - Within Bison itself, numbers (e.g., goto numbers) are no longer
1429 arbitrarily limited to 16-bit counts.
d600ee67 1430
82de6b0d 1431 - Semicolons are now allowed before "|" in grammar rules, as POSIX requires.
d600ee67 1432\f
d6fb461d 1433* Changes in version 1.875, 2003-01-01:
963fcc17 1434
d6fb461d 1435** The documentation license has been upgraded to version 1.2
dc546b0f 1436 of the GNU Free Documentation License.
75eb3bc4 1437
d6fb461d 1438** syntax error processing
75eb3bc4 1439
dc546b0f
PE
1440 - In Yacc-style parsers YYLLOC_DEFAULT is now used to compute error
1441 locations too. This fixes bugs in error-location computation.
75eb3bc4 1442
dc546b0f
PE
1443 - %destructor
1444 It is now possible to reclaim the memory associated to symbols
1445 discarded during error recovery. This feature is still experimental.
20daca06 1446
dc546b0f
PE
1447 - %error-verbose
1448 This new directive is preferred over YYERROR_VERBOSE.
74724a70 1449
dc546b0f
PE
1450 - #defining yyerror to steal internal variables is discouraged.
1451 It is not guaranteed to work forever.
d1de5372 1452
d6fb461d 1453** POSIX conformance
d1de5372 1454
dc546b0f
PE
1455 - Semicolons are once again optional at the end of grammar rules.
1456 This reverts to the behavior of Bison 1.33 and earlier, and improves
1457 compatibility with Yacc.
74724a70 1458
e4ab1254
AD
1459 - "parse error" -> "syntax error"
1460 Bison now uniformly uses the term "syntax error"; formerly, the code
1461 and manual sometimes used the term "parse error" instead. POSIX
1462 requires "syntax error" in diagnostics, and it was thought better to
dc546b0f 1463 be consistent.
74724a70 1464
dc546b0f
PE
1465 - The documentation now emphasizes that yylex and yyerror must be
1466 declared before use. C99 requires this.
d1de5372 1467
dc546b0f
PE
1468 - Bison now parses C99 lexical constructs like UCNs and
1469 backslash-newline within C escape sequences, as POSIX 1003.1-2001 requires.
d1de5372 1470
dc546b0f
PE
1471 - File names are properly escaped in C output. E.g., foo\bar.y is
1472 output as "foo\\bar.y".
6780ca7a 1473
dc546b0f 1474 - Yacc command and library now available
e4ab1254 1475 The Bison distribution now installs a "yacc" command, as POSIX requires.
dc546b0f
PE
1476 Also, Bison now installs a small library liby.a containing
1477 implementations of Yacc-compatible yyerror and main functions.
1478 This library is normally not useful, but POSIX requires it.
6e649e65 1479
dc546b0f 1480 - Type clashes now generate warnings, not errors.
6e649e65 1481
dc546b0f
PE
1482 - If the user does not define YYSTYPE as a macro, Bison now declares it
1483 using typedef instead of defining it as a macro.
1484 For consistency, YYLTYPE is also declared instead of defined.
9501dc6e 1485
d6fb461d 1486** Other compatibility issues
886a425c 1487
e4ab1254
AD
1488 - %union directives can now have a tag before the "{", e.g., the
1489 directive "%union foo {...}" now generates the C code
1490 "typedef union foo { ... } YYSTYPE;"; this is for Yacc compatibility.
1491 The default union tag is "YYSTYPE", for compatibility with Solaris 9 Yacc.
1492 For consistency, YYLTYPE's struct tag is now "YYLTYPE" not "yyltype".
dc546b0f 1493 This is for compatibility with both Yacc and Bison 1.35.
72f889cc 1494
e4ab1254 1495 - ";" is output before the terminating "}" of an action, for
dc546b0f 1496 compatibility with Bison 1.35.
886a425c 1497
dc546b0f 1498 - Bison now uses a Yacc-style format for conflict reports, e.g.,
e4ab1254 1499 "conflicts: 2 shift/reduce, 1 reduce/reduce".
437c2d80 1500
e4ab1254 1501 - "yystype" and "yyltype" are now obsolescent macros instead of being
dc546b0f
PE
1502 typedefs or tags; they are no longer documented and are planned to be
1503 withdrawn in a future release.
2a8d363a 1504
d6fb461d 1505** GLR parser notes
2a8d363a 1506
dc546b0f
PE
1507 - GLR and inline
1508 Users of Bison have to decide how they handle the portability of the
e4ab1254 1509 C keyword "inline".
959e5f51 1510
e4ab1254
AD
1511 - "parsing stack overflow..." -> "parser stack overflow"
1512 GLR parsers now report "parser stack overflow" as per the Bison manual.
900c5db5 1513
18ad57b3
AD
1514** %parse-param and %lex-param
1515 The macros YYPARSE_PARAM and YYLEX_PARAM provide a means to pass
1516 additional context to yyparse and yylex. They suffer from several
1517 shortcomings:
1518
1519 - a single argument only can be added,
1520 - their types are weak (void *),
242cc08e 1521 - this context is not passed to ancillary functions such as yyerror,
18ad57b3
AD
1522 - only yacc.c parsers support them.
1523
1524 The new %parse-param/%lex-param directives provide a more precise control.
1525 For instance:
1526
1527 %parse-param {int *nastiness}
1528 %lex-param {int *nastiness}
1529 %parse-param {int *randomness}
1530
1531 results in the following signatures:
1532
1533 int yylex (int *nastiness);
1534 int yyparse (int *nastiness, int *randomness);
1535
1536 or, if both %pure-parser and %locations are used:
1537
1538 int yylex (YYSTYPE *lvalp, YYLTYPE *llocp, int *nastiness);
1539 int yyparse (int *nastiness, int *randomness);
1540
d6fb461d 1541** Bison now warns if it detects conflicting outputs to the same file,
e4ab1254 1542 e.g., it generates a warning for "bison -d -o foo.h foo.y" since
dc546b0f 1543 that command outputs both code and header to foo.h.
6e40b4eb 1544
d6fb461d 1545** #line in output files
dc546b0f 1546 - --no-line works properly.
6e40b4eb 1547
d6fb461d 1548** Bison can no longer be built by a K&R C compiler; it requires C89 or
6e40b4eb
AD
1549 later to be built. This change originally took place a few versions
1550 ago, but nobody noticed until we recently asked someone to try
1551 building Bison with a K&R C compiler.
d600ee67 1552\f
d6fb461d 1553* Changes in version 1.75, 2002-10-14:
7933f2b5 1554
d6fb461d 1555** Bison should now work on 64-bit hosts.
7933f2b5 1556
d6fb461d 1557** Indonesian translation thanks to Tedi Heriyanto.
7933f2b5 1558
d6fb461d 1559** GLR parsers
f50adbbd
AD
1560 Fix spurious parse errors.
1561
d6fb461d 1562** Pure parsers
f50adbbd
AD
1563 Some people redefine yyerror to steal yyparse' private variables.
1564 Reenable this trick until an official feature replaces it.
1565
d6fb461d 1566** Type Clashes
d90c934c
AD
1567 In agreement with POSIX and with other Yaccs, leaving a default
1568 action is valid when $$ is untyped, and $1 typed:
1569
e29f0771 1570 untyped: ... typed;
d90c934c
AD
1571
1572 but the converse remains an error:
1573
e29f0771 1574 typed: ... untyped;
d90c934c 1575
d6fb461d 1576** Values of mid-rule actions
d90c934c
AD
1577 The following code:
1578
e29f0771 1579 foo: { ... } { $$ = $1; } ...
d90c934c
AD
1580
1581 was incorrectly rejected: $1 is defined in the second mid-rule
1582 action, and is equal to the $$ of the first mid-rule action.
d600ee67 1583\f
d6fb461d 1584* Changes in version 1.50, 2002-10-04:
adc8c848 1585
d6fb461d 1586** GLR parsing
676385e2
PH
1587 The declaration
1588 %glr-parser
1589 causes Bison to produce a Generalized LR (GLR) parser, capable of handling
1590 almost any context-free grammar, ambiguous or not. The new declarations
e8832397 1591 %dprec and %merge on grammar rules allow parse-time resolution of
676385e2
PH
1592 ambiguities. Contributed by Paul Hilfinger.
1593
7933f2b5 1594 Unfortunately Bison 1.50 does not work properly on 64-bit hosts
420f93c8
PE
1595 like the Alpha, so please stick to 32-bit hosts for now.
1596
d6fb461d 1597** Output Directory
8c165d89 1598 When not in Yacc compatibility mode, when the output file was not
e4ab1254
AD
1599 specified, running "bison foo/bar.y" created "foo/bar.c". It
1600 now creates "bar.c".
8c165d89 1601
d6fb461d 1602** Undefined token
007a50a4 1603 The undefined token was systematically mapped to 2 which prevented
e88dbdbf 1604 the use of 2 by the user. This is no longer the case.
007a50a4 1605
d6fb461d 1606** Unknown token numbers
e88dbdbf 1607 If yylex returned an out of range value, yyparse could die. This is
007a50a4
AD
1608 no longer the case.
1609
d6fb461d 1610** Error token
e88dbdbf 1611 According to POSIX, the error token must be 256.
23c5a174
AD
1612 Bison extends this requirement by making it a preference: *if* the
1613 user specified that one of her tokens is numbered 256, then error
1614 will be mapped onto another number.
1615
d6fb461d 1616** Verbose error messages
e4ab1254 1617 They no longer report "..., expecting error or..." for states where
217598da
AD
1618 error recovery is possible.
1619
d6fb461d 1620** End token
e4ab1254 1621 Defaults to "$end" instead of "$".
217598da 1622
d6fb461d 1623** Error recovery now conforms to documentation and to POSIX
68cd8af3
PE
1624 When a Bison-generated parser encounters a syntax error, it now pops
1625 the stack until it finds a state that allows shifting the error
1626 token. Formerly, it popped the stack until it found a state that
1627 allowed some non-error action other than a default reduction on the
1628 error token. The new behavior has long been the documented behavior,
1629 and has long been required by POSIX. For more details, please see
337116ba
PE
1630 Paul Eggert, "Reductions during Bison error handling" (2002-05-20)
1631 <http://lists.gnu.org/archive/html/bug-bison/2002-05/msg00038.html>.
68cd8af3 1632
d6fb461d 1633** Traces
5504898e
AD
1634 Popped tokens and nonterminals are now reported.
1635
d6fb461d 1636** Larger grammars
a861a339
PE
1637 Larger grammars are now supported (larger token numbers, larger grammar
1638 size (= sum of the LHS and RHS lengths), larger LALR tables).
1639 Formerly, many of these numbers ran afoul of 16-bit limits;
1640 now these limits are 32 bits on most hosts.
355e7c1c 1641
d6fb461d 1642** Explicit initial rule
643a5994
AD
1643 Bison used to play hacks with the initial rule, which the user does
1644 not write. It is now explicit, and visible in the reports and
1645 graphs as rule 0.
23c5a174 1646
d6fb461d 1647** Useless rules
643a5994 1648 Before, Bison reported the useless rules, but, although not used,
77714df2 1649 included them in the parsers. They are now actually removed.
23c5a174 1650
d6fb461d 1651** Useless rules, useless nonterminals
6b98e4b5
AD
1652 They are now reported, as a warning, with their locations.
1653
d6fb461d 1654** Rules never reduced
e8832397
AD
1655 Rules that can never be reduced because of conflicts are now
1656 reported.
1657
e4ab1254 1658** Incorrect "Token not used"
11652ab3
AD
1659 On a grammar such as
1660
e29f0771
AD
1661 %token useless useful
1662 %%
1663 exp: '0' %prec useful;
11652ab3
AD
1664
1665 where a token was used to set the precedence of the last rule,
e4ab1254 1666 bison reported both "useful" and "useless" as useless tokens.
11652ab3 1667
d6fb461d 1668** Revert the C++ namespace changes introduced in 1.31
77714df2 1669 as they caused too many portability hassles.
0179dd65 1670
d6fb461d 1671** Default locations
b2d52318
AD
1672 By an accident of design, the default computation of @$ was
1673 performed after another default computation was performed: @$ = @1.
1674 The latter is now removed: YYLLOC_DEFAULT is fully responsible of
1675 the computation of @$.
adc8c848 1676
d6fb461d 1677** Token end-of-file
b7c49edf
AD
1678 The token end of file may be specified by the user, in which case,
1679 the user symbol is used in the reports, the graphs, and the verbose
e4ab1254 1680 error messages instead of "$end", which remains being the default.
b7c49edf 1681 For instance
e29f0771 1682 %token MYEOF 0
b7c49edf 1683 or
e29f0771 1684 %token MYEOF 0 "end of file"
fdbcd8e2 1685
d6fb461d 1686** Semantic parser
fdbcd8e2
AD
1687 This old option, which has been broken for ages, is removed.
1688
d6fb461d 1689** New translations
a861a339 1690 Brazilian Portuguese, thanks to Alexandre Folle de Menezes.
84614e13
AD
1691 Croatian, thanks to Denis Lackovic.
1692
d6fb461d 1693** Incorrect token definitions
e4ab1254
AD
1694 When given
1695 %token 'a' "A"
1696 bison used to output
1697 #define 'a' 65
b87f8b21 1698
d6fb461d 1699** Token definitions as enums
77714df2
AD
1700 Tokens are output both as the traditional #define's, and, provided
1701 the compiler supports ANSI C or is a C++ compiler, as enums.
e88dbdbf 1702 This lets debuggers display names instead of integers.
77714df2 1703
d6fb461d 1704** Reports
ec3bc396
AD
1705 In addition to --verbose, bison supports --report=THINGS, which
1706 produces additional information:
b408954b
AD
1707 - itemset
1708 complete the core item sets with their closure
e4ab1254 1709 - lookahead [changed to "look-ahead" in 1.875e through 2.3, but changed back]
9e6e7ed2 1710 explicitly associate lookahead tokens to items
b408954b
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1711 - solved
1712 describe shift/reduce conflicts solving.
1713 Bison used to systematically output this information on top of
1714 the report. Solved conflicts are now attached to their states.
ec3bc396 1715
d6fb461d 1716** Type clashes
9af3fbce
AD
1717 Previous versions don't complain when there is a type clash on
1718 the default action if the rule has a mid-rule action, such as in:
1719
e29f0771
AD
1720 %type <foo> bar
1721 %%
1722 bar: '0' {} '0';
9af3fbce
AD
1723
1724 This is fixed.
a861a339 1725
d6fb461d 1726** GNU M4 is now required when using Bison.
f987e9d2 1727\f
d6fb461d 1728* Changes in version 1.35, 2002-03-25:
76551463 1729
d6fb461d 1730** C Skeleton
76551463
AD
1731 Some projects use Bison's C parser with C++ compilers, and define
1732 YYSTYPE as a class. The recent adjustment of C parsers for data
1733 alignment and 64 bit architectures made this impossible.
1734
1735 Because for the time being no real solution for C++ parser
1736 generation exists, kludges were implemented in the parser to
1737 maintain this use. In the future, when Bison has C++ parsers, this
1738 kludge will be disabled.
1739
1740 This kludge also addresses some C++ problems when the stack was
1741 extended.
76551463 1742\f
d6fb461d 1743* Changes in version 1.34, 2002-03-12:
76551463 1744
d6fb461d 1745** File name clashes are detected
76551463 1746 $ bison foo.y -d -o foo.x
e4ab1254 1747 fatal error: header and parser would both be named "foo.x"
76551463 1748
e4ab1254 1749** A missing ";" at the end of a rule triggers a warning
76551463
AD
1750 In accordance with POSIX, and in agreement with other
1751 Yacc implementations, Bison will mandate this semicolon in the near
1752 future. This eases the implementation of a Bison parser of Bison
1753 grammars by making this grammar LALR(1) instead of LR(2). To
1754 facilitate the transition, this release introduces a warning.
1755
d6fb461d 1756** Revert the C++ namespace changes introduced in 1.31, as they caused too
76551463
AD
1757 many portability hassles.
1758
d6fb461d 1759** DJGPP support added.
76551463 1760
d6fb461d 1761** Fix test suite portability problems.
76551463 1762\f
d6fb461d 1763* Changes in version 1.33, 2002-02-07:
76551463 1764
d6fb461d 1765** Fix C++ issues
76551463
AD
1766 Groff could not be compiled for the definition of size_t was lacking
1767 under some conditions.
1768
d6fb461d 1769** Catch invalid @n
76551463
AD
1770 As is done with $n.
1771\f
d6fb461d 1772* Changes in version 1.32, 2002-01-23:
76551463 1773
d6fb461d 1774** Fix Yacc output file names
76551463 1775
d6fb461d 1776** Portability fixes
76551463 1777
d6fb461d 1778** Italian, Dutch translations
76551463 1779\f
d6fb461d 1780* Changes in version 1.31, 2002-01-14:
52d1aeee 1781
d6fb461d 1782** Many Bug Fixes
52d1aeee 1783
d6fb461d 1784** GNU Gettext and %expect
52d1aeee
MA
1785 GNU Gettext asserts 10 s/r conflicts, but there are 7. Now that
1786 Bison dies on incorrect %expectations, we fear there will be
1787 too many bug reports for Gettext, so _for the time being_, %expect
e4ab1254 1788 does not trigger an error when the input file is named "plural.y".
52d1aeee 1789
d6fb461d 1790** Use of alloca in parsers
52d1aeee
MA
1791 If YYSTACK_USE_ALLOCA is defined to 0, then the parsers will use
1792 malloc exclusively. Since 1.29, but was not NEWS'ed.
1793
1794 alloca is used only when compiled with GCC, to avoid portability
1795 problems as on AIX.
1796
d6fb461d 1797** yyparse now returns 2 if memory is exhausted; formerly it dumped core.
b47dbebe 1798
d6fb461d 1799** When the generated parser lacks debugging code, YYDEBUG is now 0
52d1aeee
MA
1800 (as POSIX requires) instead of being undefined.
1801
d6fb461d 1802** User Actions
52d1aeee
MA
1803 Bison has always permitted actions such as { $$ = $1 }: it adds the
1804 ending semicolon. Now if in Yacc compatibility mode, the semicolon
1805 is no longer output: one has to write { $$ = $1; }.
1806
d6fb461d 1807** Better C++ compliance
52d1aeee 1808 The output parsers try to respect C++ namespaces.
76551463 1809 [This turned out to be a failed experiment, and it was reverted later.]
52d1aeee 1810
d6fb461d 1811** Reduced Grammars
52d1aeee
MA
1812 Fixed bugs when reporting useless nonterminals.
1813
d6fb461d 1814** 64 bit hosts
52d1aeee
MA
1815 The parsers work properly on 64 bit hosts.
1816
d6fb461d 1817** Error messages
52d1aeee
MA
1818 Some calls to strerror resulted in scrambled or missing error messages.
1819
d6fb461d 1820** %expect
52d1aeee
MA
1821 When the number of shift/reduce conflicts is correct, don't issue
1822 any warning.
1823
d6fb461d 1824** The verbose report includes the rule line numbers.
52d1aeee 1825
d6fb461d 1826** Rule line numbers are fixed in traces.
52d1aeee 1827
d6fb461d 1828** Swedish translation
52d1aeee 1829
d6fb461d 1830** Parse errors
52d1aeee
MA
1831 Verbose parse error messages from the parsers are better looking.
1832 Before: parse error: unexpected `'/'', expecting `"number"' or `'-'' or `'(''
1833 Now: parse error: unexpected '/', expecting "number" or '-' or '('
1834
d6fb461d 1835** Fixed parser memory leaks.
52d1aeee
MA
1836 When the generated parser was using malloc to extend its stacks, the
1837 previous allocations were not freed.
1838
d6fb461d 1839** Fixed verbose output file.
52d1aeee
MA
1840 Some newlines were missing.
1841 Some conflicts in state descriptions were missing.
1842
d6fb461d 1843** Fixed conflict report.
52d1aeee
MA
1844 Option -v was needed to get the result.
1845
d6fb461d 1846** %expect
52d1aeee
MA
1847 Was not used.
1848 Mismatches are errors, not warnings.
1849
d6fb461d 1850** Fixed incorrect processing of some invalid input.
52d1aeee 1851
d6fb461d 1852** Fixed CPP guards: 9foo.h uses BISON_9FOO_H instead of 9FOO_H.
52d1aeee 1853
d6fb461d 1854** Fixed some typos in the documentation.
52d1aeee 1855
d6fb461d 1856** %token MY_EOF 0 is supported.
52d1aeee
MA
1857 Before, MY_EOF was silently renumbered as 257.
1858
d6fb461d 1859** doc/refcard.tex is updated.
52d1aeee 1860
d6fb461d 1861** %output, %file-prefix, %name-prefix.
52d1aeee
MA
1862 New.
1863
d6fb461d 1864** --output
e4ab1254 1865 New, aliasing "--output-file".
52d1aeee 1866\f
d6fb461d 1867* Changes in version 1.30, 2001-10-26:
342b8b6e 1868
e4ab1254
AD
1869** "--defines" and "--graph" have now an optional argument which is the
1870 output file name. "-d" and "-g" do not change; they do not take any
342b8b6e
AD
1871 argument.
1872
e4ab1254 1873** "%source_extension" and "%header_extension" are removed, failed
342b8b6e
AD
1874 experiment.
1875
d6fb461d 1876** Portability fixes.
f987e9d2 1877\f
d6fb461d 1878* Changes in version 1.29, 2001-09-07:
342b8b6e 1879
d6fb461d 1880** The output file does not define const, as this caused problems when used
342b8b6e
AD
1881 with common autoconfiguration schemes. If you still use ancient compilers
1882 that lack const, compile with the equivalent of the C compiler option
e4ab1254 1883 "-Dconst=". Autoconf's AC_C_CONST macro provides one way to do this.
342b8b6e 1884
e4ab1254 1885** Added "-g" and "--graph".
f87a2205 1886
d6fb461d 1887** The Bison manual is now distributed under the terms of the GNU FDL.
f2b5126e 1888
d6fb461d 1889** The input and the output files has automatically a similar extension.
234a3be3 1890
d6fb461d 1891** Russian translation added.
f87a2205 1892
d6fb461d 1893** NLS support updated; should hopefully be less troublesome.
f87a2205 1894
d6fb461d 1895** Added the old Bison reference card.
c33638bb 1896
e4ab1254 1897** Added "--locations" and "%locations".
6deb4447 1898
e4ab1254 1899** Added "-S" and "--skeleton".
cd5bd6ac 1900
e4ab1254 1901** "%raw", "-r", "--raw" is disabled.
62ab6972 1902
d6fb461d 1903** Special characters are escaped when output. This solves the problems
cd5bd6ac
AD
1904 of the #line lines with path names including backslashes.
1905
d6fb461d 1906** New directives.
e4ab1254
AD
1907 "%yacc", "%fixed_output_files", "%defines", "%no_parser", "%verbose",
1908 "%debug", "%source_extension" and "%header_extension".
f987e9d2 1909
d6fb461d 1910** @$
f987e9d2 1911 Automatic location tracking.
f87a2205 1912\f
d6fb461d 1913* Changes in version 1.28, 1999-07-06:
d2e00347 1914
d6fb461d 1915** Should compile better now with K&R compilers.
d2e00347 1916
d6fb461d 1917** Added NLS.
d2e00347 1918
d6fb461d 1919** Fixed a problem with escaping the double quote character.
d2e00347 1920
d6fb461d 1921** There is now a FAQ.
d2e00347 1922\f
d6fb461d 1923* Changes in version 1.27:
5c31c3c2 1924
d6fb461d 1925** The make rule which prevented bison.simple from being created on
5c31c3c2
JT
1926 some systems has been fixed.
1927\f
d6fb461d 1928* Changes in version 1.26:
4be07551 1929
7e508a2b 1930** Bison now uses Automake.
4be07551 1931
d6fb461d 1932** New mailing lists: <bug-bison@gnu.org> and <help-bison@gnu.org>.
4be07551 1933
d6fb461d 1934** Token numbers now start at 257 as previously documented, not 258.
4be07551 1935
d6fb461d 1936** Bison honors the TMPDIR environment variable.
4be07551 1937
d6fb461d 1938** A couple of buffer overruns have been fixed.
f51dbca1 1939
d6fb461d 1940** Problems when closing files should now be reported.
f51dbca1 1941
d6fb461d 1942** Generated parsers should now work even on operating systems which do
f51dbca1 1943 not provide alloca().
4be07551 1944\f
d6fb461d 1945* Changes in version 1.25, 1995-10-16:
df8878c5 1946
d6fb461d 1947** Errors in the input grammar are not fatal; Bison keeps reading
df8878c5 1948the grammar file, and reports all the errors found in it.
8c44d3ec 1949
d6fb461d 1950** Tokens can now be specified as multiple-character strings: for
df8878c5 1951example, you could use "<=" for a token which looks like <=, instead
7e508a2b 1952of choosing a name like LESSEQ.
df8878c5 1953
d6fb461d 1954** The %token_table declaration says to write a table of tokens (names
df8878c5
RS
1955and numbers) into the parser file. The yylex function can use this
1956table to recognize multiple-character string tokens, or for other
1957purposes.
1958
d6fb461d 1959** The %no_lines declaration says not to generate any #line preprocessor
df8878c5
RS
1960directives in the parser file.
1961
d6fb461d 1962** The %raw declaration says to use internal Bison token numbers, not
df8878c5
RS
1963Yacc-compatible token numbers, when token names are defined as macros.
1964
d6fb461d 1965** The --no-parser option produces the parser tables without including
df8878c5
RS
1966the parser engine; a project can now use its own parser engine.
1967The actions go into a separate file called NAME.act, in the form of
1968a switch statement body.
1969\f
d6fb461d 1970* Changes in version 1.23:
6780ca7a 1971
4d019228
DM
1972The user can define YYPARSE_PARAM as the name of an argument to be
1973passed into yyparse. The argument should have type void *. It should
1974actually point to an object. Grammar actions can access the variable
1975by casting it to the proper pointer type.
6780ca7a 1976
6780ca7a 1977Line numbers in output file corrected.
6780ca7a 1978\f
d6fb461d 1979* Changes in version 1.22:
6780ca7a
DM
1980
1981--help option added.
6780ca7a 1982\f
d6fb461d 1983* Changes in version 1.20:
6780ca7a
DM
1984
1985Output file does not redefine const for C++.
9f4503d6 1986
76551463
AD
1987-----
1988
c932d613 1989Copyright (C) 1995-2012 Free Software Foundation, Inc.
76551463 1990
8defe11b 1991This file is part of Bison, the GNU Parser Generator.
76551463 1992
f16b0819 1993This program is free software: you can redistribute it and/or modify
76551463 1994it under the terms of the GNU General Public License as published by
f16b0819
PE
1995the Free Software Foundation, either version 3 of the License, or
1996(at your option) any later version.
76551463 1997
f16b0819 1998This program is distributed in the hope that it will be useful,
76551463
AD
1999but WITHOUT ANY WARRANTY; without even the implied warranty of
2000MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
2001GNU General Public License for more details.
2002
2003You should have received a copy of the GNU General Public License
f16b0819 2004along with this program. If not, see <http://www.gnu.org/licenses/>.
7e508a2b
AD
2005
2006 LocalWords: yacc YYBACKUP glr GCC lalr ArrayIndexOutOfBoundsException nullptr
2007 LocalWords: cplusplus liby rpl fprintf mfcalc Wyacc stmt cond expr mk sym lr
2008 LocalWords: IELR ielr Lookahead YYERROR nonassoc LALR's api lookaheads yychar
2009 LocalWords: destructor lookahead YYRHSLOC YYLLOC Rhs ifndef YYFAIL cpp sr rr
2010 LocalWords: preprocessor initializer Wno Wnone Werror FreeBSD prec livelocks
2011 LocalWords: Solaris AIX UX RHEL Tru LHS gcc's Wundef YYENABLE NLS YYLTYPE VCG
2012 LocalWords: yyerror cpp's Wunused yylval yylloc prepend yyparse yylex yypush
2013 LocalWords: Graphviz xml nonterminals midrule destructor's YYSTYPE typedef ly
2014 LocalWords: CHR chr printf stdout namespace preprocessing enum pre include's
2015 LocalWords: YYRECOVERING nonfree destructors YYABORT YYACCEPT params enums de
2016 LocalWords: struct yystype DJGPP lex param Haible NUM alloca YYSTACK NUL goto
2017 LocalWords: YYMAXDEPTH Unescaped UCNs YYLTYPE's yyltype typedefs inline Yaccs
2018 LocalWords: Heriyanto Reenable dprec Hilfinger Eggert MYEOF Folle Menezes EOF
242cc08e 2019 LocalWords: Lackovic define's itemset Groff Gettext malloc NEWS'ed YYDEBUG YY
7e508a2b 2020 LocalWords: namespaces strerror const autoconfiguration Dconst Autoconf's FDL
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AD
2021 LocalWords: Automake TMPDIR LESSEQ ylwrap endif yydebug YYTOKEN YYLSP ival hh
2022 LocalWords: extern YYTOKENTYPE TOKENTYPE yytokentype tokentype STYPE lval pdf
7287be84
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2023 LocalWords: lang yyoutput dvi html ps POSIX lvalp llocp calc yyo fval Wmaybe
2024 LocalWords: yyvsp pragmas noreturn java's
7e508a2b
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2025
2026Local Variables:
2027mode: outline
e4ab1254 2028fill-column: 76
7e508a2b 2029End: