yacc.c: always initialize yylloc
[bison.git] / NEWS
CommitLineData
ed7658fe 1GNU Bison NEWS
3af4feb2 2
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3* Noteworthy changes in release ?.? (????-??-??) [?]
4
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5** Bug fixes
6
7 Warnings about uninitialized yylloc in yyparse have been fixed.
8
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9** Documentation
10
11 The sections about shift/reduce and reduce/reduce conflicts resolution
12 have been fixed and extended.
9d2423f5 13
9d3f7eaf 14* Noteworthy changes in release 2.6.5 (2012-11-07) [stable]
6f1360bd 15
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16 We consider compiler warnings about Bison generated parsers to be bugs.
17 Rather than working around them in your own project, please consider
18 reporting them to us.
19
20** Bug fixes
21
22 Warnings about uninitialized yylval and/or yylloc for push parsers with a
23 pure interface have been fixed for GCC 4.0 up to 4.8, and Clang 2.9 to
24 3.2.
25
26 Other issues in the test suite have been addressed.
6f1360bd 27
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28 Nul characters are correctly displayed in error messages.
29
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30 When possible, yylloc is correctly initialized before calling yylex. It
31 is no longer necessary to initialize it in the %initial-action.
32
0ac15849 33* Noteworthy changes in release 2.6.4 (2012-10-23) [stable]
a4eb820f 34
468455e1 35 Bison 2.6.3's --version was incorrect. This release fixes this issue.
a4eb820f 36
6eb8f74f 37* Noteworthy changes in release 2.6.3 (2012-10-22) [stable]
933ec544 38
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39** Bug fixes
40
9a50c55a 41 Bugs and portability issues in the test suite have been fixed.
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42
43 Some errors in translations have been addressed, and --help now directs
44 users to the appropriate place to report them.
45
46 Stray Info files shipped by accident are removed.
47
48 Incorrect definitions of YY_, issued by yacc.c when no parser header is
49 generated, are removed.
933ec544 50
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51 All the generated headers are self-contained.
52
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53** Header guards (yacc.c, glr.c, glr.cc)
54
55 In order to avoid collisions, the header guards are now
56 YY_<PREFIX>_<FILE>_INCLUDED, instead of merely <PREFIX>_<FILE>.
57 For instance the header generated from
58
59 %define api.prefix "calc"
60 %defines "lib/parse.h"
61
62 will use YY_CALC_LIB_PARSE_H_INCLUDED as guard.
63
7b70847e 64** Fix compiler warnings in the generated parser (yacc.c, glr.c)
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65
66 The compilation of pure parsers (%define api.pure) can trigger GCC
67 warnings such as:
68
69 input.c: In function 'yyparse':
70 input.c:1503:12: warning: 'yylval' may be used uninitialized in this
71 function [-Wmaybe-uninitialized]
72 *++yyvsp = yylval;
73 ^
74
75 This is now fixed; pragmas to avoid these warnings are no longer needed.
76
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77 Warnings from clang ("equality comparison with extraneous parentheses" and
78 "function declared 'noreturn' should not return") have also been
79 addressed.
80
e1eeecd3 81* Noteworthy changes in release 2.6.2 (2012-08-03) [stable]
9c26b8fc 82
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83** Bug fixes
84
85 Buffer overruns, complaints from Flex, and portability issues in the test
86 suite have been fixed.
87
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88** Spaces in %lex- and %parse-param (lalr1.cc, glr.cc)
89
90 Trailing end-of-lines in %parse-param or %lex-param would result in
91 invalid C++. This is fixed.
9c26b8fc 92
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93** Spurious spaces and end-of-lines
94
95 The generated files no longer end (nor start) with empty lines.
96
77b214ef 97* Noteworthy changes in release 2.6.1 (2012-07-30) [stable]
a4107f24 98
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99 Bison no longer executes user-specified M4 code when processing a grammar.
100
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101** Future Changes
102
103 In addition to the removal of the features announced in Bison 2.6, the
104 next major release will remove the "Temporary hack for adding a semicolon
105 to the user action", as announced in the release 2.5. Instead of:
106
107 exp: exp "+" exp { $$ = $1 + $3 };
108
109 write:
110
111 exp: exp "+" exp { $$ = $1 + $3; };
112
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113** Bug fixes
114
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115*** Type names are now properly escaped.
116
117*** glr.cc: set_debug_level and debug_level work as expected.
a4107f24 118
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119*** Stray @ or $ in actions
120
121 While Bison used to warn about stray $ or @ in action rules, it did not
122 for other actions such as printers, destructors, or initial actions. It
123 now does.
124
cd735a8c 125** Type names in actions
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126
127 For consistency with rule actions, it is now possible to qualify $$ by a
cd735a8c 128 type-name in destructors, printers, and initial actions. For instance:
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129
130 %printer { fprintf (yyo, "(%d, %f)", $<ival>$, $<fval>$); } <*> <>;
131
132 will display two values for each typed and untyped symbol (provided
cd735a8c 133 that YYSTYPE has both "ival" and "fval" fields).
4982f078 134
1505e8bb 135* Noteworthy changes in release 2.6 (2012-07-19) [stable]
ad6b775f 136
c2425191 137** Future Changes
0f11eec2 138
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139 The next major release of Bison will drop support for the following
140 deprecated features. Please report disagreements to bug-bison@gnu.org.
0f11eec2 141
aaf61036 142*** K&R C parsers
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143
144 Support for generating parsers in K&R C will be removed. Parsers
242cc08e 145 generated for C support ISO C90, and are tested with ISO C99 and ISO C11
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146 compilers.
147
258cddbc 148*** Features deprecated since Bison 1.875
55d1006f 149
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150 The definitions of yystype and yyltype will be removed; use YYSTYPE and
151 YYLTYPE.
55d1006f 152
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153 YYPARSE_PARAM and YYLEX_PARAM, deprecated in favor of %parse-param and
154 %lex-param, will no longer be supported.
155
156 Support for the preprocessor symbol YYERROR_VERBOSE will be removed, use
157 %error-verbose.
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158
159*** The generated header will be included (yacc.c)
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160
161 Instead of duplicating the content of the generated header (definition of
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162 YYSTYPE, yyparse declaration etc.), the generated parser will include it,
163 as is already the case for GLR or C++ parsers. This change is deferred
164 because existing versions of ylwrap (e.g., Automake 1.12.1) do not support
165 it.
0f11eec2 166
c2425191 167** Generated Parser Headers
56ca3d8f 168
258cddbc 169*** Guards (yacc.c, glr.c, glr.cc)
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170
171 The generated headers are now guarded, as is already the case for C++
242cc08e 172 parsers (lalr1.cc). For instance, with --defines=foo.h:
c3e9f08f 173
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174 #ifndef YY_FOO_H
175 # define YY_FOO_H
176 ...
177 #endif /* !YY_FOO_H */
c3e9f08f 178
258cddbc 179*** New declarations (yacc.c, glr.c)
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180
181 The generated header now declares yydebug and yyparse. Both honor
182 --name-prefix=bar_, and yield
183
e29f0771 184 int bar_parse (void);
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185
186 rather than
187
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188 #define yyparse bar_parse
189 int yyparse (void);
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190
191 in order to facilitate the inclusion of several parser headers inside a
192 single compilation unit.
c3e9f08f 193
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194*** Exported symbols in C++
195
196 The symbols YYTOKEN_TABLE and YYERROR_VERBOSE, which were defined in the
197 header, are removed, as they prevent the possibility of including several
198 generated headers from a single compilation unit.
199
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200*** YYLSP_NEEDED
201
202 For the same reasons, the undocumented and unused macro YYLSP_NEEDED is no
203 longer defined.
204
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205** New %define variable: api.prefix
206
207 Now that the generated headers are more complete and properly protected
208 against multiple inclusions, constant names, such as YYSTYPE are a
209 problem. While yyparse and others are properly renamed by %name-prefix,
210 YYSTYPE, YYDEBUG and others have never been affected by it. Because it
211 would introduce backward compatibility issues in projects not expecting
212 YYSTYPE to be renamed, instead of changing the behavior of %name-prefix,
213 it is deprecated in favor of a new %define variable: api.prefix.
214
215 The following examples compares both:
216
217 %name-prefix "bar_" | %define api.prefix "bar_"
218 %token <ival> FOO %token <ival> FOO
219 %union { int ival; } %union { int ival; }
220 %% %%
221 exp: 'a'; exp: 'a';
222
223 bison generates:
224
225 #ifndef BAR_FOO_H #ifndef BAR_FOO_H
226 # define BAR_FOO_H # define BAR_FOO_H
227
228 /* Enabling traces. */ /* Enabling traces. */
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229 # ifndef YYDEBUG | # ifndef BAR_DEBUG
230 > # if defined YYDEBUG
231 > # if YYDEBUG
232 > # define BAR_DEBUG 1
233 > # else
234 > # define BAR_DEBUG 0
235 > # endif
236 > # else
237 # define YYDEBUG 0 | # define BAR_DEBUG 0
238 > # endif
239 # endif | # endif
240
241 # if YYDEBUG | # if BAR_DEBUG
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242 extern int bar_debug; extern int bar_debug;
243 # endif # endif
244
245 /* Tokens. */ /* Tokens. */
246 # ifndef YYTOKENTYPE | # ifndef BAR_TOKENTYPE
247 # define YYTOKENTYPE | # define BAR_TOKENTYPE
248 enum yytokentype { | enum bar_tokentype {
249 FOO = 258 FOO = 258
250 }; };
251 # endif # endif
252
253 #if ! defined YYSTYPE \ | #if ! defined BAR_STYPE \
254 && ! defined YYSTYPE_IS_DECLARED | && ! defined BAR_STYPE_IS_DECLARED
255 typedef union YYSTYPE | typedef union BAR_STYPE
256 { {
257 int ival; int ival;
258 } YYSTYPE; | } BAR_STYPE;
259 # define YYSTYPE_IS_DECLARED 1 | # define BAR_STYPE_IS_DECLARED 1
260 #endif #endif
261
262 extern YYSTYPE bar_lval; | extern BAR_STYPE bar_lval;
263
264 int bar_parse (void); int bar_parse (void);
265
266 #endif /* !BAR_FOO_H */ #endif /* !BAR_FOO_H */
267
dfaac272 268* Noteworthy changes in release 2.5.1 (2012-06-05) [stable]
90dcd415 269
debe2c03 270** Future changes:
041308d0 271
e4ab1254 272 The next major release will drop support for generating parsers in K&R C.
ef51bfa7 273
466b4cf2 274** yacc.c: YYBACKUP works as expected.
94556574 275
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276** glr.c improvements:
277
278*** Location support is eliminated when not requested:
279
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280 GLR parsers used to include location-related code even when locations were
281 not requested, and therefore not even usable.
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282
283*** __attribute__ is preserved:
debe2c03 284
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285 __attribute__ is no longer disabled when __STRICT_ANSI__ is defined (i.e.,
286 when -std is passed to GCC).
debe2c03 287
466b4cf2 288** lalr1.java: several fixes:
041308d0 289
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290 The Java parser no longer throws ArrayIndexOutOfBoundsException if the
291 first token leads to a syntax error. Some minor clean ups.
041308d0 292
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293** Changes for C++:
294
295*** C++11 compatibility:
ef51bfa7 296
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297 C and C++ parsers use "nullptr" instead of "0" when __cplusplus is 201103L
298 or higher.
ef51bfa7 299
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300*** Header guards
301
302 The header files such as "parser.hh", "location.hh", etc. used a constant
303 name for preprocessor guards, for instance:
304
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305 #ifndef BISON_LOCATION_HH
306 # define BISON_LOCATION_HH
307 ...
308 #endif // !BISON_LOCATION_HH
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309
310 The inclusion guard is now computed from "PREFIX/FILE-NAME", where lower
311 case characters are converted to upper case, and series of
312 non-alphanumerical characters are converted to an underscore.
313
314 With "bison -o lang++/parser.cc", "location.hh" would now include:
315
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316 #ifndef YY_LANG_LOCATION_HH
317 # define YY_LANG_LOCATION_HH
318 ...
319 #endif // !YY_LANG_LOCATION_HH
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320
321*** C++ locations:
936c88d1 322
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323 The position and location constructors (and their initialize methods)
324 accept new arguments for line and column. Several issues in the
325 documentation were fixed.
936c88d1 326
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327** liby is no longer asking for "rpl_fprintf" on some platforms.
328
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329** Changes in the manual:
330
331*** %printer is documented
332
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333 The "%printer" directive, supported since at least Bison 1.50, is finally
334 documented. The "mfcalc" example is extended to demonstrate it.
7e508a2b 335
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336 For consistency with the C skeletons, the C++ parsers now also support
337 "yyoutput" (as an alias to "debug_stream ()").
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338
339*** Several improvements have been made:
466b4cf2 340
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341 The layout for grammar excerpts was changed to a more compact scheme.
342 Named references are motivated. The description of the automaton
343 description file (*.output) is updated to the current format. Incorrect
344 index entries were fixed. Some other errors were fixed.
466b4cf2 345
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346** Building bison:
347
348*** Conflicting prototypes with recent/modified Flex.
349
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350 Fixed build problems with the current, unreleased, version of Flex, and
351 some modified versions of 2.5.35, which have modified function prototypes.
466b4cf2 352
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353*** Warnings during the build procedure have been eliminated.
354
355*** Several portability problems in the test suite have been fixed:
466b4cf2 356
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357 This includes warnings with some compilers, unexpected behavior of tools
358 such as diff, warning messages from the test suite itself, etc.
466b4cf2 359
91aadcc7 360*** The install-pdf target works properly:
8ef26c2a 361
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362 Running "make install-pdf" (or -dvi, -html, -info, and -ps) no longer
363 halts in the middle of its course.
8ef26c2a 364
b2bc8a1b 365* Changes in version 2.5 (2011-05-14):
006faedf 366
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367** Grammar symbol names can now contain non-initial dashes:
368
369 Consistently with directives (such as %error-verbose) and with
370 %define variables (e.g. push-pull), grammar symbol names may contain
371 dashes in any position except the beginning. This is a GNU
372 extension over POSIX Yacc. Thus, use of this extension is reported
373 by -Wyacc and rejected in Yacc mode (--yacc).
374
3b1977ea 375** Named references:
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376
377 Historically, Yacc and Bison have supported positional references
378 ($n, $$) to allow access to symbol values from inside of semantic
379 actions code.
380
381 Starting from this version, Bison can also accept named references.
382 When no ambiguity is possible, original symbol names may be used
383 as named references:
384
ac3297d5 385 if_stmt : "if" cond_expr "then" then_stmt ';'
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386 { $if_stmt = mk_if_stmt($cond_expr, $then_stmt); }
387
388 In the more common case, explicit names may be declared:
389
ac3297d5 390 stmt[res] : "if" expr[cond] "then" stmt[then] "else" stmt[else] ';'
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391 { $res = mk_if_stmt($cond, $then, $else); }
392
f840c05a 393 Location information is also accessible using @name syntax. When
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394 accessing symbol names containing dots or dashes, explicit bracketing
395 ($[sym.1]) must be used.
396
f840c05a 397 These features are experimental in this version. More user feedback
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398 will help to stabilize them.
399
3b1977ea 400** IELR(1) and canonical LR(1):
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401
402 IELR(1) is a minimal LR(1) parser table generation algorithm. That
403 is, given any context-free grammar, IELR(1) generates parser tables
723206df 404 with the full language-recognition power of canonical LR(1) but with
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405 nearly the same number of parser states as LALR(1). This reduction
406 in parser states is often an order of magnitude. More importantly,
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407 because canonical LR(1)'s extra parser states may contain duplicate
408 conflicts in the case of non-LR(1) grammars, the number of conflicts
409 for IELR(1) is often an order of magnitude less as well. This can
410 significantly reduce the complexity of developing of a grammar.
411
412 Bison can now generate IELR(1) and canonical LR(1) parser tables in
413 place of its traditional LALR(1) parser tables, which remain the
414 default. You can specify the type of parser tables in the grammar
415 file with these directives:
416
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417 %define lr.type lalr
418 %define lr.type ielr
419 %define lr.type canonical-lr
34a6c2d1 420
6f04ee6c 421 The default-reduction optimization in the parser tables can also be
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422 adjusted using "%define lr.default-reductions". For details on both
423 of these features, see the new section "Tuning LR" in the Bison
6f04ee6c 424 manual.
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425
426 These features are experimental. More user feedback will help to
427 stabilize them.
428
6f04ee6c 429** LAC (Lookahead Correction) for syntax error handling:
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430
431 Canonical LR, IELR, and LALR can suffer from a couple of problems
432 upon encountering a syntax error. First, the parser might perform
433 additional parser stack reductions before discovering the syntax
6f04ee6c 434 error. Such reductions can perform user semantic actions that are
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435 unexpected because they are based on an invalid token, and they
436 cause error recovery to begin in a different syntactic context than
437 the one in which the invalid token was encountered. Second, when
6f04ee6c 438 verbose error messages are enabled (with %error-verbose or the
e4ab1254 439 obsolete "#define YYERROR_VERBOSE"), the expected token list in the
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440 syntax error message can both contain invalid tokens and omit valid
441 tokens.
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442
443 The culprits for the above problems are %nonassoc, default
444 reductions in inconsistent states, and parser state merging. Thus,
445 IELR and LALR suffer the most. Canonical LR can suffer only if
446 %nonassoc is used or if default reductions are enabled for
447 inconsistent states.
448
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449 LAC is a new mechanism within the parsing algorithm that solves
450 these problems for canonical LR, IELR, and LALR without sacrificing
451 %nonassoc, default reductions, or state merging. When LAC is in
452 use, canonical LR and IELR behave almost exactly the same for both
453 syntactically acceptable and syntactically unacceptable input.
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454 While LALR still does not support the full language-recognition
455 power of canonical LR and IELR, LAC at least enables LALR's syntax
456 error handling to correctly reflect LALR's language-recognition
457 power.
458
459 Currently, LAC is only supported for deterministic parsers in C.
460 You can enable LAC with the following directive:
461
462 %define parse.lac full
463
e4ab1254 464 See the new section "LAC" in the Bison manual for additional
6f04ee6c 465 details including a few caveats.
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466
467 LAC is an experimental feature. More user feedback will help to
468 stabilize it.
469
6ee881f6 470** %define improvements:
f37495f6 471
3b1977ea 472*** Can now be invoked via the command line:
4ecd3681 473
34d41938 474 Each of these command-line options
4ecd3681 475
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476 -D NAME[=VALUE]
477 --define=NAME[=VALUE]
478
479 -F NAME[=VALUE]
480 --force-define=NAME[=VALUE]
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481
482 is equivalent to this grammar file declaration
483
34d41938 484 %define NAME ["VALUE"]
4ecd3681 485
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486 except that the manner in which Bison processes multiple definitions
487 for the same NAME differs. Most importantly, -F and --force-define
488 quietly override %define, but -D and --define do not. For further
e4ab1254 489 details, see the section "Bison Options" in the Bison manual.
4ecd3681 490
3b1977ea 491*** Variables renamed:
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492
493 The following %define variables
494
495 api.push_pull
496 lr.keep_unreachable_states
497
498 have been renamed to
499
500 api.push-pull
501 lr.keep-unreachable-states
502
503 The old names are now deprecated but will be maintained indefinitely
504 for backward compatibility.
505
723206df 506*** Values no longer need to be quoted in the grammar file:
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507
508 If a %define value is an identifier, it no longer needs to be placed
509 within quotations marks. For example,
510
511 %define api.push-pull "push"
512
513 can be rewritten as
514
515 %define api.push-pull push
516
6ee881f6 517*** Unrecognized variables are now errors not warnings.
c046698e 518
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519*** Multiple invocations for any variable is now an error not a warning.
520
521** Unrecognized %code qualifiers are now errors not warnings.
522
523** Character literals not of length one:
524
525 Previously, Bison quietly converted all character literals to length
526 one. For example, without warning, Bison interpreted the operators in
527 the following grammar to be the same token:
528
529 exp: exp '++'
530 | exp '+' exp
531 ;
532
533 Bison now warns when a character literal is not of length one. In
534 some future release, Bison will start reporting an error instead.
535
536** Destructor calls fixed for lookaheads altered in semantic actions:
537
538 Previously for deterministic parsers in C, if a user semantic action
539 altered yychar, the parser in some cases used the old yychar value to
540 determine which destructor to call for the lookahead upon a syntax
541 error or upon parser return. This bug has been fixed.
542
543** C++ parsers use YYRHSLOC:
544
545 Similarly to the C parsers, the C++ parsers now define the YYRHSLOC
546 macro and use it in the default YYLLOC_DEFAULT. You are encouraged
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547 to use it. If, for instance, your location structure has "first"
548 and "last" members, instead of
6ee881f6 549
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550 # define YYLLOC_DEFAULT(Current, Rhs, N) \
551 do \
552 if (N) \
553 { \
554 (Current).first = (Rhs)[1].location.first; \
555 (Current).last = (Rhs)[N].location.last; \
556 } \
557 else \
558 { \
559 (Current).first = (Current).last = (Rhs)[0].location.last; \
560 } \
561 while (false)
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562
563 use:
564
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565 # define YYLLOC_DEFAULT(Current, Rhs, N) \
566 do \
567 if (N) \
568 { \
569 (Current).first = YYRHSLOC (Rhs, 1).first; \
570 (Current).last = YYRHSLOC (Rhs, N).last; \
571 } \
572 else \
573 { \
574 (Current).first = (Current).last = YYRHSLOC (Rhs, 0).last; \
575 } \
576 while (false)
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577
578** YYLLOC_DEFAULT in C++:
579
580 The default implementation of YYLLOC_DEFAULT used to be issued in
581 the header file. It is now output in the implementation file, after
582 the user %code sections so that its #ifndef guard does not try to
583 override the user's YYLLOC_DEFAULT if provided.
c046698e 584
3b1977ea 585** YYFAIL now produces warnings and Java parsers no longer implement it:
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586
587 YYFAIL has existed for many years as an undocumented feature of
588 deterministic parsers in C generated by Bison. More recently, it was
589 a documented feature of Bison's experimental Java parsers. As
590 promised in Bison 2.4.2's NEWS entry, any appearance of YYFAIL in a
591 semantic action now produces a deprecation warning, and Java parsers
592 no longer implement YYFAIL at all. For further details, including a
593 discussion of how to suppress C preprocessor warnings about YYFAIL
594 being unused, see the Bison 2.4.2 NEWS entry.
595
3b1977ea 596** Temporary hack for adding a semicolon to the user action:
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597
598 Previously, Bison appended a semicolon to every user action for
599 reductions when the output language defaulted to C (specifically, when
600 neither %yacc, %language, %skeleton, or equivalent command-line
601 options were specified). This allowed actions such as
602
603 exp: exp "+" exp { $$ = $1 + $3 };
604
605 instead of
606
607 exp: exp "+" exp { $$ = $1 + $3; };
608
609 As a first step in removing this misfeature, Bison now issues a
610 warning when it appends a semicolon. Moreover, in cases where Bison
611 cannot easily determine whether a semicolon is needed (for example, an
612 action ending with a cpp directive or a braced compound initializer),
613 it no longer appends one. Thus, the C compiler might now complain
614 about a missing semicolon where it did not before. Future releases of
615 Bison will cease to append semicolons entirely.
616
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617** Verbose syntax error message fixes:
618
e4ab1254 619 When %error-verbose or the obsolete "#define YYERROR_VERBOSE" is
6f04ee6c
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620 specified, syntax error messages produced by the generated parser
621 include the unexpected token as well as a list of expected tokens.
622 The effect of %nonassoc on these verbose messages has been corrected
623 in two ways, but a more complete fix requires LAC, described above:
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624
625*** When %nonassoc is used, there can exist parser states that accept no
626 tokens, and so the parser does not always require a lookahead token
627 in order to detect a syntax error. Because no unexpected token or
628 expected tokens can then be reported, the verbose syntax error
629 message described above is suppressed, and the parser instead
e4ab1254 630 reports the simpler message, "syntax error". Previously, this
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631 suppression was sometimes erroneously triggered by %nonassoc when a
632 lookahead was actually required. Now verbose messages are
633 suppressed only when all previous lookaheads have already been
634 shifted or discarded.
635
636*** Previously, the list of expected tokens erroneously included tokens
637 that would actually induce a syntax error because conflicts for them
638 were resolved with %nonassoc in the current parser state. Such
639 tokens are now properly omitted from the list.
640
641*** Expected token lists are still often wrong due to state merging
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642 (from LALR or IELR) and default reductions, which can both add
643 invalid tokens and subtract valid tokens. Canonical LR almost
644 completely fixes this problem by eliminating state merging and
645 default reductions. However, there is one minor problem left even
646 when using canonical LR and even after the fixes above. That is,
647 if the resolution of a conflict with %nonassoc appears in a later
648 parser state than the one at which some syntax error is
649 discovered, the conflicted token is still erroneously included in
650 the expected token list. Bison's new LAC implementation,
651 described above, eliminates this problem and the need for
652 canonical LR. However, LAC is still experimental and is disabled
653 by default.
1fa30307 654
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655** Java skeleton fixes:
656
657*** A location handling bug has been fixed.
658
659*** The top element of each of the value stack and location stack is now
660 cleared when popped so that it can be garbage collected.
77768165 661
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662*** Parser traces now print the top element of the stack.
663
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664** -W/--warnings fixes:
665
e4ab1254 666*** Bison now properly recognizes the "no-" versions of categories:
248dba53
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667
668 For example, given the following command line, Bison now enables all
669 warnings except warnings for incompatibilities with POSIX Yacc:
670
671 bison -Wall,no-yacc gram.y
672
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673*** Bison now treats S/R and R/R conflicts like other warnings:
674
675 Previously, conflict reports were independent of Bison's normal
676 warning system. Now, Bison recognizes the warning categories
e4ab1254 677 "conflicts-sr" and "conflicts-rr". This change has important
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678 consequences for the -W and --warnings command-line options. For
679 example:
680
681 bison -Wno-conflicts-sr gram.y # S/R conflicts not reported
682 bison -Wno-conflicts-rr gram.y # R/R conflicts not reported
683 bison -Wnone gram.y # no conflicts are reported
684 bison -Werror gram.y # any conflict is an error
685
686 However, as before, if the %expect or %expect-rr directive is
687 specified, an unexpected number of conflicts is an error, and an
688 expected number of conflicts is not reported, so -W and --warning
689 then have no effect on the conflict report.
690
e4ab1254 691*** The "none" category no longer disables a preceding "error":
dab96632
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692
693 For example, for the following command line, Bison now reports
694 errors instead of warnings for incompatibilities with POSIX Yacc:
695
696 bison -Werror,none,yacc gram.y
697
e4ab1254 698*** The "none" category now disables all Bison warnings:
8ffd7912 699
e4ab1254 700 Previously, the "none" category disabled only Bison warnings for
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701 which there existed a specific -W/--warning category. However,
702 given the following command line, Bison is now guaranteed to
703 suppress all warnings:
704
705 bison -Wnone gram.y
706
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707** Precedence directives can now assign token number 0:
708
709 Since Bison 2.3b, which restored the ability of precedence
710 directives to assign token numbers, doing so for token number 0 has
711 produced an assertion failure. For example:
712
713 %left END 0
714
715 This bug has been fixed.
716
7527c744 717* Changes in version 2.4.3 (2010-08-05):
7a9c3cb3 718
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719** Bison now obeys -Werror and --warnings=error for warnings about
720 grammar rules that are useless in the parser due to conflicts.
721
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722** Problems with spawning M4 on at least FreeBSD 8 and FreeBSD 9 have
723 been fixed.
724
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725** Failures in the test suite for GCC 4.5 have been fixed.
726
88bb35d6
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727** Failures in the test suite for some versions of Sun Studio C++ have
728 been fixed.
729
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730** Contrary to Bison 2.4.2's NEWS entry, it has been decided that
731 warnings about undefined %prec identifiers will not be converted to
732 errors in Bison 2.5. They will remain warnings, which should be
733 sufficient for POSIX while avoiding backward compatibility issues.
734
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735** Minor documentation fixes.
736
ea66d039 737* Changes in version 2.4.2 (2010-03-20):
8defe11b 738
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739** Some portability problems that resulted in failures and livelocks
740 in the test suite on some versions of at least Solaris, AIX, HP-UX,
ea66d039
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741 RHEL4, and Tru64 have been addressed. As a result, fatal Bison
742 errors should no longer cause M4 to report a broken pipe on the
47fa5747
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743 affected platforms.
744
e4ab1254 745** "%prec IDENTIFIER" requires IDENTIFIER to be defined separately.
2c203528
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746
747 POSIX specifies that an error be reported for any identifier that does
748 not appear on the LHS of a grammar rule and that is not defined by
749 %token, %left, %right, or %nonassoc. Bison 2.3b and later lost this
750 error report for the case when an identifier appears only after a
751 %prec directive. It is now restored. However, for backward
752 compatibility with recent Bison releases, it is only a warning for
753 now. In Bison 2.5 and later, it will return to being an error.
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754 [Between the 2.4.2 and 2.4.3 releases, it was decided that this
755 warning will not be converted to an error in Bison 2.5.]
2c203528 756
c5196098
EB
757** Detection of GNU M4 1.4.6 or newer during configure is improved.
758
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759** Warnings from gcc's -Wundef option about undefined YYENABLE_NLS,
760 YYLTYPE_IS_TRIVIAL, and __STRICT_ANSI__ in C/C++ parsers are now
761 avoided.
af2ffe5c 762
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763** %code is now a permanent feature.
764
765 A traditional Yacc prologue directive is written in the form:
766
767 %{CODE%}
768
769 To provide a more flexible alternative, Bison 2.3b introduced the
770 %code directive with the following forms for C/C++:
771
772 %code {CODE}
773 %code requires {CODE}
774 %code provides {CODE}
775 %code top {CODE}
776
777 These forms are now considered permanent features of Bison. See the
778 %code entries in the section "Bison Declaration Summary" in the Bison
779 manual for a summary of their functionality. See the section
780 "Prologue Alternatives" for a detailed discussion including the
781 advantages of %code over the traditional Yacc prologue directive.
782
783 Bison's Java feature as a whole including its current usage of %code
784 is still considered experimental.
785
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786** YYFAIL is deprecated and will eventually be removed.
787
788 YYFAIL has existed for many years as an undocumented feature of
789 deterministic parsers in C generated by Bison. Previously, it was
790 documented for Bison's experimental Java parsers. YYFAIL is no longer
791 documented for Java parsers and is formally deprecated in both cases.
792 Users are strongly encouraged to migrate to YYERROR, which is
793 specified by POSIX.
794
795 Like YYERROR, you can invoke YYFAIL from a semantic action in order to
796 induce a syntax error. The most obvious difference from YYERROR is
797 that YYFAIL will automatically invoke yyerror to report the syntax
798 error so that you don't have to. However, there are several other
799 subtle differences between YYERROR and YYFAIL, and YYFAIL suffers from
e4ab1254 800 inherent flaws when %error-verbose or "#define YYERROR_VERBOSE" is
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801 used. For a more detailed discussion, see:
802
803 http://lists.gnu.org/archive/html/bison-patches/2009-12/msg00024.html
804
805 The upcoming Bison 2.5 will remove YYFAIL from Java parsers, but
806 deterministic parsers in C will continue to implement it. However,
807 because YYFAIL is already flawed, it seems futile to try to make new
808 Bison features compatible with it. Thus, during parser generation,
809 Bison 2.5 will produce a warning whenever it discovers YYFAIL in a
810 rule action. In a later release, YYFAIL will be disabled for
e4ab1254 811 %error-verbose and "#define YYERROR_VERBOSE". Eventually, YYFAIL will
41d35e54
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812 be removed altogether.
813
814 There exists at least one case where Bison 2.5's YYFAIL warning will
815 be a false positive. Some projects add phony uses of YYFAIL and other
816 Bison-defined macros for the sole purpose of suppressing C
817 preprocessor warnings (from GCC cpp's -Wunused-macros, for example).
818 To avoid Bison's future warning, such YYFAIL uses can be moved to the
e4ab1254 819 epilogue (that is, after the second "%%") in the Bison input file. In
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820 this release (2.4.2), Bison already generates its own code to suppress
821 C preprocessor warnings for YYFAIL, so projects can remove their own
822 phony uses of YYFAIL if compatibility with Bison releases prior to
823 2.4.2 is not necessary.
824
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825** Internationalization.
826
827 Fix a regression introduced in Bison 2.4: Under some circumstances,
828 message translations were not installed although supported by the
829 host system.
830
41930e7a 831* Changes in version 2.4.1 (2008-12-11):
c9ba9e59 832
a957d06c
JD
833** In the GLR defines file, unexpanded M4 macros in the yylval and yylloc
834 declarations have been fixed.
835
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836** Temporary hack for adding a semicolon to the user action.
837
838 Bison used to prepend a trailing semicolon at the end of the user
839 action for reductions. This allowed actions such as
840
841 exp: exp "+" exp { $$ = $1 + $3 };
842
843 instead of
844
845 exp: exp "+" exp { $$ = $1 + $3; };
846
e4ab1254 847 Some grammars still depend on this "feature". Bison 2.4.1 restores
d07932ef
JD
848 the previous behavior in the case of C output (specifically, when
849 neither %language or %skeleton or equivalent command-line options
850 are used) to leave more time for grammars depending on the old
851 behavior to be adjusted. Future releases of Bison will disable this
852 feature.
a957d06c
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853
854** A few minor improvements to the Bison manual.
c9ba9e59 855
d6fb461d 856* Changes in version 2.4 (2008-11-02):
7bd1665a 857
d6fb461d 858** %language is an experimental feature.
ed4d67dc
JD
859
860 We first introduced this feature in test release 2.3b as a cleaner
861 alternative to %skeleton. Since then, we have discussed the possibility of
862 modifying its effect on Bison's output file names. Thus, in this release,
863 we consider %language to be an experimental feature that will likely evolve
864 in future releases.
7bd1665a 865
d6fb461d 866** Forward compatibility with GNU M4 has been improved.
241fda7a 867
d6fb461d 868** Several bugs in the C++ skeleton and the experimental Java skeleton have been
241fda7a
JD
869 fixed.
870
d6fb461d 871* Changes in version 2.3b (2008-05-27):
35fe0834 872
d6fb461d 873** The quotes around NAME that used to be required in the following directive
d9df47b6
JD
874 are now deprecated:
875
876 %define NAME "VALUE"
877
e4ab1254 878** The directive "%pure-parser" is now deprecated in favor of:
d9df47b6
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879
880 %define api.pure
881
882 which has the same effect except that Bison is more careful to warn about
883 unreasonable usage in the latter case.
884
d6fb461d 885** Push Parsing
c373bf8b
JD
886
887 Bison can now generate an LALR(1) parser in C with a push interface. That
e4ab1254
AD
888 is, instead of invoking "yyparse", which pulls tokens from "yylex", you can
889 push one token at a time to the parser using "yypush_parse", which will
c373bf8b
JD
890 return to the caller after processing each token. By default, the push
891 interface is disabled. Either of the following directives will enable it:
892
893 %define api.push_pull "push" // Just push; does not require yylex.
894 %define api.push_pull "both" // Push and pull; requires yylex.
895
e4ab1254 896 See the new section "A Push Parser" in the Bison manual for details.
c373bf8b 897
59da312b
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898 The current push parsing interface is experimental and may evolve. More user
899 feedback will help to stabilize it.
900
d6fb461d 901** The -g and --graph options now output graphs in Graphviz DOT format,
8e55b3aa
JD
902 not VCG format. Like --graph, -g now also takes an optional FILE argument
903 and thus cannot be bundled with other short options.
c373bf8b 904
d6fb461d 905** Java
59da312b
JD
906
907 Bison can now generate an LALR(1) parser in Java. The skeleton is
e4ab1254 908 "data/lalr1.java". Consider using the new %language directive instead of
59da312b
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909 %skeleton to select it.
910
e4ab1254 911 See the new section "Java Parsers" in the Bison manual for details.
59da312b
JD
912
913 The current Java interface is experimental and may evolve. More user
914 feedback will help to stabilize it.
915
d6fb461d 916** %language
59da312b
JD
917
918 This new directive specifies the programming language of the generated
d43f77e7
PB
919 parser, which can be C (the default), C++, or Java. Besides the skeleton
920 that Bison uses, the directive affects the names of the generated files if
921 the grammar file's name ends in ".y".
59da312b 922
d6fb461d 923** XML Automaton Report
59da312b
JD
924
925 Bison can now generate an XML report of the LALR(1) automaton using the new
e4ab1254 926 "--xml" option. The current XML schema is experimental and may evolve. More
59da312b 927 user feedback will help to stabilize it.
c373bf8b 928
d6fb461d 929** The grammar file may now specify the name of the parser header file using
c373bf8b
JD
930 %defines. For example:
931
932 %defines "parser.h"
933
d6fb461d 934** When reporting useless rules, useless nonterminals, and unused terminals,
d80fb37a
JD
935 Bison now employs the terms "useless in grammar" instead of "useless",
936 "useless in parser" instead of "never reduced", and "unused in grammar"
937 instead of "unused".
cff03fb2 938
d6fb461d 939** Unreachable State Removal
c373bf8b
JD
940
941 Previously, Bison sometimes generated parser tables containing unreachable
31984206
JD
942 states. A state can become unreachable during conflict resolution if Bison
943 disables a shift action leading to it from a predecessor state. Bison now:
75ad86ee
JD
944
945 1. Removes unreachable states.
946
947 2. Does not report any conflicts that appeared in unreachable states.
948 WARNING: As a result, you may need to update %expect and %expect-rr
949 directives in existing grammar files.
950
951 3. For any rule used only in such states, Bison now reports the rule as
cff03fb2 952 "useless in parser due to conflicts".
75ad86ee 953
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JD
954 This feature can be disabled with the following directive:
955
956 %define lr.keep_unreachable_states
957
e4ab1254 958 See the %define entry in the "Bison Declaration Summary" in the Bison manual
31984206
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959 for further discussion.
960
e4ab1254 961** Lookahead Set Correction in the ".output" Report
b1cc23c4 962
e4ab1254
AD
963 When instructed to generate a ".output" file including lookahead sets
964 (using "--report=lookahead", for example), Bison now prints each reduction's
88c78747
JD
965 lookahead set only next to the associated state's one item that (1) is
966 associated with the same rule as the reduction and (2) has its dot at the end
967 of its RHS. Previously, Bison also erroneously printed the lookahead set
968 next to all of the state's other items associated with the same rule. This
e4ab1254 969 bug affected only the ".output" file and not the generated parser source
88c78747
JD
970 code.
971
e4ab1254 972** --report-file=FILE is a new option to override the default ".output" file
59da312b 973 name.
1bb2bd75 974
e4ab1254 975** The "=" that used to be required in the following directives is now
02975b9a
JD
976 deprecated:
977
978 %file-prefix "parser"
979 %name-prefix "c_"
980 %output "parser.c"
981
e4ab1254 982** An Alternative to "%{...%}" -- "%code QUALIFIER {CODE}"
c373bf8b
JD
983
984 Bison 2.3a provided a new set of directives as a more flexible alternative to
8e0a5e9e
JD
985 the traditional Yacc prologue blocks. Those have now been consolidated into
986 a single %code directive with an optional qualifier field, which identifies
987 the purpose of the code and thus the location(s) where Bison should generate
988 it:
989
e4ab1254
AD
990 1. "%code {CODE}" replaces "%after-header {CODE}"
991 2. "%code requires {CODE}" replaces "%start-header {CODE}"
992 3. "%code provides {CODE}" replaces "%end-header {CODE}"
993 4. "%code top {CODE}" replaces "%before-header {CODE}"
8e0a5e9e 994
e4ab1254
AD
995 See the %code entries in section "Bison Declaration Summary" in the Bison
996 manual for a summary of the new functionality. See the new section "Prologue
997 Alternatives" for a detailed discussion including the advantages of %code
8e0a5e9e
JD
998 over the traditional Yacc prologues.
999
1000 The prologue alternatives are experimental. More user feedback will help to
1001 determine whether they should become permanent features.
1002
d6fb461d 1003** Revised warning: unset or unused mid-rule values
17bd8a73
JD
1004
1005 Since Bison 2.2, Bison has warned about mid-rule values that are set but not
1006 used within any of the actions of the parent rule. For example, Bison warns
1007 about unused $2 in:
1008
1009 exp: '1' { $$ = 1; } '+' exp { $$ = $1 + $4; };
1010
1011 Now, Bison also warns about mid-rule values that are used but not set. For
1012 example, Bison warns about unset $$ in the mid-rule action in:
1013
1014 exp: '1' { $1 = 1; } '+' exp { $$ = $2 + $4; };
1015
1016 However, Bison now disables both of these warnings by default since they
1017 sometimes prove to be false alarms in existing grammars employing the Yacc
1018 constructs $0 or $-N (where N is some positive integer).
1019
e4ab1254
AD
1020 To enable these warnings, specify the option "--warnings=midrule-values" or
1021 "-W", which is a synonym for "--warnings=all".
17bd8a73 1022
e4ab1254 1023** Default %destructor or %printer with "<*>" or "<>"
c373bf8b
JD
1024
1025 Bison now recognizes two separate kinds of default %destructor's and
12e35840
JD
1026 %printer's:
1027
e4ab1254 1028 1. Place "<*>" in a %destructor/%printer symbol list to define a default
12e35840
JD
1029 %destructor/%printer for all grammar symbols for which you have formally
1030 declared semantic type tags.
1031
e4ab1254 1032 2. Place "<>" in a %destructor/%printer symbol list to define a default
12e35840
JD
1033 %destructor/%printer for all grammar symbols without declared semantic
1034 type tags.
1035
e4ab1254
AD
1036 Bison no longer supports the "%symbol-default" notation from Bison 2.3a.
1037 "<*>" and "<>" combined achieve the same effect with one exception: Bison no
12e35840
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1038 longer applies any %destructor to a mid-rule value if that mid-rule value is
1039 not actually ever referenced using either $$ or $n in a semantic action.
1040
85894313
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1041 The default %destructor's and %printer's are experimental. More user
1042 feedback will help to determine whether they should become permanent
1043 features.
1044
e4ab1254 1045 See the section "Freeing Discarded Symbols" in the Bison manual for further
12e35840
JD
1046 details.
1047
d6fb461d 1048** %left, %right, and %nonassoc can now declare token numbers. This is required
e4ab1254 1049 by POSIX. However, see the end of section "Operator Precedence" in the Bison
ab7f29f8
JD
1050 manual for a caveat concerning the treatment of literal strings.
1051
d6fb461d 1052** The nonfunctional --no-parser, -n, and %no-parser options have been
b1cc23c4
JD
1053 completely removed from Bison.
1054
d6fb461d 1055* Changes in version 2.3a, 2006-09-13:
742e4900 1056
d6fb461d 1057** Instead of %union, you can define and use your own union type
ddc8ede1
PE
1058 YYSTYPE if your grammar contains at least one <type> tag.
1059 Your YYSTYPE need not be a macro; it can be a typedef.
1060 This change is for compatibility with other Yacc implementations,
1061 and is required by POSIX.
1062
d6fb461d 1063** Locations columns and lines start at 1.
cd48d21d
AD
1064 In accordance with the GNU Coding Standards and Emacs.
1065
d6fb461d 1066** You may now declare per-type and default %destructor's and %printer's:
ec5479ce
JD
1067
1068 For example:
1069
b2a0b7ca
JD
1070 %union { char *string; }
1071 %token <string> STRING1
1072 %token <string> STRING2
1073 %type <string> string1
1074 %type <string> string2
1075 %union { char character; }
1076 %token <character> CHR
1077 %type <character> chr
1078 %destructor { free ($$); } %symbol-default
1079 %destructor { free ($$); printf ("%d", @$.first_line); } STRING1 string1
1080 %destructor { } <character>
1081
1082 guarantees that, when the parser discards any user-defined symbol that has a
e4ab1254
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1083 semantic type tag other than "<character>", it passes its semantic value to
1084 "free". However, when the parser discards a "STRING1" or a "string1", it
1085 also prints its line number to "stdout". It performs only the second
1086 "%destructor" in this case, so it invokes "free" only once.
ec5479ce 1087
85894313
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1088 [Although we failed to mention this here in the 2.3a release, the default
1089 %destructor's and %printer's were experimental, and they were rewritten in
1090 future versions.]
1091
e4ab1254
AD
1092** Except for LALR(1) parsers in C with POSIX Yacc emulation enabled (with "-y",
1093 "--yacc", or "%yacc"), Bison no longer generates #define statements for
b931235e
JD
1094 associating token numbers with token names. Removing the #define statements
1095 helps to sanitize the global namespace during preprocessing, but POSIX Yacc
1096 requires them. Bison still generates an enum for token names in all cases.
1097
d6fb461d 1098** Handling of traditional Yacc prologue blocks is now more consistent but
34f98f46 1099 potentially incompatible with previous releases of Bison.
9bc0dd67
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1100
1101 As before, you declare prologue blocks in your grammar file with the
e4ab1254 1102 "%{ ... %}" syntax. To generate the pre-prologue, Bison concatenates all
34f98f46
JD
1103 prologue blocks that you've declared before the first %union. To generate
1104 the post-prologue, Bison concatenates all prologue blocks that you've
ddc8ede1 1105 declared after the first %union.
9bc0dd67 1106
34f98f46 1107 Previous releases of Bison inserted the pre-prologue into both the header
9bc0dd67
JD
1108 file and the code file in all cases except for LALR(1) parsers in C. In the
1109 latter case, Bison inserted it only into the code file. For parsers in C++,
1110 the point of insertion was before any token definitions (which associate
1111 token numbers with names). For parsers in C, the point of insertion was
1112 after the token definitions.
1113
1114 Now, Bison never inserts the pre-prologue into the header file. In the code
1115 file, it always inserts it before the token definitions.
1116
d6fb461d 1117** Bison now provides a more flexible alternative to the traditional Yacc
34f98f46
JD
1118 prologue blocks: %before-header, %start-header, %end-header, and
1119 %after-header.
1120
1121 For example, the following declaration order in the grammar file reflects the
1122 order in which Bison will output these code blocks. However, you are free to
1123 declare these code blocks in your grammar file in whatever order is most
1124 convenient for you:
1125
1126 %before-header {
1127 /* Bison treats this block like a pre-prologue block: it inserts it into
1128 * the code file before the contents of the header file. It does *not*
1129 * insert it into the header file. This is a good place to put
1130 * #include's that you want at the top of your code file. A common
e4ab1254 1131 * example is '#include "system.h"'. */
34f98f46
JD
1132 }
1133 %start-header {
1134 /* Bison inserts this block into both the header file and the code file.
1135 * In both files, the point of insertion is before any Bison-generated
1136 * token, semantic type, location type, and class definitions. This is a
1137 * good place to define %union dependencies, for example. */
9bc0dd67
JD
1138 }
1139 %union {
34f98f46
JD
1140 /* Unlike the traditional Yacc prologue blocks, the output order for the
1141 * new %*-header blocks is not affected by their declaration position
1142 * relative to any %union in the grammar file. */
9bc0dd67 1143 }
34f98f46
JD
1144 %end-header {
1145 /* Bison inserts this block into both the header file and the code file.
1146 * In both files, the point of insertion is after the Bison-generated
1147 * definitions. This is a good place to declare or define public
1148 * functions or data structures that depend on the Bison-generated
1149 * definitions. */
9bc0dd67 1150 }
34f98f46
JD
1151 %after-header {
1152 /* Bison treats this block like a post-prologue block: it inserts it into
1153 * the code file after the contents of the header file. It does *not*
1154 * insert it into the header file. This is a good place to declare or
1155 * define internal functions or data structures that depend on the
1156 * Bison-generated definitions. */
1157 }
1158
1159 If you have multiple occurrences of any one of the above declarations, Bison
1160 will concatenate the contents in declaration order.
9bc0dd67 1161
85894313
JD
1162 [Although we failed to mention this here in the 2.3a release, the prologue
1163 alternatives were experimental, and they were rewritten in future versions.]
1164
e4ab1254 1165** The option "--report=look-ahead" has been changed to "--report=lookahead".
9e6e7ed2
PE
1166 The old spelling still works, but is not documented and may be removed
1167 in a future release.
742e4900 1168
d6fb461d 1169* Changes in version 2.3, 2006-06-05:
4ad3ed84 1170
e4ab1254 1171** GLR grammars should now use "YYRECOVERING ()" instead of "YYRECOVERING",
4ad3ed84
PE
1172 for compatibility with LALR(1) grammars.
1173
d6fb461d 1174** It is now documented that any definition of YYSTYPE or YYLTYPE should
4ad3ed84
PE
1175 be to a type name that does not contain parentheses or brackets.
1176
d6fb461d 1177* Changes in version 2.2, 2006-05-19:
193d7c70 1178
d6fb461d 1179** The distribution terms for all Bison-generated parsers now permit
193d7c70
PE
1180 using the parsers in nonfree programs. Previously, this permission
1181 was granted only for Bison-generated LALR(1) parsers in C.
5f4236a0 1182
d6fb461d 1183** %name-prefix changes the namespace name in C++ outputs.
aa08666d 1184
d6fb461d 1185** The C++ parsers export their token_type.
5f4236a0 1186
d6fb461d 1187** Bison now allows multiple %union declarations, and concatenates
d6ca7905
PE
1188 their contents together.
1189
d6fb461d 1190** New warning: unused values
4d7bc38c
PE
1191 Right-hand side symbols whose values are not used are reported,
1192 if the symbols have destructors. For instance:
affac613 1193
8f3596a6 1194 exp: exp "?" exp ":" exp { $1 ? $1 : $3; }
e29f0771
AD
1195 | exp "+" exp
1196 ;
affac613 1197
8f3596a6
AD
1198 will trigger a warning about $$ and $5 in the first rule, and $3 in
1199 the second ($1 is copied to $$ by the default rule). This example
4e26c69e 1200 most likely contains three errors, and could be rewritten as:
affac613 1201
4e26c69e 1202 exp: exp "?" exp ":" exp
e29f0771
AD
1203 { $$ = $1 ? $3 : $5; free ($1 ? $5 : $3); free ($1); }
1204 | exp "+" exp
1205 { $$ = $1 ? $1 : $3; if ($1) free ($3); }
1206 ;
affac613 1207
4e26c69e
PE
1208 However, if the original actions were really intended, memory leaks
1209 and all, the warnings can be suppressed by letting Bison believe the
1210 values are used, e.g.:
721be13c 1211
8f3596a6 1212 exp: exp "?" exp ":" exp { $1 ? $1 : $3; (void) ($$, $5); }
e29f0771
AD
1213 | exp "+" exp { $$ = $1; (void) $3; }
1214 ;
721be13c 1215
84866159
AD
1216 If there are mid-rule actions, the warning is issued if no action
1217 uses it. The following triggers no warning: $1 and $3 are used.
1218
1219 exp: exp { push ($1); } '+' exp { push ($3); sum (); };
1220
721be13c
PE
1221 The warning is intended to help catching lost values and memory leaks.
1222 If a value is ignored, its associated memory typically is not reclaimed.
affac613 1223
d6fb461d 1224** %destructor vs. YYABORT, YYACCEPT, and YYERROR.
9d9b8b70
PE
1225 Destructors are now called when user code invokes YYABORT, YYACCEPT,
1226 and YYERROR, for all objects on the stack, other than objects
1227 corresponding to the right-hand side of the current rule.
a85284cf 1228
d6fb461d 1229** %expect, %expect-rr
035aa4a0
PE
1230 Incorrect numbers of expected conflicts are now actual errors,
1231 instead of warnings.
1232
d6fb461d 1233** GLR, YACC parsers.
4e26c69e
PE
1234 The %parse-params are available in the destructors (and the
1235 experimental printers) as per the documentation.
4b367315 1236
e4ab1254 1237** Bison now warns if it finds a stray "$" or "@" in an action.
ad6a9b97 1238
d6fb461d 1239** %require "VERSION"
4e26c69e
PE
1240 This specifies that the grammar file depends on features implemented
1241 in Bison version VERSION or higher.
b50d2359 1242
d6fb461d 1243** lalr1.cc: The token and value types are now class members.
e14d0ab6
AD
1244 The tokens were defined as free form enums and cpp macros. YYSTYPE
1245 was defined as a free form union. They are now class members:
e4ab1254
AD
1246 tokens are enumerations of the "yy::parser::token" struct, and the
1247 semantic values have the "yy::parser::semantic_type" type.
fb9712a9
AD
1248
1249 If you do not want or can update to this scheme, the directive
e4ab1254 1250 '%define "global_tokens_and_yystype" "1"' triggers the global
b50d2359
AD
1251 definition of tokens and YYSTYPE. This change is suitable both
1252 for previous releases of Bison, and this one.
fb9712a9 1253
b50d2359 1254 If you wish to update, then make sure older version of Bison will
e4ab1254 1255 fail using '%require "2.2"'.
fb9712a9 1256
d6fb461d 1257** DJGPP support added.
193d7c70 1258\f
d6fb461d 1259* Changes in version 2.1, 2005-09-16:
1ce59070 1260
d6fb461d 1261** The C++ lalr1.cc skeleton supports %lex-param.
e14d0ab6 1262
d6fb461d 1263** Bison-generated parsers now support the translation of diagnostics like
baf785db
PE
1264 "syntax error" into languages other than English. The default
1265 language is still English. For details, please see the new
0410a6e0
PE
1266 Internationalization section of the Bison manual. Software
1267 distributors should also see the new PACKAGING file. Thanks to
1268 Bruno Haible for this new feature.
1ce59070 1269
d6fb461d 1270** Wording in the Bison-generated parsers has been changed slightly to
1a059451
PE
1271 simplify translation. In particular, the message "memory exhausted"
1272 has replaced "parser stack overflow", as the old message was not
1273 always accurate for modern Bison-generated parsers.
1274
d6fb461d 1275** Destructors are now called when the parser aborts, for all symbols left
258b75ca
PE
1276 behind on the stack. Also, the start symbol is now destroyed after a
1277 successful parse. In both cases, the behavior was formerly inconsistent.
1278
d6fb461d 1279** When generating verbose diagnostics, Bison-generated parsers no longer
72f000b0
PE
1280 quote the literal strings associated with tokens. For example, for
1281 a syntax error associated with '%token NUM "number"' they might
1282 print 'syntax error, unexpected number' instead of 'syntax error,
1283 unexpected "number"'.
193d7c70 1284\f
d6fb461d 1285* Changes in version 2.0, 2004-12-25:
efeed023 1286
d6fb461d 1287** Possibly-incompatible changes
d7e14fc0 1288
82de6b0d
PE
1289 - Bison-generated parsers no longer default to using the alloca function
1290 (when available) to extend the parser stack, due to widespread
1291 problems in unchecked stack-overflow detection. You can "#define
1292 YYSTACK_USE_ALLOCA 1" to require the use of alloca, but please read
1293 the manual to determine safe values for YYMAXDEPTH in that case.
8dd162d3 1294
82de6b0d
PE
1295 - Error token location.
1296 During error recovery, the location of the syntax error is updated
1297 to cover the whole sequence covered by the error token: it includes
1298 the shifted symbols thrown away during the first part of the error
1299 recovery, and the lookahead rejected during the second part.
18d192f0 1300
82de6b0d
PE
1301 - Semicolon changes:
1302 . Stray semicolons are no longer allowed at the start of a grammar.
1303 . Semicolons are now required after in-grammar declarations.
e342c3be 1304
82de6b0d
PE
1305 - Unescaped newlines are no longer allowed in character constants or
1306 string literals. They were never portable, and GCC 3.4.0 has
1307 dropped support for them. Better diagnostics are now generated if
1308 forget a closing quote.
8dd162d3 1309
82de6b0d 1310 - NUL bytes are no longer allowed in Bison string literals, unfortunately.
f74b6f91 1311
d6fb461d 1312** New features
1452af69 1313
82de6b0d 1314 - GLR grammars now support locations.
4febdd96 1315
82de6b0d
PE
1316 - New directive: %initial-action.
1317 This directive allows the user to run arbitrary code (including
1318 initializing @$) from yyparse before parsing starts.
1452af69 1319
82de6b0d
PE
1320 - A new directive "%expect-rr N" specifies the expected number of
1321 reduce/reduce conflicts in GLR parsers.
1452af69 1322
e4ab1254 1323 - %token numbers can now be hexadecimal integers, e.g., "%token FOO 0x12d".
82de6b0d 1324 This is a GNU extension.
4febdd96 1325
e4ab1254 1326 - The option "--report=lookahead" was changed to "--report=look-ahead".
9e6e7ed2 1327 [However, this was changed back after 2.3.]
1452af69 1328
82de6b0d 1329 - Experimental %destructor support has been added to lalr1.cc.
1452af69 1330
82de6b0d
PE
1331 - New configure option --disable-yacc, to disable installation of the
1332 yacc command and -ly library introduced in 1.875 for POSIX conformance.
6040d338 1333
d6fb461d 1334** Bug fixes
d5a3fe37 1335
82de6b0d
PE
1336 - For now, %expect-count violations are now just warnings, not errors.
1337 This is for compatibility with Bison 1.75 and earlier (when there are
1338 reduce/reduce conflicts) and with Bison 1.30 and earlier (when there
1339 are too many or too few shift/reduce conflicts). However, in future
1340 versions of Bison we plan to improve the %expect machinery so that
1341 these violations will become errors again.
3473d0f8 1342
82de6b0d
PE
1343 - Within Bison itself, numbers (e.g., goto numbers) are no longer
1344 arbitrarily limited to 16-bit counts.
d600ee67 1345
82de6b0d 1346 - Semicolons are now allowed before "|" in grammar rules, as POSIX requires.
d600ee67 1347\f
d6fb461d 1348* Changes in version 1.875, 2003-01-01:
963fcc17 1349
d6fb461d 1350** The documentation license has been upgraded to version 1.2
dc546b0f 1351 of the GNU Free Documentation License.
75eb3bc4 1352
d6fb461d 1353** syntax error processing
75eb3bc4 1354
dc546b0f
PE
1355 - In Yacc-style parsers YYLLOC_DEFAULT is now used to compute error
1356 locations too. This fixes bugs in error-location computation.
75eb3bc4 1357
dc546b0f
PE
1358 - %destructor
1359 It is now possible to reclaim the memory associated to symbols
1360 discarded during error recovery. This feature is still experimental.
20daca06 1361
dc546b0f
PE
1362 - %error-verbose
1363 This new directive is preferred over YYERROR_VERBOSE.
74724a70 1364
dc546b0f
PE
1365 - #defining yyerror to steal internal variables is discouraged.
1366 It is not guaranteed to work forever.
d1de5372 1367
d6fb461d 1368** POSIX conformance
d1de5372 1369
dc546b0f
PE
1370 - Semicolons are once again optional at the end of grammar rules.
1371 This reverts to the behavior of Bison 1.33 and earlier, and improves
1372 compatibility with Yacc.
74724a70 1373
e4ab1254
AD
1374 - "parse error" -> "syntax error"
1375 Bison now uniformly uses the term "syntax error"; formerly, the code
1376 and manual sometimes used the term "parse error" instead. POSIX
1377 requires "syntax error" in diagnostics, and it was thought better to
dc546b0f 1378 be consistent.
74724a70 1379
dc546b0f
PE
1380 - The documentation now emphasizes that yylex and yyerror must be
1381 declared before use. C99 requires this.
d1de5372 1382
dc546b0f
PE
1383 - Bison now parses C99 lexical constructs like UCNs and
1384 backslash-newline within C escape sequences, as POSIX 1003.1-2001 requires.
d1de5372 1385
dc546b0f
PE
1386 - File names are properly escaped in C output. E.g., foo\bar.y is
1387 output as "foo\\bar.y".
6780ca7a 1388
dc546b0f 1389 - Yacc command and library now available
e4ab1254 1390 The Bison distribution now installs a "yacc" command, as POSIX requires.
dc546b0f
PE
1391 Also, Bison now installs a small library liby.a containing
1392 implementations of Yacc-compatible yyerror and main functions.
1393 This library is normally not useful, but POSIX requires it.
6e649e65 1394
dc546b0f 1395 - Type clashes now generate warnings, not errors.
6e649e65 1396
dc546b0f
PE
1397 - If the user does not define YYSTYPE as a macro, Bison now declares it
1398 using typedef instead of defining it as a macro.
1399 For consistency, YYLTYPE is also declared instead of defined.
9501dc6e 1400
d6fb461d 1401** Other compatibility issues
886a425c 1402
e4ab1254
AD
1403 - %union directives can now have a tag before the "{", e.g., the
1404 directive "%union foo {...}" now generates the C code
1405 "typedef union foo { ... } YYSTYPE;"; this is for Yacc compatibility.
1406 The default union tag is "YYSTYPE", for compatibility with Solaris 9 Yacc.
1407 For consistency, YYLTYPE's struct tag is now "YYLTYPE" not "yyltype".
dc546b0f 1408 This is for compatibility with both Yacc and Bison 1.35.
72f889cc 1409
e4ab1254 1410 - ";" is output before the terminating "}" of an action, for
dc546b0f 1411 compatibility with Bison 1.35.
886a425c 1412
dc546b0f 1413 - Bison now uses a Yacc-style format for conflict reports, e.g.,
e4ab1254 1414 "conflicts: 2 shift/reduce, 1 reduce/reduce".
437c2d80 1415
e4ab1254 1416 - "yystype" and "yyltype" are now obsolescent macros instead of being
dc546b0f
PE
1417 typedefs or tags; they are no longer documented and are planned to be
1418 withdrawn in a future release.
2a8d363a 1419
d6fb461d 1420** GLR parser notes
2a8d363a 1421
dc546b0f
PE
1422 - GLR and inline
1423 Users of Bison have to decide how they handle the portability of the
e4ab1254 1424 C keyword "inline".
959e5f51 1425
e4ab1254
AD
1426 - "parsing stack overflow..." -> "parser stack overflow"
1427 GLR parsers now report "parser stack overflow" as per the Bison manual.
900c5db5 1428
18ad57b3
AD
1429** %parse-param and %lex-param
1430 The macros YYPARSE_PARAM and YYLEX_PARAM provide a means to pass
1431 additional context to yyparse and yylex. They suffer from several
1432 shortcomings:
1433
1434 - a single argument only can be added,
1435 - their types are weak (void *),
242cc08e 1436 - this context is not passed to ancillary functions such as yyerror,
18ad57b3
AD
1437 - only yacc.c parsers support them.
1438
1439 The new %parse-param/%lex-param directives provide a more precise control.
1440 For instance:
1441
1442 %parse-param {int *nastiness}
1443 %lex-param {int *nastiness}
1444 %parse-param {int *randomness}
1445
1446 results in the following signatures:
1447
1448 int yylex (int *nastiness);
1449 int yyparse (int *nastiness, int *randomness);
1450
1451 or, if both %pure-parser and %locations are used:
1452
1453 int yylex (YYSTYPE *lvalp, YYLTYPE *llocp, int *nastiness);
1454 int yyparse (int *nastiness, int *randomness);
1455
d6fb461d 1456** Bison now warns if it detects conflicting outputs to the same file,
e4ab1254 1457 e.g., it generates a warning for "bison -d -o foo.h foo.y" since
dc546b0f 1458 that command outputs both code and header to foo.h.
6e40b4eb 1459
d6fb461d 1460** #line in output files
dc546b0f 1461 - --no-line works properly.
6e40b4eb 1462
d6fb461d 1463** Bison can no longer be built by a K&R C compiler; it requires C89 or
6e40b4eb
AD
1464 later to be built. This change originally took place a few versions
1465 ago, but nobody noticed until we recently asked someone to try
1466 building Bison with a K&R C compiler.
d600ee67 1467\f
d6fb461d 1468* Changes in version 1.75, 2002-10-14:
7933f2b5 1469
d6fb461d 1470** Bison should now work on 64-bit hosts.
7933f2b5 1471
d6fb461d 1472** Indonesian translation thanks to Tedi Heriyanto.
7933f2b5 1473
d6fb461d 1474** GLR parsers
f50adbbd
AD
1475 Fix spurious parse errors.
1476
d6fb461d 1477** Pure parsers
f50adbbd
AD
1478 Some people redefine yyerror to steal yyparse' private variables.
1479 Reenable this trick until an official feature replaces it.
1480
d6fb461d 1481** Type Clashes
d90c934c
AD
1482 In agreement with POSIX and with other Yaccs, leaving a default
1483 action is valid when $$ is untyped, and $1 typed:
1484
e29f0771 1485 untyped: ... typed;
d90c934c
AD
1486
1487 but the converse remains an error:
1488
e29f0771 1489 typed: ... untyped;
d90c934c 1490
d6fb461d 1491** Values of mid-rule actions
d90c934c
AD
1492 The following code:
1493
e29f0771 1494 foo: { ... } { $$ = $1; } ...
d90c934c
AD
1495
1496 was incorrectly rejected: $1 is defined in the second mid-rule
1497 action, and is equal to the $$ of the first mid-rule action.
d600ee67 1498\f
d6fb461d 1499* Changes in version 1.50, 2002-10-04:
adc8c848 1500
d6fb461d 1501** GLR parsing
676385e2
PH
1502 The declaration
1503 %glr-parser
1504 causes Bison to produce a Generalized LR (GLR) parser, capable of handling
1505 almost any context-free grammar, ambiguous or not. The new declarations
e8832397 1506 %dprec and %merge on grammar rules allow parse-time resolution of
676385e2
PH
1507 ambiguities. Contributed by Paul Hilfinger.
1508
7933f2b5 1509 Unfortunately Bison 1.50 does not work properly on 64-bit hosts
420f93c8
PE
1510 like the Alpha, so please stick to 32-bit hosts for now.
1511
d6fb461d 1512** Output Directory
8c165d89 1513 When not in Yacc compatibility mode, when the output file was not
e4ab1254
AD
1514 specified, running "bison foo/bar.y" created "foo/bar.c". It
1515 now creates "bar.c".
8c165d89 1516
d6fb461d 1517** Undefined token
007a50a4 1518 The undefined token was systematically mapped to 2 which prevented
e88dbdbf 1519 the use of 2 by the user. This is no longer the case.
007a50a4 1520
d6fb461d 1521** Unknown token numbers
e88dbdbf 1522 If yylex returned an out of range value, yyparse could die. This is
007a50a4
AD
1523 no longer the case.
1524
d6fb461d 1525** Error token
e88dbdbf 1526 According to POSIX, the error token must be 256.
23c5a174
AD
1527 Bison extends this requirement by making it a preference: *if* the
1528 user specified that one of her tokens is numbered 256, then error
1529 will be mapped onto another number.
1530
d6fb461d 1531** Verbose error messages
e4ab1254 1532 They no longer report "..., expecting error or..." for states where
217598da
AD
1533 error recovery is possible.
1534
d6fb461d 1535** End token
e4ab1254 1536 Defaults to "$end" instead of "$".
217598da 1537
d6fb461d 1538** Error recovery now conforms to documentation and to POSIX
68cd8af3
PE
1539 When a Bison-generated parser encounters a syntax error, it now pops
1540 the stack until it finds a state that allows shifting the error
1541 token. Formerly, it popped the stack until it found a state that
1542 allowed some non-error action other than a default reduction on the
1543 error token. The new behavior has long been the documented behavior,
1544 and has long been required by POSIX. For more details, please see
337116ba
PE
1545 Paul Eggert, "Reductions during Bison error handling" (2002-05-20)
1546 <http://lists.gnu.org/archive/html/bug-bison/2002-05/msg00038.html>.
68cd8af3 1547
d6fb461d 1548** Traces
5504898e
AD
1549 Popped tokens and nonterminals are now reported.
1550
d6fb461d 1551** Larger grammars
a861a339
PE
1552 Larger grammars are now supported (larger token numbers, larger grammar
1553 size (= sum of the LHS and RHS lengths), larger LALR tables).
1554 Formerly, many of these numbers ran afoul of 16-bit limits;
1555 now these limits are 32 bits on most hosts.
355e7c1c 1556
d6fb461d 1557** Explicit initial rule
643a5994
AD
1558 Bison used to play hacks with the initial rule, which the user does
1559 not write. It is now explicit, and visible in the reports and
1560 graphs as rule 0.
23c5a174 1561
d6fb461d 1562** Useless rules
643a5994 1563 Before, Bison reported the useless rules, but, although not used,
77714df2 1564 included them in the parsers. They are now actually removed.
23c5a174 1565
d6fb461d 1566** Useless rules, useless nonterminals
6b98e4b5
AD
1567 They are now reported, as a warning, with their locations.
1568
d6fb461d 1569** Rules never reduced
e8832397
AD
1570 Rules that can never be reduced because of conflicts are now
1571 reported.
1572
e4ab1254 1573** Incorrect "Token not used"
11652ab3
AD
1574 On a grammar such as
1575
e29f0771
AD
1576 %token useless useful
1577 %%
1578 exp: '0' %prec useful;
11652ab3
AD
1579
1580 where a token was used to set the precedence of the last rule,
e4ab1254 1581 bison reported both "useful" and "useless" as useless tokens.
11652ab3 1582
d6fb461d 1583** Revert the C++ namespace changes introduced in 1.31
77714df2 1584 as they caused too many portability hassles.
0179dd65 1585
d6fb461d 1586** Default locations
b2d52318
AD
1587 By an accident of design, the default computation of @$ was
1588 performed after another default computation was performed: @$ = @1.
1589 The latter is now removed: YYLLOC_DEFAULT is fully responsible of
1590 the computation of @$.
adc8c848 1591
d6fb461d 1592** Token end-of-file
b7c49edf
AD
1593 The token end of file may be specified by the user, in which case,
1594 the user symbol is used in the reports, the graphs, and the verbose
e4ab1254 1595 error messages instead of "$end", which remains being the default.
b7c49edf 1596 For instance
e29f0771 1597 %token MYEOF 0
b7c49edf 1598 or
e29f0771 1599 %token MYEOF 0 "end of file"
fdbcd8e2 1600
d6fb461d 1601** Semantic parser
fdbcd8e2
AD
1602 This old option, which has been broken for ages, is removed.
1603
d6fb461d 1604** New translations
a861a339 1605 Brazilian Portuguese, thanks to Alexandre Folle de Menezes.
84614e13
AD
1606 Croatian, thanks to Denis Lackovic.
1607
d6fb461d 1608** Incorrect token definitions
e4ab1254
AD
1609 When given
1610 %token 'a' "A"
1611 bison used to output
1612 #define 'a' 65
b87f8b21 1613
d6fb461d 1614** Token definitions as enums
77714df2
AD
1615 Tokens are output both as the traditional #define's, and, provided
1616 the compiler supports ANSI C or is a C++ compiler, as enums.
e88dbdbf 1617 This lets debuggers display names instead of integers.
77714df2 1618
d6fb461d 1619** Reports
ec3bc396
AD
1620 In addition to --verbose, bison supports --report=THINGS, which
1621 produces additional information:
b408954b
AD
1622 - itemset
1623 complete the core item sets with their closure
e4ab1254 1624 - lookahead [changed to "look-ahead" in 1.875e through 2.3, but changed back]
9e6e7ed2 1625 explicitly associate lookahead tokens to items
b408954b
AD
1626 - solved
1627 describe shift/reduce conflicts solving.
1628 Bison used to systematically output this information on top of
1629 the report. Solved conflicts are now attached to their states.
ec3bc396 1630
d6fb461d 1631** Type clashes
9af3fbce
AD
1632 Previous versions don't complain when there is a type clash on
1633 the default action if the rule has a mid-rule action, such as in:
1634
e29f0771
AD
1635 %type <foo> bar
1636 %%
1637 bar: '0' {} '0';
9af3fbce
AD
1638
1639 This is fixed.
a861a339 1640
d6fb461d 1641** GNU M4 is now required when using Bison.
f987e9d2 1642\f
d6fb461d 1643* Changes in version 1.35, 2002-03-25:
76551463 1644
d6fb461d 1645** C Skeleton
76551463
AD
1646 Some projects use Bison's C parser with C++ compilers, and define
1647 YYSTYPE as a class. The recent adjustment of C parsers for data
1648 alignment and 64 bit architectures made this impossible.
1649
1650 Because for the time being no real solution for C++ parser
1651 generation exists, kludges were implemented in the parser to
1652 maintain this use. In the future, when Bison has C++ parsers, this
1653 kludge will be disabled.
1654
1655 This kludge also addresses some C++ problems when the stack was
1656 extended.
76551463 1657\f
d6fb461d 1658* Changes in version 1.34, 2002-03-12:
76551463 1659
d6fb461d 1660** File name clashes are detected
76551463 1661 $ bison foo.y -d -o foo.x
e4ab1254 1662 fatal error: header and parser would both be named "foo.x"
76551463 1663
e4ab1254 1664** A missing ";" at the end of a rule triggers a warning
76551463
AD
1665 In accordance with POSIX, and in agreement with other
1666 Yacc implementations, Bison will mandate this semicolon in the near
1667 future. This eases the implementation of a Bison parser of Bison
1668 grammars by making this grammar LALR(1) instead of LR(2). To
1669 facilitate the transition, this release introduces a warning.
1670
d6fb461d 1671** Revert the C++ namespace changes introduced in 1.31, as they caused too
76551463
AD
1672 many portability hassles.
1673
d6fb461d 1674** DJGPP support added.
76551463 1675
d6fb461d 1676** Fix test suite portability problems.
76551463 1677\f
d6fb461d 1678* Changes in version 1.33, 2002-02-07:
76551463 1679
d6fb461d 1680** Fix C++ issues
76551463
AD
1681 Groff could not be compiled for the definition of size_t was lacking
1682 under some conditions.
1683
d6fb461d 1684** Catch invalid @n
76551463
AD
1685 As is done with $n.
1686\f
d6fb461d 1687* Changes in version 1.32, 2002-01-23:
76551463 1688
d6fb461d 1689** Fix Yacc output file names
76551463 1690
d6fb461d 1691** Portability fixes
76551463 1692
d6fb461d 1693** Italian, Dutch translations
76551463 1694\f
d6fb461d 1695* Changes in version 1.31, 2002-01-14:
52d1aeee 1696
d6fb461d 1697** Many Bug Fixes
52d1aeee 1698
d6fb461d 1699** GNU Gettext and %expect
52d1aeee
MA
1700 GNU Gettext asserts 10 s/r conflicts, but there are 7. Now that
1701 Bison dies on incorrect %expectations, we fear there will be
1702 too many bug reports for Gettext, so _for the time being_, %expect
e4ab1254 1703 does not trigger an error when the input file is named "plural.y".
52d1aeee 1704
d6fb461d 1705** Use of alloca in parsers
52d1aeee
MA
1706 If YYSTACK_USE_ALLOCA is defined to 0, then the parsers will use
1707 malloc exclusively. Since 1.29, but was not NEWS'ed.
1708
1709 alloca is used only when compiled with GCC, to avoid portability
1710 problems as on AIX.
1711
d6fb461d 1712** yyparse now returns 2 if memory is exhausted; formerly it dumped core.
b47dbebe 1713
d6fb461d 1714** When the generated parser lacks debugging code, YYDEBUG is now 0
52d1aeee
MA
1715 (as POSIX requires) instead of being undefined.
1716
d6fb461d 1717** User Actions
52d1aeee
MA
1718 Bison has always permitted actions such as { $$ = $1 }: it adds the
1719 ending semicolon. Now if in Yacc compatibility mode, the semicolon
1720 is no longer output: one has to write { $$ = $1; }.
1721
d6fb461d 1722** Better C++ compliance
52d1aeee 1723 The output parsers try to respect C++ namespaces.
76551463 1724 [This turned out to be a failed experiment, and it was reverted later.]
52d1aeee 1725
d6fb461d 1726** Reduced Grammars
52d1aeee
MA
1727 Fixed bugs when reporting useless nonterminals.
1728
d6fb461d 1729** 64 bit hosts
52d1aeee
MA
1730 The parsers work properly on 64 bit hosts.
1731
d6fb461d 1732** Error messages
52d1aeee
MA
1733 Some calls to strerror resulted in scrambled or missing error messages.
1734
d6fb461d 1735** %expect
52d1aeee
MA
1736 When the number of shift/reduce conflicts is correct, don't issue
1737 any warning.
1738
d6fb461d 1739** The verbose report includes the rule line numbers.
52d1aeee 1740
d6fb461d 1741** Rule line numbers are fixed in traces.
52d1aeee 1742
d6fb461d 1743** Swedish translation
52d1aeee 1744
d6fb461d 1745** Parse errors
52d1aeee
MA
1746 Verbose parse error messages from the parsers are better looking.
1747 Before: parse error: unexpected `'/'', expecting `"number"' or `'-'' or `'(''
1748 Now: parse error: unexpected '/', expecting "number" or '-' or '('
1749
d6fb461d 1750** Fixed parser memory leaks.
52d1aeee
MA
1751 When the generated parser was using malloc to extend its stacks, the
1752 previous allocations were not freed.
1753
d6fb461d 1754** Fixed verbose output file.
52d1aeee
MA
1755 Some newlines were missing.
1756 Some conflicts in state descriptions were missing.
1757
d6fb461d 1758** Fixed conflict report.
52d1aeee
MA
1759 Option -v was needed to get the result.
1760
d6fb461d 1761** %expect
52d1aeee
MA
1762 Was not used.
1763 Mismatches are errors, not warnings.
1764
d6fb461d 1765** Fixed incorrect processing of some invalid input.
52d1aeee 1766
d6fb461d 1767** Fixed CPP guards: 9foo.h uses BISON_9FOO_H instead of 9FOO_H.
52d1aeee 1768
d6fb461d 1769** Fixed some typos in the documentation.
52d1aeee 1770
d6fb461d 1771** %token MY_EOF 0 is supported.
52d1aeee
MA
1772 Before, MY_EOF was silently renumbered as 257.
1773
d6fb461d 1774** doc/refcard.tex is updated.
52d1aeee 1775
d6fb461d 1776** %output, %file-prefix, %name-prefix.
52d1aeee
MA
1777 New.
1778
d6fb461d 1779** --output
e4ab1254 1780 New, aliasing "--output-file".
52d1aeee 1781\f
d6fb461d 1782* Changes in version 1.30, 2001-10-26:
342b8b6e 1783
e4ab1254
AD
1784** "--defines" and "--graph" have now an optional argument which is the
1785 output file name. "-d" and "-g" do not change; they do not take any
342b8b6e
AD
1786 argument.
1787
e4ab1254 1788** "%source_extension" and "%header_extension" are removed, failed
342b8b6e
AD
1789 experiment.
1790
d6fb461d 1791** Portability fixes.
f987e9d2 1792\f
d6fb461d 1793* Changes in version 1.29, 2001-09-07:
342b8b6e 1794
d6fb461d 1795** The output file does not define const, as this caused problems when used
342b8b6e
AD
1796 with common autoconfiguration schemes. If you still use ancient compilers
1797 that lack const, compile with the equivalent of the C compiler option
e4ab1254 1798 "-Dconst=". Autoconf's AC_C_CONST macro provides one way to do this.
342b8b6e 1799
e4ab1254 1800** Added "-g" and "--graph".
f87a2205 1801
d6fb461d 1802** The Bison manual is now distributed under the terms of the GNU FDL.
f2b5126e 1803
d6fb461d 1804** The input and the output files has automatically a similar extension.
234a3be3 1805
d6fb461d 1806** Russian translation added.
f87a2205 1807
d6fb461d 1808** NLS support updated; should hopefully be less troublesome.
f87a2205 1809
d6fb461d 1810** Added the old Bison reference card.
c33638bb 1811
e4ab1254 1812** Added "--locations" and "%locations".
6deb4447 1813
e4ab1254 1814** Added "-S" and "--skeleton".
cd5bd6ac 1815
e4ab1254 1816** "%raw", "-r", "--raw" is disabled.
62ab6972 1817
d6fb461d 1818** Special characters are escaped when output. This solves the problems
cd5bd6ac
AD
1819 of the #line lines with path names including backslashes.
1820
d6fb461d 1821** New directives.
e4ab1254
AD
1822 "%yacc", "%fixed_output_files", "%defines", "%no_parser", "%verbose",
1823 "%debug", "%source_extension" and "%header_extension".
f987e9d2 1824
d6fb461d 1825** @$
f987e9d2 1826 Automatic location tracking.
f87a2205 1827\f
d6fb461d 1828* Changes in version 1.28, 1999-07-06:
d2e00347 1829
d6fb461d 1830** Should compile better now with K&R compilers.
d2e00347 1831
d6fb461d 1832** Added NLS.
d2e00347 1833
d6fb461d 1834** Fixed a problem with escaping the double quote character.
d2e00347 1835
d6fb461d 1836** There is now a FAQ.
d2e00347 1837\f
d6fb461d 1838* Changes in version 1.27:
5c31c3c2 1839
d6fb461d 1840** The make rule which prevented bison.simple from being created on
5c31c3c2
JT
1841 some systems has been fixed.
1842\f
d6fb461d 1843* Changes in version 1.26:
4be07551 1844
7e508a2b 1845** Bison now uses Automake.
4be07551 1846
d6fb461d 1847** New mailing lists: <bug-bison@gnu.org> and <help-bison@gnu.org>.
4be07551 1848
d6fb461d 1849** Token numbers now start at 257 as previously documented, not 258.
4be07551 1850
d6fb461d 1851** Bison honors the TMPDIR environment variable.
4be07551 1852
d6fb461d 1853** A couple of buffer overruns have been fixed.
f51dbca1 1854
d6fb461d 1855** Problems when closing files should now be reported.
f51dbca1 1856
d6fb461d 1857** Generated parsers should now work even on operating systems which do
f51dbca1 1858 not provide alloca().
4be07551 1859\f
d6fb461d 1860* Changes in version 1.25, 1995-10-16:
df8878c5 1861
d6fb461d 1862** Errors in the input grammar are not fatal; Bison keeps reading
df8878c5 1863the grammar file, and reports all the errors found in it.
8c44d3ec 1864
d6fb461d 1865** Tokens can now be specified as multiple-character strings: for
df8878c5 1866example, you could use "<=" for a token which looks like <=, instead
7e508a2b 1867of choosing a name like LESSEQ.
df8878c5 1868
d6fb461d 1869** The %token_table declaration says to write a table of tokens (names
df8878c5
RS
1870and numbers) into the parser file. The yylex function can use this
1871table to recognize multiple-character string tokens, or for other
1872purposes.
1873
d6fb461d 1874** The %no_lines declaration says not to generate any #line preprocessor
df8878c5
RS
1875directives in the parser file.
1876
d6fb461d 1877** The %raw declaration says to use internal Bison token numbers, not
df8878c5
RS
1878Yacc-compatible token numbers, when token names are defined as macros.
1879
d6fb461d 1880** The --no-parser option produces the parser tables without including
df8878c5
RS
1881the parser engine; a project can now use its own parser engine.
1882The actions go into a separate file called NAME.act, in the form of
1883a switch statement body.
1884\f
d6fb461d 1885* Changes in version 1.23:
6780ca7a 1886
4d019228
DM
1887The user can define YYPARSE_PARAM as the name of an argument to be
1888passed into yyparse. The argument should have type void *. It should
1889actually point to an object. Grammar actions can access the variable
1890by casting it to the proper pointer type.
6780ca7a 1891
6780ca7a 1892Line numbers in output file corrected.
6780ca7a 1893\f
d6fb461d 1894* Changes in version 1.22:
6780ca7a
DM
1895
1896--help option added.
6780ca7a 1897\f
d6fb461d 1898* Changes in version 1.20:
6780ca7a
DM
1899
1900Output file does not redefine const for C++.
9f4503d6 1901
76551463
AD
1902-----
1903
c932d613 1904Copyright (C) 1995-2012 Free Software Foundation, Inc.
76551463 1905
8defe11b 1906This file is part of Bison, the GNU Parser Generator.
76551463 1907
f16b0819 1908This program is free software: you can redistribute it and/or modify
76551463 1909it under the terms of the GNU General Public License as published by
f16b0819
PE
1910the Free Software Foundation, either version 3 of the License, or
1911(at your option) any later version.
76551463 1912
f16b0819 1913This program is distributed in the hope that it will be useful,
76551463
AD
1914but WITHOUT ANY WARRANTY; without even the implied warranty of
1915MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
1916GNU General Public License for more details.
1917
1918You should have received a copy of the GNU General Public License
f16b0819 1919along with this program. If not, see <http://www.gnu.org/licenses/>.
7e508a2b
AD
1920
1921 LocalWords: yacc YYBACKUP glr GCC lalr ArrayIndexOutOfBoundsException nullptr
1922 LocalWords: cplusplus liby rpl fprintf mfcalc Wyacc stmt cond expr mk sym lr
1923 LocalWords: IELR ielr Lookahead YYERROR nonassoc LALR's api lookaheads yychar
1924 LocalWords: destructor lookahead YYRHSLOC YYLLOC Rhs ifndef YYFAIL cpp sr rr
1925 LocalWords: preprocessor initializer Wno Wnone Werror FreeBSD prec livelocks
1926 LocalWords: Solaris AIX UX RHEL Tru LHS gcc's Wundef YYENABLE NLS YYLTYPE VCG
1927 LocalWords: yyerror cpp's Wunused yylval yylloc prepend yyparse yylex yypush
1928 LocalWords: Graphviz xml nonterminals midrule destructor's YYSTYPE typedef ly
1929 LocalWords: CHR chr printf stdout namespace preprocessing enum pre include's
1930 LocalWords: YYRECOVERING nonfree destructors YYABORT YYACCEPT params enums de
1931 LocalWords: struct yystype DJGPP lex param Haible NUM alloca YYSTACK NUL goto
1932 LocalWords: YYMAXDEPTH Unescaped UCNs YYLTYPE's yyltype typedefs inline Yaccs
1933 LocalWords: Heriyanto Reenable dprec Hilfinger Eggert MYEOF Folle Menezes EOF
242cc08e 1934 LocalWords: Lackovic define's itemset Groff Gettext malloc NEWS'ed YYDEBUG YY
7e508a2b 1935 LocalWords: namespaces strerror const autoconfiguration Dconst Autoconf's FDL
242cc08e
AD
1936 LocalWords: Automake TMPDIR LESSEQ ylwrap endif yydebug YYTOKEN YYLSP ival hh
1937 LocalWords: extern YYTOKENTYPE TOKENTYPE yytokentype tokentype STYPE lval pdf
90b1335a 1938 LocalWords: lang yyoutput dvi html ps POSIX lvalp llocp calc yyo fval
7e508a2b
AD
1939
1940Local Variables:
1941mode: outline
e4ab1254 1942fill-column: 76
7e508a2b 1943End: