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4* Changes in version ?.? (????-??-??):
5
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6** Additional yylex/yyparse arguments
7
8 The new directive %param declare additional argument to both yylex
bb9191dd 9 and yyparse. The %lex-param, %parse-param, and %param directives
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10 support one or more arguments. Instead of
11
12 %lex-param {arg1_type *arg1}
13 %lex-param {arg2_type *arg2}
14 %parse-param {arg1_type *arg1}
15 %parse-param {arg2_type *arg2}
16
17 one may now declare
18
19 %param {arg1_type *arg1} {arg2_type *arg2}
20
21** Java skeleton improvements
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22
23 The constants for token names were moved to the Lexer interface.
24 Also, it is possible to add code to the parser's constructors using
25 "%code init" and "%define init_throws".
26
4c6622c2 27** Variable api.tokens.prefix
99c08fb6 28
4c6622c2 29 The variable api.tokens.prefix changes the way tokens are identified in
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30 the generated files. This is especially useful to avoid collisions
31 with identifiers in the target language. For instance
32
33 %token FILE for ERROR
4c6622c2 34 %define api.tokens.prefix "TOK_"
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35 %%
36 start: FILE for ERROR;
37
38 will generate the definition of the symbols TOK_FILE, TOK_for, and
39 TOK_ERROR in the generated sources. In particular, the scanner must
40 use these prefixed token names, although the grammar itself still
41 uses the short names (as in the sample rule given above).
42
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43** Variable api.namespace
44
45 The "namespace" variable is renamed "api.namespace". Backward
46 compatibility is ensured, but upgrading is recommended.
47
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48** Variable parse.error
49
50 The variable error controls the verbosity of error messages. The
51 use of the %error-verbose directive is deprecated in favor of
52 %define parse.error "verbose".
53
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54** Semantic predicates
55
56 The new, experimental, semantic-predicate feature allows actions of
57 the form %?{ BOOLEAN-EXPRESSION }, which cause syntax errors (as for
58 YYERROR) if the expression evaluates to 0, and are evaluated immediately
59 in GLR parsers, rather than being deferred. The result is that they
60 allow the programmer to prune possible parses based on the values of
61 runtime expressions.
62
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63* Changes in version 2.5 (????-??-??):
64
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65** Grammar symbol names can now contain non-initial dashes:
66
67 Consistently with directives (such as %error-verbose) and with
68 %define variables (e.g. push-pull), grammar symbol names may contain
69 dashes in any position except the beginning. This is a GNU
70 extension over POSIX Yacc. Thus, use of this extension is reported
71 by -Wyacc and rejected in Yacc mode (--yacc).
72
f1b238df 73** Named references:
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74
75 Historically, Yacc and Bison have supported positional references
76 ($n, $$) to allow access to symbol values from inside of semantic
77 actions code.
78
79 Starting from this version, Bison can also accept named references.
80 When no ambiguity is possible, original symbol names may be used
81 as named references:
82
83 if_stmt : 'if' cond_expr 'then' then_stmt ';'
84 { $if_stmt = mk_if_stmt($cond_expr, $then_stmt); }
85
86 In the more common case, explicit names may be declared:
87
88 stmt[res] : 'if' expr[cond] 'then' stmt[then] 'else' stmt[else] ';'
89 { $res = mk_if_stmt($cond, $then, $else); }
90
5b1ff423 91 Location information is also accessible using @name syntax. When
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92 accessing symbol names containing dots or dashes, explicit bracketing
93 ($[sym.1]) must be used.
94
5b1ff423 95 These features are experimental in this version. More user feedback
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96 will help to stabilize them.
97
f1b238df 98** IELR(1) and canonical LR(1):
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99
100 IELR(1) is a minimal LR(1) parser table generation algorithm. That
101 is, given any context-free grammar, IELR(1) generates parser tables
102 with the full language recognition power of canonical LR(1) but with
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103 nearly the same number of parser states as LALR(1). This reduction
104 in parser states is often an order of magnitude. More importantly,
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105 because canonical LR(1)'s extra parser states may contain duplicate
106 conflicts in the case of non-LR(1) grammars, the number of conflicts
107 for IELR(1) is often an order of magnitude less as well. This can
108 significantly reduce the complexity of developing of a grammar.
109
110 Bison can now generate IELR(1) and canonical LR(1) parser tables in
111 place of its traditional LALR(1) parser tables, which remain the
112 default. You can specify the type of parser tables in the grammar
113 file with these directives:
114
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115 %define lr.type lalr
116 %define lr.type ielr
117 %define lr.type canonical-lr
eb45ef3b 118
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119 The default-reduction optimization in the parser tables can also be
120 adjusted using `%define lr.default-reductions'. For details on both
121 of these features, see the new section `Tuning LR' in the Bison
122 manual.
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123
124 These features are experimental. More user feedback will help to
125 stabilize them.
126
7fceb615 127** LAC (Lookahead Correction) for syntax error handling:
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128
129 Canonical LR, IELR, and LALR can suffer from a couple of problems
130 upon encountering a syntax error. First, the parser might perform
131 additional parser stack reductions before discovering the syntax
7fceb615 132 error. Such reductions can perform user semantic actions that are
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133 unexpected because they are based on an invalid token, and they
134 cause error recovery to begin in a different syntactic context than
135 the one in which the invalid token was encountered. Second, when
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136 verbose error messages are enabled (with %error-verbose or the
137 obsolete `#define YYERROR_VERBOSE'), the expected token list in the
138 syntax error message can both contain invalid tokens and omit valid
139 tokens.
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140
141 The culprits for the above problems are %nonassoc, default
142 reductions in inconsistent states, and parser state merging. Thus,
143 IELR and LALR suffer the most. Canonical LR can suffer only if
144 %nonassoc is used or if default reductions are enabled for
145 inconsistent states.
146
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147 LAC is a new mechanism within the parsing algorithm that solves
148 these problems for canonical LR, IELR, and LALR without sacrificing
149 %nonassoc, default reductions, or state merging. When LAC is in
150 use, canonical LR and IELR behave almost exactly the same for both
151 syntactically acceptable and syntactically unacceptable input.
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152 While LALR still does not support the full language-recognition
153 power of canonical LR and IELR, LAC at least enables LALR's syntax
154 error handling to correctly reflect LALR's language-recognition
155 power.
156
157 Currently, LAC is only supported for deterministic parsers in C.
158 You can enable LAC with the following directive:
159
160 %define parse.lac full
161
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162 See the new section `LAC' in the Bison manual for additional
163 details including a few caveats.
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164
165 LAC is an experimental feature. More user feedback will help to
166 stabilize it.
167
d397d9f0 168** %define improvements:
cf499cff 169
f1b238df 170*** Can now be invoked via the command line:
50cca368 171
de5ab940 172 Each of these command-line options
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174 -D NAME[=VALUE]
175 --define=NAME[=VALUE]
176
177 -F NAME[=VALUE]
178 --force-define=NAME[=VALUE]
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179
180 is equivalent to this grammar file declaration
181
de5ab940 182 %define NAME ["VALUE"]
50cca368 183
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184 except that the manner in which Bison processes multiple definitions
185 for the same NAME differs. Most importantly, -F and --force-define
186 quietly override %define, but -D and --define do not. For further
187 details, see the section "Bison Options" in the Bison manual.
50cca368 188
f1b238df 189*** Variables renamed:
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190
191 The following %define variables
192
193 api.push_pull
194 lr.keep_unreachable_states
195
196 have been renamed to
197
198 api.push-pull
199 lr.keep-unreachable-states
200
201 The old names are now deprecated but will be maintained indefinitely
202 for backward compatibility.
203
f1b238df 204*** Values no longer need to be quoted in grammar file:
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205
206 If a %define value is an identifier, it no longer needs to be placed
207 within quotations marks. For example,
208
209 %define api.push-pull "push"
210
211 can be rewritten as
212
213 %define api.push-pull push
214
d397d9f0 215*** Unrecognized variables are now errors not warnings.
cdf3f113 216
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217*** Multiple invocations for any variable is now an error not a warning.
218
219** Unrecognized %code qualifiers are now errors not warnings.
220
221** Character literals not of length one:
222
223 Previously, Bison quietly converted all character literals to length
224 one. For example, without warning, Bison interpreted the operators in
225 the following grammar to be the same token:
226
227 exp: exp '++'
228 | exp '+' exp
229 ;
230
231 Bison now warns when a character literal is not of length one. In
232 some future release, Bison will start reporting an error instead.
233
234** Destructor calls fixed for lookaheads altered in semantic actions:
235
236 Previously for deterministic parsers in C, if a user semantic action
237 altered yychar, the parser in some cases used the old yychar value to
238 determine which destructor to call for the lookahead upon a syntax
239 error or upon parser return. This bug has been fixed.
240
241** C++ parsers use YYRHSLOC:
242
243 Similarly to the C parsers, the C++ parsers now define the YYRHSLOC
244 macro and use it in the default YYLLOC_DEFAULT. You are encouraged
245 to use it. If, for instance, your location structure has "first"
246 and "last" members, instead of
247
248 # define YYLLOC_DEFAULT(Current, Rhs, N) \
249 do \
250 if (N) \
251 { \
252 (Current).first = (Rhs)[1].location.first; \
253 (Current).last = (Rhs)[N].location.last; \
254 } \
255 else \
256 { \
257 (Current).first = (Current).last = (Rhs)[0].location.last; \
258 } \
259 while (false)
260
261 use:
262
263 # define YYLLOC_DEFAULT(Current, Rhs, N) \
264 do \
265 if (N) \
266 { \
267 (Current).first = YYRHSLOC (Rhs, 1).first; \
268 (Current).last = YYRHSLOC (Rhs, N).last; \
269 } \
270 else \
271 { \
272 (Current).first = (Current).last = YYRHSLOC (Rhs, 0).last; \
273 } \
274 while (false)
275
276** YYLLOC_DEFAULT in C++:
277
278 The default implementation of YYLLOC_DEFAULT used to be issued in
279 the header file. It is now output in the implementation file, after
280 the user %code sections so that its #ifndef guard does not try to
281 override the user's YYLLOC_DEFAULT if provided.
cdf3f113 282
f1b238df 283** YYFAIL now produces warnings and Java parsers no longer implement it:
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284
285 YYFAIL has existed for many years as an undocumented feature of
286 deterministic parsers in C generated by Bison. More recently, it was
287 a documented feature of Bison's experimental Java parsers. As
288 promised in Bison 2.4.2's NEWS entry, any appearance of YYFAIL in a
289 semantic action now produces a deprecation warning, and Java parsers
290 no longer implement YYFAIL at all. For further details, including a
291 discussion of how to suppress C preprocessor warnings about YYFAIL
292 being unused, see the Bison 2.4.2 NEWS entry.
293
f1b238df 294** Temporary hack for adding a semicolon to the user action:
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295
296 Previously, Bison appended a semicolon to every user action for
297 reductions when the output language defaulted to C (specifically, when
298 neither %yacc, %language, %skeleton, or equivalent command-line
299 options were specified). This allowed actions such as
300
301 exp: exp "+" exp { $$ = $1 + $3 };
302
303 instead of
304
305 exp: exp "+" exp { $$ = $1 + $3; };
306
307 As a first step in removing this misfeature, Bison now issues a
308 warning when it appends a semicolon. Moreover, in cases where Bison
309 cannot easily determine whether a semicolon is needed (for example, an
310 action ending with a cpp directive or a braced compound initializer),
311 it no longer appends one. Thus, the C compiler might now complain
312 about a missing semicolon where it did not before. Future releases of
313 Bison will cease to append semicolons entirely.
314
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315** Verbose syntax error message fixes:
316
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317 When %error-verbose or the obsolete `#define YYERROR_VERBOSE' is
318 specified, syntax error messages produced by the generated parser
319 include the unexpected token as well as a list of expected tokens.
320 The effect of %nonassoc on these verbose messages has been corrected
321 in two ways, but a more complete fix requires LAC, described above:
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322
323*** When %nonassoc is used, there can exist parser states that accept no
324 tokens, and so the parser does not always require a lookahead token
325 in order to detect a syntax error. Because no unexpected token or
326 expected tokens can then be reported, the verbose syntax error
327 message described above is suppressed, and the parser instead
328 reports the simpler message, "syntax error". Previously, this
329 suppression was sometimes erroneously triggered by %nonassoc when a
330 lookahead was actually required. Now verbose messages are
331 suppressed only when all previous lookaheads have already been
332 shifted or discarded.
333
334*** Previously, the list of expected tokens erroneously included tokens
335 that would actually induce a syntax error because conflicts for them
336 were resolved with %nonassoc in the current parser state. Such
337 tokens are now properly omitted from the list.
338
339*** Expected token lists are still often wrong due to state merging
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340 (from LALR or IELR) and default reductions, which can both add
341 invalid tokens and subtract valid tokens. Canonical LR almost
342 completely fixes this problem by eliminating state merging and
343 default reductions. However, there is one minor problem left even
344 when using canonical LR and even after the fixes above. That is,
345 if the resolution of a conflict with %nonassoc appears in a later
346 parser state than the one at which some syntax error is
347 discovered, the conflicted token is still erroneously included in
348 the expected token list. Bison's new LAC implementation,
349 described above, eliminates this problem and the need for
350 canonical LR. However, LAC is still experimental and is disabled
351 by default.
53f036ce 352
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353** Java skeleton fixes:
354
355*** A location handling bug has been fixed.
356
357*** The top element of each of the value stack and location stack is now
358 cleared when popped so that it can be garbage collected.
6771a463 359
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360*** Parser traces now print the top element of the stack.
361
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362** -W/--warnings fixes:
363
364*** Bison now properly recognizes the "no-" versions of categories:
365
366 For example, given the following command line, Bison now enables all
367 warnings except warnings for incompatibilities with POSIX Yacc:
368
369 bison -Wall,no-yacc gram.y
370
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371*** Bison now treats S/R and R/R conflicts like other warnings:
372
373 Previously, conflict reports were independent of Bison's normal
374 warning system. Now, Bison recognizes the warning categories
375 "conflicts-sr" and "conflicts-rr". This change has important
376 consequences for the -W and --warnings command-line options. For
377 example:
378
379 bison -Wno-conflicts-sr gram.y # S/R conflicts not reported
380 bison -Wno-conflicts-rr gram.y # R/R conflicts not reported
381 bison -Wnone gram.y # no conflicts are reported
382 bison -Werror gram.y # any conflict is an error
383
384 However, as before, if the %expect or %expect-rr directive is
385 specified, an unexpected number of conflicts is an error, and an
386 expected number of conflicts is not reported, so -W and --warning
387 then have no effect on the conflict report.
388
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389*** The "none" category no longer disables a preceding "error":
390
391 For example, for the following command line, Bison now reports
392 errors instead of warnings for incompatibilities with POSIX Yacc:
393
394 bison -Werror,none,yacc gram.y
395
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396*** The "none" category now disables all Bison warnings.
397
398 Previously, the "none" category disabled only Bison warnings for
399 which there existed a specific -W/--warning category. However,
400 given the following command line, Bison is now guaranteed to
401 suppress all warnings:
402
403 bison -Wnone gram.y
404
64877e5e 405* Changes in version 2.4.3 (2010-08-05):
8b9e021f 406
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407** Bison now obeys -Werror and --warnings=error for warnings about
408 grammar rules that are useless in the parser due to conflicts.
409
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410** Problems with spawning M4 on at least FreeBSD 8 and FreeBSD 9 have
411 been fixed.
412
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413** Failures in the test suite for GCC 4.5 have been fixed.
414
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415** Failures in the test suite for some versions of Sun Studio C++ have
416 been fixed.
417
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418** Contrary to Bison 2.4.2's NEWS entry, it has been decided that
419 warnings about undefined %prec identifiers will not be converted to
420 errors in Bison 2.5. They will remain warnings, which should be
421 sufficient for POSIX while avoiding backward compatibility issues.
422
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423** Minor documentation fixes.
424
e19a049c 425* Changes in version 2.4.2 (2010-03-20):
74553c98 426
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427** Some portability problems that resulted in failures and livelocks
428 in the test suite on some versions of at least Solaris, AIX, HP-UX,
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429 RHEL4, and Tru64 have been addressed. As a result, fatal Bison
430 errors should no longer cause M4 to report a broken pipe on the
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431 affected platforms.
432
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433** `%prec IDENTIFIER' requires IDENTIFIER to be defined separately.
434
435 POSIX specifies that an error be reported for any identifier that does
436 not appear on the LHS of a grammar rule and that is not defined by
437 %token, %left, %right, or %nonassoc. Bison 2.3b and later lost this
438 error report for the case when an identifier appears only after a
439 %prec directive. It is now restored. However, for backward
440 compatibility with recent Bison releases, it is only a warning for
441 now. In Bison 2.5 and later, it will return to being an error.
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442 [Between the 2.4.2 and 2.4.3 releases, it was decided that this
443 warning will not be converted to an error in Bison 2.5.]
8bb3a2e7 444
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445** Detection of GNU M4 1.4.6 or newer during configure is improved.
446
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447** Warnings from gcc's -Wundef option about undefined YYENABLE_NLS,
448 YYLTYPE_IS_TRIVIAL, and __STRICT_ANSI__ in C/C++ parsers are now
449 avoided.
c938d650 450
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451** %code is now a permanent feature.
452
453 A traditional Yacc prologue directive is written in the form:
454
455 %{CODE%}
456
457 To provide a more flexible alternative, Bison 2.3b introduced the
458 %code directive with the following forms for C/C++:
459
460 %code {CODE}
461 %code requires {CODE}
462 %code provides {CODE}
463 %code top {CODE}
464
465 These forms are now considered permanent features of Bison. See the
466 %code entries in the section "Bison Declaration Summary" in the Bison
467 manual for a summary of their functionality. See the section
468 "Prologue Alternatives" for a detailed discussion including the
469 advantages of %code over the traditional Yacc prologue directive.
470
471 Bison's Java feature as a whole including its current usage of %code
472 is still considered experimental.
473
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474** YYFAIL is deprecated and will eventually be removed.
475
476 YYFAIL has existed for many years as an undocumented feature of
477 deterministic parsers in C generated by Bison. Previously, it was
478 documented for Bison's experimental Java parsers. YYFAIL is no longer
479 documented for Java parsers and is formally deprecated in both cases.
480 Users are strongly encouraged to migrate to YYERROR, which is
481 specified by POSIX.
482
483 Like YYERROR, you can invoke YYFAIL from a semantic action in order to
484 induce a syntax error. The most obvious difference from YYERROR is
485 that YYFAIL will automatically invoke yyerror to report the syntax
486 error so that you don't have to. However, there are several other
487 subtle differences between YYERROR and YYFAIL, and YYFAIL suffers from
488 inherent flaws when %error-verbose or `#define YYERROR_VERBOSE' is
489 used. For a more detailed discussion, see:
490
491 http://lists.gnu.org/archive/html/bison-patches/2009-12/msg00024.html
492
493 The upcoming Bison 2.5 will remove YYFAIL from Java parsers, but
494 deterministic parsers in C will continue to implement it. However,
495 because YYFAIL is already flawed, it seems futile to try to make new
496 Bison features compatible with it. Thus, during parser generation,
497 Bison 2.5 will produce a warning whenever it discovers YYFAIL in a
498 rule action. In a later release, YYFAIL will be disabled for
499 %error-verbose and `#define YYERROR_VERBOSE'. Eventually, YYFAIL will
500 be removed altogether.
501
502 There exists at least one case where Bison 2.5's YYFAIL warning will
503 be a false positive. Some projects add phony uses of YYFAIL and other
504 Bison-defined macros for the sole purpose of suppressing C
505 preprocessor warnings (from GCC cpp's -Wunused-macros, for example).
506 To avoid Bison's future warning, such YYFAIL uses can be moved to the
507 epilogue (that is, after the second `%%') in the Bison input file. In
508 this release (2.4.2), Bison already generates its own code to suppress
509 C preprocessor warnings for YYFAIL, so projects can remove their own
510 phony uses of YYFAIL if compatibility with Bison releases prior to
511 2.4.2 is not necessary.
512
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513** Internationalization.
514
515 Fix a regression introduced in Bison 2.4: Under some circumstances,
516 message translations were not installed although supported by the
517 host system.
518
74553c98 519* Changes in version 2.4.1 (2008-12-11):
c9ba9e59 520
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521** In the GLR defines file, unexpanded M4 macros in the yylval and yylloc
522 declarations have been fixed.
1979121c 523
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524** Temporary hack for adding a semicolon to the user action.
525
526 Bison used to prepend a trailing semicolon at the end of the user
527 action for reductions. This allowed actions such as
528
529 exp: exp "+" exp { $$ = $1 + $3 };
530
531 instead of
532
533 exp: exp "+" exp { $$ = $1 + $3; };
534
535 Some grammars still depend on this `feature'. Bison 2.4.1 restores
536 the previous behavior in the case of C output (specifically, when
537 neither %language or %skeleton or equivalent command-line options
538 are used) to leave more time for grammars depending on the old
539 behavior to be adjusted. Future releases of Bison will disable this
540 feature.
541
542** A few minor improvements to the Bison manual.
c9ba9e59 543
402b123d 544* Changes in version 2.4 (2008-11-02):
7bd1665a 545
402b123d 546** %language is an experimental feature.
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547
548 We first introduced this feature in test release 2.3b as a cleaner
549 alternative to %skeleton. Since then, we have discussed the possibility of
550 modifying its effect on Bison's output file names. Thus, in this release,
551 we consider %language to be an experimental feature that will likely evolve
552 in future releases.
7bd1665a 553
402b123d 554** Forward compatibility with GNU M4 has been improved.
241fda7a 555
402b123d 556** Several bugs in the C++ skeleton and the experimental Java skeleton have been
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557 fixed.
558
402b123d 559* Changes in version 2.3b (2008-05-27):
35fe0834 560
402b123d 561** The quotes around NAME that used to be required in the following directive
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562 are now deprecated:
563
564 %define NAME "VALUE"
565
402b123d 566** The directive `%pure-parser' is now deprecated in favor of:
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567
568 %define api.pure
569
570 which has the same effect except that Bison is more careful to warn about
571 unreasonable usage in the latter case.
572
402b123d 573** Push Parsing
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574
575 Bison can now generate an LALR(1) parser in C with a push interface. That
ef1b4273 576 is, instead of invoking `yyparse', which pulls tokens from `yylex', you can
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577 push one token at a time to the parser using `yypush_parse', which will
578 return to the caller after processing each token. By default, the push
579 interface is disabled. Either of the following directives will enable it:
580
581 %define api.push_pull "push" // Just push; does not require yylex.
582 %define api.push_pull "both" // Push and pull; requires yylex.
583
584 See the new section `A Push Parser' in the Bison manual for details.
585
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586 The current push parsing interface is experimental and may evolve. More user
587 feedback will help to stabilize it.
588
402b123d 589** The -g and --graph options now output graphs in Graphviz DOT format,
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590 not VCG format. Like --graph, -g now also takes an optional FILE argument
591 and thus cannot be bundled with other short options.
c373bf8b 592
402b123d 593** Java
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594
595 Bison can now generate an LALR(1) parser in Java. The skeleton is
596 `data/lalr1.java'. Consider using the new %language directive instead of
597 %skeleton to select it.
598
599 See the new section `Java Parsers' in the Bison manual for details.
600
601 The current Java interface is experimental and may evolve. More user
602 feedback will help to stabilize it.
603
402b123d 604** %language
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605
606 This new directive specifies the programming language of the generated
d43f77e7
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607 parser, which can be C (the default), C++, or Java. Besides the skeleton
608 that Bison uses, the directive affects the names of the generated files if
609 the grammar file's name ends in ".y".
59da312b 610
402b123d 611** XML Automaton Report
59da312b
JD
612
613 Bison can now generate an XML report of the LALR(1) automaton using the new
614 `--xml' option. The current XML schema is experimental and may evolve. More
615 user feedback will help to stabilize it.
c373bf8b 616
402b123d 617** The grammar file may now specify the name of the parser header file using
c373bf8b
JD
618 %defines. For example:
619
620 %defines "parser.h"
621
402b123d 622** When reporting useless rules, useless nonterminals, and unused terminals,
d80fb37a
JD
623 Bison now employs the terms "useless in grammar" instead of "useless",
624 "useless in parser" instead of "never reduced", and "unused in grammar"
625 instead of "unused".
cff03fb2 626
402b123d 627** Unreachable State Removal
c373bf8b
JD
628
629 Previously, Bison sometimes generated parser tables containing unreachable
31984206
JD
630 states. A state can become unreachable during conflict resolution if Bison
631 disables a shift action leading to it from a predecessor state. Bison now:
75ad86ee
JD
632
633 1. Removes unreachable states.
634
635 2. Does not report any conflicts that appeared in unreachable states.
636 WARNING: As a result, you may need to update %expect and %expect-rr
637 directives in existing grammar files.
638
639 3. For any rule used only in such states, Bison now reports the rule as
cff03fb2 640 "useless in parser due to conflicts".
75ad86ee 641
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642 This feature can be disabled with the following directive:
643
644 %define lr.keep_unreachable_states
645
646 See the %define entry in the `Bison Declaration Summary' in the Bison manual
647 for further discussion.
648
402b123d 649** Lookahead Set Correction in the `.output' Report
b1cc23c4 650
c373bf8b 651 When instructed to generate a `.output' file including lookahead sets
88c78747
JD
652 (using `--report=lookahead', for example), Bison now prints each reduction's
653 lookahead set only next to the associated state's one item that (1) is
654 associated with the same rule as the reduction and (2) has its dot at the end
655 of its RHS. Previously, Bison also erroneously printed the lookahead set
656 next to all of the state's other items associated with the same rule. This
657 bug affected only the `.output' file and not the generated parser source
658 code.
659
402b123d 660** --report-file=FILE is a new option to override the default `.output' file
59da312b 661 name.
1bb2bd75 662
402b123d 663** The `=' that used to be required in the following directives is now
02975b9a
JD
664 deprecated:
665
666 %file-prefix "parser"
667 %name-prefix "c_"
668 %output "parser.c"
669
402b123d 670** An Alternative to `%{...%}' -- `%code QUALIFIER {CODE}'
c373bf8b
JD
671
672 Bison 2.3a provided a new set of directives as a more flexible alternative to
8e0a5e9e
JD
673 the traditional Yacc prologue blocks. Those have now been consolidated into
674 a single %code directive with an optional qualifier field, which identifies
675 the purpose of the code and thus the location(s) where Bison should generate
676 it:
677
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678 1. `%code {CODE}' replaces `%after-header {CODE}'
679 2. `%code requires {CODE}' replaces `%start-header {CODE}'
680 3. `%code provides {CODE}' replaces `%end-header {CODE}'
681 4. `%code top {CODE}' replaces `%before-header {CODE}'
8e0a5e9e 682
61fee93e
JD
683 See the %code entries in section `Bison Declaration Summary' in the Bison
684 manual for a summary of the new functionality. See the new section `Prologue
8e0a5e9e
JD
685 Alternatives' for a detailed discussion including the advantages of %code
686 over the traditional Yacc prologues.
687
688 The prologue alternatives are experimental. More user feedback will help to
689 determine whether they should become permanent features.
690
402b123d 691** Revised warning: unset or unused mid-rule values
17bd8a73
JD
692
693 Since Bison 2.2, Bison has warned about mid-rule values that are set but not
694 used within any of the actions of the parent rule. For example, Bison warns
695 about unused $2 in:
696
697 exp: '1' { $$ = 1; } '+' exp { $$ = $1 + $4; };
698
699 Now, Bison also warns about mid-rule values that are used but not set. For
700 example, Bison warns about unset $$ in the mid-rule action in:
701
702 exp: '1' { $1 = 1; } '+' exp { $$ = $2 + $4; };
703
704 However, Bison now disables both of these warnings by default since they
705 sometimes prove to be false alarms in existing grammars employing the Yacc
706 constructs $0 or $-N (where N is some positive integer).
707
59da312b 708 To enable these warnings, specify the option `--warnings=midrule-values' or
17bd8a73
JD
709 `-W', which is a synonym for `--warnings=all'.
710
402b123d 711** Default %destructor or %printer with `<*>' or `<>'
c373bf8b
JD
712
713 Bison now recognizes two separate kinds of default %destructor's and
12e35840
JD
714 %printer's:
715
716 1. Place `<*>' in a %destructor/%printer symbol list to define a default
717 %destructor/%printer for all grammar symbols for which you have formally
718 declared semantic type tags.
719
3ebecc24 720 2. Place `<>' in a %destructor/%printer symbol list to define a default
12e35840
JD
721 %destructor/%printer for all grammar symbols without declared semantic
722 type tags.
723
724 Bison no longer supports the `%symbol-default' notation from Bison 2.3a.
3ebecc24 725 `<*>' and `<>' combined achieve the same effect with one exception: Bison no
12e35840
JD
726 longer applies any %destructor to a mid-rule value if that mid-rule value is
727 not actually ever referenced using either $$ or $n in a semantic action.
728
85894313
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729 The default %destructor's and %printer's are experimental. More user
730 feedback will help to determine whether they should become permanent
731 features.
732
12e35840
JD
733 See the section `Freeing Discarded Symbols' in the Bison manual for further
734 details.
735
402b123d 736** %left, %right, and %nonassoc can now declare token numbers. This is required
ab7f29f8
JD
737 by POSIX. However, see the end of section `Operator Precedence' in the Bison
738 manual for a caveat concerning the treatment of literal strings.
739
402b123d 740** The nonfunctional --no-parser, -n, and %no-parser options have been
b1cc23c4
JD
741 completely removed from Bison.
742
402b123d 743* Changes in version 2.3a, 2006-09-13:
742e4900 744
402b123d 745** Instead of %union, you can define and use your own union type
ddc8ede1
PE
746 YYSTYPE if your grammar contains at least one <type> tag.
747 Your YYSTYPE need not be a macro; it can be a typedef.
748 This change is for compatibility with other Yacc implementations,
749 and is required by POSIX.
750
402b123d 751** Locations columns and lines start at 1.
cd48d21d
AD
752 In accordance with the GNU Coding Standards and Emacs.
753
402b123d 754** You may now declare per-type and default %destructor's and %printer's:
ec5479ce
JD
755
756 For example:
757
b2a0b7ca
JD
758 %union { char *string; }
759 %token <string> STRING1
760 %token <string> STRING2
761 %type <string> string1
762 %type <string> string2
763 %union { char character; }
764 %token <character> CHR
765 %type <character> chr
766 %destructor { free ($$); } %symbol-default
767 %destructor { free ($$); printf ("%d", @$.first_line); } STRING1 string1
768 %destructor { } <character>
769
770 guarantees that, when the parser discards any user-defined symbol that has a
771 semantic type tag other than `<character>', it passes its semantic value to
772 `free'. However, when the parser discards a `STRING1' or a `string1', it
773 also prints its line number to `stdout'. It performs only the second
774 `%destructor' in this case, so it invokes `free' only once.
ec5479ce 775
85894313
JD
776 [Although we failed to mention this here in the 2.3a release, the default
777 %destructor's and %printer's were experimental, and they were rewritten in
778 future versions.]
779
402b123d 780** Except for LALR(1) parsers in C with POSIX Yacc emulation enabled (with `-y',
b931235e
JD
781 `--yacc', or `%yacc'), Bison no longer generates #define statements for
782 associating token numbers with token names. Removing the #define statements
783 helps to sanitize the global namespace during preprocessing, but POSIX Yacc
784 requires them. Bison still generates an enum for token names in all cases.
785
402b123d 786** Handling of traditional Yacc prologue blocks is now more consistent but
34f98f46 787 potentially incompatible with previous releases of Bison.
9bc0dd67
JD
788
789 As before, you declare prologue blocks in your grammar file with the
790 `%{ ... %}' syntax. To generate the pre-prologue, Bison concatenates all
34f98f46
JD
791 prologue blocks that you've declared before the first %union. To generate
792 the post-prologue, Bison concatenates all prologue blocks that you've
ddc8ede1 793 declared after the first %union.
9bc0dd67 794
34f98f46 795 Previous releases of Bison inserted the pre-prologue into both the header
9bc0dd67
JD
796 file and the code file in all cases except for LALR(1) parsers in C. In the
797 latter case, Bison inserted it only into the code file. For parsers in C++,
798 the point of insertion was before any token definitions (which associate
799 token numbers with names). For parsers in C, the point of insertion was
800 after the token definitions.
801
802 Now, Bison never inserts the pre-prologue into the header file. In the code
803 file, it always inserts it before the token definitions.
804
402b123d 805** Bison now provides a more flexible alternative to the traditional Yacc
34f98f46
JD
806 prologue blocks: %before-header, %start-header, %end-header, and
807 %after-header.
808
809 For example, the following declaration order in the grammar file reflects the
810 order in which Bison will output these code blocks. However, you are free to
811 declare these code blocks in your grammar file in whatever order is most
812 convenient for you:
813
814 %before-header {
815 /* Bison treats this block like a pre-prologue block: it inserts it into
816 * the code file before the contents of the header file. It does *not*
817 * insert it into the header file. This is a good place to put
818 * #include's that you want at the top of your code file. A common
819 * example is `#include "system.h"'. */
820 }
821 %start-header {
822 /* Bison inserts this block into both the header file and the code file.
823 * In both files, the point of insertion is before any Bison-generated
824 * token, semantic type, location type, and class definitions. This is a
825 * good place to define %union dependencies, for example. */
9bc0dd67
JD
826 }
827 %union {
34f98f46
JD
828 /* Unlike the traditional Yacc prologue blocks, the output order for the
829 * new %*-header blocks is not affected by their declaration position
830 * relative to any %union in the grammar file. */
9bc0dd67 831 }
34f98f46
JD
832 %end-header {
833 /* Bison inserts this block into both the header file and the code file.
834 * In both files, the point of insertion is after the Bison-generated
835 * definitions. This is a good place to declare or define public
836 * functions or data structures that depend on the Bison-generated
837 * definitions. */
9bc0dd67 838 }
34f98f46
JD
839 %after-header {
840 /* Bison treats this block like a post-prologue block: it inserts it into
841 * the code file after the contents of the header file. It does *not*
842 * insert it into the header file. This is a good place to declare or
843 * define internal functions or data structures that depend on the
844 * Bison-generated definitions. */
845 }
846
847 If you have multiple occurrences of any one of the above declarations, Bison
848 will concatenate the contents in declaration order.
9bc0dd67 849
85894313
JD
850 [Although we failed to mention this here in the 2.3a release, the prologue
851 alternatives were experimental, and they were rewritten in future versions.]
852
402b123d 853** The option `--report=look-ahead' has been changed to `--report=lookahead'.
9e6e7ed2
PE
854 The old spelling still works, but is not documented and may be removed
855 in a future release.
742e4900 856
402b123d 857* Changes in version 2.3, 2006-06-05:
4ad3ed84 858
402b123d 859** GLR grammars should now use `YYRECOVERING ()' instead of `YYRECOVERING',
4ad3ed84
PE
860 for compatibility with LALR(1) grammars.
861
402b123d 862** It is now documented that any definition of YYSTYPE or YYLTYPE should
4ad3ed84
PE
863 be to a type name that does not contain parentheses or brackets.
864
402b123d 865* Changes in version 2.2, 2006-05-19:
193d7c70 866
402b123d 867** The distribution terms for all Bison-generated parsers now permit
193d7c70
PE
868 using the parsers in nonfree programs. Previously, this permission
869 was granted only for Bison-generated LALR(1) parsers in C.
5f4236a0 870
402b123d 871** %name-prefix changes the namespace name in C++ outputs.
aa08666d 872
402b123d 873** The C++ parsers export their token_type.
5f4236a0 874
402b123d 875** Bison now allows multiple %union declarations, and concatenates
d6ca7905
PE
876 their contents together.
877
402b123d 878** New warning: unused values
4d7bc38c
PE
879 Right-hand side symbols whose values are not used are reported,
880 if the symbols have destructors. For instance:
affac613 881
8f3596a6 882 exp: exp "?" exp ":" exp { $1 ? $1 : $3; }
721be13c
PE
883 | exp "+" exp
884 ;
affac613 885
8f3596a6
AD
886 will trigger a warning about $$ and $5 in the first rule, and $3 in
887 the second ($1 is copied to $$ by the default rule). This example
4e26c69e 888 most likely contains three errors, and could be rewritten as:
affac613 889
4e26c69e
PE
890 exp: exp "?" exp ":" exp
891 { $$ = $1 ? $3 : $5; free ($1 ? $5 : $3); free ($1); }
892 | exp "+" exp
893 { $$ = $1 ? $1 : $3; if ($1) free ($3); }
721be13c 894 ;
affac613 895
4e26c69e
PE
896 However, if the original actions were really intended, memory leaks
897 and all, the warnings can be suppressed by letting Bison believe the
898 values are used, e.g.:
721be13c 899
8f3596a6 900 exp: exp "?" exp ":" exp { $1 ? $1 : $3; (void) ($$, $5); }
721be13c
PE
901 | exp "+" exp { $$ = $1; (void) $3; }
902 ;
903
84866159
AD
904 If there are mid-rule actions, the warning is issued if no action
905 uses it. The following triggers no warning: $1 and $3 are used.
906
907 exp: exp { push ($1); } '+' exp { push ($3); sum (); };
908
721be13c
PE
909 The warning is intended to help catching lost values and memory leaks.
910 If a value is ignored, its associated memory typically is not reclaimed.
affac613 911
402b123d 912** %destructor vs. YYABORT, YYACCEPT, and YYERROR.
9d9b8b70
PE
913 Destructors are now called when user code invokes YYABORT, YYACCEPT,
914 and YYERROR, for all objects on the stack, other than objects
915 corresponding to the right-hand side of the current rule.
a85284cf 916
402b123d 917** %expect, %expect-rr
035aa4a0
PE
918 Incorrect numbers of expected conflicts are now actual errors,
919 instead of warnings.
920
402b123d 921** GLR, YACC parsers.
4e26c69e
PE
922 The %parse-params are available in the destructors (and the
923 experimental printers) as per the documentation.
4b367315 924
402b123d 925** Bison now warns if it finds a stray `$' or `@' in an action.
ad6a9b97 926
402b123d 927** %require "VERSION"
4e26c69e
PE
928 This specifies that the grammar file depends on features implemented
929 in Bison version VERSION or higher.
b50d2359 930
402b123d 931** lalr1.cc: The token and value types are now class members.
e14d0ab6
AD
932 The tokens were defined as free form enums and cpp macros. YYSTYPE
933 was defined as a free form union. They are now class members:
fb9712a9
AD
934 tokens are enumerations of the `yy::parser::token' struct, and the
935 semantic values have the `yy::parser::semantic_type' type.
936
937 If you do not want or can update to this scheme, the directive
938 `%define "global_tokens_and_yystype" "1"' triggers the global
b50d2359
AD
939 definition of tokens and YYSTYPE. This change is suitable both
940 for previous releases of Bison, and this one.
fb9712a9 941
b50d2359 942 If you wish to update, then make sure older version of Bison will
ab8d9dc5 943 fail using `%require "2.2"'.
fb9712a9 944
402b123d 945** DJGPP support added.
193d7c70 946\f
402b123d 947* Changes in version 2.1, 2005-09-16:
1ce59070 948
402b123d 949** The C++ lalr1.cc skeleton supports %lex-param.
e14d0ab6 950
402b123d 951** Bison-generated parsers now support the translation of diagnostics like
baf785db
PE
952 "syntax error" into languages other than English. The default
953 language is still English. For details, please see the new
0410a6e0
PE
954 Internationalization section of the Bison manual. Software
955 distributors should also see the new PACKAGING file. Thanks to
956 Bruno Haible for this new feature.
1ce59070 957
402b123d 958** Wording in the Bison-generated parsers has been changed slightly to
1a059451
PE
959 simplify translation. In particular, the message "memory exhausted"
960 has replaced "parser stack overflow", as the old message was not
961 always accurate for modern Bison-generated parsers.
962
402b123d 963** Destructors are now called when the parser aborts, for all symbols left
258b75ca
PE
964 behind on the stack. Also, the start symbol is now destroyed after a
965 successful parse. In both cases, the behavior was formerly inconsistent.
966
402b123d 967** When generating verbose diagnostics, Bison-generated parsers no longer
72f000b0
PE
968 quote the literal strings associated with tokens. For example, for
969 a syntax error associated with '%token NUM "number"' they might
970 print 'syntax error, unexpected number' instead of 'syntax error,
971 unexpected "number"'.
193d7c70 972\f
402b123d 973* Changes in version 2.0, 2004-12-25:
efeed023 974
402b123d 975** Possibly-incompatible changes
d7e14fc0 976
82de6b0d
PE
977 - Bison-generated parsers no longer default to using the alloca function
978 (when available) to extend the parser stack, due to widespread
979 problems in unchecked stack-overflow detection. You can "#define
980 YYSTACK_USE_ALLOCA 1" to require the use of alloca, but please read
981 the manual to determine safe values for YYMAXDEPTH in that case.
8dd162d3 982
82de6b0d
PE
983 - Error token location.
984 During error recovery, the location of the syntax error is updated
985 to cover the whole sequence covered by the error token: it includes
986 the shifted symbols thrown away during the first part of the error
987 recovery, and the lookahead rejected during the second part.
18d192f0 988
82de6b0d
PE
989 - Semicolon changes:
990 . Stray semicolons are no longer allowed at the start of a grammar.
991 . Semicolons are now required after in-grammar declarations.
e342c3be 992
82de6b0d
PE
993 - Unescaped newlines are no longer allowed in character constants or
994 string literals. They were never portable, and GCC 3.4.0 has
995 dropped support for them. Better diagnostics are now generated if
996 forget a closing quote.
8dd162d3 997
82de6b0d 998 - NUL bytes are no longer allowed in Bison string literals, unfortunately.
f74b6f91 999
402b123d 1000** New features
1452af69 1001
82de6b0d 1002 - GLR grammars now support locations.
4febdd96 1003
82de6b0d
PE
1004 - New directive: %initial-action.
1005 This directive allows the user to run arbitrary code (including
1006 initializing @$) from yyparse before parsing starts.
1452af69 1007
82de6b0d
PE
1008 - A new directive "%expect-rr N" specifies the expected number of
1009 reduce/reduce conflicts in GLR parsers.
1452af69 1010
82de6b0d
PE
1011 - %token numbers can now be hexadecimal integers, e.g., `%token FOO 0x12d'.
1012 This is a GNU extension.
4febdd96 1013
82de6b0d 1014 - The option `--report=lookahead' was changed to `--report=look-ahead'.
9e6e7ed2 1015 [However, this was changed back after 2.3.]
1452af69 1016
82de6b0d 1017 - Experimental %destructor support has been added to lalr1.cc.
1452af69 1018
82de6b0d
PE
1019 - New configure option --disable-yacc, to disable installation of the
1020 yacc command and -ly library introduced in 1.875 for POSIX conformance.
6040d338 1021
402b123d 1022** Bug fixes
d5a3fe37 1023
82de6b0d
PE
1024 - For now, %expect-count violations are now just warnings, not errors.
1025 This is for compatibility with Bison 1.75 and earlier (when there are
1026 reduce/reduce conflicts) and with Bison 1.30 and earlier (when there
1027 are too many or too few shift/reduce conflicts). However, in future
1028 versions of Bison we plan to improve the %expect machinery so that
1029 these violations will become errors again.
3473d0f8 1030
82de6b0d
PE
1031 - Within Bison itself, numbers (e.g., goto numbers) are no longer
1032 arbitrarily limited to 16-bit counts.
d600ee67 1033
82de6b0d 1034 - Semicolons are now allowed before "|" in grammar rules, as POSIX requires.
d600ee67 1035\f
402b123d 1036* Changes in version 1.875, 2003-01-01:
963fcc17 1037
402b123d 1038** The documentation license has been upgraded to version 1.2
dc546b0f 1039 of the GNU Free Documentation License.
75eb3bc4 1040
402b123d 1041** syntax error processing
75eb3bc4 1042
dc546b0f
PE
1043 - In Yacc-style parsers YYLLOC_DEFAULT is now used to compute error
1044 locations too. This fixes bugs in error-location computation.
75eb3bc4 1045
dc546b0f
PE
1046 - %destructor
1047 It is now possible to reclaim the memory associated to symbols
1048 discarded during error recovery. This feature is still experimental.
20daca06 1049
dc546b0f
PE
1050 - %error-verbose
1051 This new directive is preferred over YYERROR_VERBOSE.
74724a70 1052
dc546b0f
PE
1053 - #defining yyerror to steal internal variables is discouraged.
1054 It is not guaranteed to work forever.
d1de5372 1055
402b123d 1056** POSIX conformance
d1de5372 1057
dc546b0f
PE
1058 - Semicolons are once again optional at the end of grammar rules.
1059 This reverts to the behavior of Bison 1.33 and earlier, and improves
1060 compatibility with Yacc.
74724a70 1061
dc546b0f
PE
1062 - `parse error' -> `syntax error'
1063 Bison now uniformly uses the term `syntax error'; formerly, the code
1064 and manual sometimes used the term `parse error' instead. POSIX
1065 requires `syntax error' in diagnostics, and it was thought better to
1066 be consistent.
74724a70 1067
dc546b0f
PE
1068 - The documentation now emphasizes that yylex and yyerror must be
1069 declared before use. C99 requires this.
d1de5372 1070
dc546b0f
PE
1071 - Bison now parses C99 lexical constructs like UCNs and
1072 backslash-newline within C escape sequences, as POSIX 1003.1-2001 requires.
d1de5372 1073
dc546b0f
PE
1074 - File names are properly escaped in C output. E.g., foo\bar.y is
1075 output as "foo\\bar.y".
6780ca7a 1076
dc546b0f
PE
1077 - Yacc command and library now available
1078 The Bison distribution now installs a `yacc' command, as POSIX requires.
1079 Also, Bison now installs a small library liby.a containing
1080 implementations of Yacc-compatible yyerror and main functions.
1081 This library is normally not useful, but POSIX requires it.
6e649e65 1082
dc546b0f 1083 - Type clashes now generate warnings, not errors.
6e649e65 1084
dc546b0f
PE
1085 - If the user does not define YYSTYPE as a macro, Bison now declares it
1086 using typedef instead of defining it as a macro.
1087 For consistency, YYLTYPE is also declared instead of defined.
9501dc6e 1088
402b123d 1089** Other compatibility issues
886a425c 1090
dc546b0f
PE
1091 - %union directives can now have a tag before the `{', e.g., the
1092 directive `%union foo {...}' now generates the C code
1093 `typedef union foo { ... } YYSTYPE;'; this is for Yacc compatibility.
1094 The default union tag is `YYSTYPE', for compatibility with Solaris 9 Yacc.
1095 For consistency, YYLTYPE's struct tag is now `YYLTYPE' not `yyltype'.
1096 This is for compatibility with both Yacc and Bison 1.35.
72f889cc 1097
dc546b0f
PE
1098 - `;' is output before the terminating `}' of an action, for
1099 compatibility with Bison 1.35.
886a425c 1100
dc546b0f
PE
1101 - Bison now uses a Yacc-style format for conflict reports, e.g.,
1102 `conflicts: 2 shift/reduce, 1 reduce/reduce'.
437c2d80 1103
dc546b0f
PE
1104 - `yystype' and `yyltype' are now obsolescent macros instead of being
1105 typedefs or tags; they are no longer documented and are planned to be
1106 withdrawn in a future release.
2a8d363a 1107
402b123d 1108** GLR parser notes
2a8d363a 1109
dc546b0f
PE
1110 - GLR and inline
1111 Users of Bison have to decide how they handle the portability of the
1112 C keyword `inline'.
959e5f51 1113
dc546b0f
PE
1114 - `parsing stack overflow...' -> `parser stack overflow'
1115 GLR parsers now report `parser stack overflow' as per the Bison manual.
900c5db5 1116
402b123d 1117** Bison now warns if it detects conflicting outputs to the same file,
dc546b0f
PE
1118 e.g., it generates a warning for `bison -d -o foo.h foo.y' since
1119 that command outputs both code and header to foo.h.
6e40b4eb 1120
402b123d 1121** #line in output files
dc546b0f 1122 - --no-line works properly.
6e40b4eb 1123
402b123d 1124** Bison can no longer be built by a K&R C compiler; it requires C89 or
6e40b4eb
AD
1125 later to be built. This change originally took place a few versions
1126 ago, but nobody noticed until we recently asked someone to try
1127 building Bison with a K&R C compiler.
d600ee67 1128\f
402b123d 1129* Changes in version 1.75, 2002-10-14:
7933f2b5 1130
402b123d 1131** Bison should now work on 64-bit hosts.
7933f2b5 1132
402b123d 1133** Indonesian translation thanks to Tedi Heriyanto.
7933f2b5 1134
402b123d 1135** GLR parsers
f50adbbd
AD
1136 Fix spurious parse errors.
1137
402b123d 1138** Pure parsers
f50adbbd
AD
1139 Some people redefine yyerror to steal yyparse' private variables.
1140 Reenable this trick until an official feature replaces it.
1141
402b123d 1142** Type Clashes
d90c934c
AD
1143 In agreement with POSIX and with other Yaccs, leaving a default
1144 action is valid when $$ is untyped, and $1 typed:
1145
1146 untyped: ... typed;
1147
1148 but the converse remains an error:
1149
1150 typed: ... untyped;
1151
402b123d 1152** Values of mid-rule actions
d90c934c
AD
1153 The following code:
1154
1155 foo: { ... } { $$ = $1; } ...
1156
1157 was incorrectly rejected: $1 is defined in the second mid-rule
1158 action, and is equal to the $$ of the first mid-rule action.
d600ee67 1159\f
402b123d 1160* Changes in version 1.50, 2002-10-04:
adc8c848 1161
402b123d 1162** GLR parsing
676385e2
PH
1163 The declaration
1164 %glr-parser
1165 causes Bison to produce a Generalized LR (GLR) parser, capable of handling
1166 almost any context-free grammar, ambiguous or not. The new declarations
e8832397 1167 %dprec and %merge on grammar rules allow parse-time resolution of
676385e2
PH
1168 ambiguities. Contributed by Paul Hilfinger.
1169
7933f2b5 1170 Unfortunately Bison 1.50 does not work properly on 64-bit hosts
420f93c8
PE
1171 like the Alpha, so please stick to 32-bit hosts for now.
1172
402b123d 1173** Output Directory
8c165d89 1174 When not in Yacc compatibility mode, when the output file was not
e88dbdbf 1175 specified, running `bison foo/bar.y' created `foo/bar.c'. It
8c165d89
AD
1176 now creates `bar.c'.
1177
402b123d 1178** Undefined token
007a50a4 1179 The undefined token was systematically mapped to 2 which prevented
e88dbdbf 1180 the use of 2 by the user. This is no longer the case.
007a50a4 1181
402b123d 1182** Unknown token numbers
e88dbdbf 1183 If yylex returned an out of range value, yyparse could die. This is
007a50a4
AD
1184 no longer the case.
1185
402b123d 1186** Error token
e88dbdbf 1187 According to POSIX, the error token must be 256.
23c5a174
AD
1188 Bison extends this requirement by making it a preference: *if* the
1189 user specified that one of her tokens is numbered 256, then error
1190 will be mapped onto another number.
1191
402b123d 1192** Verbose error messages
e88dbdbf 1193 They no longer report `..., expecting error or...' for states where
217598da
AD
1194 error recovery is possible.
1195
402b123d 1196** End token
217598da
AD
1197 Defaults to `$end' instead of `$'.
1198
402b123d 1199** Error recovery now conforms to documentation and to POSIX
68cd8af3
PE
1200 When a Bison-generated parser encounters a syntax error, it now pops
1201 the stack until it finds a state that allows shifting the error
1202 token. Formerly, it popped the stack until it found a state that
1203 allowed some non-error action other than a default reduction on the
1204 error token. The new behavior has long been the documented behavior,
1205 and has long been required by POSIX. For more details, please see
337116ba
PE
1206 Paul Eggert, "Reductions during Bison error handling" (2002-05-20)
1207 <http://lists.gnu.org/archive/html/bug-bison/2002-05/msg00038.html>.
68cd8af3 1208
402b123d 1209** Traces
5504898e
AD
1210 Popped tokens and nonterminals are now reported.
1211
402b123d 1212** Larger grammars
a861a339
PE
1213 Larger grammars are now supported (larger token numbers, larger grammar
1214 size (= sum of the LHS and RHS lengths), larger LALR tables).
1215 Formerly, many of these numbers ran afoul of 16-bit limits;
1216 now these limits are 32 bits on most hosts.
355e7c1c 1217
402b123d 1218** Explicit initial rule
643a5994
AD
1219 Bison used to play hacks with the initial rule, which the user does
1220 not write. It is now explicit, and visible in the reports and
1221 graphs as rule 0.
23c5a174 1222
402b123d 1223** Useless rules
643a5994 1224 Before, Bison reported the useless rules, but, although not used,
77714df2 1225 included them in the parsers. They are now actually removed.
23c5a174 1226
402b123d 1227** Useless rules, useless nonterminals
6b98e4b5
AD
1228 They are now reported, as a warning, with their locations.
1229
402b123d 1230** Rules never reduced
e8832397
AD
1231 Rules that can never be reduced because of conflicts are now
1232 reported.
1233
402b123d 1234** Incorrect `Token not used'
11652ab3
AD
1235 On a grammar such as
1236
1237 %token useless useful
1238 %%
1239 exp: '0' %prec useful;
1240
1241 where a token was used to set the precedence of the last rule,
1242 bison reported both `useful' and `useless' as useless tokens.
1243
402b123d 1244** Revert the C++ namespace changes introduced in 1.31
77714df2 1245 as they caused too many portability hassles.
0179dd65 1246
402b123d 1247** Default locations
b2d52318
AD
1248 By an accident of design, the default computation of @$ was
1249 performed after another default computation was performed: @$ = @1.
1250 The latter is now removed: YYLLOC_DEFAULT is fully responsible of
1251 the computation of @$.
adc8c848 1252
402b123d 1253** Token end-of-file
b7c49edf
AD
1254 The token end of file may be specified by the user, in which case,
1255 the user symbol is used in the reports, the graphs, and the verbose
a861a339 1256 error messages instead of `$end', which remains being the default.
b7c49edf 1257 For instance
7bd6c77e 1258 %token MYEOF 0
b7c49edf 1259 or
7bd6c77e 1260 %token MYEOF 0 "end of file"
fdbcd8e2 1261
402b123d 1262** Semantic parser
fdbcd8e2
AD
1263 This old option, which has been broken for ages, is removed.
1264
402b123d 1265** New translations
a861a339 1266 Brazilian Portuguese, thanks to Alexandre Folle de Menezes.
84614e13
AD
1267 Croatian, thanks to Denis Lackovic.
1268
402b123d 1269** Incorrect token definitions
e88dbdbf 1270 When given `%token 'a' "A"', Bison used to output `#define 'a' 65'.
b87f8b21 1271
402b123d 1272** Token definitions as enums
77714df2
AD
1273 Tokens are output both as the traditional #define's, and, provided
1274 the compiler supports ANSI C or is a C++ compiler, as enums.
e88dbdbf 1275 This lets debuggers display names instead of integers.
77714df2 1276
402b123d 1277** Reports
ec3bc396
AD
1278 In addition to --verbose, bison supports --report=THINGS, which
1279 produces additional information:
b408954b
AD
1280 - itemset
1281 complete the core item sets with their closure
9e6e7ed2
PE
1282 - lookahead [changed to `look-ahead' in 1.875e through 2.3, but changed back]
1283 explicitly associate lookahead tokens to items
b408954b
AD
1284 - solved
1285 describe shift/reduce conflicts solving.
1286 Bison used to systematically output this information on top of
1287 the report. Solved conflicts are now attached to their states.
ec3bc396 1288
402b123d 1289** Type clashes
9af3fbce
AD
1290 Previous versions don't complain when there is a type clash on
1291 the default action if the rule has a mid-rule action, such as in:
1292
1293 %type <foo> bar
1294 %%
1295 bar: '0' {} '0';
1296
1297 This is fixed.
a861a339 1298
402b123d 1299** GNU M4 is now required when using Bison.
f987e9d2 1300\f
402b123d 1301* Changes in version 1.35, 2002-03-25:
76551463 1302
402b123d 1303** C Skeleton
76551463
AD
1304 Some projects use Bison's C parser with C++ compilers, and define
1305 YYSTYPE as a class. The recent adjustment of C parsers for data
1306 alignment and 64 bit architectures made this impossible.
1307
1308 Because for the time being no real solution for C++ parser
1309 generation exists, kludges were implemented in the parser to
1310 maintain this use. In the future, when Bison has C++ parsers, this
1311 kludge will be disabled.
1312
1313 This kludge also addresses some C++ problems when the stack was
1314 extended.
76551463 1315\f
402b123d 1316* Changes in version 1.34, 2002-03-12:
76551463 1317
402b123d 1318** File name clashes are detected
76551463
AD
1319 $ bison foo.y -d -o foo.x
1320 fatal error: header and parser would both be named `foo.x'
1321
402b123d 1322** A missing `;' at the end of a rule triggers a warning
76551463
AD
1323 In accordance with POSIX, and in agreement with other
1324 Yacc implementations, Bison will mandate this semicolon in the near
1325 future. This eases the implementation of a Bison parser of Bison
1326 grammars by making this grammar LALR(1) instead of LR(2). To
1327 facilitate the transition, this release introduces a warning.
1328
402b123d 1329** Revert the C++ namespace changes introduced in 1.31, as they caused too
76551463
AD
1330 many portability hassles.
1331
402b123d 1332** DJGPP support added.
76551463 1333
402b123d 1334** Fix test suite portability problems.
76551463 1335\f
402b123d 1336* Changes in version 1.33, 2002-02-07:
76551463 1337
402b123d 1338** Fix C++ issues
76551463
AD
1339 Groff could not be compiled for the definition of size_t was lacking
1340 under some conditions.
1341
402b123d 1342** Catch invalid @n
76551463
AD
1343 As is done with $n.
1344\f
402b123d 1345* Changes in version 1.32, 2002-01-23:
76551463 1346
402b123d 1347** Fix Yacc output file names
76551463 1348
402b123d 1349** Portability fixes
76551463 1350
402b123d 1351** Italian, Dutch translations
76551463 1352\f
402b123d 1353* Changes in version 1.31, 2002-01-14:
52d1aeee 1354
402b123d 1355** Many Bug Fixes
52d1aeee 1356
402b123d 1357** GNU Gettext and %expect
52d1aeee
MA
1358 GNU Gettext asserts 10 s/r conflicts, but there are 7. Now that
1359 Bison dies on incorrect %expectations, we fear there will be
1360 too many bug reports for Gettext, so _for the time being_, %expect
1361 does not trigger an error when the input file is named `plural.y'.
1362
402b123d 1363** Use of alloca in parsers
52d1aeee
MA
1364 If YYSTACK_USE_ALLOCA is defined to 0, then the parsers will use
1365 malloc exclusively. Since 1.29, but was not NEWS'ed.
1366
1367 alloca is used only when compiled with GCC, to avoid portability
1368 problems as on AIX.
1369
402b123d 1370** yyparse now returns 2 if memory is exhausted; formerly it dumped core.
b47dbebe 1371
402b123d 1372** When the generated parser lacks debugging code, YYDEBUG is now 0
52d1aeee
MA
1373 (as POSIX requires) instead of being undefined.
1374
402b123d 1375** User Actions
52d1aeee
MA
1376 Bison has always permitted actions such as { $$ = $1 }: it adds the
1377 ending semicolon. Now if in Yacc compatibility mode, the semicolon
1378 is no longer output: one has to write { $$ = $1; }.
1379
402b123d 1380** Better C++ compliance
52d1aeee 1381 The output parsers try to respect C++ namespaces.
76551463 1382 [This turned out to be a failed experiment, and it was reverted later.]
52d1aeee 1383
402b123d 1384** Reduced Grammars
52d1aeee
MA
1385 Fixed bugs when reporting useless nonterminals.
1386
402b123d 1387** 64 bit hosts
52d1aeee
MA
1388 The parsers work properly on 64 bit hosts.
1389
402b123d 1390** Error messages
52d1aeee
MA
1391 Some calls to strerror resulted in scrambled or missing error messages.
1392
402b123d 1393** %expect
52d1aeee
MA
1394 When the number of shift/reduce conflicts is correct, don't issue
1395 any warning.
1396
402b123d 1397** The verbose report includes the rule line numbers.
52d1aeee 1398
402b123d 1399** Rule line numbers are fixed in traces.
52d1aeee 1400
402b123d 1401** Swedish translation
52d1aeee 1402
402b123d 1403** Parse errors
52d1aeee
MA
1404 Verbose parse error messages from the parsers are better looking.
1405 Before: parse error: unexpected `'/'', expecting `"number"' or `'-'' or `'(''
1406 Now: parse error: unexpected '/', expecting "number" or '-' or '('
1407
402b123d 1408** Fixed parser memory leaks.
52d1aeee
MA
1409 When the generated parser was using malloc to extend its stacks, the
1410 previous allocations were not freed.
1411
402b123d 1412** Fixed verbose output file.
52d1aeee
MA
1413 Some newlines were missing.
1414 Some conflicts in state descriptions were missing.
1415
402b123d 1416** Fixed conflict report.
52d1aeee
MA
1417 Option -v was needed to get the result.
1418
402b123d 1419** %expect
52d1aeee
MA
1420 Was not used.
1421 Mismatches are errors, not warnings.
1422
402b123d 1423** Fixed incorrect processing of some invalid input.
52d1aeee 1424
402b123d 1425** Fixed CPP guards: 9foo.h uses BISON_9FOO_H instead of 9FOO_H.
52d1aeee 1426
402b123d 1427** Fixed some typos in the documentation.
52d1aeee 1428
402b123d 1429** %token MY_EOF 0 is supported.
52d1aeee
MA
1430 Before, MY_EOF was silently renumbered as 257.
1431
402b123d 1432** doc/refcard.tex is updated.
52d1aeee 1433
402b123d 1434** %output, %file-prefix, %name-prefix.
52d1aeee
MA
1435 New.
1436
402b123d 1437** --output
52d1aeee
MA
1438 New, aliasing `--output-file'.
1439\f
402b123d 1440* Changes in version 1.30, 2001-10-26:
342b8b6e 1441
402b123d 1442** `--defines' and `--graph' have now an optional argument which is the
fdac0091 1443 output file name. `-d' and `-g' do not change; they do not take any
342b8b6e
AD
1444 argument.
1445
402b123d 1446** `%source_extension' and `%header_extension' are removed, failed
342b8b6e
AD
1447 experiment.
1448
402b123d 1449** Portability fixes.
f987e9d2 1450\f
402b123d 1451* Changes in version 1.29, 2001-09-07:
342b8b6e 1452
402b123d 1453** The output file does not define const, as this caused problems when used
342b8b6e
AD
1454 with common autoconfiguration schemes. If you still use ancient compilers
1455 that lack const, compile with the equivalent of the C compiler option
1456 `-Dconst='. autoconf's AC_C_CONST macro provides one way to do this.
1457
402b123d 1458** Added `-g' and `--graph'.
f87a2205 1459
402b123d 1460** The Bison manual is now distributed under the terms of the GNU FDL.
f2b5126e 1461
402b123d 1462** The input and the output files has automatically a similar extension.
234a3be3 1463
402b123d 1464** Russian translation added.
f87a2205 1465
402b123d 1466** NLS support updated; should hopefully be less troublesome.
f87a2205 1467
402b123d 1468** Added the old Bison reference card.
c33638bb 1469
402b123d 1470** Added `--locations' and `%locations'.
6deb4447 1471
402b123d 1472** Added `-S' and `--skeleton'.
cd5bd6ac 1473
402b123d 1474** `%raw', `-r', `--raw' is disabled.
62ab6972 1475
402b123d 1476** Special characters are escaped when output. This solves the problems
cd5bd6ac
AD
1477 of the #line lines with path names including backslashes.
1478
402b123d 1479** New directives.
4ecbf796
MA
1480 `%yacc', `%fixed_output_files', `%defines', `%no_parser', `%verbose',
1481 `%debug', `%source_extension' and `%header_extension'.
f987e9d2 1482
402b123d 1483** @$
f987e9d2 1484 Automatic location tracking.
f87a2205 1485\f
402b123d 1486* Changes in version 1.28, 1999-07-06:
d2e00347 1487
402b123d 1488** Should compile better now with K&R compilers.
d2e00347 1489
402b123d 1490** Added NLS.
d2e00347 1491
402b123d 1492** Fixed a problem with escaping the double quote character.
d2e00347 1493
402b123d 1494** There is now a FAQ.
d2e00347 1495\f
402b123d 1496* Changes in version 1.27:
5c31c3c2 1497
402b123d 1498** The make rule which prevented bison.simple from being created on
5c31c3c2
JT
1499 some systems has been fixed.
1500\f
402b123d 1501* Changes in version 1.26:
4be07551 1502
402b123d 1503** Bison now uses automake.
4be07551 1504
402b123d 1505** New mailing lists: <bug-bison@gnu.org> and <help-bison@gnu.org>.
4be07551 1506
402b123d 1507** Token numbers now start at 257 as previously documented, not 258.
4be07551 1508
402b123d 1509** Bison honors the TMPDIR environment variable.
4be07551 1510
402b123d 1511** A couple of buffer overruns have been fixed.
f51dbca1 1512
402b123d 1513** Problems when closing files should now be reported.
f51dbca1 1514
402b123d 1515** Generated parsers should now work even on operating systems which do
f51dbca1 1516 not provide alloca().
4be07551 1517\f
402b123d 1518* Changes in version 1.25, 1995-10-16:
df8878c5 1519
402b123d 1520** Errors in the input grammar are not fatal; Bison keeps reading
df8878c5 1521the grammar file, and reports all the errors found in it.
8c44d3ec 1522
402b123d 1523** Tokens can now be specified as multiple-character strings: for
df8878c5
RS
1524example, you could use "<=" for a token which looks like <=, instead
1525of chosing a name like LESSEQ.
1526
402b123d 1527** The %token_table declaration says to write a table of tokens (names
df8878c5
RS
1528and numbers) into the parser file. The yylex function can use this
1529table to recognize multiple-character string tokens, or for other
1530purposes.
1531
402b123d 1532** The %no_lines declaration says not to generate any #line preprocessor
df8878c5
RS
1533directives in the parser file.
1534
402b123d 1535** The %raw declaration says to use internal Bison token numbers, not
df8878c5
RS
1536Yacc-compatible token numbers, when token names are defined as macros.
1537
402b123d 1538** The --no-parser option produces the parser tables without including
df8878c5
RS
1539the parser engine; a project can now use its own parser engine.
1540The actions go into a separate file called NAME.act, in the form of
1541a switch statement body.
1542\f
402b123d 1543* Changes in version 1.23:
6780ca7a 1544
4d019228
DM
1545The user can define YYPARSE_PARAM as the name of an argument to be
1546passed into yyparse. The argument should have type void *. It should
1547actually point to an object. Grammar actions can access the variable
1548by casting it to the proper pointer type.
6780ca7a 1549
6780ca7a 1550Line numbers in output file corrected.
6780ca7a 1551\f
402b123d 1552* Changes in version 1.22:
6780ca7a
DM
1553
1554--help option added.
6780ca7a 1555\f
402b123d 1556* Changes in version 1.20:
6780ca7a
DM
1557
1558Output file does not redefine const for C++.
9f4503d6
AD
1559
1560Local Variables:
1561mode: outline
1562End:
76551463
AD
1563
1564-----
1565
575619af 1566Copyright (C) 1995-2011 Free Software Foundation, Inc.
76551463 1567
74553c98 1568This file is part of Bison, the GNU Parser Generator.
76551463 1569
f16b0819 1570This program is free software: you can redistribute it and/or modify
76551463 1571it under the terms of the GNU General Public License as published by
f16b0819
PE
1572the Free Software Foundation, either version 3 of the License, or
1573(at your option) any later version.
76551463 1574
f16b0819 1575This program is distributed in the hope that it will be useful,
76551463
AD
1576but WITHOUT ANY WARRANTY; without even the implied warranty of
1577MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
1578GNU General Public License for more details.
1579
1580You should have received a copy of the GNU General Public License
f16b0819 1581along with this program. If not, see <http://www.gnu.org/licenses/>.