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ed7658fe 1GNU Bison NEWS
3af4feb2 2
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3* Noteworthy changes in release ?.? (????-??-??) [?]
4
5a05f42e 5** Changes in the format of error messages
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6
7 This used to be the format of many error reports:
8
9 foo.y:5.10-24: result type clash on merge function 'merge': <t3> != <t2>
10 foo.y:4.13-27: previous declaration
11
12 It is now:
13
14 foo.y:5.10-25: result type clash on merge function 'merge': <t3> != <t2>
15 foo.y:4.13-27: previous declaration
16
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17** Exception safety (lalr1.cc)
18
19 The parse function now catches exceptions, uses the %destructors to
20 release memory (the lookahead symbol and the symbols pushed on the stack)
7287be84 21 before re-throwing the exception.
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22
23 This feature is somewhat experimental. User feedback would be
24 appreciated.
25
7287be84 26** New %define variable: api.location.type (glr.cc, lalr1.cc, lalr1.java)
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27
28 The %define variable api.location.type defines the name of the type to use
29 for locations. When defined, Bison no longer generates the position.hh
30 and location.hh files, nor does the parser will include them: the user is
31 then responsible to define her type.
32
33 This can be used in programs with several parsers to factor their location
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34 and position files: let one of them generate them, and the others just use
35 them.
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36
37 This feature was actually introduced, but not documented, in Bison 2.5,
38 under the name "location_type" (which is maintained for backward
39 compatibility).
40
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41 For consistency, lalr1.java's %define variables location_type and
42 position_type are deprecated in favor of api.location.type and
43 api.position.type.
44
9c16d399 45** Graph improvements in DOT and XSLT
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46
47 The graphical presentation of the states is more readable: their shape is
48 now rectangular, the state number is clearly displayed, and the items are
49 numbered and left-justified.
50
51 The reductions are now explicitly represented as transitions to other
52 diamond shaped nodes.
53
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54 These changes are present in both --graph output and xml2dot.xsl XSLT
55 processing, with minor (documented) differences.
56
57 Two nodes were added to the documentation: Xml and Graphviz.
58
9d3f7eaf 59* Noteworthy changes in release 2.6.5 (2012-11-07) [stable]
6f1360bd 60
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61 We consider compiler warnings about Bison generated parsers to be bugs.
62 Rather than working around them in your own project, please consider
63 reporting them to us.
64
65** Bug fixes
66
67 Warnings about uninitialized yylval and/or yylloc for push parsers with a
68 pure interface have been fixed for GCC 4.0 up to 4.8, and Clang 2.9 to
69 3.2.
70
71 Other issues in the test suite have been addressed.
6f1360bd 72
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73 Nul characters are correctly displayed in error messages.
74
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75 When possible, yylloc is correctly initialized before calling yylex. It
76 is no longer necessary to initialize it in the %initial-action.
77
0ac15849 78* Noteworthy changes in release 2.6.4 (2012-10-23) [stable]
a4eb820f 79
468455e1 80 Bison 2.6.3's --version was incorrect. This release fixes this issue.
a4eb820f 81
6eb8f74f 82* Noteworthy changes in release 2.6.3 (2012-10-22) [stable]
933ec544 83
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84** Bug fixes
85
9a50c55a 86 Bugs and portability issues in the test suite have been fixed.
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87
88 Some errors in translations have been addressed, and --help now directs
89 users to the appropriate place to report them.
90
91 Stray Info files shipped by accident are removed.
92
93 Incorrect definitions of YY_, issued by yacc.c when no parser header is
94 generated, are removed.
933ec544 95
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96 All the generated headers are self-contained.
97
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98** Header guards (yacc.c, glr.c, glr.cc)
99
100 In order to avoid collisions, the header guards are now
101 YY_<PREFIX>_<FILE>_INCLUDED, instead of merely <PREFIX>_<FILE>.
102 For instance the header generated from
103
104 %define api.prefix "calc"
105 %defines "lib/parse.h"
106
107 will use YY_CALC_LIB_PARSE_H_INCLUDED as guard.
108
7b70847e 109** Fix compiler warnings in the generated parser (yacc.c, glr.c)
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110
111 The compilation of pure parsers (%define api.pure) can trigger GCC
112 warnings such as:
113
114 input.c: In function 'yyparse':
115 input.c:1503:12: warning: 'yylval' may be used uninitialized in this
116 function [-Wmaybe-uninitialized]
117 *++yyvsp = yylval;
118 ^
119
120 This is now fixed; pragmas to avoid these warnings are no longer needed.
121
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122 Warnings from clang ("equality comparison with extraneous parentheses" and
123 "function declared 'noreturn' should not return") have also been
124 addressed.
125
e1eeecd3 126* Noteworthy changes in release 2.6.2 (2012-08-03) [stable]
9c26b8fc 127
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128** Bug fixes
129
130 Buffer overruns, complaints from Flex, and portability issues in the test
131 suite have been fixed.
132
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133** Spaces in %lex- and %parse-param (lalr1.cc, glr.cc)
134
135 Trailing end-of-lines in %parse-param or %lex-param would result in
136 invalid C++. This is fixed.
9c26b8fc 137
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138** Spurious spaces and end-of-lines
139
140 The generated files no longer end (nor start) with empty lines.
141
77b214ef 142* Noteworthy changes in release 2.6.1 (2012-07-30) [stable]
a4107f24 143
cbaea010 144 Bison no longer executes user-specified M4 code when processing a grammar.
8617d87e 145
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146** Future Changes
147
148 In addition to the removal of the features announced in Bison 2.6, the
149 next major release will remove the "Temporary hack for adding a semicolon
150 to the user action", as announced in the release 2.5. Instead of:
151
152 exp: exp "+" exp { $$ = $1 + $3 };
153
154 write:
155
156 exp: exp "+" exp { $$ = $1 + $3; };
157
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158** Bug fixes
159
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160*** Type names are now properly escaped.
161
162*** glr.cc: set_debug_level and debug_level work as expected.
a4107f24 163
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164*** Stray @ or $ in actions
165
166 While Bison used to warn about stray $ or @ in action rules, it did not
167 for other actions such as printers, destructors, or initial actions. It
168 now does.
169
cd735a8c 170** Type names in actions
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171
172 For consistency with rule actions, it is now possible to qualify $$ by a
cd735a8c 173 type-name in destructors, printers, and initial actions. For instance:
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174
175 %printer { fprintf (yyo, "(%d, %f)", $<ival>$, $<fval>$); } <*> <>;
176
177 will display two values for each typed and untyped symbol (provided
cd735a8c 178 that YYSTYPE has both "ival" and "fval" fields).
4982f078 179
1505e8bb 180* Noteworthy changes in release 2.6 (2012-07-19) [stable]
ad6b775f 181
c2425191 182** Future Changes
0f11eec2 183
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184 The next major release of Bison will drop support for the following
185 deprecated features. Please report disagreements to bug-bison@gnu.org.
0f11eec2 186
aaf61036 187*** K&R C parsers
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188
189 Support for generating parsers in K&R C will be removed. Parsers
242cc08e 190 generated for C support ISO C90, and are tested with ISO C99 and ISO C11
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191 compilers.
192
258cddbc 193*** Features deprecated since Bison 1.875
55d1006f 194
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195 The definitions of yystype and yyltype will be removed; use YYSTYPE and
196 YYLTYPE.
55d1006f 197
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198 YYPARSE_PARAM and YYLEX_PARAM, deprecated in favor of %parse-param and
199 %lex-param, will no longer be supported.
200
201 Support for the preprocessor symbol YYERROR_VERBOSE will be removed, use
202 %error-verbose.
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203
204*** The generated header will be included (yacc.c)
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205
206 Instead of duplicating the content of the generated header (definition of
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207 YYSTYPE, yyparse declaration etc.), the generated parser will include it,
208 as is already the case for GLR or C++ parsers. This change is deferred
209 because existing versions of ylwrap (e.g., Automake 1.12.1) do not support
210 it.
0f11eec2 211
c2425191 212** Generated Parser Headers
56ca3d8f 213
258cddbc 214*** Guards (yacc.c, glr.c, glr.cc)
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215
216 The generated headers are now guarded, as is already the case for C++
242cc08e 217 parsers (lalr1.cc). For instance, with --defines=foo.h:
c3e9f08f 218
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219 #ifndef YY_FOO_H
220 # define YY_FOO_H
221 ...
222 #endif /* !YY_FOO_H */
c3e9f08f 223
258cddbc 224*** New declarations (yacc.c, glr.c)
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225
226 The generated header now declares yydebug and yyparse. Both honor
227 --name-prefix=bar_, and yield
228
e29f0771 229 int bar_parse (void);
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230
231 rather than
232
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233 #define yyparse bar_parse
234 int yyparse (void);
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235
236 in order to facilitate the inclusion of several parser headers inside a
237 single compilation unit.
c3e9f08f 238
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239*** Exported symbols in C++
240
241 The symbols YYTOKEN_TABLE and YYERROR_VERBOSE, which were defined in the
242 header, are removed, as they prevent the possibility of including several
243 generated headers from a single compilation unit.
244
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245*** YYLSP_NEEDED
246
247 For the same reasons, the undocumented and unused macro YYLSP_NEEDED is no
248 longer defined.
249
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250** New %define variable: api.prefix
251
252 Now that the generated headers are more complete and properly protected
253 against multiple inclusions, constant names, such as YYSTYPE are a
254 problem. While yyparse and others are properly renamed by %name-prefix,
255 YYSTYPE, YYDEBUG and others have never been affected by it. Because it
256 would introduce backward compatibility issues in projects not expecting
257 YYSTYPE to be renamed, instead of changing the behavior of %name-prefix,
258 it is deprecated in favor of a new %define variable: api.prefix.
259
260 The following examples compares both:
261
262 %name-prefix "bar_" | %define api.prefix "bar_"
263 %token <ival> FOO %token <ival> FOO
264 %union { int ival; } %union { int ival; }
265 %% %%
266 exp: 'a'; exp: 'a';
267
268 bison generates:
269
270 #ifndef BAR_FOO_H #ifndef BAR_FOO_H
271 # define BAR_FOO_H # define BAR_FOO_H
272
273 /* Enabling traces. */ /* Enabling traces. */
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274 # ifndef YYDEBUG | # ifndef BAR_DEBUG
275 > # if defined YYDEBUG
276 > # if YYDEBUG
277 > # define BAR_DEBUG 1
278 > # else
279 > # define BAR_DEBUG 0
280 > # endif
281 > # else
282 # define YYDEBUG 0 | # define BAR_DEBUG 0
283 > # endif
284 # endif | # endif
285
286 # if YYDEBUG | # if BAR_DEBUG
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287 extern int bar_debug; extern int bar_debug;
288 # endif # endif
289
290 /* Tokens. */ /* Tokens. */
291 # ifndef YYTOKENTYPE | # ifndef BAR_TOKENTYPE
292 # define YYTOKENTYPE | # define BAR_TOKENTYPE
293 enum yytokentype { | enum bar_tokentype {
294 FOO = 258 FOO = 258
295 }; };
296 # endif # endif
297
298 #if ! defined YYSTYPE \ | #if ! defined BAR_STYPE \
299 && ! defined YYSTYPE_IS_DECLARED | && ! defined BAR_STYPE_IS_DECLARED
300 typedef union YYSTYPE | typedef union BAR_STYPE
301 { {
302 int ival; int ival;
303 } YYSTYPE; | } BAR_STYPE;
304 # define YYSTYPE_IS_DECLARED 1 | # define BAR_STYPE_IS_DECLARED 1
305 #endif #endif
306
307 extern YYSTYPE bar_lval; | extern BAR_STYPE bar_lval;
308
309 int bar_parse (void); int bar_parse (void);
310
311 #endif /* !BAR_FOO_H */ #endif /* !BAR_FOO_H */
312
dfaac272 313* Noteworthy changes in release 2.5.1 (2012-06-05) [stable]
90dcd415 314
debe2c03 315** Future changes:
041308d0 316
e4ab1254 317 The next major release will drop support for generating parsers in K&R C.
ef51bfa7 318
466b4cf2 319** yacc.c: YYBACKUP works as expected.
94556574 320
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321** glr.c improvements:
322
323*** Location support is eliminated when not requested:
324
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325 GLR parsers used to include location-related code even when locations were
326 not requested, and therefore not even usable.
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327
328*** __attribute__ is preserved:
debe2c03 329
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330 __attribute__ is no longer disabled when __STRICT_ANSI__ is defined (i.e.,
331 when -std is passed to GCC).
debe2c03 332
466b4cf2 333** lalr1.java: several fixes:
041308d0 334
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335 The Java parser no longer throws ArrayIndexOutOfBoundsException if the
336 first token leads to a syntax error. Some minor clean ups.
041308d0 337
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338** Changes for C++:
339
340*** C++11 compatibility:
ef51bfa7 341
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342 C and C++ parsers use "nullptr" instead of "0" when __cplusplus is 201103L
343 or higher.
ef51bfa7 344
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345*** Header guards
346
347 The header files such as "parser.hh", "location.hh", etc. used a constant
348 name for preprocessor guards, for instance:
349
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350 #ifndef BISON_LOCATION_HH
351 # define BISON_LOCATION_HH
352 ...
353 #endif // !BISON_LOCATION_HH
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354
355 The inclusion guard is now computed from "PREFIX/FILE-NAME", where lower
356 case characters are converted to upper case, and series of
357 non-alphanumerical characters are converted to an underscore.
358
359 With "bison -o lang++/parser.cc", "location.hh" would now include:
360
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361 #ifndef YY_LANG_LOCATION_HH
362 # define YY_LANG_LOCATION_HH
363 ...
364 #endif // !YY_LANG_LOCATION_HH
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365
366*** C++ locations:
936c88d1 367
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368 The position and location constructors (and their initialize methods)
369 accept new arguments for line and column. Several issues in the
370 documentation were fixed.
936c88d1 371
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372** liby is no longer asking for "rpl_fprintf" on some platforms.
373
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374** Changes in the manual:
375
376*** %printer is documented
377
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378 The "%printer" directive, supported since at least Bison 1.50, is finally
379 documented. The "mfcalc" example is extended to demonstrate it.
7e508a2b 380
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381 For consistency with the C skeletons, the C++ parsers now also support
382 "yyoutput" (as an alias to "debug_stream ()").
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383
384*** Several improvements have been made:
466b4cf2 385
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386 The layout for grammar excerpts was changed to a more compact scheme.
387 Named references are motivated. The description of the automaton
388 description file (*.output) is updated to the current format. Incorrect
389 index entries were fixed. Some other errors were fixed.
466b4cf2 390
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391** Building bison:
392
393*** Conflicting prototypes with recent/modified Flex.
394
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395 Fixed build problems with the current, unreleased, version of Flex, and
396 some modified versions of 2.5.35, which have modified function prototypes.
466b4cf2 397
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398*** Warnings during the build procedure have been eliminated.
399
400*** Several portability problems in the test suite have been fixed:
466b4cf2 401
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402 This includes warnings with some compilers, unexpected behavior of tools
403 such as diff, warning messages from the test suite itself, etc.
466b4cf2 404
91aadcc7 405*** The install-pdf target works properly:
8ef26c2a 406
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407 Running "make install-pdf" (or -dvi, -html, -info, and -ps) no longer
408 halts in the middle of its course.
8ef26c2a 409
b2bc8a1b 410* Changes in version 2.5 (2011-05-14):
006faedf 411
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412** Grammar symbol names can now contain non-initial dashes:
413
414 Consistently with directives (such as %error-verbose) and with
415 %define variables (e.g. push-pull), grammar symbol names may contain
416 dashes in any position except the beginning. This is a GNU
417 extension over POSIX Yacc. Thus, use of this extension is reported
418 by -Wyacc and rejected in Yacc mode (--yacc).
419
3b1977ea 420** Named references:
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421
422 Historically, Yacc and Bison have supported positional references
423 ($n, $$) to allow access to symbol values from inside of semantic
424 actions code.
425
426 Starting from this version, Bison can also accept named references.
427 When no ambiguity is possible, original symbol names may be used
428 as named references:
429
ac3297d5 430 if_stmt : "if" cond_expr "then" then_stmt ';'
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431 { $if_stmt = mk_if_stmt($cond_expr, $then_stmt); }
432
433 In the more common case, explicit names may be declared:
434
ac3297d5 435 stmt[res] : "if" expr[cond] "then" stmt[then] "else" stmt[else] ';'
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436 { $res = mk_if_stmt($cond, $then, $else); }
437
f840c05a 438 Location information is also accessible using @name syntax. When
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439 accessing symbol names containing dots or dashes, explicit bracketing
440 ($[sym.1]) must be used.
441
f840c05a 442 These features are experimental in this version. More user feedback
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443 will help to stabilize them.
444
3b1977ea 445** IELR(1) and canonical LR(1):
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446
447 IELR(1) is a minimal LR(1) parser table generation algorithm. That
448 is, given any context-free grammar, IELR(1) generates parser tables
723206df 449 with the full language-recognition power of canonical LR(1) but with
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450 nearly the same number of parser states as LALR(1). This reduction
451 in parser states is often an order of magnitude. More importantly,
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452 because canonical LR(1)'s extra parser states may contain duplicate
453 conflicts in the case of non-LR(1) grammars, the number of conflicts
454 for IELR(1) is often an order of magnitude less as well. This can
455 significantly reduce the complexity of developing of a grammar.
456
457 Bison can now generate IELR(1) and canonical LR(1) parser tables in
458 place of its traditional LALR(1) parser tables, which remain the
459 default. You can specify the type of parser tables in the grammar
460 file with these directives:
461
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462 %define lr.type lalr
463 %define lr.type ielr
464 %define lr.type canonical-lr
34a6c2d1 465
6f04ee6c 466 The default-reduction optimization in the parser tables can also be
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467 adjusted using "%define lr.default-reductions". For details on both
468 of these features, see the new section "Tuning LR" in the Bison
6f04ee6c 469 manual.
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470
471 These features are experimental. More user feedback will help to
472 stabilize them.
473
6f04ee6c 474** LAC (Lookahead Correction) for syntax error handling:
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475
476 Canonical LR, IELR, and LALR can suffer from a couple of problems
477 upon encountering a syntax error. First, the parser might perform
478 additional parser stack reductions before discovering the syntax
6f04ee6c 479 error. Such reductions can perform user semantic actions that are
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480 unexpected because they are based on an invalid token, and they
481 cause error recovery to begin in a different syntactic context than
482 the one in which the invalid token was encountered. Second, when
6f04ee6c 483 verbose error messages are enabled (with %error-verbose or the
e4ab1254 484 obsolete "#define YYERROR_VERBOSE"), the expected token list in the
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485 syntax error message can both contain invalid tokens and omit valid
486 tokens.
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487
488 The culprits for the above problems are %nonassoc, default
489 reductions in inconsistent states, and parser state merging. Thus,
490 IELR and LALR suffer the most. Canonical LR can suffer only if
491 %nonassoc is used or if default reductions are enabled for
492 inconsistent states.
493
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494 LAC is a new mechanism within the parsing algorithm that solves
495 these problems for canonical LR, IELR, and LALR without sacrificing
496 %nonassoc, default reductions, or state merging. When LAC is in
497 use, canonical LR and IELR behave almost exactly the same for both
498 syntactically acceptable and syntactically unacceptable input.
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499 While LALR still does not support the full language-recognition
500 power of canonical LR and IELR, LAC at least enables LALR's syntax
501 error handling to correctly reflect LALR's language-recognition
502 power.
503
504 Currently, LAC is only supported for deterministic parsers in C.
505 You can enable LAC with the following directive:
506
507 %define parse.lac full
508
e4ab1254 509 See the new section "LAC" in the Bison manual for additional
6f04ee6c 510 details including a few caveats.
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511
512 LAC is an experimental feature. More user feedback will help to
513 stabilize it.
514
6ee881f6 515** %define improvements:
f37495f6 516
3b1977ea 517*** Can now be invoked via the command line:
4ecd3681 518
34d41938 519 Each of these command-line options
4ecd3681 520
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521 -D NAME[=VALUE]
522 --define=NAME[=VALUE]
523
524 -F NAME[=VALUE]
525 --force-define=NAME[=VALUE]
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526
527 is equivalent to this grammar file declaration
528
34d41938 529 %define NAME ["VALUE"]
4ecd3681 530
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531 except that the manner in which Bison processes multiple definitions
532 for the same NAME differs. Most importantly, -F and --force-define
533 quietly override %define, but -D and --define do not. For further
e4ab1254 534 details, see the section "Bison Options" in the Bison manual.
4ecd3681 535
3b1977ea 536*** Variables renamed:
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537
538 The following %define variables
539
540 api.push_pull
541 lr.keep_unreachable_states
542
543 have been renamed to
544
545 api.push-pull
546 lr.keep-unreachable-states
547
548 The old names are now deprecated but will be maintained indefinitely
549 for backward compatibility.
550
723206df 551*** Values no longer need to be quoted in the grammar file:
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552
553 If a %define value is an identifier, it no longer needs to be placed
554 within quotations marks. For example,
555
556 %define api.push-pull "push"
557
558 can be rewritten as
559
560 %define api.push-pull push
561
6ee881f6 562*** Unrecognized variables are now errors not warnings.
c046698e 563
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564*** Multiple invocations for any variable is now an error not a warning.
565
566** Unrecognized %code qualifiers are now errors not warnings.
567
568** Character literals not of length one:
569
570 Previously, Bison quietly converted all character literals to length
571 one. For example, without warning, Bison interpreted the operators in
572 the following grammar to be the same token:
573
574 exp: exp '++'
575 | exp '+' exp
576 ;
577
578 Bison now warns when a character literal is not of length one. In
579 some future release, Bison will start reporting an error instead.
580
581** Destructor calls fixed for lookaheads altered in semantic actions:
582
583 Previously for deterministic parsers in C, if a user semantic action
584 altered yychar, the parser in some cases used the old yychar value to
585 determine which destructor to call for the lookahead upon a syntax
586 error or upon parser return. This bug has been fixed.
587
588** C++ parsers use YYRHSLOC:
589
590 Similarly to the C parsers, the C++ parsers now define the YYRHSLOC
591 macro and use it in the default YYLLOC_DEFAULT. You are encouraged
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592 to use it. If, for instance, your location structure has "first"
593 and "last" members, instead of
6ee881f6 594
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595 # define YYLLOC_DEFAULT(Current, Rhs, N) \
596 do \
597 if (N) \
598 { \
599 (Current).first = (Rhs)[1].location.first; \
600 (Current).last = (Rhs)[N].location.last; \
601 } \
602 else \
603 { \
604 (Current).first = (Current).last = (Rhs)[0].location.last; \
605 } \
606 while (false)
6ee881f6
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607
608 use:
609
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610 # define YYLLOC_DEFAULT(Current, Rhs, N) \
611 do \
612 if (N) \
613 { \
614 (Current).first = YYRHSLOC (Rhs, 1).first; \
615 (Current).last = YYRHSLOC (Rhs, N).last; \
616 } \
617 else \
618 { \
619 (Current).first = (Current).last = YYRHSLOC (Rhs, 0).last; \
620 } \
621 while (false)
6ee881f6
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622
623** YYLLOC_DEFAULT in C++:
624
625 The default implementation of YYLLOC_DEFAULT used to be issued in
626 the header file. It is now output in the implementation file, after
627 the user %code sections so that its #ifndef guard does not try to
628 override the user's YYLLOC_DEFAULT if provided.
c046698e 629
3b1977ea 630** YYFAIL now produces warnings and Java parsers no longer implement it:
62efdd2a
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631
632 YYFAIL has existed for many years as an undocumented feature of
633 deterministic parsers in C generated by Bison. More recently, it was
634 a documented feature of Bison's experimental Java parsers. As
635 promised in Bison 2.4.2's NEWS entry, any appearance of YYFAIL in a
636 semantic action now produces a deprecation warning, and Java parsers
637 no longer implement YYFAIL at all. For further details, including a
638 discussion of how to suppress C preprocessor warnings about YYFAIL
639 being unused, see the Bison 2.4.2 NEWS entry.
640
3b1977ea 641** Temporary hack for adding a semicolon to the user action:
a2d05674
JD
642
643 Previously, Bison appended a semicolon to every user action for
644 reductions when the output language defaulted to C (specifically, when
645 neither %yacc, %language, %skeleton, or equivalent command-line
646 options were specified). This allowed actions such as
647
648 exp: exp "+" exp { $$ = $1 + $3 };
649
650 instead of
651
652 exp: exp "+" exp { $$ = $1 + $3; };
653
654 As a first step in removing this misfeature, Bison now issues a
655 warning when it appends a semicolon. Moreover, in cases where Bison
656 cannot easily determine whether a semicolon is needed (for example, an
657 action ending with a cpp directive or a braced compound initializer),
658 it no longer appends one. Thus, the C compiler might now complain
659 about a missing semicolon where it did not before. Future releases of
660 Bison will cease to append semicolons entirely.
661
095a1d11
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662** Verbose syntax error message fixes:
663
e4ab1254 664 When %error-verbose or the obsolete "#define YYERROR_VERBOSE" is
6f04ee6c
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665 specified, syntax error messages produced by the generated parser
666 include the unexpected token as well as a list of expected tokens.
667 The effect of %nonassoc on these verbose messages has been corrected
668 in two ways, but a more complete fix requires LAC, described above:
095a1d11
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669
670*** When %nonassoc is used, there can exist parser states that accept no
671 tokens, and so the parser does not always require a lookahead token
672 in order to detect a syntax error. Because no unexpected token or
673 expected tokens can then be reported, the verbose syntax error
674 message described above is suppressed, and the parser instead
e4ab1254 675 reports the simpler message, "syntax error". Previously, this
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676 suppression was sometimes erroneously triggered by %nonassoc when a
677 lookahead was actually required. Now verbose messages are
678 suppressed only when all previous lookaheads have already been
679 shifted or discarded.
680
681*** Previously, the list of expected tokens erroneously included tokens
682 that would actually induce a syntax error because conflicts for them
683 were resolved with %nonassoc in the current parser state. Such
684 tokens are now properly omitted from the list.
685
686*** Expected token lists are still often wrong due to state merging
4c38b19e
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687 (from LALR or IELR) and default reductions, which can both add
688 invalid tokens and subtract valid tokens. Canonical LR almost
689 completely fixes this problem by eliminating state merging and
690 default reductions. However, there is one minor problem left even
691 when using canonical LR and even after the fixes above. That is,
692 if the resolution of a conflict with %nonassoc appears in a later
693 parser state than the one at which some syntax error is
694 discovered, the conflicted token is still erroneously included in
695 the expected token list. Bison's new LAC implementation,
696 described above, eliminates this problem and the need for
697 canonical LR. However, LAC is still experimental and is disabled
698 by default.
1fa30307 699
4c2a6e42
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700** Java skeleton fixes:
701
702*** A location handling bug has been fixed.
703
704*** The top element of each of the value stack and location stack is now
705 cleared when popped so that it can be garbage collected.
77768165 706
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707*** Parser traces now print the top element of the stack.
708
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709** -W/--warnings fixes:
710
e4ab1254 711*** Bison now properly recognizes the "no-" versions of categories:
248dba53
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712
713 For example, given the following command line, Bison now enables all
714 warnings except warnings for incompatibilities with POSIX Yacc:
715
716 bison -Wall,no-yacc gram.y
717
6f8bdce2
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718*** Bison now treats S/R and R/R conflicts like other warnings:
719
720 Previously, conflict reports were independent of Bison's normal
721 warning system. Now, Bison recognizes the warning categories
e4ab1254 722 "conflicts-sr" and "conflicts-rr". This change has important
6f8bdce2
JD
723 consequences for the -W and --warnings command-line options. For
724 example:
725
726 bison -Wno-conflicts-sr gram.y # S/R conflicts not reported
727 bison -Wno-conflicts-rr gram.y # R/R conflicts not reported
728 bison -Wnone gram.y # no conflicts are reported
729 bison -Werror gram.y # any conflict is an error
730
731 However, as before, if the %expect or %expect-rr directive is
732 specified, an unexpected number of conflicts is an error, and an
733 expected number of conflicts is not reported, so -W and --warning
734 then have no effect on the conflict report.
735
e4ab1254 736*** The "none" category no longer disables a preceding "error":
dab96632
JD
737
738 For example, for the following command line, Bison now reports
739 errors instead of warnings for incompatibilities with POSIX Yacc:
740
741 bison -Werror,none,yacc gram.y
742
e4ab1254 743*** The "none" category now disables all Bison warnings:
8ffd7912 744
e4ab1254 745 Previously, the "none" category disabled only Bison warnings for
8ffd7912
JD
746 which there existed a specific -W/--warning category. However,
747 given the following command line, Bison is now guaranteed to
748 suppress all warnings:
749
750 bison -Wnone gram.y
751
9d6af153
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752** Precedence directives can now assign token number 0:
753
754 Since Bison 2.3b, which restored the ability of precedence
755 directives to assign token numbers, doing so for token number 0 has
756 produced an assertion failure. For example:
757
758 %left END 0
759
760 This bug has been fixed.
761
7527c744 762* Changes in version 2.4.3 (2010-08-05):
7a9c3cb3 763
4631c34f
JD
764** Bison now obeys -Werror and --warnings=error for warnings about
765 grammar rules that are useless in the parser due to conflicts.
766
7a9c3cb3
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767** Problems with spawning M4 on at least FreeBSD 8 and FreeBSD 9 have
768 been fixed.
769
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770** Failures in the test suite for GCC 4.5 have been fixed.
771
88bb35d6
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772** Failures in the test suite for some versions of Sun Studio C++ have
773 been fixed.
774
43fdc9fd
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775** Contrary to Bison 2.4.2's NEWS entry, it has been decided that
776 warnings about undefined %prec identifiers will not be converted to
777 errors in Bison 2.5. They will remain warnings, which should be
778 sufficient for POSIX while avoiding backward compatibility issues.
779
cf22447c
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780** Minor documentation fixes.
781
ea66d039 782* Changes in version 2.4.2 (2010-03-20):
8defe11b 783
47fa5747
JD
784** Some portability problems that resulted in failures and livelocks
785 in the test suite on some versions of at least Solaris, AIX, HP-UX,
ea66d039
JD
786 RHEL4, and Tru64 have been addressed. As a result, fatal Bison
787 errors should no longer cause M4 to report a broken pipe on the
47fa5747
JD
788 affected platforms.
789
e4ab1254 790** "%prec IDENTIFIER" requires IDENTIFIER to be defined separately.
2c203528
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791
792 POSIX specifies that an error be reported for any identifier that does
793 not appear on the LHS of a grammar rule and that is not defined by
794 %token, %left, %right, or %nonassoc. Bison 2.3b and later lost this
795 error report for the case when an identifier appears only after a
796 %prec directive. It is now restored. However, for backward
797 compatibility with recent Bison releases, it is only a warning for
798 now. In Bison 2.5 and later, it will return to being an error.
43fdc9fd
JD
799 [Between the 2.4.2 and 2.4.3 releases, it was decided that this
800 warning will not be converted to an error in Bison 2.5.]
2c203528 801
c5196098
EB
802** Detection of GNU M4 1.4.6 or newer during configure is improved.
803
34731471
JD
804** Warnings from gcc's -Wundef option about undefined YYENABLE_NLS,
805 YYLTYPE_IS_TRIVIAL, and __STRICT_ANSI__ in C/C++ parsers are now
806 avoided.
af2ffe5c 807
966aba65
JD
808** %code is now a permanent feature.
809
810 A traditional Yacc prologue directive is written in the form:
811
812 %{CODE%}
813
814 To provide a more flexible alternative, Bison 2.3b introduced the
815 %code directive with the following forms for C/C++:
816
817 %code {CODE}
818 %code requires {CODE}
819 %code provides {CODE}
820 %code top {CODE}
821
822 These forms are now considered permanent features of Bison. See the
823 %code entries in the section "Bison Declaration Summary" in the Bison
824 manual for a summary of their functionality. See the section
825 "Prologue Alternatives" for a detailed discussion including the
826 advantages of %code over the traditional Yacc prologue directive.
827
828 Bison's Java feature as a whole including its current usage of %code
829 is still considered experimental.
830
41d35e54
JD
831** YYFAIL is deprecated and will eventually be removed.
832
833 YYFAIL has existed for many years as an undocumented feature of
834 deterministic parsers in C generated by Bison. Previously, it was
835 documented for Bison's experimental Java parsers. YYFAIL is no longer
836 documented for Java parsers and is formally deprecated in both cases.
837 Users are strongly encouraged to migrate to YYERROR, which is
838 specified by POSIX.
839
840 Like YYERROR, you can invoke YYFAIL from a semantic action in order to
841 induce a syntax error. The most obvious difference from YYERROR is
842 that YYFAIL will automatically invoke yyerror to report the syntax
843 error so that you don't have to. However, there are several other
844 subtle differences between YYERROR and YYFAIL, and YYFAIL suffers from
e4ab1254 845 inherent flaws when %error-verbose or "#define YYERROR_VERBOSE" is
41d35e54
JD
846 used. For a more detailed discussion, see:
847
848 http://lists.gnu.org/archive/html/bison-patches/2009-12/msg00024.html
849
850 The upcoming Bison 2.5 will remove YYFAIL from Java parsers, but
851 deterministic parsers in C will continue to implement it. However,
852 because YYFAIL is already flawed, it seems futile to try to make new
853 Bison features compatible with it. Thus, during parser generation,
854 Bison 2.5 will produce a warning whenever it discovers YYFAIL in a
855 rule action. In a later release, YYFAIL will be disabled for
e4ab1254 856 %error-verbose and "#define YYERROR_VERBOSE". Eventually, YYFAIL will
41d35e54
JD
857 be removed altogether.
858
859 There exists at least one case where Bison 2.5's YYFAIL warning will
860 be a false positive. Some projects add phony uses of YYFAIL and other
861 Bison-defined macros for the sole purpose of suppressing C
862 preprocessor warnings (from GCC cpp's -Wunused-macros, for example).
863 To avoid Bison's future warning, such YYFAIL uses can be moved to the
e4ab1254 864 epilogue (that is, after the second "%%") in the Bison input file. In
41d35e54
JD
865 this release (2.4.2), Bison already generates its own code to suppress
866 C preprocessor warnings for YYFAIL, so projects can remove their own
867 phony uses of YYFAIL if compatibility with Bison releases prior to
868 2.4.2 is not necessary.
869
dac8cc0d
AD
870** Internationalization.
871
872 Fix a regression introduced in Bison 2.4: Under some circumstances,
873 message translations were not installed although supported by the
874 host system.
875
41930e7a 876* Changes in version 2.4.1 (2008-12-11):
c9ba9e59 877
a957d06c
JD
878** In the GLR defines file, unexpanded M4 macros in the yylval and yylloc
879 declarations have been fixed.
880
738cde3e
AD
881** Temporary hack for adding a semicolon to the user action.
882
883 Bison used to prepend a trailing semicolon at the end of the user
884 action for reductions. This allowed actions such as
885
886 exp: exp "+" exp { $$ = $1 + $3 };
887
888 instead of
889
890 exp: exp "+" exp { $$ = $1 + $3; };
891
e4ab1254 892 Some grammars still depend on this "feature". Bison 2.4.1 restores
d07932ef
JD
893 the previous behavior in the case of C output (specifically, when
894 neither %language or %skeleton or equivalent command-line options
895 are used) to leave more time for grammars depending on the old
896 behavior to be adjusted. Future releases of Bison will disable this
897 feature.
a957d06c
JD
898
899** A few minor improvements to the Bison manual.
c9ba9e59 900
d6fb461d 901* Changes in version 2.4 (2008-11-02):
7bd1665a 902
d6fb461d 903** %language is an experimental feature.
ed4d67dc
JD
904
905 We first introduced this feature in test release 2.3b as a cleaner
906 alternative to %skeleton. Since then, we have discussed the possibility of
907 modifying its effect on Bison's output file names. Thus, in this release,
908 we consider %language to be an experimental feature that will likely evolve
909 in future releases.
7bd1665a 910
d6fb461d 911** Forward compatibility with GNU M4 has been improved.
241fda7a 912
d6fb461d 913** Several bugs in the C++ skeleton and the experimental Java skeleton have been
241fda7a
JD
914 fixed.
915
d6fb461d 916* Changes in version 2.3b (2008-05-27):
35fe0834 917
d6fb461d 918** The quotes around NAME that used to be required in the following directive
d9df47b6
JD
919 are now deprecated:
920
921 %define NAME "VALUE"
922
e4ab1254 923** The directive "%pure-parser" is now deprecated in favor of:
d9df47b6
JD
924
925 %define api.pure
926
927 which has the same effect except that Bison is more careful to warn about
928 unreasonable usage in the latter case.
929
d6fb461d 930** Push Parsing
c373bf8b
JD
931
932 Bison can now generate an LALR(1) parser in C with a push interface. That
e4ab1254
AD
933 is, instead of invoking "yyparse", which pulls tokens from "yylex", you can
934 push one token at a time to the parser using "yypush_parse", which will
c373bf8b
JD
935 return to the caller after processing each token. By default, the push
936 interface is disabled. Either of the following directives will enable it:
937
938 %define api.push_pull "push" // Just push; does not require yylex.
939 %define api.push_pull "both" // Push and pull; requires yylex.
940
e4ab1254 941 See the new section "A Push Parser" in the Bison manual for details.
c373bf8b 942
59da312b
JD
943 The current push parsing interface is experimental and may evolve. More user
944 feedback will help to stabilize it.
945
d6fb461d 946** The -g and --graph options now output graphs in Graphviz DOT format,
8e55b3aa
JD
947 not VCG format. Like --graph, -g now also takes an optional FILE argument
948 and thus cannot be bundled with other short options.
c373bf8b 949
d6fb461d 950** Java
59da312b
JD
951
952 Bison can now generate an LALR(1) parser in Java. The skeleton is
e4ab1254 953 "data/lalr1.java". Consider using the new %language directive instead of
59da312b
JD
954 %skeleton to select it.
955
e4ab1254 956 See the new section "Java Parsers" in the Bison manual for details.
59da312b
JD
957
958 The current Java interface is experimental and may evolve. More user
959 feedback will help to stabilize it.
960
d6fb461d 961** %language
59da312b
JD
962
963 This new directive specifies the programming language of the generated
d43f77e7
PB
964 parser, which can be C (the default), C++, or Java. Besides the skeleton
965 that Bison uses, the directive affects the names of the generated files if
966 the grammar file's name ends in ".y".
59da312b 967
d6fb461d 968** XML Automaton Report
59da312b
JD
969
970 Bison can now generate an XML report of the LALR(1) automaton using the new
e4ab1254 971 "--xml" option. The current XML schema is experimental and may evolve. More
59da312b 972 user feedback will help to stabilize it.
c373bf8b 973
d6fb461d 974** The grammar file may now specify the name of the parser header file using
c373bf8b
JD
975 %defines. For example:
976
977 %defines "parser.h"
978
d6fb461d 979** When reporting useless rules, useless nonterminals, and unused terminals,
d80fb37a
JD
980 Bison now employs the terms "useless in grammar" instead of "useless",
981 "useless in parser" instead of "never reduced", and "unused in grammar"
982 instead of "unused".
cff03fb2 983
d6fb461d 984** Unreachable State Removal
c373bf8b
JD
985
986 Previously, Bison sometimes generated parser tables containing unreachable
31984206
JD
987 states. A state can become unreachable during conflict resolution if Bison
988 disables a shift action leading to it from a predecessor state. Bison now:
75ad86ee
JD
989
990 1. Removes unreachable states.
991
992 2. Does not report any conflicts that appeared in unreachable states.
993 WARNING: As a result, you may need to update %expect and %expect-rr
994 directives in existing grammar files.
995
996 3. For any rule used only in such states, Bison now reports the rule as
cff03fb2 997 "useless in parser due to conflicts".
75ad86ee 998
31984206
JD
999 This feature can be disabled with the following directive:
1000
1001 %define lr.keep_unreachable_states
1002
e4ab1254 1003 See the %define entry in the "Bison Declaration Summary" in the Bison manual
31984206
JD
1004 for further discussion.
1005
e4ab1254 1006** Lookahead Set Correction in the ".output" Report
b1cc23c4 1007
e4ab1254
AD
1008 When instructed to generate a ".output" file including lookahead sets
1009 (using "--report=lookahead", for example), Bison now prints each reduction's
88c78747
JD
1010 lookahead set only next to the associated state's one item that (1) is
1011 associated with the same rule as the reduction and (2) has its dot at the end
1012 of its RHS. Previously, Bison also erroneously printed the lookahead set
1013 next to all of the state's other items associated with the same rule. This
e4ab1254 1014 bug affected only the ".output" file and not the generated parser source
88c78747
JD
1015 code.
1016
e4ab1254 1017** --report-file=FILE is a new option to override the default ".output" file
59da312b 1018 name.
1bb2bd75 1019
e4ab1254 1020** The "=" that used to be required in the following directives is now
02975b9a
JD
1021 deprecated:
1022
1023 %file-prefix "parser"
1024 %name-prefix "c_"
1025 %output "parser.c"
1026
e4ab1254 1027** An Alternative to "%{...%}" -- "%code QUALIFIER {CODE}"
c373bf8b
JD
1028
1029 Bison 2.3a provided a new set of directives as a more flexible alternative to
8e0a5e9e
JD
1030 the traditional Yacc prologue blocks. Those have now been consolidated into
1031 a single %code directive with an optional qualifier field, which identifies
1032 the purpose of the code and thus the location(s) where Bison should generate
1033 it:
1034
e4ab1254
AD
1035 1. "%code {CODE}" replaces "%after-header {CODE}"
1036 2. "%code requires {CODE}" replaces "%start-header {CODE}"
1037 3. "%code provides {CODE}" replaces "%end-header {CODE}"
1038 4. "%code top {CODE}" replaces "%before-header {CODE}"
8e0a5e9e 1039
e4ab1254
AD
1040 See the %code entries in section "Bison Declaration Summary" in the Bison
1041 manual for a summary of the new functionality. See the new section "Prologue
1042 Alternatives" for a detailed discussion including the advantages of %code
8e0a5e9e
JD
1043 over the traditional Yacc prologues.
1044
1045 The prologue alternatives are experimental. More user feedback will help to
1046 determine whether they should become permanent features.
1047
d6fb461d 1048** Revised warning: unset or unused mid-rule values
17bd8a73
JD
1049
1050 Since Bison 2.2, Bison has warned about mid-rule values that are set but not
1051 used within any of the actions of the parent rule. For example, Bison warns
1052 about unused $2 in:
1053
1054 exp: '1' { $$ = 1; } '+' exp { $$ = $1 + $4; };
1055
1056 Now, Bison also warns about mid-rule values that are used but not set. For
1057 example, Bison warns about unset $$ in the mid-rule action in:
1058
1059 exp: '1' { $1 = 1; } '+' exp { $$ = $2 + $4; };
1060
1061 However, Bison now disables both of these warnings by default since they
1062 sometimes prove to be false alarms in existing grammars employing the Yacc
1063 constructs $0 or $-N (where N is some positive integer).
1064
e4ab1254
AD
1065 To enable these warnings, specify the option "--warnings=midrule-values" or
1066 "-W", which is a synonym for "--warnings=all".
17bd8a73 1067
e4ab1254 1068** Default %destructor or %printer with "<*>" or "<>"
c373bf8b
JD
1069
1070 Bison now recognizes two separate kinds of default %destructor's and
12e35840
JD
1071 %printer's:
1072
e4ab1254 1073 1. Place "<*>" in a %destructor/%printer symbol list to define a default
12e35840
JD
1074 %destructor/%printer for all grammar symbols for which you have formally
1075 declared semantic type tags.
1076
e4ab1254 1077 2. Place "<>" in a %destructor/%printer symbol list to define a default
12e35840
JD
1078 %destructor/%printer for all grammar symbols without declared semantic
1079 type tags.
1080
e4ab1254
AD
1081 Bison no longer supports the "%symbol-default" notation from Bison 2.3a.
1082 "<*>" and "<>" combined achieve the same effect with one exception: Bison no
12e35840
JD
1083 longer applies any %destructor to a mid-rule value if that mid-rule value is
1084 not actually ever referenced using either $$ or $n in a semantic action.
1085
85894313
JD
1086 The default %destructor's and %printer's are experimental. More user
1087 feedback will help to determine whether they should become permanent
1088 features.
1089
e4ab1254 1090 See the section "Freeing Discarded Symbols" in the Bison manual for further
12e35840
JD
1091 details.
1092
d6fb461d 1093** %left, %right, and %nonassoc can now declare token numbers. This is required
e4ab1254 1094 by POSIX. However, see the end of section "Operator Precedence" in the Bison
ab7f29f8
JD
1095 manual for a caveat concerning the treatment of literal strings.
1096
d6fb461d 1097** The nonfunctional --no-parser, -n, and %no-parser options have been
b1cc23c4
JD
1098 completely removed from Bison.
1099
d6fb461d 1100* Changes in version 2.3a, 2006-09-13:
742e4900 1101
d6fb461d 1102** Instead of %union, you can define and use your own union type
ddc8ede1
PE
1103 YYSTYPE if your grammar contains at least one <type> tag.
1104 Your YYSTYPE need not be a macro; it can be a typedef.
1105 This change is for compatibility with other Yacc implementations,
1106 and is required by POSIX.
1107
d6fb461d 1108** Locations columns and lines start at 1.
cd48d21d
AD
1109 In accordance with the GNU Coding Standards and Emacs.
1110
d6fb461d 1111** You may now declare per-type and default %destructor's and %printer's:
ec5479ce
JD
1112
1113 For example:
1114
b2a0b7ca
JD
1115 %union { char *string; }
1116 %token <string> STRING1
1117 %token <string> STRING2
1118 %type <string> string1
1119 %type <string> string2
1120 %union { char character; }
1121 %token <character> CHR
1122 %type <character> chr
1123 %destructor { free ($$); } %symbol-default
1124 %destructor { free ($$); printf ("%d", @$.first_line); } STRING1 string1
1125 %destructor { } <character>
1126
1127 guarantees that, when the parser discards any user-defined symbol that has a
e4ab1254
AD
1128 semantic type tag other than "<character>", it passes its semantic value to
1129 "free". However, when the parser discards a "STRING1" or a "string1", it
1130 also prints its line number to "stdout". It performs only the second
1131 "%destructor" in this case, so it invokes "free" only once.
ec5479ce 1132
85894313
JD
1133 [Although we failed to mention this here in the 2.3a release, the default
1134 %destructor's and %printer's were experimental, and they were rewritten in
1135 future versions.]
1136
e4ab1254
AD
1137** Except for LALR(1) parsers in C with POSIX Yacc emulation enabled (with "-y",
1138 "--yacc", or "%yacc"), Bison no longer generates #define statements for
b931235e
JD
1139 associating token numbers with token names. Removing the #define statements
1140 helps to sanitize the global namespace during preprocessing, but POSIX Yacc
1141 requires them. Bison still generates an enum for token names in all cases.
1142
d6fb461d 1143** Handling of traditional Yacc prologue blocks is now more consistent but
34f98f46 1144 potentially incompatible with previous releases of Bison.
9bc0dd67
JD
1145
1146 As before, you declare prologue blocks in your grammar file with the
e4ab1254 1147 "%{ ... %}" syntax. To generate the pre-prologue, Bison concatenates all
34f98f46
JD
1148 prologue blocks that you've declared before the first %union. To generate
1149 the post-prologue, Bison concatenates all prologue blocks that you've
ddc8ede1 1150 declared after the first %union.
9bc0dd67 1151
34f98f46 1152 Previous releases of Bison inserted the pre-prologue into both the header
9bc0dd67
JD
1153 file and the code file in all cases except for LALR(1) parsers in C. In the
1154 latter case, Bison inserted it only into the code file. For parsers in C++,
1155 the point of insertion was before any token definitions (which associate
1156 token numbers with names). For parsers in C, the point of insertion was
1157 after the token definitions.
1158
1159 Now, Bison never inserts the pre-prologue into the header file. In the code
1160 file, it always inserts it before the token definitions.
1161
d6fb461d 1162** Bison now provides a more flexible alternative to the traditional Yacc
34f98f46
JD
1163 prologue blocks: %before-header, %start-header, %end-header, and
1164 %after-header.
1165
1166 For example, the following declaration order in the grammar file reflects the
1167 order in which Bison will output these code blocks. However, you are free to
1168 declare these code blocks in your grammar file in whatever order is most
1169 convenient for you:
1170
1171 %before-header {
1172 /* Bison treats this block like a pre-prologue block: it inserts it into
1173 * the code file before the contents of the header file. It does *not*
1174 * insert it into the header file. This is a good place to put
1175 * #include's that you want at the top of your code file. A common
e4ab1254 1176 * example is '#include "system.h"'. */
34f98f46
JD
1177 }
1178 %start-header {
1179 /* Bison inserts this block into both the header file and the code file.
1180 * In both files, the point of insertion is before any Bison-generated
1181 * token, semantic type, location type, and class definitions. This is a
1182 * good place to define %union dependencies, for example. */
9bc0dd67
JD
1183 }
1184 %union {
34f98f46
JD
1185 /* Unlike the traditional Yacc prologue blocks, the output order for the
1186 * new %*-header blocks is not affected by their declaration position
1187 * relative to any %union in the grammar file. */
9bc0dd67 1188 }
34f98f46
JD
1189 %end-header {
1190 /* Bison inserts this block into both the header file and the code file.
1191 * In both files, the point of insertion is after the Bison-generated
1192 * definitions. This is a good place to declare or define public
1193 * functions or data structures that depend on the Bison-generated
1194 * definitions. */
9bc0dd67 1195 }
34f98f46
JD
1196 %after-header {
1197 /* Bison treats this block like a post-prologue block: it inserts it into
1198 * the code file after the contents of the header file. It does *not*
1199 * insert it into the header file. This is a good place to declare or
1200 * define internal functions or data structures that depend on the
1201 * Bison-generated definitions. */
1202 }
1203
1204 If you have multiple occurrences of any one of the above declarations, Bison
1205 will concatenate the contents in declaration order.
9bc0dd67 1206
85894313
JD
1207 [Although we failed to mention this here in the 2.3a release, the prologue
1208 alternatives were experimental, and they were rewritten in future versions.]
1209
e4ab1254 1210** The option "--report=look-ahead" has been changed to "--report=lookahead".
9e6e7ed2
PE
1211 The old spelling still works, but is not documented and may be removed
1212 in a future release.
742e4900 1213
d6fb461d 1214* Changes in version 2.3, 2006-06-05:
4ad3ed84 1215
e4ab1254 1216** GLR grammars should now use "YYRECOVERING ()" instead of "YYRECOVERING",
4ad3ed84
PE
1217 for compatibility with LALR(1) grammars.
1218
d6fb461d 1219** It is now documented that any definition of YYSTYPE or YYLTYPE should
4ad3ed84
PE
1220 be to a type name that does not contain parentheses or brackets.
1221
d6fb461d 1222* Changes in version 2.2, 2006-05-19:
193d7c70 1223
d6fb461d 1224** The distribution terms for all Bison-generated parsers now permit
193d7c70
PE
1225 using the parsers in nonfree programs. Previously, this permission
1226 was granted only for Bison-generated LALR(1) parsers in C.
5f4236a0 1227
d6fb461d 1228** %name-prefix changes the namespace name in C++ outputs.
aa08666d 1229
d6fb461d 1230** The C++ parsers export their token_type.
5f4236a0 1231
d6fb461d 1232** Bison now allows multiple %union declarations, and concatenates
d6ca7905
PE
1233 their contents together.
1234
d6fb461d 1235** New warning: unused values
4d7bc38c
PE
1236 Right-hand side symbols whose values are not used are reported,
1237 if the symbols have destructors. For instance:
affac613 1238
8f3596a6 1239 exp: exp "?" exp ":" exp { $1 ? $1 : $3; }
e29f0771
AD
1240 | exp "+" exp
1241 ;
affac613 1242
8f3596a6
AD
1243 will trigger a warning about $$ and $5 in the first rule, and $3 in
1244 the second ($1 is copied to $$ by the default rule). This example
4e26c69e 1245 most likely contains three errors, and could be rewritten as:
affac613 1246
4e26c69e 1247 exp: exp "?" exp ":" exp
e29f0771
AD
1248 { $$ = $1 ? $3 : $5; free ($1 ? $5 : $3); free ($1); }
1249 | exp "+" exp
1250 { $$ = $1 ? $1 : $3; if ($1) free ($3); }
1251 ;
affac613 1252
4e26c69e
PE
1253 However, if the original actions were really intended, memory leaks
1254 and all, the warnings can be suppressed by letting Bison believe the
1255 values are used, e.g.:
721be13c 1256
8f3596a6 1257 exp: exp "?" exp ":" exp { $1 ? $1 : $3; (void) ($$, $5); }
e29f0771
AD
1258 | exp "+" exp { $$ = $1; (void) $3; }
1259 ;
721be13c 1260
84866159
AD
1261 If there are mid-rule actions, the warning is issued if no action
1262 uses it. The following triggers no warning: $1 and $3 are used.
1263
1264 exp: exp { push ($1); } '+' exp { push ($3); sum (); };
1265
721be13c
PE
1266 The warning is intended to help catching lost values and memory leaks.
1267 If a value is ignored, its associated memory typically is not reclaimed.
affac613 1268
d6fb461d 1269** %destructor vs. YYABORT, YYACCEPT, and YYERROR.
9d9b8b70
PE
1270 Destructors are now called when user code invokes YYABORT, YYACCEPT,
1271 and YYERROR, for all objects on the stack, other than objects
1272 corresponding to the right-hand side of the current rule.
a85284cf 1273
d6fb461d 1274** %expect, %expect-rr
035aa4a0
PE
1275 Incorrect numbers of expected conflicts are now actual errors,
1276 instead of warnings.
1277
d6fb461d 1278** GLR, YACC parsers.
4e26c69e
PE
1279 The %parse-params are available in the destructors (and the
1280 experimental printers) as per the documentation.
4b367315 1281
e4ab1254 1282** Bison now warns if it finds a stray "$" or "@" in an action.
ad6a9b97 1283
d6fb461d 1284** %require "VERSION"
4e26c69e
PE
1285 This specifies that the grammar file depends on features implemented
1286 in Bison version VERSION or higher.
b50d2359 1287
d6fb461d 1288** lalr1.cc: The token and value types are now class members.
e14d0ab6
AD
1289 The tokens were defined as free form enums and cpp macros. YYSTYPE
1290 was defined as a free form union. They are now class members:
e4ab1254
AD
1291 tokens are enumerations of the "yy::parser::token" struct, and the
1292 semantic values have the "yy::parser::semantic_type" type.
fb9712a9
AD
1293
1294 If you do not want or can update to this scheme, the directive
e4ab1254 1295 '%define "global_tokens_and_yystype" "1"' triggers the global
b50d2359
AD
1296 definition of tokens and YYSTYPE. This change is suitable both
1297 for previous releases of Bison, and this one.
fb9712a9 1298
b50d2359 1299 If you wish to update, then make sure older version of Bison will
e4ab1254 1300 fail using '%require "2.2"'.
fb9712a9 1301
d6fb461d 1302** DJGPP support added.
193d7c70 1303\f
d6fb461d 1304* Changes in version 2.1, 2005-09-16:
1ce59070 1305
d6fb461d 1306** The C++ lalr1.cc skeleton supports %lex-param.
e14d0ab6 1307
d6fb461d 1308** Bison-generated parsers now support the translation of diagnostics like
baf785db
PE
1309 "syntax error" into languages other than English. The default
1310 language is still English. For details, please see the new
0410a6e0
PE
1311 Internationalization section of the Bison manual. Software
1312 distributors should also see the new PACKAGING file. Thanks to
1313 Bruno Haible for this new feature.
1ce59070 1314
d6fb461d 1315** Wording in the Bison-generated parsers has been changed slightly to
1a059451
PE
1316 simplify translation. In particular, the message "memory exhausted"
1317 has replaced "parser stack overflow", as the old message was not
1318 always accurate for modern Bison-generated parsers.
1319
d6fb461d 1320** Destructors are now called when the parser aborts, for all symbols left
258b75ca
PE
1321 behind on the stack. Also, the start symbol is now destroyed after a
1322 successful parse. In both cases, the behavior was formerly inconsistent.
1323
d6fb461d 1324** When generating verbose diagnostics, Bison-generated parsers no longer
72f000b0
PE
1325 quote the literal strings associated with tokens. For example, for
1326 a syntax error associated with '%token NUM "number"' they might
1327 print 'syntax error, unexpected number' instead of 'syntax error,
1328 unexpected "number"'.
193d7c70 1329\f
d6fb461d 1330* Changes in version 2.0, 2004-12-25:
efeed023 1331
d6fb461d 1332** Possibly-incompatible changes
d7e14fc0 1333
82de6b0d
PE
1334 - Bison-generated parsers no longer default to using the alloca function
1335 (when available) to extend the parser stack, due to widespread
1336 problems in unchecked stack-overflow detection. You can "#define
1337 YYSTACK_USE_ALLOCA 1" to require the use of alloca, but please read
1338 the manual to determine safe values for YYMAXDEPTH in that case.
8dd162d3 1339
82de6b0d
PE
1340 - Error token location.
1341 During error recovery, the location of the syntax error is updated
1342 to cover the whole sequence covered by the error token: it includes
1343 the shifted symbols thrown away during the first part of the error
1344 recovery, and the lookahead rejected during the second part.
18d192f0 1345
82de6b0d
PE
1346 - Semicolon changes:
1347 . Stray semicolons are no longer allowed at the start of a grammar.
1348 . Semicolons are now required after in-grammar declarations.
e342c3be 1349
82de6b0d
PE
1350 - Unescaped newlines are no longer allowed in character constants or
1351 string literals. They were never portable, and GCC 3.4.0 has
1352 dropped support for them. Better diagnostics are now generated if
1353 forget a closing quote.
8dd162d3 1354
82de6b0d 1355 - NUL bytes are no longer allowed in Bison string literals, unfortunately.
f74b6f91 1356
d6fb461d 1357** New features
1452af69 1358
82de6b0d 1359 - GLR grammars now support locations.
4febdd96 1360
82de6b0d
PE
1361 - New directive: %initial-action.
1362 This directive allows the user to run arbitrary code (including
1363 initializing @$) from yyparse before parsing starts.
1452af69 1364
82de6b0d
PE
1365 - A new directive "%expect-rr N" specifies the expected number of
1366 reduce/reduce conflicts in GLR parsers.
1452af69 1367
e4ab1254 1368 - %token numbers can now be hexadecimal integers, e.g., "%token FOO 0x12d".
82de6b0d 1369 This is a GNU extension.
4febdd96 1370
e4ab1254 1371 - The option "--report=lookahead" was changed to "--report=look-ahead".
9e6e7ed2 1372 [However, this was changed back after 2.3.]
1452af69 1373
82de6b0d 1374 - Experimental %destructor support has been added to lalr1.cc.
1452af69 1375
82de6b0d
PE
1376 - New configure option --disable-yacc, to disable installation of the
1377 yacc command and -ly library introduced in 1.875 for POSIX conformance.
6040d338 1378
d6fb461d 1379** Bug fixes
d5a3fe37 1380
82de6b0d
PE
1381 - For now, %expect-count violations are now just warnings, not errors.
1382 This is for compatibility with Bison 1.75 and earlier (when there are
1383 reduce/reduce conflicts) and with Bison 1.30 and earlier (when there
1384 are too many or too few shift/reduce conflicts). However, in future
1385 versions of Bison we plan to improve the %expect machinery so that
1386 these violations will become errors again.
3473d0f8 1387
82de6b0d
PE
1388 - Within Bison itself, numbers (e.g., goto numbers) are no longer
1389 arbitrarily limited to 16-bit counts.
d600ee67 1390
82de6b0d 1391 - Semicolons are now allowed before "|" in grammar rules, as POSIX requires.
d600ee67 1392\f
d6fb461d 1393* Changes in version 1.875, 2003-01-01:
963fcc17 1394
d6fb461d 1395** The documentation license has been upgraded to version 1.2
dc546b0f 1396 of the GNU Free Documentation License.
75eb3bc4 1397
d6fb461d 1398** syntax error processing
75eb3bc4 1399
dc546b0f
PE
1400 - In Yacc-style parsers YYLLOC_DEFAULT is now used to compute error
1401 locations too. This fixes bugs in error-location computation.
75eb3bc4 1402
dc546b0f
PE
1403 - %destructor
1404 It is now possible to reclaim the memory associated to symbols
1405 discarded during error recovery. This feature is still experimental.
20daca06 1406
dc546b0f
PE
1407 - %error-verbose
1408 This new directive is preferred over YYERROR_VERBOSE.
74724a70 1409
dc546b0f
PE
1410 - #defining yyerror to steal internal variables is discouraged.
1411 It is not guaranteed to work forever.
d1de5372 1412
d6fb461d 1413** POSIX conformance
d1de5372 1414
dc546b0f
PE
1415 - Semicolons are once again optional at the end of grammar rules.
1416 This reverts to the behavior of Bison 1.33 and earlier, and improves
1417 compatibility with Yacc.
74724a70 1418
e4ab1254
AD
1419 - "parse error" -> "syntax error"
1420 Bison now uniformly uses the term "syntax error"; formerly, the code
1421 and manual sometimes used the term "parse error" instead. POSIX
1422 requires "syntax error" in diagnostics, and it was thought better to
dc546b0f 1423 be consistent.
74724a70 1424
dc546b0f
PE
1425 - The documentation now emphasizes that yylex and yyerror must be
1426 declared before use. C99 requires this.
d1de5372 1427
dc546b0f
PE
1428 - Bison now parses C99 lexical constructs like UCNs and
1429 backslash-newline within C escape sequences, as POSIX 1003.1-2001 requires.
d1de5372 1430
dc546b0f
PE
1431 - File names are properly escaped in C output. E.g., foo\bar.y is
1432 output as "foo\\bar.y".
6780ca7a 1433
dc546b0f 1434 - Yacc command and library now available
e4ab1254 1435 The Bison distribution now installs a "yacc" command, as POSIX requires.
dc546b0f
PE
1436 Also, Bison now installs a small library liby.a containing
1437 implementations of Yacc-compatible yyerror and main functions.
1438 This library is normally not useful, but POSIX requires it.
6e649e65 1439
dc546b0f 1440 - Type clashes now generate warnings, not errors.
6e649e65 1441
dc546b0f
PE
1442 - If the user does not define YYSTYPE as a macro, Bison now declares it
1443 using typedef instead of defining it as a macro.
1444 For consistency, YYLTYPE is also declared instead of defined.
9501dc6e 1445
d6fb461d 1446** Other compatibility issues
886a425c 1447
e4ab1254
AD
1448 - %union directives can now have a tag before the "{", e.g., the
1449 directive "%union foo {...}" now generates the C code
1450 "typedef union foo { ... } YYSTYPE;"; this is for Yacc compatibility.
1451 The default union tag is "YYSTYPE", for compatibility with Solaris 9 Yacc.
1452 For consistency, YYLTYPE's struct tag is now "YYLTYPE" not "yyltype".
dc546b0f 1453 This is for compatibility with both Yacc and Bison 1.35.
72f889cc 1454
e4ab1254 1455 - ";" is output before the terminating "}" of an action, for
dc546b0f 1456 compatibility with Bison 1.35.
886a425c 1457
dc546b0f 1458 - Bison now uses a Yacc-style format for conflict reports, e.g.,
e4ab1254 1459 "conflicts: 2 shift/reduce, 1 reduce/reduce".
437c2d80 1460
e4ab1254 1461 - "yystype" and "yyltype" are now obsolescent macros instead of being
dc546b0f
PE
1462 typedefs or tags; they are no longer documented and are planned to be
1463 withdrawn in a future release.
2a8d363a 1464
d6fb461d 1465** GLR parser notes
2a8d363a 1466
dc546b0f
PE
1467 - GLR and inline
1468 Users of Bison have to decide how they handle the portability of the
e4ab1254 1469 C keyword "inline".
959e5f51 1470
e4ab1254
AD
1471 - "parsing stack overflow..." -> "parser stack overflow"
1472 GLR parsers now report "parser stack overflow" as per the Bison manual.
900c5db5 1473
18ad57b3
AD
1474** %parse-param and %lex-param
1475 The macros YYPARSE_PARAM and YYLEX_PARAM provide a means to pass
1476 additional context to yyparse and yylex. They suffer from several
1477 shortcomings:
1478
1479 - a single argument only can be added,
1480 - their types are weak (void *),
242cc08e 1481 - this context is not passed to ancillary functions such as yyerror,
18ad57b3
AD
1482 - only yacc.c parsers support them.
1483
1484 The new %parse-param/%lex-param directives provide a more precise control.
1485 For instance:
1486
1487 %parse-param {int *nastiness}
1488 %lex-param {int *nastiness}
1489 %parse-param {int *randomness}
1490
1491 results in the following signatures:
1492
1493 int yylex (int *nastiness);
1494 int yyparse (int *nastiness, int *randomness);
1495
1496 or, if both %pure-parser and %locations are used:
1497
1498 int yylex (YYSTYPE *lvalp, YYLTYPE *llocp, int *nastiness);
1499 int yyparse (int *nastiness, int *randomness);
1500
d6fb461d 1501** Bison now warns if it detects conflicting outputs to the same file,
e4ab1254 1502 e.g., it generates a warning for "bison -d -o foo.h foo.y" since
dc546b0f 1503 that command outputs both code and header to foo.h.
6e40b4eb 1504
d6fb461d 1505** #line in output files
dc546b0f 1506 - --no-line works properly.
6e40b4eb 1507
d6fb461d 1508** Bison can no longer be built by a K&R C compiler; it requires C89 or
6e40b4eb
AD
1509 later to be built. This change originally took place a few versions
1510 ago, but nobody noticed until we recently asked someone to try
1511 building Bison with a K&R C compiler.
d600ee67 1512\f
d6fb461d 1513* Changes in version 1.75, 2002-10-14:
7933f2b5 1514
d6fb461d 1515** Bison should now work on 64-bit hosts.
7933f2b5 1516
d6fb461d 1517** Indonesian translation thanks to Tedi Heriyanto.
7933f2b5 1518
d6fb461d 1519** GLR parsers
f50adbbd
AD
1520 Fix spurious parse errors.
1521
d6fb461d 1522** Pure parsers
f50adbbd
AD
1523 Some people redefine yyerror to steal yyparse' private variables.
1524 Reenable this trick until an official feature replaces it.
1525
d6fb461d 1526** Type Clashes
d90c934c
AD
1527 In agreement with POSIX and with other Yaccs, leaving a default
1528 action is valid when $$ is untyped, and $1 typed:
1529
e29f0771 1530 untyped: ... typed;
d90c934c
AD
1531
1532 but the converse remains an error:
1533
e29f0771 1534 typed: ... untyped;
d90c934c 1535
d6fb461d 1536** Values of mid-rule actions
d90c934c
AD
1537 The following code:
1538
e29f0771 1539 foo: { ... } { $$ = $1; } ...
d90c934c
AD
1540
1541 was incorrectly rejected: $1 is defined in the second mid-rule
1542 action, and is equal to the $$ of the first mid-rule action.
d600ee67 1543\f
d6fb461d 1544* Changes in version 1.50, 2002-10-04:
adc8c848 1545
d6fb461d 1546** GLR parsing
676385e2
PH
1547 The declaration
1548 %glr-parser
1549 causes Bison to produce a Generalized LR (GLR) parser, capable of handling
1550 almost any context-free grammar, ambiguous or not. The new declarations
e8832397 1551 %dprec and %merge on grammar rules allow parse-time resolution of
676385e2
PH
1552 ambiguities. Contributed by Paul Hilfinger.
1553
7933f2b5 1554 Unfortunately Bison 1.50 does not work properly on 64-bit hosts
420f93c8
PE
1555 like the Alpha, so please stick to 32-bit hosts for now.
1556
d6fb461d 1557** Output Directory
8c165d89 1558 When not in Yacc compatibility mode, when the output file was not
e4ab1254
AD
1559 specified, running "bison foo/bar.y" created "foo/bar.c". It
1560 now creates "bar.c".
8c165d89 1561
d6fb461d 1562** Undefined token
007a50a4 1563 The undefined token was systematically mapped to 2 which prevented
e88dbdbf 1564 the use of 2 by the user. This is no longer the case.
007a50a4 1565
d6fb461d 1566** Unknown token numbers
e88dbdbf 1567 If yylex returned an out of range value, yyparse could die. This is
007a50a4
AD
1568 no longer the case.
1569
d6fb461d 1570** Error token
e88dbdbf 1571 According to POSIX, the error token must be 256.
23c5a174
AD
1572 Bison extends this requirement by making it a preference: *if* the
1573 user specified that one of her tokens is numbered 256, then error
1574 will be mapped onto another number.
1575
d6fb461d 1576** Verbose error messages
e4ab1254 1577 They no longer report "..., expecting error or..." for states where
217598da
AD
1578 error recovery is possible.
1579
d6fb461d 1580** End token
e4ab1254 1581 Defaults to "$end" instead of "$".
217598da 1582
d6fb461d 1583** Error recovery now conforms to documentation and to POSIX
68cd8af3
PE
1584 When a Bison-generated parser encounters a syntax error, it now pops
1585 the stack until it finds a state that allows shifting the error
1586 token. Formerly, it popped the stack until it found a state that
1587 allowed some non-error action other than a default reduction on the
1588 error token. The new behavior has long been the documented behavior,
1589 and has long been required by POSIX. For more details, please see
337116ba
PE
1590 Paul Eggert, "Reductions during Bison error handling" (2002-05-20)
1591 <http://lists.gnu.org/archive/html/bug-bison/2002-05/msg00038.html>.
68cd8af3 1592
d6fb461d 1593** Traces
5504898e
AD
1594 Popped tokens and nonterminals are now reported.
1595
d6fb461d 1596** Larger grammars
a861a339
PE
1597 Larger grammars are now supported (larger token numbers, larger grammar
1598 size (= sum of the LHS and RHS lengths), larger LALR tables).
1599 Formerly, many of these numbers ran afoul of 16-bit limits;
1600 now these limits are 32 bits on most hosts.
355e7c1c 1601
d6fb461d 1602** Explicit initial rule
643a5994
AD
1603 Bison used to play hacks with the initial rule, which the user does
1604 not write. It is now explicit, and visible in the reports and
1605 graphs as rule 0.
23c5a174 1606
d6fb461d 1607** Useless rules
643a5994 1608 Before, Bison reported the useless rules, but, although not used,
77714df2 1609 included them in the parsers. They are now actually removed.
23c5a174 1610
d6fb461d 1611** Useless rules, useless nonterminals
6b98e4b5
AD
1612 They are now reported, as a warning, with their locations.
1613
d6fb461d 1614** Rules never reduced
e8832397
AD
1615 Rules that can never be reduced because of conflicts are now
1616 reported.
1617
e4ab1254 1618** Incorrect "Token not used"
11652ab3
AD
1619 On a grammar such as
1620
e29f0771
AD
1621 %token useless useful
1622 %%
1623 exp: '0' %prec useful;
11652ab3
AD
1624
1625 where a token was used to set the precedence of the last rule,
e4ab1254 1626 bison reported both "useful" and "useless" as useless tokens.
11652ab3 1627
d6fb461d 1628** Revert the C++ namespace changes introduced in 1.31
77714df2 1629 as they caused too many portability hassles.
0179dd65 1630
d6fb461d 1631** Default locations
b2d52318
AD
1632 By an accident of design, the default computation of @$ was
1633 performed after another default computation was performed: @$ = @1.
1634 The latter is now removed: YYLLOC_DEFAULT is fully responsible of
1635 the computation of @$.
adc8c848 1636
d6fb461d 1637** Token end-of-file
b7c49edf
AD
1638 The token end of file may be specified by the user, in which case,
1639 the user symbol is used in the reports, the graphs, and the verbose
e4ab1254 1640 error messages instead of "$end", which remains being the default.
b7c49edf 1641 For instance
e29f0771 1642 %token MYEOF 0
b7c49edf 1643 or
e29f0771 1644 %token MYEOF 0 "end of file"
fdbcd8e2 1645
d6fb461d 1646** Semantic parser
fdbcd8e2
AD
1647 This old option, which has been broken for ages, is removed.
1648
d6fb461d 1649** New translations
a861a339 1650 Brazilian Portuguese, thanks to Alexandre Folle de Menezes.
84614e13
AD
1651 Croatian, thanks to Denis Lackovic.
1652
d6fb461d 1653** Incorrect token definitions
e4ab1254
AD
1654 When given
1655 %token 'a' "A"
1656 bison used to output
1657 #define 'a' 65
b87f8b21 1658
d6fb461d 1659** Token definitions as enums
77714df2
AD
1660 Tokens are output both as the traditional #define's, and, provided
1661 the compiler supports ANSI C or is a C++ compiler, as enums.
e88dbdbf 1662 This lets debuggers display names instead of integers.
77714df2 1663
d6fb461d 1664** Reports
ec3bc396
AD
1665 In addition to --verbose, bison supports --report=THINGS, which
1666 produces additional information:
b408954b
AD
1667 - itemset
1668 complete the core item sets with their closure
e4ab1254 1669 - lookahead [changed to "look-ahead" in 1.875e through 2.3, but changed back]
9e6e7ed2 1670 explicitly associate lookahead tokens to items
b408954b
AD
1671 - solved
1672 describe shift/reduce conflicts solving.
1673 Bison used to systematically output this information on top of
1674 the report. Solved conflicts are now attached to their states.
ec3bc396 1675
d6fb461d 1676** Type clashes
9af3fbce
AD
1677 Previous versions don't complain when there is a type clash on
1678 the default action if the rule has a mid-rule action, such as in:
1679
e29f0771
AD
1680 %type <foo> bar
1681 %%
1682 bar: '0' {} '0';
9af3fbce
AD
1683
1684 This is fixed.
a861a339 1685
d6fb461d 1686** GNU M4 is now required when using Bison.
f987e9d2 1687\f
d6fb461d 1688* Changes in version 1.35, 2002-03-25:
76551463 1689
d6fb461d 1690** C Skeleton
76551463
AD
1691 Some projects use Bison's C parser with C++ compilers, and define
1692 YYSTYPE as a class. The recent adjustment of C parsers for data
1693 alignment and 64 bit architectures made this impossible.
1694
1695 Because for the time being no real solution for C++ parser
1696 generation exists, kludges were implemented in the parser to
1697 maintain this use. In the future, when Bison has C++ parsers, this
1698 kludge will be disabled.
1699
1700 This kludge also addresses some C++ problems when the stack was
1701 extended.
76551463 1702\f
d6fb461d 1703* Changes in version 1.34, 2002-03-12:
76551463 1704
d6fb461d 1705** File name clashes are detected
76551463 1706 $ bison foo.y -d -o foo.x
e4ab1254 1707 fatal error: header and parser would both be named "foo.x"
76551463 1708
e4ab1254 1709** A missing ";" at the end of a rule triggers a warning
76551463
AD
1710 In accordance with POSIX, and in agreement with other
1711 Yacc implementations, Bison will mandate this semicolon in the near
1712 future. This eases the implementation of a Bison parser of Bison
1713 grammars by making this grammar LALR(1) instead of LR(2). To
1714 facilitate the transition, this release introduces a warning.
1715
d6fb461d 1716** Revert the C++ namespace changes introduced in 1.31, as they caused too
76551463
AD
1717 many portability hassles.
1718
d6fb461d 1719** DJGPP support added.
76551463 1720
d6fb461d 1721** Fix test suite portability problems.
76551463 1722\f
d6fb461d 1723* Changes in version 1.33, 2002-02-07:
76551463 1724
d6fb461d 1725** Fix C++ issues
76551463
AD
1726 Groff could not be compiled for the definition of size_t was lacking
1727 under some conditions.
1728
d6fb461d 1729** Catch invalid @n
76551463
AD
1730 As is done with $n.
1731\f
d6fb461d 1732* Changes in version 1.32, 2002-01-23:
76551463 1733
d6fb461d 1734** Fix Yacc output file names
76551463 1735
d6fb461d 1736** Portability fixes
76551463 1737
d6fb461d 1738** Italian, Dutch translations
76551463 1739\f
d6fb461d 1740* Changes in version 1.31, 2002-01-14:
52d1aeee 1741
d6fb461d 1742** Many Bug Fixes
52d1aeee 1743
d6fb461d 1744** GNU Gettext and %expect
52d1aeee
MA
1745 GNU Gettext asserts 10 s/r conflicts, but there are 7. Now that
1746 Bison dies on incorrect %expectations, we fear there will be
1747 too many bug reports for Gettext, so _for the time being_, %expect
e4ab1254 1748 does not trigger an error when the input file is named "plural.y".
52d1aeee 1749
d6fb461d 1750** Use of alloca in parsers
52d1aeee
MA
1751 If YYSTACK_USE_ALLOCA is defined to 0, then the parsers will use
1752 malloc exclusively. Since 1.29, but was not NEWS'ed.
1753
1754 alloca is used only when compiled with GCC, to avoid portability
1755 problems as on AIX.
1756
d6fb461d 1757** yyparse now returns 2 if memory is exhausted; formerly it dumped core.
b47dbebe 1758
d6fb461d 1759** When the generated parser lacks debugging code, YYDEBUG is now 0
52d1aeee
MA
1760 (as POSIX requires) instead of being undefined.
1761
d6fb461d 1762** User Actions
52d1aeee
MA
1763 Bison has always permitted actions such as { $$ = $1 }: it adds the
1764 ending semicolon. Now if in Yacc compatibility mode, the semicolon
1765 is no longer output: one has to write { $$ = $1; }.
1766
d6fb461d 1767** Better C++ compliance
52d1aeee 1768 The output parsers try to respect C++ namespaces.
76551463 1769 [This turned out to be a failed experiment, and it was reverted later.]
52d1aeee 1770
d6fb461d 1771** Reduced Grammars
52d1aeee
MA
1772 Fixed bugs when reporting useless nonterminals.
1773
d6fb461d 1774** 64 bit hosts
52d1aeee
MA
1775 The parsers work properly on 64 bit hosts.
1776
d6fb461d 1777** Error messages
52d1aeee
MA
1778 Some calls to strerror resulted in scrambled or missing error messages.
1779
d6fb461d 1780** %expect
52d1aeee
MA
1781 When the number of shift/reduce conflicts is correct, don't issue
1782 any warning.
1783
d6fb461d 1784** The verbose report includes the rule line numbers.
52d1aeee 1785
d6fb461d 1786** Rule line numbers are fixed in traces.
52d1aeee 1787
d6fb461d 1788** Swedish translation
52d1aeee 1789
d6fb461d 1790** Parse errors
52d1aeee
MA
1791 Verbose parse error messages from the parsers are better looking.
1792 Before: parse error: unexpected `'/'', expecting `"number"' or `'-'' or `'(''
1793 Now: parse error: unexpected '/', expecting "number" or '-' or '('
1794
d6fb461d 1795** Fixed parser memory leaks.
52d1aeee
MA
1796 When the generated parser was using malloc to extend its stacks, the
1797 previous allocations were not freed.
1798
d6fb461d 1799** Fixed verbose output file.
52d1aeee
MA
1800 Some newlines were missing.
1801 Some conflicts in state descriptions were missing.
1802
d6fb461d 1803** Fixed conflict report.
52d1aeee
MA
1804 Option -v was needed to get the result.
1805
d6fb461d 1806** %expect
52d1aeee
MA
1807 Was not used.
1808 Mismatches are errors, not warnings.
1809
d6fb461d 1810** Fixed incorrect processing of some invalid input.
52d1aeee 1811
d6fb461d 1812** Fixed CPP guards: 9foo.h uses BISON_9FOO_H instead of 9FOO_H.
52d1aeee 1813
d6fb461d 1814** Fixed some typos in the documentation.
52d1aeee 1815
d6fb461d 1816** %token MY_EOF 0 is supported.
52d1aeee
MA
1817 Before, MY_EOF was silently renumbered as 257.
1818
d6fb461d 1819** doc/refcard.tex is updated.
52d1aeee 1820
d6fb461d 1821** %output, %file-prefix, %name-prefix.
52d1aeee
MA
1822 New.
1823
d6fb461d 1824** --output
e4ab1254 1825 New, aliasing "--output-file".
52d1aeee 1826\f
d6fb461d 1827* Changes in version 1.30, 2001-10-26:
342b8b6e 1828
e4ab1254
AD
1829** "--defines" and "--graph" have now an optional argument which is the
1830 output file name. "-d" and "-g" do not change; they do not take any
342b8b6e
AD
1831 argument.
1832
e4ab1254 1833** "%source_extension" and "%header_extension" are removed, failed
342b8b6e
AD
1834 experiment.
1835
d6fb461d 1836** Portability fixes.
f987e9d2 1837\f
d6fb461d 1838* Changes in version 1.29, 2001-09-07:
342b8b6e 1839
d6fb461d 1840** The output file does not define const, as this caused problems when used
342b8b6e
AD
1841 with common autoconfiguration schemes. If you still use ancient compilers
1842 that lack const, compile with the equivalent of the C compiler option
e4ab1254 1843 "-Dconst=". Autoconf's AC_C_CONST macro provides one way to do this.
342b8b6e 1844
e4ab1254 1845** Added "-g" and "--graph".
f87a2205 1846
d6fb461d 1847** The Bison manual is now distributed under the terms of the GNU FDL.
f2b5126e 1848
d6fb461d 1849** The input and the output files has automatically a similar extension.
234a3be3 1850
d6fb461d 1851** Russian translation added.
f87a2205 1852
d6fb461d 1853** NLS support updated; should hopefully be less troublesome.
f87a2205 1854
d6fb461d 1855** Added the old Bison reference card.
c33638bb 1856
e4ab1254 1857** Added "--locations" and "%locations".
6deb4447 1858
e4ab1254 1859** Added "-S" and "--skeleton".
cd5bd6ac 1860
e4ab1254 1861** "%raw", "-r", "--raw" is disabled.
62ab6972 1862
d6fb461d 1863** Special characters are escaped when output. This solves the problems
cd5bd6ac
AD
1864 of the #line lines with path names including backslashes.
1865
d6fb461d 1866** New directives.
e4ab1254
AD
1867 "%yacc", "%fixed_output_files", "%defines", "%no_parser", "%verbose",
1868 "%debug", "%source_extension" and "%header_extension".
f987e9d2 1869
d6fb461d 1870** @$
f987e9d2 1871 Automatic location tracking.
f87a2205 1872\f
d6fb461d 1873* Changes in version 1.28, 1999-07-06:
d2e00347 1874
d6fb461d 1875** Should compile better now with K&R compilers.
d2e00347 1876
d6fb461d 1877** Added NLS.
d2e00347 1878
d6fb461d 1879** Fixed a problem with escaping the double quote character.
d2e00347 1880
d6fb461d 1881** There is now a FAQ.
d2e00347 1882\f
d6fb461d 1883* Changes in version 1.27:
5c31c3c2 1884
d6fb461d 1885** The make rule which prevented bison.simple from being created on
5c31c3c2
JT
1886 some systems has been fixed.
1887\f
d6fb461d 1888* Changes in version 1.26:
4be07551 1889
7e508a2b 1890** Bison now uses Automake.
4be07551 1891
d6fb461d 1892** New mailing lists: <bug-bison@gnu.org> and <help-bison@gnu.org>.
4be07551 1893
d6fb461d 1894** Token numbers now start at 257 as previously documented, not 258.
4be07551 1895
d6fb461d 1896** Bison honors the TMPDIR environment variable.
4be07551 1897
d6fb461d 1898** A couple of buffer overruns have been fixed.
f51dbca1 1899
d6fb461d 1900** Problems when closing files should now be reported.
f51dbca1 1901
d6fb461d 1902** Generated parsers should now work even on operating systems which do
f51dbca1 1903 not provide alloca().
4be07551 1904\f
d6fb461d 1905* Changes in version 1.25, 1995-10-16:
df8878c5 1906
d6fb461d 1907** Errors in the input grammar are not fatal; Bison keeps reading
df8878c5 1908the grammar file, and reports all the errors found in it.
8c44d3ec 1909
d6fb461d 1910** Tokens can now be specified as multiple-character strings: for
df8878c5 1911example, you could use "<=" for a token which looks like <=, instead
7e508a2b 1912of choosing a name like LESSEQ.
df8878c5 1913
d6fb461d 1914** The %token_table declaration says to write a table of tokens (names
df8878c5
RS
1915and numbers) into the parser file. The yylex function can use this
1916table to recognize multiple-character string tokens, or for other
1917purposes.
1918
d6fb461d 1919** The %no_lines declaration says not to generate any #line preprocessor
df8878c5
RS
1920directives in the parser file.
1921
d6fb461d 1922** The %raw declaration says to use internal Bison token numbers, not
df8878c5
RS
1923Yacc-compatible token numbers, when token names are defined as macros.
1924
d6fb461d 1925** The --no-parser option produces the parser tables without including
df8878c5
RS
1926the parser engine; a project can now use its own parser engine.
1927The actions go into a separate file called NAME.act, in the form of
1928a switch statement body.
1929\f
d6fb461d 1930* Changes in version 1.23:
6780ca7a 1931
4d019228
DM
1932The user can define YYPARSE_PARAM as the name of an argument to be
1933passed into yyparse. The argument should have type void *. It should
1934actually point to an object. Grammar actions can access the variable
1935by casting it to the proper pointer type.
6780ca7a 1936
6780ca7a 1937Line numbers in output file corrected.
6780ca7a 1938\f
d6fb461d 1939* Changes in version 1.22:
6780ca7a
DM
1940
1941--help option added.
6780ca7a 1942\f
d6fb461d 1943* Changes in version 1.20:
6780ca7a
DM
1944
1945Output file does not redefine const for C++.
9f4503d6 1946
76551463
AD
1947-----
1948
c932d613 1949Copyright (C) 1995-2012 Free Software Foundation, Inc.
76551463 1950
8defe11b 1951This file is part of Bison, the GNU Parser Generator.
76551463 1952
f16b0819 1953This program is free software: you can redistribute it and/or modify
76551463 1954it under the terms of the GNU General Public License as published by
f16b0819
PE
1955the Free Software Foundation, either version 3 of the License, or
1956(at your option) any later version.
76551463 1957
f16b0819 1958This program is distributed in the hope that it will be useful,
76551463
AD
1959but WITHOUT ANY WARRANTY; without even the implied warranty of
1960MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
1961GNU General Public License for more details.
1962
1963You should have received a copy of the GNU General Public License
f16b0819 1964along with this program. If not, see <http://www.gnu.org/licenses/>.
7e508a2b
AD
1965
1966 LocalWords: yacc YYBACKUP glr GCC lalr ArrayIndexOutOfBoundsException nullptr
1967 LocalWords: cplusplus liby rpl fprintf mfcalc Wyacc stmt cond expr mk sym lr
1968 LocalWords: IELR ielr Lookahead YYERROR nonassoc LALR's api lookaheads yychar
1969 LocalWords: destructor lookahead YYRHSLOC YYLLOC Rhs ifndef YYFAIL cpp sr rr
1970 LocalWords: preprocessor initializer Wno Wnone Werror FreeBSD prec livelocks
1971 LocalWords: Solaris AIX UX RHEL Tru LHS gcc's Wundef YYENABLE NLS YYLTYPE VCG
1972 LocalWords: yyerror cpp's Wunused yylval yylloc prepend yyparse yylex yypush
1973 LocalWords: Graphviz xml nonterminals midrule destructor's YYSTYPE typedef ly
1974 LocalWords: CHR chr printf stdout namespace preprocessing enum pre include's
1975 LocalWords: YYRECOVERING nonfree destructors YYABORT YYACCEPT params enums de
1976 LocalWords: struct yystype DJGPP lex param Haible NUM alloca YYSTACK NUL goto
1977 LocalWords: YYMAXDEPTH Unescaped UCNs YYLTYPE's yyltype typedefs inline Yaccs
1978 LocalWords: Heriyanto Reenable dprec Hilfinger Eggert MYEOF Folle Menezes EOF
242cc08e 1979 LocalWords: Lackovic define's itemset Groff Gettext malloc NEWS'ed YYDEBUG YY
7e508a2b 1980 LocalWords: namespaces strerror const autoconfiguration Dconst Autoconf's FDL
242cc08e
AD
1981 LocalWords: Automake TMPDIR LESSEQ ylwrap endif yydebug YYTOKEN YYLSP ival hh
1982 LocalWords: extern YYTOKENTYPE TOKENTYPE yytokentype tokentype STYPE lval pdf
7287be84
AD
1983 LocalWords: lang yyoutput dvi html ps POSIX lvalp llocp calc yyo fval Wmaybe
1984 LocalWords: yyvsp pragmas noreturn java's
7e508a2b
AD
1985
1986Local Variables:
1987mode: outline
e4ab1254 1988fill-column: 76
7e508a2b 1989End: