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ed7658fe 1GNU Bison NEWS
3af4feb2 2
52718713 3* Noteworthy changes in release ?.? (????-??-??) [?]
74553c98 4
8458a411 5** WARNING: Future backward-incompatibilities!
597afd73 6
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7 Like other GNU packages, Bison will start using some of the C99 features
8 for its own code, especially the definition of variables after statements.
9 The generated C parsers still aim at C90.
10
8458a411 11** Backward incompatible changes
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12
13*** Obsolete features
14
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15 Support for YYFAIL is removed (deprecated in Bison 2.4.2): use YYERROR.
16
17 Support for yystype and yyltype is removed (deprecated in Bison 1.875):
18 use YYSTYPE and YYLTYPE.
19
20 Support for YYLEX_PARAM and YYPARSE_PARAM is removed (deprecated in Bison
21 1.875): use %lex-param, %parse-param, or %param.
47db7ed1 22
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23 Missing semicolons at the end of actions are no longer added (as announced
24 in the release 2.5).
25
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26*** Use of YACC='bison -y'
27
28 TL;DR: With Autoconf <= 2.69, pass -Wno-yacc to (AM_)YFLAGS if you use
29 Bison extensions.
30
31 Traditional Yacc generates 'y.tab.c' whatever the name of the input file.
32 Therefore Makefiles written for Yacc expect 'y.tab.c' (and possibly
33 'y.tab.h' and 'y.outout') to be generated from 'foo.y'.
34
35 To this end, for ages, AC_PROG_YACC, Autoconf's macro to look for an
36 implementation of Yacc, was using Bison as 'bison -y'. While it does
37 ensure compatible output file names, it also enables warnings for
38 incompatibilities with POSIX Yacc. In other words, 'bison -y' triggers
39 warnings for Bison extensions.
40
41 Autoconf 2.70+ fixes this incompatibility by using YACC='bison -o y.tab.c'
42 (which also generates 'y.tab.h' and 'y.output' when needed).
43 Alternatively, disable Yacc warnings by passing '-Wno-yacc' to your Yacc
44 flags (YFLAGS, or AM_YFLAGS with Automake).
45
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46** Bug fixes
47
c21e515e 48*** The epilogue is no longer affected by internal #defines (glr.c)
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49
50 The glr.c skeleton uses defines such as #define yylval (yystackp->yyval) in
51 generated code. These weren't properly undefined before the inclusion of
52 the user epilogue, so functions such as the following were butchered by the
53 preprocessor expansion:
54
55 int yylex (YYSTYPE *yylval);
56
6c7022f7 57 This is fixed: yylval, yynerrs, yychar, and yylloc are now valid
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58 identifiers for user-provided variables.
59
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60*** stdio.h is no longer needed when locations are enabled (yacc.c)
61
62 Changes in Bison 2.7 introduced a dependency on FILE and fprintf when
63 locations are enabled. This is fixed.
64
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65** Diagnostics reported by Bison
66
67 Most of these features were contributed by Théophile Ranquet and Victor
68 Santet.
73370a9d 69
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70*** Carets
71
72 Version 2.7 introduced caret errors, for a prettier output. These are now
73 activated by default. The old format can still be used by invoking Bison
74 with -fno-caret (or -fnone).
75
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76 Some error messages that reproduced excerpts of the grammar are now using
77 the caret information only. For instance on:
78
79 %%
80 exp: 'a' | 'a';
81
82 Bison 2.7 reports:
83
84 in.y: warning: 1 reduce/reduce conflict [-Wconflicts-rr]
85 in.y:2.12-14: warning: rule useless in parser due to conflicts: exp: 'a' [-Wother]
86
87 Now bison reports:
88
89 in.y: warning: 1 reduce/reduce conflict [-Wconflicts-rr]
90 in.y:2.12-14: warning: rule useless in parser due to conflicts [-Wother]
91 exp: 'a' | 'a';
92 ^^^
93
94 and "bison -fno-caret" reports:
95
96 in.y: warning: 1 reduce/reduce conflict [-Wconflicts-rr]
97 in.y:2.12-14: warning: rule useless in parser due to conflicts [-Wother]
98
1048a1c9 99*** Enhancements of the -Werror option
518e8830 100
1048a1c9 101 The -Werror=CATEGORY option is now recognized, and will treat specified
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102 warnings as errors. The warnings need not have been explicitly activated
103 using the -W option, this is similar to what GCC 4.7 does.
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104
105 For example, given the following command line, Bison will treat both
d949eefd 106 warnings related to POSIX Yacc incompatibilities and S/R conflicts as
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107 errors (and only those):
108
109 $ bison -Werror=yacc,error=conflicts-sr input.y
110
111 If no categories are specified, -Werror will make all active warnings into
112 errors. For example, the following line does the same the previous example:
113
114 $ bison -Werror -Wnone -Wyacc -Wconflicts-sr input.y
115
116 (By default -Wconflicts-sr,conflicts-rr,deprecated,other is enabled.)
117
118 Note that the categories in this -Werror option may not be prefixed with
119 "no-". However, -Wno-error[=CATEGORY] is valid.
120
121 Note that -y enables -Werror=yacc. Therefore it is now possible to require
122 Yacc-like behavior (e.g., always generate y.tab.c), but to report
123 incompatibilities as warnings: "-y -Wno-error=yacc".
518e8830 124
46bdb8ec 125*** The display of warnings is now richer
73370a9d 126
46bdb8ec 127 The option that controls a given warning is now displayed:
73370a9d 128
46bdb8ec 129 foo.y:4.6: warning: type clash on default action: <foo> != <bar> [-Wother]
73370a9d 130
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131 In the case of warnings treated as errors, the prefix is changed from
132 "warning: " to "error: ", and the suffix is displayed, in a manner similar
d949eefd 133 to GCC, as [-Werror=CATEGORY].
1048a1c9 134
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135 For instance, where the previous version of Bison would report (and exit
136 with failure):
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137
138 bison: warnings being treated as errors
46bdb8ec 139 input.y:1.1: warning: stray ',' treated as white space
1048a1c9 140
46bdb8ec 141 it now reports:
1048a1c9 142
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143 input.y:1.1: error: stray ',' treated as white space [-Werror=other]
144
145*** Deprecated constructs
146
147 The new 'deprecated' warning category flags obsolete constructs whose
148 support will be discontinued. It is enabled by default. These warnings
149 used to be reported as 'other' warnings.
150
73370a9d 151*** Useless semantic types
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152
153 Bison now warns about useless (uninhabited) semantic types. Since
154 semantic types are not declared to Bison (they are defined in the opaque
155 %union structure), it is %printer/%destructor directives about useless
156 types that trigger the warning:
157
158 %token <type1> term
159 %type <type2> nterm
160 %printer {} <type1> <type3>
161 %destructor {} <type2> <type4>
162 %%
163 nterm: term { $$ = $1; };
164
165 3.28-34: warning: type <type3> is used, but is not associated to any symbol
166 4.28-34: warning: type <type4> is used, but is not associated to any symbol
167
31557b9e 168*** Undefined but unused symbols
b921d92f 169
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170 Bison used to raise an error for undefined symbols that are not used in
171 the grammar. This is now only a warning.
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172
173 %printer {} symbol1
174 %destructor {} symbol2
31557b9e 175 %type <type> symbol3
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176 %%
177 exp: "a";
178
73370a9d 179*** Useless destructors or printers
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180
181 Bison now warns about useless destructors or printers. In the following
182 example, the printer for <type1>, and the destructor for <type2> are
183 useless: all symbols of <type1> (token1) already have a printer, and all
184 symbols of type <type2> (token2) already have a destructor.
185
186 %token <type1> token1
187 <type2> token2
188 <type3> token3
189 <type4> token4
190 %printer {} token1 <type1> <type3>
191 %destructor {} token2 <type2> <type4>
192
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193*** Conflicts
194
195 The warnings and error messages about shift/reduce and reduce/reduce
196 conflicts have been normalized. For instance on the following foo.y file:
197
198 %glr-parser
199 %%
200 exp: exp '+' exp | '0' | '0';
201
202 compare the previous version of bison:
203
204 $ bison foo.y
205 foo.y: conflicts: 1 shift/reduce, 2 reduce/reduce
206 $ bison -Werror foo.y
207 bison: warnings being treated as errors
208 foo.y: conflicts: 1 shift/reduce, 2 reduce/reduce
209
210 with the new behavior:
211
212 $ bison foo.y
213 foo.y: warning: 1 shift/reduce conflict [-Wconflicts-sr]
214 foo.y: warning: 2 reduce/reduce conflicts [-Wconflicts-rr]
215 $ bison -Werror foo.y
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216 foo.y: error: 1 shift/reduce conflict [-Werror=conflicts-sr]
217 foo.y: error: 2 reduce/reduce conflicts [-Werror=conflicts-rr]
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218
219 When %expect or %expect-rr is used, such as with bar.y:
220
221 %expect 0
222 %glr-parser
223 %%
224 exp: exp '+' exp | '0' | '0';
225
226 Former behavior:
227
228 $ bison bar.y
229 bar.y: conflicts: 1 shift/reduce, 2 reduce/reduce
230 bar.y: expected 0 shift/reduce conflicts
231 bar.y: expected 0 reduce/reduce conflicts
232
233 New one:
234
235 $ bison bar.y
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236 bar.y: error: shift/reduce conflicts: 1 found, 0 expected
237 bar.y: error: reduce/reduce conflicts: 2 found, 0 expected
d87ea54c 238
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239** Incompatibilities with POSIX Yacc
240
241 The 'yacc' category is no longer part of '-Wall', enable it explicitly
242 with '-Wyacc'.
243
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244** Additional yylex/yyparse arguments
245
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246 The new directive %param declares additional arguments to both yylex and
247 yyparse. The %lex-param, %parse-param, and %param directives support one
248 or more arguments. Instead of
2055a44e 249
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250 %lex-param {arg1_type *arg1}
251 %lex-param {arg2_type *arg2}
252 %parse-param {arg1_type *arg1}
253 %parse-param {arg2_type *arg2}
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254
255 one may now declare
256
e436fa67 257 %param {arg1_type *arg1} {arg2_type *arg2}
2055a44e 258
2a6b66c5 259** Variable api.token.prefix
99c08fb6 260
2a6b66c5 261 The variable api.token.prefix changes the way tokens are identified in
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262 the generated files. This is especially useful to avoid collisions
263 with identifiers in the target language. For instance
264
e436fa67 265 %token FILE for ERROR
2a6b66c5 266 %define api.token.prefix "TOK_"
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267 %%
268 start: FILE for ERROR;
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269
270 will generate the definition of the symbols TOK_FILE, TOK_for, and
271 TOK_ERROR in the generated sources. In particular, the scanner must
272 use these prefixed token names, although the grammar itself still
273 uses the short names (as in the sample rule given above).
274
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275** Variable api.value.type
276
277 This new %define variable supersedes the #define macro YYSTYPE. The use
278 of YYSTYPE is discouraged. In particular, #defining YYSTYPE *and* either
279 using %union or %defining api.value.type results in undefined behavior.
280
281 Either define api.value.type, or use "%union":
282
283 %union
284 {
285 int ival;
286 char *sval;
287 }
288 %token <ival> INT "integer"
289 %token <sval> STRING "string"
290 %printer { fprintf (yyo, "%d", $$); } <ival>
291 %destructor { free ($$); } <sval>
292
293 /* In yylex(). */
294 yylval.ival = 42; return INT;
295 yylval.sval = "42"; return STRING;
296
297 The %define variable api.value.type supports several special values. The
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298 keyword value 'union' means that the user provides genuine types, not
299 union member names such as "ival" and "sval" above (WARNING: will fail if
1fa19a76 300 -y/--yacc/%yacc is enabled).
6574576c 301
435575cb 302 %define api.value.type union
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303 %token <int> INT "integer"
304 %token <char *> STRING "string"
305 %printer { fprintf (yyo, "%d", $$); } <int>
306 %destructor { free ($$); } <char *>
307
308 /* In yylex(). */
309 yylval.INT = 42; return INT;
310 yylval.STRING = "42"; return STRING;
311
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312 The keyword value variant is somewhat equivalent, but for C++ special
313 provision is made to allow classes to be used (more about this below).
6574576c 314
435575cb 315 %define api.value.type variant
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316 %token <int> INT "integer"
317 %token <std::string> STRING "string"
318
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319 Values between braces denote user defined types. This is where YYSTYPE
320 used to be used.
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321
322 %code requires
323 {
324 struct my_value
325 {
326 enum
327 {
328 is_int, is_string
329 } kind;
330 union
331 {
332 int ival;
333 char *sval;
334 } u;
335 };
336 }
435575cb 337 %define api.value.type {struct my_value}
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338 %token <u.ival> INT "integer"
339 %token <u.sval> STRING "string"
340 %printer { fprintf (yyo, "%d", $$); } <u.ival>
341 %destructor { free ($$); } <u.sval>
342
343 /* In yylex(). */
344 yylval.u.ival = 42; return INT;
345 yylval.u.sval = "42"; return STRING;
346
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347** Variable parse.error
348
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349 This variable controls the verbosity of error messages. The use of the
350 %error-verbose directive is deprecated in favor of "%define parse.error
351 verbose".
31b850d2 352
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353** Renamed %define variables
354
355 The following variables have been renamed for consistency. Backward
356 compatibility is ensured, but upgrading is recommended.
357
358 lr.default-reductions -> lr.default-reduction
359 lr.keep-unreachable-states -> lr.keep-unreachable-state
360 namespace -> api.namespace
361 stype -> api.value.type
362
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363** Semantic predicates
364
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365 Contributed by Paul Hilfinger.
366
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367 The new, experimental, semantic-predicate feature allows actions of the
368 form "%?{ BOOLEAN-EXPRESSION }", which cause syntax errors (as for
ca2a6d15 369 YYERROR) if the expression evaluates to 0, and are evaluated immediately
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370 in GLR parsers, rather than being deferred. The result is that they allow
371 the programmer to prune possible parses based on the values of run-time
372 expressions.
ca2a6d15 373
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374** The directive %expect-rr is now an error in non GLR mode
375
376 It used to be an error only if used in non GLR mode, _and_ if there are
377 reduce/reduce conflicts.
378
5202b6ac 379** Tokens are numbered in their order of appearance
93561c21 380
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381 Contributed by Valentin Tolmer.
382
383 With '%token A B', A had a number less than the one of B. However,
384 precedence declarations used to generate a reversed order. This is now
385 fixed, and introducing tokens with any of %token, %left, %right,
386 %precedence, or %nonassoc yields the same result.
387
388 When mixing declarations of tokens with a litteral character (e.g., 'a')
389 or with an identifier (e.g., B) in a precedence declaration, Bison
390 numbered the litteral characters first. For example
391
392 %right A B 'c' 'd'
393
394 would lead to the tokens declared in this order: 'c' 'd' A B. Again, the
395 input order is now preserved.
396
397 These changes were made so that one can remove useless precedence and
398 associativity declarations (i.e., map %nonassoc, %left or %right to
399 %precedence, or to %token) and get exactly the same output.
93561c21 400
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401** Useless precedence and associativity
402
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403 Contributed by Valentin Tolmer.
404
1282c124 405 When developing and maintaining a grammar, useless associativity and
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406 precedence directives are common. They can be a nuisance: new ambiguities
407 arising are sometimes masked because their conflicts are resolved due to
408 the extra precedence or associativity information. Furthermore, it can
409 hinder the comprehension of a new grammar: one will wonder about the role
410 of a precedence, where in fact it is useless. The following changes aim
411 at detecting and reporting these extra directives.
412
413*** Precedence warning category
414
415 A new category of warning, -Wprecedence, was introduced. It flags the
416 useless precedence and associativity directives.
417
418*** Useless associativity
419
420 Bison now warns about symbols with a declared associativity that is never
421 used to resolve conflicts. In that case, using %precedence is sufficient;
422 the parsing tables will remain unchanged. Solving these warnings may raise
423 useless precedence warnings, as the symbols no longer have associativity.
424 For example:
425
426 %left '+'
427 %left '*'
428 %%
429 exp:
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430 "number"
431 | exp '+' "number"
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432 | exp '*' exp
433 ;
434
435 will produce a
436
437 warning: useless associativity for '+', use %precedence [-Wprecedence]
438 %left '+'
439 ^^^
440
441*** Useless precedence
442
443 Bison now warns about symbols with a declared precedence and no declared
444 associativity (i.e., declared with %precedence), and whose precedence is
445 never used. In that case, the symbol can be safely declared with %token
446 instead, without modifying the parsing tables. For example:
447
448 %precedence '='
449 %%
1282c124 450 exp: "var" '=' "number";
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451
452 will produce a
453
454 warning: useless precedence for '=' [-Wprecedence]
455 %precedence '='
456 ^^^
457
458*** Useless precedence and associativity
459
460 In case of both useless precedence and associativity, the issue is flagged
461 as follows:
462
463 %nonassoc '='
464 %%
1282c124 465 exp: "var" '=' "number";
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466
467 The warning is:
468
469 warning: useless precedence and associativity for '=' [-Wprecedence]
470 %nonassoc '='
471 ^^^
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472
473** Empty rules
474
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475 With help from Joel E. Denny and Gabriel Rassoul.
476
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477 Empty rules (i.e., with an empty right-hand side) can now be explicitly
478 marked by the new %empty directive. Using %empty on a non-empty rule is
479 an error. The new -Wempty-rule warning reports empty rules without
480 %empty. On the following grammar:
481
482 %%
483 s: a b c;
484 a: ;
485 b: %empty;
486 c: 'a' %empty;
487
488 bison reports:
489
490 3.4-5: warning: empty rule without %empty [-Wempty-rule]
491 a: {}
492 ^^
493 5.8-13: error: %empty on non-empty rule
494 c: 'a' %empty {};
495 ^^^^^^
cc2235ac 496
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497** Java skeleton improvements
498
499 Contributed by Paolo Bonzini.
500
501 The constants for token names were moved to the Lexer interface. Also, it
502 is possible to add code to the parser's constructors using "%code init"
503 and "%define init_throws".
504
505** C++ skeletons improvements
506
507*** The parser header is no longer mandatory (lalr1.cc, glr.cc)
508
509 Using %defines is now optional. Without it, the needed support classes
510 are defined in the generated parser, instead of additional files (such as
511 location.hh, position.hh and stack.hh).
512
513*** Locations are no longer mandatory (lalr1.cc, glr.cc)
514
515 Both lalr1.cc and glr.cc no longer require %location.
516
517*** syntax_error exception (lalr1.cc)
518
519 The C++ parser features a syntax_error exception, which can be
520 thrown from the scanner or from user rules to raise syntax errors.
521 This facilitates reporting errors caught in sub-functions (e.g.,
522 rejecting too large integral literals from a conversion function
523 used by the scanner, or rejecting invalid combinations from a
524 factory invoked by the user actions).
525
526*** %define api.value.type variant
527
528 This is based on a submission from Michiel De Wilde. With help
529 from Théophile Ranquet.
530
531 In this mode, complex C++ objects can be used as semantic values. For
532 instance:
533
534 %token <::std::string> TEXT;
535 %token <int> NUMBER;
536 %token SEMICOLON ";"
537 %type <::std::string> item;
538 %type <::std::list<std::string>> list;
539 %%
540 result:
541 list { std::cout << $1 << std::endl; }
542 ;
543
544 list:
6240346a 545 %empty { /* Generates an empty string list. */ }
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546 | list item ";" { std::swap ($$, $1); $$.push_back ($2); }
547 ;
548
549 item:
550 TEXT { std::swap ($$, $1); }
551 | NUMBER { $$ = string_cast ($1); }
552 ;
553
554*** %define api.token.constructor
555
556 When variants are enabled, Bison can generate functions to build the
557 tokens. This guarantees that the token type (e.g., NUMBER) is consistent
558 with the semantic value (e.g., int):
559
560 parser::symbol_type yylex ()
561 {
562 parser::location_type loc = ...;
563 ...
564 return parser::make_TEXT ("Hello, world!", loc);
565 ...
566 return parser::make_NUMBER (42, loc);
567 ...
568 return parser::make_SEMICOLON (loc);
569 ...
570 }
571
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572* Noteworthy changes in release ?.? (????-??-??) [?]
573
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574** Bug fixes
575
576*** Fix compiler attribute portability (yacc.c)
577
578 With locations enabled, __attribute__ was used unprotected.
0a7b8559 579
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580*** Fix some compiler warnings (lalr1.cc)
581
c13bb348 582* Noteworthy changes in release 2.7 (2012-12-12) [stable]
effd30c0 583
edf9a06f 584** Bug fixes
7bada535 585
edf9a06f 586 Warnings about uninitialized yylloc in yyparse have been fixed.
7bada535 587
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588 Restored C90 compliance (yet no report was ever made).
589
d4fe9e88 590** Diagnostics are improved
7bada535 591
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592 Contributed by Théophile Ranquet.
593
d4fe9e88 594*** Changes in the format of error messages
7bada535 595
d4fe9e88 596 This used to be the format of many error reports:
1f1bd572 597
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598 input.y:2.7-12: %type redeclaration for exp
599 input.y:1.7-12: previous declaration
1f1bd572 600
d4fe9e88 601 It is now:
1f1bd572 602
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603 input.y:2.7-12: error: %type redeclaration for exp
604 input.y:1.7-12: previous declaration
cbaea010 605
d4fe9e88 606*** New format for error reports: carets
cbaea010 607
d4fe9e88 608 Caret errors have been added to Bison:
cbaea010 609
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610 input.y:2.7-12: error: %type redeclaration for exp
611 %type <sval> exp
612 ^^^^^^
613 input.y:1.7-12: previous declaration
614 %type <ival> exp
615 ^^^^^^
cbaea010 616
d4fe9e88 617 or
cbaea010 618
7bada535 619 input.y:3.20-23: error: ambiguous reference: '$exp'
fb6040f0 620 exp: exp '+' exp { $exp = $1 + $3; };
7bada535 621 ^^^^
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622 input.y:3.1-3: refers to: $exp at $$
623 exp: exp '+' exp { $exp = $1 + $3; };
624 ^^^
625 input.y:3.6-8: refers to: $exp at $1
626 exp: exp '+' exp { $exp = $1 + $3; };
627 ^^^
628 input.y:3.14-16: refers to: $exp at $3
629 exp: exp '+' exp { $exp = $1 + $3; };
630 ^^^
7bada535 631
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632 The default behavior for now is still not to display these unless
633 explicitly asked with -fcaret (or -fall). However, in a later release, it
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634 will be made the default behavior (but may still be deactivated with
635 -fno-caret).
d3e4409a 636
1f1bd572 637** New value for %define variable: api.pure full
d3e4409a 638
1f1bd572 639 The %define variable api.pure requests a pure (reentrant) parser. However,
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640 for historical reasons, using it in a location-tracking Yacc parser
641 resulted in a yyerror function that did not take a location as a
642 parameter. With this new value, the user may request a better pure parser,
643 where yyerror does take a location as a parameter (in location-tracking
644 parsers).
1f1bd572
TR
645
646 The use of "%define api.pure true" is deprecated in favor of this new
647 "%define api.pure full".
d3e4409a 648
7287be84 649** New %define variable: api.location.type (glr.cc, lalr1.cc, lalr1.java)
db8ab2be
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650
651 The %define variable api.location.type defines the name of the type to use
652 for locations. When defined, Bison no longer generates the position.hh
653 and location.hh files, nor does the parser will include them: the user is
654 then responsible to define her type.
655
656 This can be used in programs with several parsers to factor their location
7287be84
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657 and position files: let one of them generate them, and the others just use
658 them.
db8ab2be
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659
660 This feature was actually introduced, but not documented, in Bison 2.5,
661 under the name "location_type" (which is maintained for backward
662 compatibility).
663
7287be84
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664 For consistency, lalr1.java's %define variables location_type and
665 position_type are deprecated in favor of api.location.type and
666 api.position.type.
667
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668** Exception safety (lalr1.cc)
669
670 The parse function now catches exceptions, uses the %destructors to
671 release memory (the lookahead symbol and the symbols pushed on the stack)
672 before re-throwing the exception.
673
674 This feature is somewhat experimental. User feedback would be
675 appreciated.
676
9c16d399 677** Graph improvements in DOT and XSLT
fc4fdd62 678
8458a411
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679 Contributed by Théophile Ranquet.
680
fc4fdd62
TR
681 The graphical presentation of the states is more readable: their shape is
682 now rectangular, the state number is clearly displayed, and the items are
683 numbered and left-justified.
684
685 The reductions are now explicitly represented as transitions to other
686 diamond shaped nodes.
687
9c16d399
TR
688 These changes are present in both --graph output and xml2dot.xsl XSLT
689 processing, with minor (documented) differences.
690
d4fe9e88 691** %language is no longer an experimental feature.
fb4c8a7c 692
d4fe9e88
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693 The introduction of this feature, in 2.4, was four years ago. The
694 --language option and the %language directive are no longer experimental.
fb4c8a7c 695
53e2cd1e
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696** Documentation
697
698 The sections about shift/reduce and reduce/reduce conflicts resolution
699 have been fixed and extended.
9d2423f5 700
d4fe9e88
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701 Although introduced more than four years ago, XML and Graphviz reports
702 were not properly documented.
703
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704 The translation of mid-rule actions is now described.
705
9d3f7eaf 706* Noteworthy changes in release 2.6.5 (2012-11-07) [stable]
6f1360bd 707
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708 We consider compiler warnings about Bison generated parsers to be bugs.
709 Rather than working around them in your own project, please consider
710 reporting them to us.
711
712** Bug fixes
713
714 Warnings about uninitialized yylval and/or yylloc for push parsers with a
715 pure interface have been fixed for GCC 4.0 up to 4.8, and Clang 2.9 to
716 3.2.
717
718 Other issues in the test suite have been addressed.
6f1360bd 719
1282c124 720 Null characters are correctly displayed in error messages.
95066e92 721
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722 When possible, yylloc is correctly initialized before calling yylex. It
723 is no longer necessary to initialize it in the %initial-action.
724
0ac15849 725* Noteworthy changes in release 2.6.4 (2012-10-23) [stable]
a4eb820f 726
468455e1 727 Bison 2.6.3's --version was incorrect. This release fixes this issue.
a4eb820f 728
6eb8f74f 729* Noteworthy changes in release 2.6.3 (2012-10-22) [stable]
933ec544 730
6b4cb804
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731** Bug fixes
732
a1a77e1f 733 Bugs and portability issues in the test suite have been fixed.
6b4cb804
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734
735 Some errors in translations have been addressed, and --help now directs
736 users to the appropriate place to report them.
737
738 Stray Info files shipped by accident are removed.
739
740 Incorrect definitions of YY_, issued by yacc.c when no parser header is
741 generated, are removed.
9c26b8fc 742
a2b3f101
TR
743 All the generated headers are self-contained.
744
c9d5bcc9
AD
745** Header guards (yacc.c, glr.c, glr.cc)
746
747 In order to avoid collisions, the header guards are now
748 YY_<PREFIX>_<FILE>_INCLUDED, instead of merely <PREFIX>_<FILE>.
749 For instance the header generated from
750
751 %define api.prefix "calc"
752 %defines "lib/parse.h"
753
754 will use YY_CALC_LIB_PARSE_H_INCLUDED as guard.
755
c12c4c50 756** Fix compiler warnings in the generated parser (yacc.c, glr.c)
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757
758 The compilation of pure parsers (%define api.pure) can trigger GCC
759 warnings such as:
760
761 input.c: In function 'yyparse':
762 input.c:1503:12: warning: 'yylval' may be used uninitialized in this
763 function [-Wmaybe-uninitialized]
764 *++yyvsp = yylval;
765 ^
766
767 This is now fixed; pragmas to avoid these warnings are no longer needed.
768
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769 Warnings from clang ("equality comparison with extraneous parentheses" and
770 "function declared 'noreturn' should not return") have also been
771 addressed.
772
e1eeecd3 773* Noteworthy changes in release 2.6.2 (2012-08-03) [stable]
9c26b8fc 774
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775** Bug fixes
776
777 Buffer overruns, complaints from Flex, and portability issues in the test
778 suite have been fixed.
779
c9d546b2
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780** Spaces in %lex- and %parse-param (lalr1.cc, glr.cc)
781
782 Trailing end-of-lines in %parse-param or %lex-param would result in
783 invalid C++. This is fixed.
9c26b8fc 784
dcd5344d
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785** Spurious spaces and end-of-lines
786
787 The generated files no longer end (nor start) with empty lines.
788
77b214ef 789* Noteworthy changes in release 2.6.1 (2012-07-30) [stable]
a4107f24 790
8617d87e
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791 Bison no longer executes user-specified M4 code when processing a grammar.
792
e20e6a50
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793** Future Changes
794
795 In addition to the removal of the features announced in Bison 2.6, the
796 next major release will remove the "Temporary hack for adding a semicolon
797 to the user action", as announced in the release 2.5. Instead of:
798
799 exp: exp "+" exp { $$ = $1 + $3 };
800
801 write:
802
803 exp: exp "+" exp { $$ = $1 + $3; };
804
8617d87e
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805** Bug fixes
806
0e164d43
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807*** Type names are now properly escaped.
808
809*** glr.cc: set_debug_level and debug_level work as expected.
a4107f24 810
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811*** Stray @ or $ in actions
812
813 While Bison used to warn about stray $ or @ in action rules, it did not
814 for other actions such as printers, destructors, or initial actions. It
815 now does.
816
cd735a8c 817** Type names in actions
4982f078
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818
819 For consistency with rule actions, it is now possible to qualify $$ by a
cd735a8c 820 type-name in destructors, printers, and initial actions. For instance:
4982f078
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821
822 %printer { fprintf (yyo, "(%d, %f)", $<ival>$, $<fval>$); } <*> <>;
823
824 will display two values for each typed and untyped symbol (provided
cd735a8c 825 that YYSTYPE has both "ival" and "fval" fields).
60aa04a2 826
1505e8bb 827* Noteworthy changes in release 2.6 (2012-07-19) [stable]
0f11eec2 828
d0a30438 829** Future changes
9553083c 830
55d1006f
AD
831 The next major release of Bison will drop support for the following
832 deprecated features. Please report disagreements to bug-bison@gnu.org.
0f11eec2 833
aaf61036 834*** K&R C parsers
55d1006f
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835
836 Support for generating parsers in K&R C will be removed. Parsers
242cc08e 837 generated for C support ISO C90, and are tested with ISO C99 and ISO C11
55d1006f
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838 compilers.
839
258cddbc 840*** Features deprecated since Bison 1.875
0f11eec2 841
258cddbc
AD
842 The definitions of yystype and yyltype will be removed; use YYSTYPE and
843 YYLTYPE.
0f11eec2 844
258cddbc
AD
845 YYPARSE_PARAM and YYLEX_PARAM, deprecated in favor of %parse-param and
846 %lex-param, will no longer be supported.
847
848 Support for the preprocessor symbol YYERROR_VERBOSE will be removed, use
849 %error-verbose.
55d1006f
AD
850
851*** The generated header will be included (yacc.c)
0f11eec2
AD
852
853 Instead of duplicating the content of the generated header (definition of
55d1006f
AD
854 YYSTYPE, yyparse declaration etc.), the generated parser will include it,
855 as is already the case for GLR or C++ parsers. This change is deferred
856 because existing versions of ylwrap (e.g., Automake 1.12.1) do not support
857 it.
0f11eec2 858
c2425191 859** Generated Parser Headers
56ca3d8f 860
258cddbc 861*** Guards (yacc.c, glr.c, glr.cc)
c3e9f08f
AD
862
863 The generated headers are now guarded, as is already the case for C++
242cc08e 864 parsers (lalr1.cc). For instance, with --defines=foo.h:
c3e9f08f 865
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AD
866 #ifndef YY_FOO_H
867 # define YY_FOO_H
868 ...
869 #endif /* !YY_FOO_H */
c3e9f08f 870
258cddbc 871*** New declarations (yacc.c, glr.c)
56ca3d8f
AD
872
873 The generated header now declares yydebug and yyparse. Both honor
874 --name-prefix=bar_, and yield
875
e29f0771 876 int bar_parse (void);
56ca3d8f
AD
877
878 rather than
879
e29f0771
AD
880 #define yyparse bar_parse
881 int yyparse (void);
56ca3d8f
AD
882
883 in order to facilitate the inclusion of several parser headers inside a
884 single compilation unit.
c3e9f08f 885
258cddbc
AD
886*** Exported symbols in C++
887
888 The symbols YYTOKEN_TABLE and YYERROR_VERBOSE, which were defined in the
889 header, are removed, as they prevent the possibility of including several
890 generated headers from a single compilation unit.
891
694af10c
AD
892*** YYLSP_NEEDED
893
894 For the same reasons, the undocumented and unused macro YYLSP_NEEDED is no
895 longer defined.
896
4b3847c3
AD
897** New %define variable: api.prefix
898
899 Now that the generated headers are more complete and properly protected
900 against multiple inclusions, constant names, such as YYSTYPE are a
901 problem. While yyparse and others are properly renamed by %name-prefix,
902 YYSTYPE, YYDEBUG and others have never been affected by it. Because it
903 would introduce backward compatibility issues in projects not expecting
904 YYSTYPE to be renamed, instead of changing the behavior of %name-prefix,
905 it is deprecated in favor of a new %define variable: api.prefix.
906
907 The following examples compares both:
908
909 %name-prefix "bar_" | %define api.prefix "bar_"
910 %token <ival> FOO %token <ival> FOO
911 %union { int ival; } %union { int ival; }
912 %% %%
913 exp: 'a'; exp: 'a';
914
915 bison generates:
916
917 #ifndef BAR_FOO_H #ifndef BAR_FOO_H
918 # define BAR_FOO_H # define BAR_FOO_H
919
920 /* Enabling traces. */ /* Enabling traces. */
5f108727
AD
921 # ifndef YYDEBUG | # ifndef BAR_DEBUG
922 > # if defined YYDEBUG
923 > # if YYDEBUG
924 > # define BAR_DEBUG 1
925 > # else
926 > # define BAR_DEBUG 0
927 > # endif
928 > # else
929 # define YYDEBUG 0 | # define BAR_DEBUG 0
930 > # endif
931 # endif | # endif
932
933 # if YYDEBUG | # if BAR_DEBUG
4b3847c3
AD
934 extern int bar_debug; extern int bar_debug;
935 # endif # endif
936
937 /* Tokens. */ /* Tokens. */
938 # ifndef YYTOKENTYPE | # ifndef BAR_TOKENTYPE
939 # define YYTOKENTYPE | # define BAR_TOKENTYPE
940 enum yytokentype { | enum bar_tokentype {
941 FOO = 258 FOO = 258
942 }; };
943 # endif # endif
944
945 #if ! defined YYSTYPE \ | #if ! defined BAR_STYPE \
946 && ! defined YYSTYPE_IS_DECLARED | && ! defined BAR_STYPE_IS_DECLARED
947 typedef union YYSTYPE | typedef union BAR_STYPE
948 { {
949 int ival; int ival;
950 } YYSTYPE; | } BAR_STYPE;
951 # define YYSTYPE_IS_DECLARED 1 | # define BAR_STYPE_IS_DECLARED 1
952 #endif #endif
953
954 extern YYSTYPE bar_lval; | extern BAR_STYPE bar_lval;
955
956 int bar_parse (void); int bar_parse (void);
957
958 #endif /* !BAR_FOO_H */ #endif /* !BAR_FOO_H */
959
dfaac272 960* Noteworthy changes in release 2.5.1 (2012-06-05) [stable]
df6e3db0 961
debe2c03 962** Future changes:
765e1bd4 963
e4ab1254 964 The next major release will drop support for generating parsers in K&R C.
041308d0 965
466b4cf2 966** yacc.c: YYBACKUP works as expected.
ef51bfa7 967
d834eca0 968** glr.c improvements:
041308d0 969
d834eca0 970*** Location support is eliminated when not requested:
041308d0 971
e4ab1254
AD
972 GLR parsers used to include location-related code even when locations were
973 not requested, and therefore not even usable.
378e917c 974
d834eca0 975*** __attribute__ is preserved:
d115aad9 976
e4ab1254
AD
977 __attribute__ is no longer disabled when __STRICT_ANSI__ is defined (i.e.,
978 when -std is passed to GCC).
041308d0 979
466b4cf2 980** lalr1.java: several fixes:
041308d0 981
e4ab1254
AD
982 The Java parser no longer throws ArrayIndexOutOfBoundsException if the
983 first token leads to a syntax error. Some minor clean ups.
041308d0 984
22172d47 985** Changes for C++:
ef51bfa7 986
22172d47 987*** C++11 compatibility:
ef51bfa7 988
e4ab1254
AD
989 C and C++ parsers use "nullptr" instead of "0" when __cplusplus is 201103L
990 or higher.
936c88d1 991
22172d47
AD
992*** Header guards
993
994 The header files such as "parser.hh", "location.hh", etc. used a constant
995 name for preprocessor guards, for instance:
996
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AD
997 #ifndef BISON_LOCATION_HH
998 # define BISON_LOCATION_HH
999 ...
1000 #endif // !BISON_LOCATION_HH
22172d47
AD
1001
1002 The inclusion guard is now computed from "PREFIX/FILE-NAME", where lower
1003 case characters are converted to upper case, and series of
1004 non-alphanumerical characters are converted to an underscore.
1005
1006 With "bison -o lang++/parser.cc", "location.hh" would now include:
1007
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AD
1008 #ifndef YY_LANG_LOCATION_HH
1009 # define YY_LANG_LOCATION_HH
1010 ...
1011 #endif // !YY_LANG_LOCATION_HH
22172d47
AD
1012
1013*** C++ locations:
936c88d1 1014
e4ab1254
AD
1015 The position and location constructors (and their initialize methods)
1016 accept new arguments for line and column. Several issues in the
1017 documentation were fixed.
936c88d1 1018
466b4cf2
AD
1019** liby is no longer asking for "rpl_fprintf" on some platforms.
1020
7e508a2b
AD
1021** Changes in the manual:
1022
1023*** %printer is documented
1024
e4ab1254
AD
1025 The "%printer" directive, supported since at least Bison 1.50, is finally
1026 documented. The "mfcalc" example is extended to demonstrate it.
7e508a2b 1027
e4ab1254
AD
1028 For consistency with the C skeletons, the C++ parsers now also support
1029 "yyoutput" (as an alias to "debug_stream ()").
7e508a2b
AD
1030
1031*** Several improvements have been made:
466b4cf2 1032
e4ab1254
AD
1033 The layout for grammar excerpts was changed to a more compact scheme.
1034 Named references are motivated. The description of the automaton
1035 description file (*.output) is updated to the current format. Incorrect
1036 index entries were fixed. Some other errors were fixed.
466b4cf2 1037
86b08b49
AD
1038** Building bison:
1039
1040*** Conflicting prototypes with recent/modified Flex.
466b4cf2 1041
e4ab1254
AD
1042 Fixed build problems with the current, unreleased, version of Flex, and
1043 some modified versions of 2.5.35, which have modified function prototypes.
466b4cf2 1044
8ef26c2a
AD
1045*** Warnings during the build procedure have been eliminated.
1046
1047*** Several portability problems in the test suite have been fixed:
466b4cf2 1048
e4ab1254
AD
1049 This includes warnings with some compilers, unexpected behavior of tools
1050 such as diff, warning messages from the test suite itself, etc.
466b4cf2 1051
91aadcc7 1052*** The install-pdf target works properly:
8ef26c2a 1053
e4ab1254
AD
1054 Running "make install-pdf" (or -dvi, -html, -info, and -ps) no longer
1055 halts in the middle of its course.
8ef26c2a 1056
28801043 1057* Changes in version 2.5 (2011-05-14):
50cca368 1058
82f3355e
JD
1059** Grammar symbol names can now contain non-initial dashes:
1060
1061 Consistently with directives (such as %error-verbose) and with
1062 %define variables (e.g. push-pull), grammar symbol names may contain
1063 dashes in any position except the beginning. This is a GNU
1064 extension over POSIX Yacc. Thus, use of this extension is reported
1065 by -Wyacc and rejected in Yacc mode (--yacc).
1066
f1b238df 1067** Named references:
66381412
AR
1068
1069 Historically, Yacc and Bison have supported positional references
1070 ($n, $$) to allow access to symbol values from inside of semantic
1071 actions code.
1072
1073 Starting from this version, Bison can also accept named references.
1074 When no ambiguity is possible, original symbol names may be used
1075 as named references:
1076
4b568fc0 1077 if_stmt : "if" cond_expr "then" then_stmt ';'
66381412
AR
1078 { $if_stmt = mk_if_stmt($cond_expr, $then_stmt); }
1079
1080 In the more common case, explicit names may be declared:
1081
4b568fc0 1082 stmt[res] : "if" expr[cond] "then" stmt[then] "else" stmt[else] ';'
66381412
AR
1083 { $res = mk_if_stmt($cond, $then, $else); }
1084
5b1ff423 1085 Location information is also accessible using @name syntax. When
66381412
AR
1086 accessing symbol names containing dots or dashes, explicit bracketing
1087 ($[sym.1]) must be used.
1088
5b1ff423 1089 These features are experimental in this version. More user feedback
66381412 1090 will help to stabilize them.
2bd435c3 1091 Contributed by Alex Rozenman.
66381412 1092
f1b238df 1093** IELR(1) and canonical LR(1):
eb45ef3b
JD
1094
1095 IELR(1) is a minimal LR(1) parser table generation algorithm. That
1096 is, given any context-free grammar, IELR(1) generates parser tables
7262f54f 1097 with the full language-recognition power of canonical LR(1) but with
f1b238df
JD
1098 nearly the same number of parser states as LALR(1). This reduction
1099 in parser states is often an order of magnitude. More importantly,
eb45ef3b
JD
1100 because canonical LR(1)'s extra parser states may contain duplicate
1101 conflicts in the case of non-LR(1) grammars, the number of conflicts
1102 for IELR(1) is often an order of magnitude less as well. This can
1103 significantly reduce the complexity of developing of a grammar.
1104
1105 Bison can now generate IELR(1) and canonical LR(1) parser tables in
1106 place of its traditional LALR(1) parser tables, which remain the
1107 default. You can specify the type of parser tables in the grammar
1108 file with these directives:
1109
cf499cff
JD
1110 %define lr.type lalr
1111 %define lr.type ielr
1112 %define lr.type canonical-lr
eb45ef3b 1113
7fceb615 1114 The default-reduction optimization in the parser tables can also be
e4ab1254
AD
1115 adjusted using "%define lr.default-reductions". For details on both
1116 of these features, see the new section "Tuning LR" in the Bison
7fceb615 1117 manual.
eb45ef3b
JD
1118
1119 These features are experimental. More user feedback will help to
1120 stabilize them.
1121
8458a411
AD
1122** LAC (Lookahead Correction) for syntax error handling
1123
1124 Contributed by Joel E. Denny.
fcf834f9
JD
1125
1126 Canonical LR, IELR, and LALR can suffer from a couple of problems
1127 upon encountering a syntax error. First, the parser might perform
1128 additional parser stack reductions before discovering the syntax
7fceb615 1129 error. Such reductions can perform user semantic actions that are
fcf834f9
JD
1130 unexpected because they are based on an invalid token, and they
1131 cause error recovery to begin in a different syntactic context than
1132 the one in which the invalid token was encountered. Second, when
7fceb615 1133 verbose error messages are enabled (with %error-verbose or the
e4ab1254 1134 obsolete "#define YYERROR_VERBOSE"), the expected token list in the
7fceb615
JD
1135 syntax error message can both contain invalid tokens and omit valid
1136 tokens.
fcf834f9
JD
1137
1138 The culprits for the above problems are %nonassoc, default
1139 reductions in inconsistent states, and parser state merging. Thus,
1140 IELR and LALR suffer the most. Canonical LR can suffer only if
1141 %nonassoc is used or if default reductions are enabled for
1142 inconsistent states.
1143
7fceb615
JD
1144 LAC is a new mechanism within the parsing algorithm that solves
1145 these problems for canonical LR, IELR, and LALR without sacrificing
1146 %nonassoc, default reductions, or state merging. When LAC is in
1147 use, canonical LR and IELR behave almost exactly the same for both
1148 syntactically acceptable and syntactically unacceptable input.
fcf834f9
JD
1149 While LALR still does not support the full language-recognition
1150 power of canonical LR and IELR, LAC at least enables LALR's syntax
1151 error handling to correctly reflect LALR's language-recognition
1152 power.
1153
1154 Currently, LAC is only supported for deterministic parsers in C.
1155 You can enable LAC with the following directive:
1156
1157 %define parse.lac full
1158
e4ab1254 1159 See the new section "LAC" in the Bison manual for additional
7fceb615 1160 details including a few caveats.
fcf834f9
JD
1161
1162 LAC is an experimental feature. More user feedback will help to
1163 stabilize it.
1164
d397d9f0 1165** %define improvements:
cf499cff 1166
f1b238df 1167*** Can now be invoked via the command line:
50cca368 1168
de5ab940 1169 Each of these command-line options
50cca368 1170
de5ab940
JD
1171 -D NAME[=VALUE]
1172 --define=NAME[=VALUE]
1173
1174 -F NAME[=VALUE]
1175 --force-define=NAME[=VALUE]
50cca368
JD
1176
1177 is equivalent to this grammar file declaration
1178
de5ab940 1179 %define NAME ["VALUE"]
50cca368 1180
de5ab940
JD
1181 except that the manner in which Bison processes multiple definitions
1182 for the same NAME differs. Most importantly, -F and --force-define
1183 quietly override %define, but -D and --define do not. For further
e4ab1254 1184 details, see the section "Bison Options" in the Bison manual.
50cca368 1185
f1b238df 1186*** Variables renamed:
67212941
JD
1187
1188 The following %define variables
1189
1190 api.push_pull
1191 lr.keep_unreachable_states
1192
1193 have been renamed to
1194
1195 api.push-pull
1196 lr.keep-unreachable-states
1197
1198 The old names are now deprecated but will be maintained indefinitely
1199 for backward compatibility.
1200
7262f54f 1201*** Values no longer need to be quoted in the grammar file:
cf499cff
JD
1202
1203 If a %define value is an identifier, it no longer needs to be placed
1204 within quotations marks. For example,
1205
1206 %define api.push-pull "push"
1207
1208 can be rewritten as
1209
1210 %define api.push-pull push
1211
d397d9f0 1212*** Unrecognized variables are now errors not warnings.
cdf3f113 1213
d397d9f0
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1214*** Multiple invocations for any variable is now an error not a warning.
1215
1216** Unrecognized %code qualifiers are now errors not warnings.
1217
1218** Character literals not of length one:
1219
1220 Previously, Bison quietly converted all character literals to length
1221 one. For example, without warning, Bison interpreted the operators in
1222 the following grammar to be the same token:
1223
1224 exp: exp '++'
1225 | exp '+' exp
1226 ;
1227
1228 Bison now warns when a character literal is not of length one. In
1229 some future release, Bison will start reporting an error instead.
1230
1231** Destructor calls fixed for lookaheads altered in semantic actions:
1232
1233 Previously for deterministic parsers in C, if a user semantic action
1234 altered yychar, the parser in some cases used the old yychar value to
1235 determine which destructor to call for the lookahead upon a syntax
1236 error or upon parser return. This bug has been fixed.
1237
1238** C++ parsers use YYRHSLOC:
1239
1240 Similarly to the C parsers, the C++ parsers now define the YYRHSLOC
1241 macro and use it in the default YYLLOC_DEFAULT. You are encouraged
e4ab1254
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1242 to use it. If, for instance, your location structure has "first"
1243 and "last" members, instead of
d397d9f0 1244
e29f0771
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1245 # define YYLLOC_DEFAULT(Current, Rhs, N) \
1246 do \
1247 if (N) \
1248 { \
1249 (Current).first = (Rhs)[1].location.first; \
1250 (Current).last = (Rhs)[N].location.last; \
1251 } \
1252 else \
1253 { \
1254 (Current).first = (Current).last = (Rhs)[0].location.last; \
1255 } \
1256 while (false)
d397d9f0
JD
1257
1258 use:
1259
e29f0771
AD
1260 # define YYLLOC_DEFAULT(Current, Rhs, N) \
1261 do \
1262 if (N) \
1263 { \
1264 (Current).first = YYRHSLOC (Rhs, 1).first; \
1265 (Current).last = YYRHSLOC (Rhs, N).last; \
1266 } \
1267 else \
1268 { \
1269 (Current).first = (Current).last = YYRHSLOC (Rhs, 0).last; \
1270 } \
1271 while (false)
d397d9f0
JD
1272
1273** YYLLOC_DEFAULT in C++:
1274
1275 The default implementation of YYLLOC_DEFAULT used to be issued in
1276 the header file. It is now output in the implementation file, after
1277 the user %code sections so that its #ifndef guard does not try to
1278 override the user's YYLLOC_DEFAULT if provided.
cdf3f113 1279
f1b238df 1280** YYFAIL now produces warnings and Java parsers no longer implement it:
4395a9ff
JD
1281
1282 YYFAIL has existed for many years as an undocumented feature of
1283 deterministic parsers in C generated by Bison. More recently, it was
1284 a documented feature of Bison's experimental Java parsers. As
1285 promised in Bison 2.4.2's NEWS entry, any appearance of YYFAIL in a
1286 semantic action now produces a deprecation warning, and Java parsers
1287 no longer implement YYFAIL at all. For further details, including a
1288 discussion of how to suppress C preprocessor warnings about YYFAIL
1289 being unused, see the Bison 2.4.2 NEWS entry.
1290
f1b238df 1291** Temporary hack for adding a semicolon to the user action:
197b82ba
JD
1292
1293 Previously, Bison appended a semicolon to every user action for
1294 reductions when the output language defaulted to C (specifically, when
1295 neither %yacc, %language, %skeleton, or equivalent command-line
1296 options were specified). This allowed actions such as
1297
1298 exp: exp "+" exp { $$ = $1 + $3 };
1299
1300 instead of
1301
1302 exp: exp "+" exp { $$ = $1 + $3; };
1303
1304 As a first step in removing this misfeature, Bison now issues a
1305 warning when it appends a semicolon. Moreover, in cases where Bison
1306 cannot easily determine whether a semicolon is needed (for example, an
1307 action ending with a cpp directive or a braced compound initializer),
1308 it no longer appends one. Thus, the C compiler might now complain
1309 about a missing semicolon where it did not before. Future releases of
1310 Bison will cease to append semicolons entirely.
1311
d2060f06
JD
1312** Verbose syntax error message fixes:
1313
e4ab1254 1314 When %error-verbose or the obsolete "#define YYERROR_VERBOSE" is
7fceb615
JD
1315 specified, syntax error messages produced by the generated parser
1316 include the unexpected token as well as a list of expected tokens.
1317 The effect of %nonassoc on these verbose messages has been corrected
1318 in two ways, but a more complete fix requires LAC, described above:
d2060f06
JD
1319
1320*** When %nonassoc is used, there can exist parser states that accept no
1321 tokens, and so the parser does not always require a lookahead token
1322 in order to detect a syntax error. Because no unexpected token or
1323 expected tokens can then be reported, the verbose syntax error
1324 message described above is suppressed, and the parser instead
e4ab1254 1325 reports the simpler message, "syntax error". Previously, this
d2060f06
JD
1326 suppression was sometimes erroneously triggered by %nonassoc when a
1327 lookahead was actually required. Now verbose messages are
1328 suppressed only when all previous lookaheads have already been
1329 shifted or discarded.
1330
1331*** Previously, the list of expected tokens erroneously included tokens
1332 that would actually induce a syntax error because conflicts for them
1333 were resolved with %nonassoc in the current parser state. Such
1334 tokens are now properly omitted from the list.
1335
1336*** Expected token lists are still often wrong due to state merging
fcf834f9
JD
1337 (from LALR or IELR) and default reductions, which can both add
1338 invalid tokens and subtract valid tokens. Canonical LR almost
1339 completely fixes this problem by eliminating state merging and
1340 default reductions. However, there is one minor problem left even
1341 when using canonical LR and even after the fixes above. That is,
1342 if the resolution of a conflict with %nonassoc appears in a later
1343 parser state than the one at which some syntax error is
1344 discovered, the conflicted token is still erroneously included in
1345 the expected token list. Bison's new LAC implementation,
1346 described above, eliminates this problem and the need for
1347 canonical LR. However, LAC is still experimental and is disabled
1348 by default.
53f036ce 1349
1a33f4f6
JD
1350** Java skeleton fixes:
1351
1352*** A location handling bug has been fixed.
1353
1354*** The top element of each of the value stack and location stack is now
1355 cleared when popped so that it can be garbage collected.
6771a463 1356
02803d55
JD
1357*** Parser traces now print the top element of the stack.
1358
86408959
JD
1359** -W/--warnings fixes:
1360
e4ab1254 1361*** Bison now properly recognizes the "no-" versions of categories:
86408959
JD
1362
1363 For example, given the following command line, Bison now enables all
1364 warnings except warnings for incompatibilities with POSIX Yacc:
1365
1366 bison -Wall,no-yacc gram.y
1367
786743d5
JD
1368*** Bison now treats S/R and R/R conflicts like other warnings:
1369
1370 Previously, conflict reports were independent of Bison's normal
1371 warning system. Now, Bison recognizes the warning categories
e4ab1254 1372 "conflicts-sr" and "conflicts-rr". This change has important
786743d5
JD
1373 consequences for the -W and --warnings command-line options. For
1374 example:
1375
1376 bison -Wno-conflicts-sr gram.y # S/R conflicts not reported
1377 bison -Wno-conflicts-rr gram.y # R/R conflicts not reported
1378 bison -Wnone gram.y # no conflicts are reported
1379 bison -Werror gram.y # any conflict is an error
1380
1381 However, as before, if the %expect or %expect-rr directive is
1382 specified, an unexpected number of conflicts is an error, and an
1383 expected number of conflicts is not reported, so -W and --warning
1384 then have no effect on the conflict report.
1385
e4ab1254 1386*** The "none" category no longer disables a preceding "error":
bf0e44e8
JD
1387
1388 For example, for the following command line, Bison now reports
1389 errors instead of warnings for incompatibilities with POSIX Yacc:
1390
1391 bison -Werror,none,yacc gram.y
1392
e4ab1254 1393*** The "none" category now disables all Bison warnings:
c39014ae 1394
e4ab1254 1395 Previously, the "none" category disabled only Bison warnings for
c39014ae
JD
1396 which there existed a specific -W/--warning category. However,
1397 given the following command line, Bison is now guaranteed to
1398 suppress all warnings:
1399
1400 bison -Wnone gram.y
1401
1f36f544
JD
1402** Precedence directives can now assign token number 0:
1403
1404 Since Bison 2.3b, which restored the ability of precedence
1405 directives to assign token numbers, doing so for token number 0 has
1406 produced an assertion failure. For example:
1407
1408 %left END 0
1409
1410 This bug has been fixed.
1411
64877e5e 1412* Changes in version 2.4.3 (2010-08-05):
8b9e021f 1413
2bfcac9a
JD
1414** Bison now obeys -Werror and --warnings=error for warnings about
1415 grammar rules that are useless in the parser due to conflicts.
1416
8b9e021f
JD
1417** Problems with spawning M4 on at least FreeBSD 8 and FreeBSD 9 have
1418 been fixed.
1419
4ad3921d
JD
1420** Failures in the test suite for GCC 4.5 have been fixed.
1421
06cb07d5
JD
1422** Failures in the test suite for some versions of Sun Studio C++ have
1423 been fixed.
1424
9b5049bd
JD
1425** Contrary to Bison 2.4.2's NEWS entry, it has been decided that
1426 warnings about undefined %prec identifiers will not be converted to
1427 errors in Bison 2.5. They will remain warnings, which should be
1428 sufficient for POSIX while avoiding backward compatibility issues.
1429
93d7dde9
JD
1430** Minor documentation fixes.
1431
e19a049c 1432* Changes in version 2.4.2 (2010-03-20):
74553c98 1433
f39ab286
JD
1434** Some portability problems that resulted in failures and livelocks
1435 in the test suite on some versions of at least Solaris, AIX, HP-UX,
e19a049c
JD
1436 RHEL4, and Tru64 have been addressed. As a result, fatal Bison
1437 errors should no longer cause M4 to report a broken pipe on the
f39ab286
JD
1438 affected platforms.
1439
e4ab1254 1440** "%prec IDENTIFIER" requires IDENTIFIER to be defined separately.
8bb3a2e7
JD
1441
1442 POSIX specifies that an error be reported for any identifier that does
1443 not appear on the LHS of a grammar rule and that is not defined by
1444 %token, %left, %right, or %nonassoc. Bison 2.3b and later lost this
1445 error report for the case when an identifier appears only after a
1446 %prec directive. It is now restored. However, for backward
1447 compatibility with recent Bison releases, it is only a warning for
1448 now. In Bison 2.5 and later, it will return to being an error.
9b5049bd
JD
1449 [Between the 2.4.2 and 2.4.3 releases, it was decided that this
1450 warning will not be converted to an error in Bison 2.5.]
8bb3a2e7 1451
d8911864
EB
1452** Detection of GNU M4 1.4.6 or newer during configure is improved.
1453
a603c6e0
JD
1454** Warnings from gcc's -Wundef option about undefined YYENABLE_NLS,
1455 YYLTYPE_IS_TRIVIAL, and __STRICT_ANSI__ in C/C++ parsers are now
1456 avoided.
c938d650 1457
98a345a2
JD
1458** %code is now a permanent feature.
1459
1460 A traditional Yacc prologue directive is written in the form:
1461
1462 %{CODE%}
1463
1464 To provide a more flexible alternative, Bison 2.3b introduced the
1465 %code directive with the following forms for C/C++:
1466
1467 %code {CODE}
1468 %code requires {CODE}
1469 %code provides {CODE}
1470 %code top {CODE}
1471
1472 These forms are now considered permanent features of Bison. See the
1473 %code entries in the section "Bison Declaration Summary" in the Bison
1474 manual for a summary of their functionality. See the section
1475 "Prologue Alternatives" for a detailed discussion including the
1476 advantages of %code over the traditional Yacc prologue directive.
1477
1478 Bison's Java feature as a whole including its current usage of %code
1479 is still considered experimental.
1480
1625df5b
JD
1481** YYFAIL is deprecated and will eventually be removed.
1482
1483 YYFAIL has existed for many years as an undocumented feature of
1484 deterministic parsers in C generated by Bison. Previously, it was
1485 documented for Bison's experimental Java parsers. YYFAIL is no longer
1486 documented for Java parsers and is formally deprecated in both cases.
1487 Users are strongly encouraged to migrate to YYERROR, which is
1488 specified by POSIX.
1489
1490 Like YYERROR, you can invoke YYFAIL from a semantic action in order to
1491 induce a syntax error. The most obvious difference from YYERROR is
1492 that YYFAIL will automatically invoke yyerror to report the syntax
1493 error so that you don't have to. However, there are several other
1494 subtle differences between YYERROR and YYFAIL, and YYFAIL suffers from
e4ab1254 1495 inherent flaws when %error-verbose or "#define YYERROR_VERBOSE" is
1625df5b
JD
1496 used. For a more detailed discussion, see:
1497
1498 http://lists.gnu.org/archive/html/bison-patches/2009-12/msg00024.html
1499
1500 The upcoming Bison 2.5 will remove YYFAIL from Java parsers, but
1501 deterministic parsers in C will continue to implement it. However,
1502 because YYFAIL is already flawed, it seems futile to try to make new
1503 Bison features compatible with it. Thus, during parser generation,
1504 Bison 2.5 will produce a warning whenever it discovers YYFAIL in a
1505 rule action. In a later release, YYFAIL will be disabled for
e4ab1254 1506 %error-verbose and "#define YYERROR_VERBOSE". Eventually, YYFAIL will
1625df5b
JD
1507 be removed altogether.
1508
1509 There exists at least one case where Bison 2.5's YYFAIL warning will
1510 be a false positive. Some projects add phony uses of YYFAIL and other
1511 Bison-defined macros for the sole purpose of suppressing C
1512 preprocessor warnings (from GCC cpp's -Wunused-macros, for example).
1513 To avoid Bison's future warning, such YYFAIL uses can be moved to the
e4ab1254 1514 epilogue (that is, after the second "%%") in the Bison input file. In
1625df5b
JD
1515 this release (2.4.2), Bison already generates its own code to suppress
1516 C preprocessor warnings for YYFAIL, so projects can remove their own
1517 phony uses of YYFAIL if compatibility with Bison releases prior to
1518 2.4.2 is not necessary.
1519
2755de8f
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1520** Internationalization.
1521
1522 Fix a regression introduced in Bison 2.4: Under some circumstances,
1523 message translations were not installed although supported by the
1524 host system.
1525
74553c98 1526* Changes in version 2.4.1 (2008-12-11):
c9ba9e59 1527
0ea583d2
AD
1528** In the GLR defines file, unexpanded M4 macros in the yylval and yylloc
1529 declarations have been fixed.
1979121c 1530
0ea583d2
AD
1531** Temporary hack for adding a semicolon to the user action.
1532
1533 Bison used to prepend a trailing semicolon at the end of the user
1534 action for reductions. This allowed actions such as
1535
1536 exp: exp "+" exp { $$ = $1 + $3 };
1537
1538 instead of
1539
1540 exp: exp "+" exp { $$ = $1 + $3; };
1541
e4ab1254 1542 Some grammars still depend on this "feature". Bison 2.4.1 restores
0ea583d2
AD
1543 the previous behavior in the case of C output (specifically, when
1544 neither %language or %skeleton or equivalent command-line options
1545 are used) to leave more time for grammars depending on the old
1546 behavior to be adjusted. Future releases of Bison will disable this
1547 feature.
1548
1549** A few minor improvements to the Bison manual.
c9ba9e59 1550
402b123d 1551* Changes in version 2.4 (2008-11-02):
7bd1665a 1552
402b123d 1553** %language is an experimental feature.
ed4d67dc
JD
1554
1555 We first introduced this feature in test release 2.3b as a cleaner
1556 alternative to %skeleton. Since then, we have discussed the possibility of
1557 modifying its effect on Bison's output file names. Thus, in this release,
1558 we consider %language to be an experimental feature that will likely evolve
1559 in future releases.
7bd1665a 1560
402b123d 1561** Forward compatibility with GNU M4 has been improved.
241fda7a 1562
402b123d 1563** Several bugs in the C++ skeleton and the experimental Java skeleton have been
241fda7a
JD
1564 fixed.
1565
402b123d 1566* Changes in version 2.3b (2008-05-27):
35fe0834 1567
402b123d 1568** The quotes around NAME that used to be required in the following directive
d9df47b6
JD
1569 are now deprecated:
1570
1571 %define NAME "VALUE"
1572
e4ab1254 1573** The directive "%pure-parser" is now deprecated in favor of:
d9df47b6
JD
1574
1575 %define api.pure
1576
1577 which has the same effect except that Bison is more careful to warn about
1578 unreasonable usage in the latter case.
1579
402b123d 1580** Push Parsing
c373bf8b
JD
1581
1582 Bison can now generate an LALR(1) parser in C with a push interface. That
e4ab1254
AD
1583 is, instead of invoking "yyparse", which pulls tokens from "yylex", you can
1584 push one token at a time to the parser using "yypush_parse", which will
c373bf8b
JD
1585 return to the caller after processing each token. By default, the push
1586 interface is disabled. Either of the following directives will enable it:
1587
1588 %define api.push_pull "push" // Just push; does not require yylex.
1589 %define api.push_pull "both" // Push and pull; requires yylex.
1590
e4ab1254 1591 See the new section "A Push Parser" in the Bison manual for details.
c373bf8b 1592
59da312b
JD
1593 The current push parsing interface is experimental and may evolve. More user
1594 feedback will help to stabilize it.
1595
402b123d 1596** The -g and --graph options now output graphs in Graphviz DOT format,
8e55b3aa
JD
1597 not VCG format. Like --graph, -g now also takes an optional FILE argument
1598 and thus cannot be bundled with other short options.
c373bf8b 1599
402b123d 1600** Java
59da312b
JD
1601
1602 Bison can now generate an LALR(1) parser in Java. The skeleton is
e4ab1254 1603 "data/lalr1.java". Consider using the new %language directive instead of
59da312b
JD
1604 %skeleton to select it.
1605
e4ab1254 1606 See the new section "Java Parsers" in the Bison manual for details.
59da312b
JD
1607
1608 The current Java interface is experimental and may evolve. More user
1609 feedback will help to stabilize it.
2bd435c3 1610 Contributed by Paolo Bonzini.
59da312b 1611
402b123d 1612** %language
59da312b
JD
1613
1614 This new directive specifies the programming language of the generated
d43f77e7
PB
1615 parser, which can be C (the default), C++, or Java. Besides the skeleton
1616 that Bison uses, the directive affects the names of the generated files if
1617 the grammar file's name ends in ".y".
59da312b 1618
402b123d 1619** XML Automaton Report
59da312b
JD
1620
1621 Bison can now generate an XML report of the LALR(1) automaton using the new
e4ab1254 1622 "--xml" option. The current XML schema is experimental and may evolve. More
59da312b 1623 user feedback will help to stabilize it.
2bd435c3 1624 Contributed by Wojciech Polak.
c373bf8b 1625
402b123d 1626** The grammar file may now specify the name of the parser header file using
c373bf8b
JD
1627 %defines. For example:
1628
1629 %defines "parser.h"
1630
402b123d 1631** When reporting useless rules, useless nonterminals, and unused terminals,
d80fb37a
JD
1632 Bison now employs the terms "useless in grammar" instead of "useless",
1633 "useless in parser" instead of "never reduced", and "unused in grammar"
1634 instead of "unused".
cff03fb2 1635
402b123d 1636** Unreachable State Removal
c373bf8b
JD
1637
1638 Previously, Bison sometimes generated parser tables containing unreachable
31984206
JD
1639 states. A state can become unreachable during conflict resolution if Bison
1640 disables a shift action leading to it from a predecessor state. Bison now:
75ad86ee
JD
1641
1642 1. Removes unreachable states.
1643
1644 2. Does not report any conflicts that appeared in unreachable states.
1645 WARNING: As a result, you may need to update %expect and %expect-rr
1646 directives in existing grammar files.
1647
1648 3. For any rule used only in such states, Bison now reports the rule as
cff03fb2 1649 "useless in parser due to conflicts".
75ad86ee 1650
31984206
JD
1651 This feature can be disabled with the following directive:
1652
1653 %define lr.keep_unreachable_states
1654
e4ab1254 1655 See the %define entry in the "Bison Declaration Summary" in the Bison manual
31984206
JD
1656 for further discussion.
1657
e4ab1254 1658** Lookahead Set Correction in the ".output" Report
b1cc23c4 1659
e4ab1254
AD
1660 When instructed to generate a ".output" file including lookahead sets
1661 (using "--report=lookahead", for example), Bison now prints each reduction's
88c78747
JD
1662 lookahead set only next to the associated state's one item that (1) is
1663 associated with the same rule as the reduction and (2) has its dot at the end
1664 of its RHS. Previously, Bison also erroneously printed the lookahead set
1665 next to all of the state's other items associated with the same rule. This
e4ab1254 1666 bug affected only the ".output" file and not the generated parser source
88c78747
JD
1667 code.
1668
e4ab1254 1669** --report-file=FILE is a new option to override the default ".output" file
59da312b 1670 name.
1bb2bd75 1671
e4ab1254 1672** The "=" that used to be required in the following directives is now
02975b9a
JD
1673 deprecated:
1674
1675 %file-prefix "parser"
1676 %name-prefix "c_"
1677 %output "parser.c"
1678
e4ab1254 1679** An Alternative to "%{...%}" -- "%code QUALIFIER {CODE}"
c373bf8b
JD
1680
1681 Bison 2.3a provided a new set of directives as a more flexible alternative to
8e0a5e9e
JD
1682 the traditional Yacc prologue blocks. Those have now been consolidated into
1683 a single %code directive with an optional qualifier field, which identifies
1684 the purpose of the code and thus the location(s) where Bison should generate
1685 it:
1686
e4ab1254
AD
1687 1. "%code {CODE}" replaces "%after-header {CODE}"
1688 2. "%code requires {CODE}" replaces "%start-header {CODE}"
1689 3. "%code provides {CODE}" replaces "%end-header {CODE}"
1690 4. "%code top {CODE}" replaces "%before-header {CODE}"
8e0a5e9e 1691
e4ab1254
AD
1692 See the %code entries in section "Bison Declaration Summary" in the Bison
1693 manual for a summary of the new functionality. See the new section "Prologue
1694 Alternatives" for a detailed discussion including the advantages of %code
8e0a5e9e
JD
1695 over the traditional Yacc prologues.
1696
1697 The prologue alternatives are experimental. More user feedback will help to
1698 determine whether they should become permanent features.
1699
402b123d 1700** Revised warning: unset or unused mid-rule values
17bd8a73
JD
1701
1702 Since Bison 2.2, Bison has warned about mid-rule values that are set but not
1703 used within any of the actions of the parent rule. For example, Bison warns
1704 about unused $2 in:
1705
1706 exp: '1' { $$ = 1; } '+' exp { $$ = $1 + $4; };
1707
1708 Now, Bison also warns about mid-rule values that are used but not set. For
1709 example, Bison warns about unset $$ in the mid-rule action in:
1710
1711 exp: '1' { $1 = 1; } '+' exp { $$ = $2 + $4; };
1712
1713 However, Bison now disables both of these warnings by default since they
1714 sometimes prove to be false alarms in existing grammars employing the Yacc
1715 constructs $0 or $-N (where N is some positive integer).
1716
e4ab1254
AD
1717 To enable these warnings, specify the option "--warnings=midrule-values" or
1718 "-W", which is a synonym for "--warnings=all".
17bd8a73 1719
e4ab1254 1720** Default %destructor or %printer with "<*>" or "<>"
c373bf8b
JD
1721
1722 Bison now recognizes two separate kinds of default %destructor's and
12e35840
JD
1723 %printer's:
1724
e4ab1254 1725 1. Place "<*>" in a %destructor/%printer symbol list to define a default
12e35840
JD
1726 %destructor/%printer for all grammar symbols for which you have formally
1727 declared semantic type tags.
1728
e4ab1254 1729 2. Place "<>" in a %destructor/%printer symbol list to define a default
12e35840
JD
1730 %destructor/%printer for all grammar symbols without declared semantic
1731 type tags.
1732
e4ab1254
AD
1733 Bison no longer supports the "%symbol-default" notation from Bison 2.3a.
1734 "<*>" and "<>" combined achieve the same effect with one exception: Bison no
12e35840
JD
1735 longer applies any %destructor to a mid-rule value if that mid-rule value is
1736 not actually ever referenced using either $$ or $n in a semantic action.
1737
85894313
JD
1738 The default %destructor's and %printer's are experimental. More user
1739 feedback will help to determine whether they should become permanent
1740 features.
1741
e4ab1254 1742 See the section "Freeing Discarded Symbols" in the Bison manual for further
12e35840
JD
1743 details.
1744
402b123d 1745** %left, %right, and %nonassoc can now declare token numbers. This is required
e4ab1254 1746 by POSIX. However, see the end of section "Operator Precedence" in the Bison
ab7f29f8
JD
1747 manual for a caveat concerning the treatment of literal strings.
1748
402b123d 1749** The nonfunctional --no-parser, -n, and %no-parser options have been
b1cc23c4
JD
1750 completely removed from Bison.
1751
402b123d 1752* Changes in version 2.3a, 2006-09-13:
742e4900 1753
402b123d 1754** Instead of %union, you can define and use your own union type
ddc8ede1
PE
1755 YYSTYPE if your grammar contains at least one <type> tag.
1756 Your YYSTYPE need not be a macro; it can be a typedef.
1757 This change is for compatibility with other Yacc implementations,
1758 and is required by POSIX.
1759
402b123d 1760** Locations columns and lines start at 1.
cd48d21d
AD
1761 In accordance with the GNU Coding Standards and Emacs.
1762
402b123d 1763** You may now declare per-type and default %destructor's and %printer's:
ec5479ce
JD
1764
1765 For example:
1766
b2a0b7ca
JD
1767 %union { char *string; }
1768 %token <string> STRING1
1769 %token <string> STRING2
1770 %type <string> string1
1771 %type <string> string2
1772 %union { char character; }
1773 %token <character> CHR
1774 %type <character> chr
1775 %destructor { free ($$); } %symbol-default
1776 %destructor { free ($$); printf ("%d", @$.first_line); } STRING1 string1
1777 %destructor { } <character>
1778
1779 guarantees that, when the parser discards any user-defined symbol that has a
e4ab1254
AD
1780 semantic type tag other than "<character>", it passes its semantic value to
1781 "free". However, when the parser discards a "STRING1" or a "string1", it
1782 also prints its line number to "stdout". It performs only the second
1783 "%destructor" in this case, so it invokes "free" only once.
ec5479ce 1784
85894313
JD
1785 [Although we failed to mention this here in the 2.3a release, the default
1786 %destructor's and %printer's were experimental, and they were rewritten in
1787 future versions.]
1788
e4ab1254
AD
1789** Except for LALR(1) parsers in C with POSIX Yacc emulation enabled (with "-y",
1790 "--yacc", or "%yacc"), Bison no longer generates #define statements for
b931235e
JD
1791 associating token numbers with token names. Removing the #define statements
1792 helps to sanitize the global namespace during preprocessing, but POSIX Yacc
1793 requires them. Bison still generates an enum for token names in all cases.
1794
402b123d 1795** Handling of traditional Yacc prologue blocks is now more consistent but
34f98f46 1796 potentially incompatible with previous releases of Bison.
9bc0dd67
JD
1797
1798 As before, you declare prologue blocks in your grammar file with the
e4ab1254 1799 "%{ ... %}" syntax. To generate the pre-prologue, Bison concatenates all
34f98f46
JD
1800 prologue blocks that you've declared before the first %union. To generate
1801 the post-prologue, Bison concatenates all prologue blocks that you've
ddc8ede1 1802 declared after the first %union.
9bc0dd67 1803
34f98f46 1804 Previous releases of Bison inserted the pre-prologue into both the header
9bc0dd67
JD
1805 file and the code file in all cases except for LALR(1) parsers in C. In the
1806 latter case, Bison inserted it only into the code file. For parsers in C++,
1807 the point of insertion was before any token definitions (which associate
1808 token numbers with names). For parsers in C, the point of insertion was
1809 after the token definitions.
1810
1811 Now, Bison never inserts the pre-prologue into the header file. In the code
1812 file, it always inserts it before the token definitions.
1813
402b123d 1814** Bison now provides a more flexible alternative to the traditional Yacc
34f98f46
JD
1815 prologue blocks: %before-header, %start-header, %end-header, and
1816 %after-header.
1817
1818 For example, the following declaration order in the grammar file reflects the
1819 order in which Bison will output these code blocks. However, you are free to
1820 declare these code blocks in your grammar file in whatever order is most
1821 convenient for you:
1822
1823 %before-header {
1824 /* Bison treats this block like a pre-prologue block: it inserts it into
1825 * the code file before the contents of the header file. It does *not*
1826 * insert it into the header file. This is a good place to put
1827 * #include's that you want at the top of your code file. A common
e4ab1254 1828 * example is '#include "system.h"'. */
34f98f46
JD
1829 }
1830 %start-header {
1831 /* Bison inserts this block into both the header file and the code file.
1832 * In both files, the point of insertion is before any Bison-generated
1833 * token, semantic type, location type, and class definitions. This is a
1834 * good place to define %union dependencies, for example. */
9bc0dd67
JD
1835 }
1836 %union {
34f98f46
JD
1837 /* Unlike the traditional Yacc prologue blocks, the output order for the
1838 * new %*-header blocks is not affected by their declaration position
1839 * relative to any %union in the grammar file. */
9bc0dd67 1840 }
34f98f46
JD
1841 %end-header {
1842 /* Bison inserts this block into both the header file and the code file.
1843 * In both files, the point of insertion is after the Bison-generated
1844 * definitions. This is a good place to declare or define public
1845 * functions or data structures that depend on the Bison-generated
1846 * definitions. */
9bc0dd67 1847 }
34f98f46
JD
1848 %after-header {
1849 /* Bison treats this block like a post-prologue block: it inserts it into
1850 * the code file after the contents of the header file. It does *not*
1851 * insert it into the header file. This is a good place to declare or
1852 * define internal functions or data structures that depend on the
1853 * Bison-generated definitions. */
1854 }
1855
1856 If you have multiple occurrences of any one of the above declarations, Bison
1857 will concatenate the contents in declaration order.
9bc0dd67 1858
85894313
JD
1859 [Although we failed to mention this here in the 2.3a release, the prologue
1860 alternatives were experimental, and they were rewritten in future versions.]
1861
e4ab1254 1862** The option "--report=look-ahead" has been changed to "--report=lookahead".
9e6e7ed2
PE
1863 The old spelling still works, but is not documented and may be removed
1864 in a future release.
742e4900 1865
402b123d 1866* Changes in version 2.3, 2006-06-05:
4ad3ed84 1867
e4ab1254 1868** GLR grammars should now use "YYRECOVERING ()" instead of "YYRECOVERING",
4ad3ed84
PE
1869 for compatibility with LALR(1) grammars.
1870
402b123d 1871** It is now documented that any definition of YYSTYPE or YYLTYPE should
4ad3ed84
PE
1872 be to a type name that does not contain parentheses or brackets.
1873
402b123d 1874* Changes in version 2.2, 2006-05-19:
193d7c70 1875
402b123d 1876** The distribution terms for all Bison-generated parsers now permit
193d7c70
PE
1877 using the parsers in nonfree programs. Previously, this permission
1878 was granted only for Bison-generated LALR(1) parsers in C.
5f4236a0 1879
402b123d 1880** %name-prefix changes the namespace name in C++ outputs.
aa08666d 1881
402b123d 1882** The C++ parsers export their token_type.
5f4236a0 1883
402b123d 1884** Bison now allows multiple %union declarations, and concatenates
d6ca7905
PE
1885 their contents together.
1886
402b123d 1887** New warning: unused values
4d7bc38c
PE
1888 Right-hand side symbols whose values are not used are reported,
1889 if the symbols have destructors. For instance:
affac613 1890
8f3596a6 1891 exp: exp "?" exp ":" exp { $1 ? $1 : $3; }
e9690142
JD
1892 | exp "+" exp
1893 ;
affac613 1894
8f3596a6
AD
1895 will trigger a warning about $$ and $5 in the first rule, and $3 in
1896 the second ($1 is copied to $$ by the default rule). This example
4e26c69e 1897 most likely contains three errors, and could be rewritten as:
affac613 1898
4e26c69e 1899 exp: exp "?" exp ":" exp
e9690142
JD
1900 { $$ = $1 ? $3 : $5; free ($1 ? $5 : $3); free ($1); }
1901 | exp "+" exp
1902 { $$ = $1 ? $1 : $3; if ($1) free ($3); }
1903 ;
affac613 1904
4e26c69e
PE
1905 However, if the original actions were really intended, memory leaks
1906 and all, the warnings can be suppressed by letting Bison believe the
1907 values are used, e.g.:
721be13c 1908
8f3596a6 1909 exp: exp "?" exp ":" exp { $1 ? $1 : $3; (void) ($$, $5); }
e9690142
JD
1910 | exp "+" exp { $$ = $1; (void) $3; }
1911 ;
721be13c 1912
84866159
AD
1913 If there are mid-rule actions, the warning is issued if no action
1914 uses it. The following triggers no warning: $1 and $3 are used.
1915
1916 exp: exp { push ($1); } '+' exp { push ($3); sum (); };
1917
721be13c
PE
1918 The warning is intended to help catching lost values and memory leaks.
1919 If a value is ignored, its associated memory typically is not reclaimed.
affac613 1920
402b123d 1921** %destructor vs. YYABORT, YYACCEPT, and YYERROR.
9d9b8b70
PE
1922 Destructors are now called when user code invokes YYABORT, YYACCEPT,
1923 and YYERROR, for all objects on the stack, other than objects
1924 corresponding to the right-hand side of the current rule.
a85284cf 1925
402b123d 1926** %expect, %expect-rr
035aa4a0
PE
1927 Incorrect numbers of expected conflicts are now actual errors,
1928 instead of warnings.
1929
402b123d 1930** GLR, YACC parsers.
4e26c69e
PE
1931 The %parse-params are available in the destructors (and the
1932 experimental printers) as per the documentation.
4b367315 1933
e4ab1254 1934** Bison now warns if it finds a stray "$" or "@" in an action.
ad6a9b97 1935
402b123d 1936** %require "VERSION"
4e26c69e
PE
1937 This specifies that the grammar file depends on features implemented
1938 in Bison version VERSION or higher.
b50d2359 1939
402b123d 1940** lalr1.cc: The token and value types are now class members.
e14d0ab6
AD
1941 The tokens were defined as free form enums and cpp macros. YYSTYPE
1942 was defined as a free form union. They are now class members:
e4ab1254
AD
1943 tokens are enumerations of the "yy::parser::token" struct, and the
1944 semantic values have the "yy::parser::semantic_type" type.
fb9712a9
AD
1945
1946 If you do not want or can update to this scheme, the directive
e4ab1254 1947 '%define "global_tokens_and_yystype" "1"' triggers the global
b50d2359
AD
1948 definition of tokens and YYSTYPE. This change is suitable both
1949 for previous releases of Bison, and this one.
fb9712a9 1950
b50d2359 1951 If you wish to update, then make sure older version of Bison will
e4ab1254 1952 fail using '%require "2.2"'.
fb9712a9 1953
402b123d 1954** DJGPP support added.
193d7c70 1955\f
402b123d 1956* Changes in version 2.1, 2005-09-16:
1ce59070 1957
402b123d 1958** The C++ lalr1.cc skeleton supports %lex-param.
e14d0ab6 1959
402b123d 1960** Bison-generated parsers now support the translation of diagnostics like
baf785db
PE
1961 "syntax error" into languages other than English. The default
1962 language is still English. For details, please see the new
0410a6e0
PE
1963 Internationalization section of the Bison manual. Software
1964 distributors should also see the new PACKAGING file. Thanks to
1965 Bruno Haible for this new feature.
1ce59070 1966
402b123d 1967** Wording in the Bison-generated parsers has been changed slightly to
1a059451
PE
1968 simplify translation. In particular, the message "memory exhausted"
1969 has replaced "parser stack overflow", as the old message was not
1970 always accurate for modern Bison-generated parsers.
1971
402b123d 1972** Destructors are now called when the parser aborts, for all symbols left
258b75ca
PE
1973 behind on the stack. Also, the start symbol is now destroyed after a
1974 successful parse. In both cases, the behavior was formerly inconsistent.
1975
402b123d 1976** When generating verbose diagnostics, Bison-generated parsers no longer
72f000b0
PE
1977 quote the literal strings associated with tokens. For example, for
1978 a syntax error associated with '%token NUM "number"' they might
1979 print 'syntax error, unexpected number' instead of 'syntax error,
1980 unexpected "number"'.
193d7c70 1981\f
402b123d 1982* Changes in version 2.0, 2004-12-25:
efeed023 1983
402b123d 1984** Possibly-incompatible changes
d7e14fc0 1985
82de6b0d
PE
1986 - Bison-generated parsers no longer default to using the alloca function
1987 (when available) to extend the parser stack, due to widespread
1988 problems in unchecked stack-overflow detection. You can "#define
1989 YYSTACK_USE_ALLOCA 1" to require the use of alloca, but please read
1990 the manual to determine safe values for YYMAXDEPTH in that case.
8dd162d3 1991
82de6b0d
PE
1992 - Error token location.
1993 During error recovery, the location of the syntax error is updated
1994 to cover the whole sequence covered by the error token: it includes
1995 the shifted symbols thrown away during the first part of the error
1996 recovery, and the lookahead rejected during the second part.
18d192f0 1997
82de6b0d
PE
1998 - Semicolon changes:
1999 . Stray semicolons are no longer allowed at the start of a grammar.
2000 . Semicolons are now required after in-grammar declarations.
e342c3be 2001
82de6b0d
PE
2002 - Unescaped newlines are no longer allowed in character constants or
2003 string literals. They were never portable, and GCC 3.4.0 has
2004 dropped support for them. Better diagnostics are now generated if
2005 forget a closing quote.
8dd162d3 2006
82de6b0d 2007 - NUL bytes are no longer allowed in Bison string literals, unfortunately.
f74b6f91 2008
402b123d 2009** New features
1452af69 2010
82de6b0d 2011 - GLR grammars now support locations.
4febdd96 2012
82de6b0d
PE
2013 - New directive: %initial-action.
2014 This directive allows the user to run arbitrary code (including
2015 initializing @$) from yyparse before parsing starts.
1452af69 2016
82de6b0d
PE
2017 - A new directive "%expect-rr N" specifies the expected number of
2018 reduce/reduce conflicts in GLR parsers.
1452af69 2019
e4ab1254 2020 - %token numbers can now be hexadecimal integers, e.g., "%token FOO 0x12d".
82de6b0d 2021 This is a GNU extension.
4febdd96 2022
e4ab1254 2023 - The option "--report=lookahead" was changed to "--report=look-ahead".
9e6e7ed2 2024 [However, this was changed back after 2.3.]
1452af69 2025
82de6b0d 2026 - Experimental %destructor support has been added to lalr1.cc.
1452af69 2027
82de6b0d
PE
2028 - New configure option --disable-yacc, to disable installation of the
2029 yacc command and -ly library introduced in 1.875 for POSIX conformance.
6040d338 2030
402b123d 2031** Bug fixes
d5a3fe37 2032
82de6b0d
PE
2033 - For now, %expect-count violations are now just warnings, not errors.
2034 This is for compatibility with Bison 1.75 and earlier (when there are
2035 reduce/reduce conflicts) and with Bison 1.30 and earlier (when there
2036 are too many or too few shift/reduce conflicts). However, in future
2037 versions of Bison we plan to improve the %expect machinery so that
2038 these violations will become errors again.
3473d0f8 2039
82de6b0d
PE
2040 - Within Bison itself, numbers (e.g., goto numbers) are no longer
2041 arbitrarily limited to 16-bit counts.
d600ee67 2042
82de6b0d 2043 - Semicolons are now allowed before "|" in grammar rules, as POSIX requires.
d600ee67 2044\f
402b123d 2045* Changes in version 1.875, 2003-01-01:
963fcc17 2046
402b123d 2047** The documentation license has been upgraded to version 1.2
dc546b0f 2048 of the GNU Free Documentation License.
75eb3bc4 2049
402b123d 2050** syntax error processing
75eb3bc4 2051
dc546b0f
PE
2052 - In Yacc-style parsers YYLLOC_DEFAULT is now used to compute error
2053 locations too. This fixes bugs in error-location computation.
75eb3bc4 2054
dc546b0f
PE
2055 - %destructor
2056 It is now possible to reclaim the memory associated to symbols
2057 discarded during error recovery. This feature is still experimental.
20daca06 2058
dc546b0f
PE
2059 - %error-verbose
2060 This new directive is preferred over YYERROR_VERBOSE.
74724a70 2061
dc546b0f
PE
2062 - #defining yyerror to steal internal variables is discouraged.
2063 It is not guaranteed to work forever.
d1de5372 2064
402b123d 2065** POSIX conformance
d1de5372 2066
dc546b0f
PE
2067 - Semicolons are once again optional at the end of grammar rules.
2068 This reverts to the behavior of Bison 1.33 and earlier, and improves
2069 compatibility with Yacc.
74724a70 2070
e4ab1254
AD
2071 - "parse error" -> "syntax error"
2072 Bison now uniformly uses the term "syntax error"; formerly, the code
2073 and manual sometimes used the term "parse error" instead. POSIX
2074 requires "syntax error" in diagnostics, and it was thought better to
dc546b0f 2075 be consistent.
74724a70 2076
dc546b0f
PE
2077 - The documentation now emphasizes that yylex and yyerror must be
2078 declared before use. C99 requires this.
d1de5372 2079
dc546b0f
PE
2080 - Bison now parses C99 lexical constructs like UCNs and
2081 backslash-newline within C escape sequences, as POSIX 1003.1-2001 requires.
d1de5372 2082
dc546b0f
PE
2083 - File names are properly escaped in C output. E.g., foo\bar.y is
2084 output as "foo\\bar.y".
6780ca7a 2085
dc546b0f 2086 - Yacc command and library now available
e4ab1254 2087 The Bison distribution now installs a "yacc" command, as POSIX requires.
dc546b0f
PE
2088 Also, Bison now installs a small library liby.a containing
2089 implementations of Yacc-compatible yyerror and main functions.
2090 This library is normally not useful, but POSIX requires it.
6e649e65 2091
dc546b0f 2092 - Type clashes now generate warnings, not errors.
6e649e65 2093
dc546b0f
PE
2094 - If the user does not define YYSTYPE as a macro, Bison now declares it
2095 using typedef instead of defining it as a macro.
2096 For consistency, YYLTYPE is also declared instead of defined.
9501dc6e 2097
402b123d 2098** Other compatibility issues
886a425c 2099
e4ab1254
AD
2100 - %union directives can now have a tag before the "{", e.g., the
2101 directive "%union foo {...}" now generates the C code
2102 "typedef union foo { ... } YYSTYPE;"; this is for Yacc compatibility.
2103 The default union tag is "YYSTYPE", for compatibility with Solaris 9 Yacc.
2104 For consistency, YYLTYPE's struct tag is now "YYLTYPE" not "yyltype".
dc546b0f 2105 This is for compatibility with both Yacc and Bison 1.35.
72f889cc 2106
e4ab1254 2107 - ";" is output before the terminating "}" of an action, for
dc546b0f 2108 compatibility with Bison 1.35.
886a425c 2109
dc546b0f 2110 - Bison now uses a Yacc-style format for conflict reports, e.g.,
e4ab1254 2111 "conflicts: 2 shift/reduce, 1 reduce/reduce".
437c2d80 2112
e4ab1254 2113 - "yystype" and "yyltype" are now obsolescent macros instead of being
dc546b0f
PE
2114 typedefs or tags; they are no longer documented and are planned to be
2115 withdrawn in a future release.
2a8d363a 2116
402b123d 2117** GLR parser notes
2a8d363a 2118
dc546b0f
PE
2119 - GLR and inline
2120 Users of Bison have to decide how they handle the portability of the
e4ab1254 2121 C keyword "inline".
959e5f51 2122
e4ab1254
AD
2123 - "parsing stack overflow..." -> "parser stack overflow"
2124 GLR parsers now report "parser stack overflow" as per the Bison manual.
900c5db5 2125
18ad57b3
AD
2126** %parse-param and %lex-param
2127 The macros YYPARSE_PARAM and YYLEX_PARAM provide a means to pass
2128 additional context to yyparse and yylex. They suffer from several
2129 shortcomings:
2130
2131 - a single argument only can be added,
2132 - their types are weak (void *),
242cc08e 2133 - this context is not passed to ancillary functions such as yyerror,
18ad57b3
AD
2134 - only yacc.c parsers support them.
2135
2136 The new %parse-param/%lex-param directives provide a more precise control.
2137 For instance:
2138
2139 %parse-param {int *nastiness}
2140 %lex-param {int *nastiness}
2141 %parse-param {int *randomness}
2142
2143 results in the following signatures:
2144
2145 int yylex (int *nastiness);
2146 int yyparse (int *nastiness, int *randomness);
2147
2148 or, if both %pure-parser and %locations are used:
2149
2150 int yylex (YYSTYPE *lvalp, YYLTYPE *llocp, int *nastiness);
2151 int yyparse (int *nastiness, int *randomness);
2152
402b123d 2153** Bison now warns if it detects conflicting outputs to the same file,
e4ab1254 2154 e.g., it generates a warning for "bison -d -o foo.h foo.y" since
dc546b0f 2155 that command outputs both code and header to foo.h.
6e40b4eb 2156
402b123d 2157** #line in output files
dc546b0f 2158 - --no-line works properly.
6e40b4eb 2159
402b123d 2160** Bison can no longer be built by a K&R C compiler; it requires C89 or
6e40b4eb
AD
2161 later to be built. This change originally took place a few versions
2162 ago, but nobody noticed until we recently asked someone to try
2163 building Bison with a K&R C compiler.
d600ee67 2164\f
402b123d 2165* Changes in version 1.75, 2002-10-14:
7933f2b5 2166
402b123d 2167** Bison should now work on 64-bit hosts.
7933f2b5 2168
402b123d 2169** Indonesian translation thanks to Tedi Heriyanto.
7933f2b5 2170
402b123d 2171** GLR parsers
f50adbbd
AD
2172 Fix spurious parse errors.
2173
402b123d 2174** Pure parsers
f50adbbd
AD
2175 Some people redefine yyerror to steal yyparse' private variables.
2176 Reenable this trick until an official feature replaces it.
2177
402b123d 2178** Type Clashes
d90c934c
AD
2179 In agreement with POSIX and with other Yaccs, leaving a default
2180 action is valid when $$ is untyped, and $1 typed:
2181
e9690142 2182 untyped: ... typed;
d90c934c
AD
2183
2184 but the converse remains an error:
2185
e9690142 2186 typed: ... untyped;
d90c934c 2187
402b123d 2188** Values of mid-rule actions
d90c934c
AD
2189 The following code:
2190
e9690142 2191 foo: { ... } { $$ = $1; } ...
d90c934c
AD
2192
2193 was incorrectly rejected: $1 is defined in the second mid-rule
2194 action, and is equal to the $$ of the first mid-rule action.
d600ee67 2195\f
402b123d 2196* Changes in version 1.50, 2002-10-04:
adc8c848 2197
402b123d 2198** GLR parsing
676385e2
PH
2199 The declaration
2200 %glr-parser
2201 causes Bison to produce a Generalized LR (GLR) parser, capable of handling
2202 almost any context-free grammar, ambiguous or not. The new declarations
e8832397 2203 %dprec and %merge on grammar rules allow parse-time resolution of
676385e2
PH
2204 ambiguities. Contributed by Paul Hilfinger.
2205
7933f2b5 2206 Unfortunately Bison 1.50 does not work properly on 64-bit hosts
420f93c8
PE
2207 like the Alpha, so please stick to 32-bit hosts for now.
2208
402b123d 2209** Output Directory
8c165d89 2210 When not in Yacc compatibility mode, when the output file was not
e4ab1254
AD
2211 specified, running "bison foo/bar.y" created "foo/bar.c". It
2212 now creates "bar.c".
8c165d89 2213
402b123d 2214** Undefined token
007a50a4 2215 The undefined token was systematically mapped to 2 which prevented
e88dbdbf 2216 the use of 2 by the user. This is no longer the case.
007a50a4 2217
402b123d 2218** Unknown token numbers
e88dbdbf 2219 If yylex returned an out of range value, yyparse could die. This is
007a50a4
AD
2220 no longer the case.
2221
402b123d 2222** Error token
e88dbdbf 2223 According to POSIX, the error token must be 256.
23c5a174
AD
2224 Bison extends this requirement by making it a preference: *if* the
2225 user specified that one of her tokens is numbered 256, then error
2226 will be mapped onto another number.
2227
402b123d 2228** Verbose error messages
e4ab1254 2229 They no longer report "..., expecting error or..." for states where
217598da
AD
2230 error recovery is possible.
2231
402b123d 2232** End token
e4ab1254 2233 Defaults to "$end" instead of "$".
217598da 2234
402b123d 2235** Error recovery now conforms to documentation and to POSIX
68cd8af3
PE
2236 When a Bison-generated parser encounters a syntax error, it now pops
2237 the stack until it finds a state that allows shifting the error
2238 token. Formerly, it popped the stack until it found a state that
2239 allowed some non-error action other than a default reduction on the
2240 error token. The new behavior has long been the documented behavior,
2241 and has long been required by POSIX. For more details, please see
337116ba
PE
2242 Paul Eggert, "Reductions during Bison error handling" (2002-05-20)
2243 <http://lists.gnu.org/archive/html/bug-bison/2002-05/msg00038.html>.
68cd8af3 2244
402b123d 2245** Traces
5504898e
AD
2246 Popped tokens and nonterminals are now reported.
2247
402b123d 2248** Larger grammars
a861a339
PE
2249 Larger grammars are now supported (larger token numbers, larger grammar
2250 size (= sum of the LHS and RHS lengths), larger LALR tables).
2251 Formerly, many of these numbers ran afoul of 16-bit limits;
2252 now these limits are 32 bits on most hosts.
355e7c1c 2253
402b123d 2254** Explicit initial rule
643a5994
AD
2255 Bison used to play hacks with the initial rule, which the user does
2256 not write. It is now explicit, and visible in the reports and
2257 graphs as rule 0.
23c5a174 2258
402b123d 2259** Useless rules
643a5994 2260 Before, Bison reported the useless rules, but, although not used,
77714df2 2261 included them in the parsers. They are now actually removed.
23c5a174 2262
402b123d 2263** Useless rules, useless nonterminals
6b98e4b5
AD
2264 They are now reported, as a warning, with their locations.
2265
402b123d 2266** Rules never reduced
e8832397
AD
2267 Rules that can never be reduced because of conflicts are now
2268 reported.
2269
e4ab1254 2270** Incorrect "Token not used"
11652ab3
AD
2271 On a grammar such as
2272
e29f0771
AD
2273 %token useless useful
2274 %%
2275 exp: '0' %prec useful;
11652ab3
AD
2276
2277 where a token was used to set the precedence of the last rule,
e4ab1254 2278 bison reported both "useful" and "useless" as useless tokens.
11652ab3 2279
402b123d 2280** Revert the C++ namespace changes introduced in 1.31
77714df2 2281 as they caused too many portability hassles.
0179dd65 2282
402b123d 2283** Default locations
b2d52318
AD
2284 By an accident of design, the default computation of @$ was
2285 performed after another default computation was performed: @$ = @1.
2286 The latter is now removed: YYLLOC_DEFAULT is fully responsible of
2287 the computation of @$.
adc8c848 2288
402b123d 2289** Token end-of-file
b7c49edf
AD
2290 The token end of file may be specified by the user, in which case,
2291 the user symbol is used in the reports, the graphs, and the verbose
e4ab1254 2292 error messages instead of "$end", which remains being the default.
b7c49edf 2293 For instance
e29f0771 2294 %token MYEOF 0
b7c49edf 2295 or
e29f0771 2296 %token MYEOF 0 "end of file"
fdbcd8e2 2297
402b123d 2298** Semantic parser
fdbcd8e2
AD
2299 This old option, which has been broken for ages, is removed.
2300
402b123d 2301** New translations
a861a339 2302 Brazilian Portuguese, thanks to Alexandre Folle de Menezes.
84614e13
AD
2303 Croatian, thanks to Denis Lackovic.
2304
402b123d 2305** Incorrect token definitions
e4ab1254
AD
2306 When given
2307 %token 'a' "A"
2308 bison used to output
2309 #define 'a' 65
b87f8b21 2310
402b123d 2311** Token definitions as enums
77714df2
AD
2312 Tokens are output both as the traditional #define's, and, provided
2313 the compiler supports ANSI C or is a C++ compiler, as enums.
e88dbdbf 2314 This lets debuggers display names instead of integers.
77714df2 2315
402b123d 2316** Reports
ec3bc396
AD
2317 In addition to --verbose, bison supports --report=THINGS, which
2318 produces additional information:
b408954b
AD
2319 - itemset
2320 complete the core item sets with their closure
e4ab1254 2321 - lookahead [changed to "look-ahead" in 1.875e through 2.3, but changed back]
9e6e7ed2 2322 explicitly associate lookahead tokens to items
b408954b
AD
2323 - solved
2324 describe shift/reduce conflicts solving.
2325 Bison used to systematically output this information on top of
2326 the report. Solved conflicts are now attached to their states.
ec3bc396 2327
402b123d 2328** Type clashes
9af3fbce
AD
2329 Previous versions don't complain when there is a type clash on
2330 the default action if the rule has a mid-rule action, such as in:
2331
e29f0771
AD
2332 %type <foo> bar
2333 %%
2334 bar: '0' {} '0';
9af3fbce
AD
2335
2336 This is fixed.
a861a339 2337
402b123d 2338** GNU M4 is now required when using Bison.
f987e9d2 2339\f
402b123d 2340* Changes in version 1.35, 2002-03-25:
76551463 2341
402b123d 2342** C Skeleton
76551463
AD
2343 Some projects use Bison's C parser with C++ compilers, and define
2344 YYSTYPE as a class. The recent adjustment of C parsers for data
2345 alignment and 64 bit architectures made this impossible.
2346
2347 Because for the time being no real solution for C++ parser
2348 generation exists, kludges were implemented in the parser to
2349 maintain this use. In the future, when Bison has C++ parsers, this
2350 kludge will be disabled.
2351
2352 This kludge also addresses some C++ problems when the stack was
2353 extended.
76551463 2354\f
402b123d 2355* Changes in version 1.34, 2002-03-12:
76551463 2356
402b123d 2357** File name clashes are detected
76551463 2358 $ bison foo.y -d -o foo.x
e4ab1254 2359 fatal error: header and parser would both be named "foo.x"
76551463 2360
e4ab1254 2361** A missing ";" at the end of a rule triggers a warning
76551463
AD
2362 In accordance with POSIX, and in agreement with other
2363 Yacc implementations, Bison will mandate this semicolon in the near
2364 future. This eases the implementation of a Bison parser of Bison
2365 grammars by making this grammar LALR(1) instead of LR(2). To
2366 facilitate the transition, this release introduces a warning.
2367
402b123d 2368** Revert the C++ namespace changes introduced in 1.31, as they caused too
76551463
AD
2369 many portability hassles.
2370
402b123d 2371** DJGPP support added.
76551463 2372
402b123d 2373** Fix test suite portability problems.
76551463 2374\f
402b123d 2375* Changes in version 1.33, 2002-02-07:
76551463 2376
402b123d 2377** Fix C++ issues
76551463
AD
2378 Groff could not be compiled for the definition of size_t was lacking
2379 under some conditions.
2380
402b123d 2381** Catch invalid @n
76551463
AD
2382 As is done with $n.
2383\f
402b123d 2384* Changes in version 1.32, 2002-01-23:
76551463 2385
402b123d 2386** Fix Yacc output file names
76551463 2387
402b123d 2388** Portability fixes
76551463 2389
402b123d 2390** Italian, Dutch translations
76551463 2391\f
402b123d 2392* Changes in version 1.31, 2002-01-14:
52d1aeee 2393
402b123d 2394** Many Bug Fixes
52d1aeee 2395
402b123d 2396** GNU Gettext and %expect
52d1aeee
MA
2397 GNU Gettext asserts 10 s/r conflicts, but there are 7. Now that
2398 Bison dies on incorrect %expectations, we fear there will be
2399 too many bug reports for Gettext, so _for the time being_, %expect
e4ab1254 2400 does not trigger an error when the input file is named "plural.y".
52d1aeee 2401
402b123d 2402** Use of alloca in parsers
52d1aeee
MA
2403 If YYSTACK_USE_ALLOCA is defined to 0, then the parsers will use
2404 malloc exclusively. Since 1.29, but was not NEWS'ed.
2405
2406 alloca is used only when compiled with GCC, to avoid portability
2407 problems as on AIX.
2408
402b123d 2409** yyparse now returns 2 if memory is exhausted; formerly it dumped core.
b47dbebe 2410
402b123d 2411** When the generated parser lacks debugging code, YYDEBUG is now 0
52d1aeee
MA
2412 (as POSIX requires) instead of being undefined.
2413
402b123d 2414** User Actions
52d1aeee
MA
2415 Bison has always permitted actions such as { $$ = $1 }: it adds the
2416 ending semicolon. Now if in Yacc compatibility mode, the semicolon
2417 is no longer output: one has to write { $$ = $1; }.
2418
402b123d 2419** Better C++ compliance
52d1aeee 2420 The output parsers try to respect C++ namespaces.
76551463 2421 [This turned out to be a failed experiment, and it was reverted later.]
52d1aeee 2422
402b123d 2423** Reduced Grammars
52d1aeee
MA
2424 Fixed bugs when reporting useless nonterminals.
2425
402b123d 2426** 64 bit hosts
52d1aeee
MA
2427 The parsers work properly on 64 bit hosts.
2428
402b123d 2429** Error messages
52d1aeee
MA
2430 Some calls to strerror resulted in scrambled or missing error messages.
2431
402b123d 2432** %expect
52d1aeee
MA
2433 When the number of shift/reduce conflicts is correct, don't issue
2434 any warning.
2435
402b123d 2436** The verbose report includes the rule line numbers.
52d1aeee 2437
402b123d 2438** Rule line numbers are fixed in traces.
52d1aeee 2439
402b123d 2440** Swedish translation
52d1aeee 2441
402b123d 2442** Parse errors
52d1aeee
MA
2443 Verbose parse error messages from the parsers are better looking.
2444 Before: parse error: unexpected `'/'', expecting `"number"' or `'-'' or `'(''
2445 Now: parse error: unexpected '/', expecting "number" or '-' or '('
2446
402b123d 2447** Fixed parser memory leaks.
52d1aeee
MA
2448 When the generated parser was using malloc to extend its stacks, the
2449 previous allocations were not freed.
2450
402b123d 2451** Fixed verbose output file.
52d1aeee
MA
2452 Some newlines were missing.
2453 Some conflicts in state descriptions were missing.
2454
402b123d 2455** Fixed conflict report.
52d1aeee
MA
2456 Option -v was needed to get the result.
2457
402b123d 2458** %expect
52d1aeee
MA
2459 Was not used.
2460 Mismatches are errors, not warnings.
2461
402b123d 2462** Fixed incorrect processing of some invalid input.
52d1aeee 2463
402b123d 2464** Fixed CPP guards: 9foo.h uses BISON_9FOO_H instead of 9FOO_H.
52d1aeee 2465
402b123d 2466** Fixed some typos in the documentation.
52d1aeee 2467
402b123d 2468** %token MY_EOF 0 is supported.
52d1aeee
MA
2469 Before, MY_EOF was silently renumbered as 257.
2470
402b123d 2471** doc/refcard.tex is updated.
52d1aeee 2472
402b123d 2473** %output, %file-prefix, %name-prefix.
52d1aeee
MA
2474 New.
2475
402b123d 2476** --output
e4ab1254 2477 New, aliasing "--output-file".
52d1aeee 2478\f
402b123d 2479* Changes in version 1.30, 2001-10-26:
342b8b6e 2480
e4ab1254
AD
2481** "--defines" and "--graph" have now an optional argument which is the
2482 output file name. "-d" and "-g" do not change; they do not take any
342b8b6e
AD
2483 argument.
2484
e4ab1254 2485** "%source_extension" and "%header_extension" are removed, failed
342b8b6e
AD
2486 experiment.
2487
402b123d 2488** Portability fixes.
f987e9d2 2489\f
402b123d 2490* Changes in version 1.29, 2001-09-07:
342b8b6e 2491
402b123d 2492** The output file does not define const, as this caused problems when used
342b8b6e
AD
2493 with common autoconfiguration schemes. If you still use ancient compilers
2494 that lack const, compile with the equivalent of the C compiler option
e4ab1254 2495 "-Dconst=". Autoconf's AC_C_CONST macro provides one way to do this.
342b8b6e 2496
e4ab1254 2497** Added "-g" and "--graph".
f87a2205 2498
402b123d 2499** The Bison manual is now distributed under the terms of the GNU FDL.
f2b5126e 2500
402b123d 2501** The input and the output files has automatically a similar extension.
234a3be3 2502
402b123d 2503** Russian translation added.
f87a2205 2504
402b123d 2505** NLS support updated; should hopefully be less troublesome.
f87a2205 2506
402b123d 2507** Added the old Bison reference card.
c33638bb 2508
e4ab1254 2509** Added "--locations" and "%locations".
6deb4447 2510
e4ab1254 2511** Added "-S" and "--skeleton".
cd5bd6ac 2512
e4ab1254 2513** "%raw", "-r", "--raw" is disabled.
62ab6972 2514
402b123d 2515** Special characters are escaped when output. This solves the problems
cd5bd6ac
AD
2516 of the #line lines with path names including backslashes.
2517
402b123d 2518** New directives.
e4ab1254
AD
2519 "%yacc", "%fixed_output_files", "%defines", "%no_parser", "%verbose",
2520 "%debug", "%source_extension" and "%header_extension".
f987e9d2 2521
402b123d 2522** @$
f987e9d2 2523 Automatic location tracking.
f87a2205 2524\f
402b123d 2525* Changes in version 1.28, 1999-07-06:
d2e00347 2526
402b123d 2527** Should compile better now with K&R compilers.
d2e00347 2528
402b123d 2529** Added NLS.
d2e00347 2530
402b123d 2531** Fixed a problem with escaping the double quote character.
d2e00347 2532
402b123d 2533** There is now a FAQ.
d2e00347 2534\f
402b123d 2535* Changes in version 1.27:
5c31c3c2 2536
402b123d 2537** The make rule which prevented bison.simple from being created on
5c31c3c2
JT
2538 some systems has been fixed.
2539\f
402b123d 2540* Changes in version 1.26:
4be07551 2541
7e508a2b 2542** Bison now uses Automake.
4be07551 2543
402b123d 2544** New mailing lists: <bug-bison@gnu.org> and <help-bison@gnu.org>.
4be07551 2545
402b123d 2546** Token numbers now start at 257 as previously documented, not 258.
4be07551 2547
402b123d 2548** Bison honors the TMPDIR environment variable.
4be07551 2549
402b123d 2550** A couple of buffer overruns have been fixed.
f51dbca1 2551
402b123d 2552** Problems when closing files should now be reported.
f51dbca1 2553
402b123d 2554** Generated parsers should now work even on operating systems which do
f51dbca1 2555 not provide alloca().
4be07551 2556\f
402b123d 2557* Changes in version 1.25, 1995-10-16:
df8878c5 2558
402b123d 2559** Errors in the input grammar are not fatal; Bison keeps reading
df8878c5 2560the grammar file, and reports all the errors found in it.
8c44d3ec 2561
402b123d 2562** Tokens can now be specified as multiple-character strings: for
df8878c5 2563example, you could use "<=" for a token which looks like <=, instead
7e508a2b 2564of choosing a name like LESSEQ.
df8878c5 2565
402b123d 2566** The %token_table declaration says to write a table of tokens (names
df8878c5
RS
2567and numbers) into the parser file. The yylex function can use this
2568table to recognize multiple-character string tokens, or for other
2569purposes.
2570
402b123d 2571** The %no_lines declaration says not to generate any #line preprocessor
df8878c5
RS
2572directives in the parser file.
2573
402b123d 2574** The %raw declaration says to use internal Bison token numbers, not
df8878c5
RS
2575Yacc-compatible token numbers, when token names are defined as macros.
2576
402b123d 2577** The --no-parser option produces the parser tables without including
df8878c5
RS
2578the parser engine; a project can now use its own parser engine.
2579The actions go into a separate file called NAME.act, in the form of
2580a switch statement body.
2581\f
402b123d 2582* Changes in version 1.23:
6780ca7a 2583
4d019228
DM
2584The user can define YYPARSE_PARAM as the name of an argument to be
2585passed into yyparse. The argument should have type void *. It should
2586actually point to an object. Grammar actions can access the variable
2587by casting it to the proper pointer type.
6780ca7a 2588
6780ca7a 2589Line numbers in output file corrected.
6780ca7a 2590\f
402b123d 2591* Changes in version 1.22:
6780ca7a
DM
2592
2593--help option added.
6780ca7a 2594\f
402b123d 2595* Changes in version 1.20:
6780ca7a
DM
2596
2597Output file does not redefine const for C++.
9f4503d6 2598
76551463
AD
2599-----
2600
7d6bad19 2601Copyright (C) 1995-2013 Free Software Foundation, Inc.
76551463 2602
74553c98 2603This file is part of Bison, the GNU Parser Generator.
76551463 2604
f16b0819 2605This program is free software: you can redistribute it and/or modify
76551463 2606it under the terms of the GNU General Public License as published by
f16b0819
PE
2607the Free Software Foundation, either version 3 of the License, or
2608(at your option) any later version.
76551463 2609
f16b0819 2610This program is distributed in the hope that it will be useful,
76551463
AD
2611but WITHOUT ANY WARRANTY; without even the implied warranty of
2612MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
2613GNU General Public License for more details.
2614
2615You should have received a copy of the GNU General Public License
f16b0819 2616along with this program. If not, see <http://www.gnu.org/licenses/>.
7e508a2b
AD
2617
2618 LocalWords: yacc YYBACKUP glr GCC lalr ArrayIndexOutOfBoundsException nullptr
2619 LocalWords: cplusplus liby rpl fprintf mfcalc Wyacc stmt cond expr mk sym lr
2620 LocalWords: IELR ielr Lookahead YYERROR nonassoc LALR's api lookaheads yychar
2621 LocalWords: destructor lookahead YYRHSLOC YYLLOC Rhs ifndef YYFAIL cpp sr rr
2622 LocalWords: preprocessor initializer Wno Wnone Werror FreeBSD prec livelocks
2623 LocalWords: Solaris AIX UX RHEL Tru LHS gcc's Wundef YYENABLE NLS YYLTYPE VCG
2624 LocalWords: yyerror cpp's Wunused yylval yylloc prepend yyparse yylex yypush
2625 LocalWords: Graphviz xml nonterminals midrule destructor's YYSTYPE typedef ly
2626 LocalWords: CHR chr printf stdout namespace preprocessing enum pre include's
2627 LocalWords: YYRECOVERING nonfree destructors YYABORT YYACCEPT params enums de
2628 LocalWords: struct yystype DJGPP lex param Haible NUM alloca YYSTACK NUL goto
2629 LocalWords: YYMAXDEPTH Unescaped UCNs YYLTYPE's yyltype typedefs inline Yaccs
2630 LocalWords: Heriyanto Reenable dprec Hilfinger Eggert MYEOF Folle Menezes EOF
242cc08e 2631 LocalWords: Lackovic define's itemset Groff Gettext malloc NEWS'ed YYDEBUG YY
7e508a2b 2632 LocalWords: namespaces strerror const autoconfiguration Dconst Autoconf's FDL
242cc08e
AD
2633 LocalWords: Automake TMPDIR LESSEQ ylwrap endif yydebug YYTOKEN YYLSP ival hh
2634 LocalWords: extern YYTOKENTYPE TOKENTYPE yytokentype tokentype STYPE lval pdf
dcb366b1 2635 LocalWords: lang yyoutput dvi html ps POSIX lvalp llocp Wother nterm arg init
1282c124
AD
2636 LocalWords: TOK calc yyo fval Wconflicts parsers yystackp yyval yynerrs
2637 LocalWords: Théophile Ranquet Santet fno fnone stype associativity Tolmer
2638 LocalWords: Wprecedence Rassoul Wempty Paolo Bonzini parser's Michiel loc
2639 LocalWords: redeclaration sval fcaret reentrant XSLT xsl Wmaybe yyvsp Tedi
2640 LocalWords: pragmas noreturn untyped Rozenman unexpanded Wojciech Polak
6574576c 2641 LocalWords: Alexandre MERCHANTABILITY yytype
7e508a2b
AD
2642
2643Local Variables:
2644mode: outline
e4ab1254 2645fill-column: 76
7e508a2b 2646End: