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4Changes in version ?.? (????-??-??):
5
6*
7
bfb40910 8Changes in version 2.4 (2008-11-02):
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10* %language is an experimental feature.
11
12 We first introduced this feature in test release 2.3b as a cleaner
13 alternative to %skeleton. Since then, we have discussed the possibility of
14 modifying its effect on Bison's output file names. Thus, in this release,
15 we consider %language to be an experimental feature that will likely evolve
16 in future releases.
7bd1665a 17
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18* Forward compatibility with GNU M4 has been improved.
19
20* Several bugs in the C++ skeleton and the experimental Java skeleton have been
21 fixed.
22
72c5b982 23Changes in version 2.3b (2008-05-27):
35fe0834 24
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25* The quotes around NAME that used to be required in the following directive
26 are now deprecated:
27
28 %define NAME "VALUE"
29
30* The directive `%pure-parser' is now deprecated in favor of:
31
32 %define api.pure
33
34 which has the same effect except that Bison is more careful to warn about
35 unreasonable usage in the latter case.
36
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37* Push Parsing
38
39 Bison can now generate an LALR(1) parser in C with a push interface. That
ef1b4273 40 is, instead of invoking `yyparse', which pulls tokens from `yylex', you can
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41 push one token at a time to the parser using `yypush_parse', which will
42 return to the caller after processing each token. By default, the push
43 interface is disabled. Either of the following directives will enable it:
44
45 %define api.push_pull "push" // Just push; does not require yylex.
46 %define api.push_pull "both" // Push and pull; requires yylex.
47
48 See the new section `A Push Parser' in the Bison manual for details.
49
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50 The current push parsing interface is experimental and may evolve. More user
51 feedback will help to stabilize it.
52
c373bf8b 53* The -g and --graph options now output graphs in Graphviz DOT format,
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54 not VCG format. Like --graph, -g now also takes an optional FILE argument
55 and thus cannot be bundled with other short options.
c373bf8b 56
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57* Java
58
59 Bison can now generate an LALR(1) parser in Java. The skeleton is
60 `data/lalr1.java'. Consider using the new %language directive instead of
61 %skeleton to select it.
62
63 See the new section `Java Parsers' in the Bison manual for details.
64
65 The current Java interface is experimental and may evolve. More user
66 feedback will help to stabilize it.
67
68* %language
69
70 This new directive specifies the programming language of the generated
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71 parser, which can be C (the default), C++, or Java. Besides the skeleton
72 that Bison uses, the directive affects the names of the generated files if
73 the grammar file's name ends in ".y".
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74
75* XML Automaton Report
76
77 Bison can now generate an XML report of the LALR(1) automaton using the new
78 `--xml' option. The current XML schema is experimental and may evolve. More
79 user feedback will help to stabilize it.
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80
81* The grammar file may now specify the name of the parser header file using
82 %defines. For example:
83
84 %defines "parser.h"
85
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86* When reporting useless rules, useless nonterminals, and unused terminals,
87 Bison now employs the terms "useless in grammar" instead of "useless",
88 "useless in parser" instead of "never reduced", and "unused in grammar"
89 instead of "unused".
cff03fb2 90
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91* Unreachable State Removal
92
93 Previously, Bison sometimes generated parser tables containing unreachable
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94 states. A state can become unreachable during conflict resolution if Bison
95 disables a shift action leading to it from a predecessor state. Bison now:
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96
97 1. Removes unreachable states.
98
99 2. Does not report any conflicts that appeared in unreachable states.
100 WARNING: As a result, you may need to update %expect and %expect-rr
101 directives in existing grammar files.
102
103 3. For any rule used only in such states, Bison now reports the rule as
cff03fb2 104 "useless in parser due to conflicts".
75ad86ee 105
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106 This feature can be disabled with the following directive:
107
108 %define lr.keep_unreachable_states
109
110 See the %define entry in the `Bison Declaration Summary' in the Bison manual
111 for further discussion.
112
c373bf8b 113* Lookahead Set Correction in the `.output' Report
b1cc23c4 114
c373bf8b 115 When instructed to generate a `.output' file including lookahead sets
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116 (using `--report=lookahead', for example), Bison now prints each reduction's
117 lookahead set only next to the associated state's one item that (1) is
118 associated with the same rule as the reduction and (2) has its dot at the end
119 of its RHS. Previously, Bison also erroneously printed the lookahead set
120 next to all of the state's other items associated with the same rule. This
121 bug affected only the `.output' file and not the generated parser source
122 code.
123
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124* --report-file=FILE is a new option to override the default `.output' file
125 name.
1bb2bd75 126
16dc6a9e 127* The `=' that used to be required in the following directives is now
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128 deprecated:
129
130 %file-prefix "parser"
131 %name-prefix "c_"
132 %output "parser.c"
133
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134* An Alternative to `%{...%}' -- `%code QUALIFIER {CODE}'
135
136 Bison 2.3a provided a new set of directives as a more flexible alternative to
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137 the traditional Yacc prologue blocks. Those have now been consolidated into
138 a single %code directive with an optional qualifier field, which identifies
139 the purpose of the code and thus the location(s) where Bison should generate
140 it:
141
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142 1. `%code {CODE}' replaces `%after-header {CODE}'
143 2. `%code requires {CODE}' replaces `%start-header {CODE}'
144 3. `%code provides {CODE}' replaces `%end-header {CODE}'
145 4. `%code top {CODE}' replaces `%before-header {CODE}'
8e0a5e9e 146
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147 See the %code entries in section `Bison Declaration Summary' in the Bison
148 manual for a summary of the new functionality. See the new section `Prologue
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149 Alternatives' for a detailed discussion including the advantages of %code
150 over the traditional Yacc prologues.
151
152 The prologue alternatives are experimental. More user feedback will help to
153 determine whether they should become permanent features.
154
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155* Revised warning: unset or unused mid-rule values
156
157 Since Bison 2.2, Bison has warned about mid-rule values that are set but not
158 used within any of the actions of the parent rule. For example, Bison warns
159 about unused $2 in:
160
161 exp: '1' { $$ = 1; } '+' exp { $$ = $1 + $4; };
162
163 Now, Bison also warns about mid-rule values that are used but not set. For
164 example, Bison warns about unset $$ in the mid-rule action in:
165
166 exp: '1' { $1 = 1; } '+' exp { $$ = $2 + $4; };
167
168 However, Bison now disables both of these warnings by default since they
169 sometimes prove to be false alarms in existing grammars employing the Yacc
170 constructs $0 or $-N (where N is some positive integer).
171
59da312b 172 To enable these warnings, specify the option `--warnings=midrule-values' or
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173 `-W', which is a synonym for `--warnings=all'.
174
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175* Default %destructor or %printer with `<*>' or `<>'
176
177 Bison now recognizes two separate kinds of default %destructor's and
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178 %printer's:
179
180 1. Place `<*>' in a %destructor/%printer symbol list to define a default
181 %destructor/%printer for all grammar symbols for which you have formally
182 declared semantic type tags.
183
3ebecc24 184 2. Place `<>' in a %destructor/%printer symbol list to define a default
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185 %destructor/%printer for all grammar symbols without declared semantic
186 type tags.
187
188 Bison no longer supports the `%symbol-default' notation from Bison 2.3a.
3ebecc24 189 `<*>' and `<>' combined achieve the same effect with one exception: Bison no
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190 longer applies any %destructor to a mid-rule value if that mid-rule value is
191 not actually ever referenced using either $$ or $n in a semantic action.
192
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193 The default %destructor's and %printer's are experimental. More user
194 feedback will help to determine whether they should become permanent
195 features.
196
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197 See the section `Freeing Discarded Symbols' in the Bison manual for further
198 details.
199
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200* %left, %right, and %nonassoc can now declare token numbers. This is required
201 by POSIX. However, see the end of section `Operator Precedence' in the Bison
202 manual for a caveat concerning the treatment of literal strings.
203
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204* The nonfunctional --no-parser, -n, and %no-parser options have been
205 completely removed from Bison.
206
21fe08ca 207Changes in version 2.3a, 2006-09-13:
742e4900 208
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209* Instead of %union, you can define and use your own union type
210 YYSTYPE if your grammar contains at least one <type> tag.
211 Your YYSTYPE need not be a macro; it can be a typedef.
212 This change is for compatibility with other Yacc implementations,
213 and is required by POSIX.
214
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215* Locations columns and lines start at 1.
216 In accordance with the GNU Coding Standards and Emacs.
217
b2a0b7ca 218* You may now declare per-type and default %destructor's and %printer's:
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219
220 For example:
221
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222 %union { char *string; }
223 %token <string> STRING1
224 %token <string> STRING2
225 %type <string> string1
226 %type <string> string2
227 %union { char character; }
228 %token <character> CHR
229 %type <character> chr
230 %destructor { free ($$); } %symbol-default
231 %destructor { free ($$); printf ("%d", @$.first_line); } STRING1 string1
232 %destructor { } <character>
233
234 guarantees that, when the parser discards any user-defined symbol that has a
235 semantic type tag other than `<character>', it passes its semantic value to
236 `free'. However, when the parser discards a `STRING1' or a `string1', it
237 also prints its line number to `stdout'. It performs only the second
238 `%destructor' in this case, so it invokes `free' only once.
ec5479ce 239
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240 [Although we failed to mention this here in the 2.3a release, the default
241 %destructor's and %printer's were experimental, and they were rewritten in
242 future versions.]
243
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244* Except for LALR(1) parsers in C with POSIX Yacc emulation enabled (with `-y',
245 `--yacc', or `%yacc'), Bison no longer generates #define statements for
246 associating token numbers with token names. Removing the #define statements
247 helps to sanitize the global namespace during preprocessing, but POSIX Yacc
248 requires them. Bison still generates an enum for token names in all cases.
249
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250* Handling of traditional Yacc prologue blocks is now more consistent but
251 potentially incompatible with previous releases of Bison.
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252
253 As before, you declare prologue blocks in your grammar file with the
254 `%{ ... %}' syntax. To generate the pre-prologue, Bison concatenates all
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255 prologue blocks that you've declared before the first %union. To generate
256 the post-prologue, Bison concatenates all prologue blocks that you've
ddc8ede1 257 declared after the first %union.
9bc0dd67 258
34f98f46 259 Previous releases of Bison inserted the pre-prologue into both the header
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260 file and the code file in all cases except for LALR(1) parsers in C. In the
261 latter case, Bison inserted it only into the code file. For parsers in C++,
262 the point of insertion was before any token definitions (which associate
263 token numbers with names). For parsers in C, the point of insertion was
264 after the token definitions.
265
266 Now, Bison never inserts the pre-prologue into the header file. In the code
267 file, it always inserts it before the token definitions.
268
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269* Bison now provides a more flexible alternative to the traditional Yacc
270 prologue blocks: %before-header, %start-header, %end-header, and
271 %after-header.
272
273 For example, the following declaration order in the grammar file reflects the
274 order in which Bison will output these code blocks. However, you are free to
275 declare these code blocks in your grammar file in whatever order is most
276 convenient for you:
277
278 %before-header {
279 /* Bison treats this block like a pre-prologue block: it inserts it into
280 * the code file before the contents of the header file. It does *not*
281 * insert it into the header file. This is a good place to put
282 * #include's that you want at the top of your code file. A common
283 * example is `#include "system.h"'. */
284 }
285 %start-header {
286 /* Bison inserts this block into both the header file and the code file.
287 * In both files, the point of insertion is before any Bison-generated
288 * token, semantic type, location type, and class definitions. This is a
289 * good place to define %union dependencies, for example. */
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290 }
291 %union {
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292 /* Unlike the traditional Yacc prologue blocks, the output order for the
293 * new %*-header blocks is not affected by their declaration position
294 * relative to any %union in the grammar file. */
9bc0dd67 295 }
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296 %end-header {
297 /* Bison inserts this block into both the header file and the code file.
298 * In both files, the point of insertion is after the Bison-generated
299 * definitions. This is a good place to declare or define public
300 * functions or data structures that depend on the Bison-generated
301 * definitions. */
9bc0dd67 302 }
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303 %after-header {
304 /* Bison treats this block like a post-prologue block: it inserts it into
305 * the code file after the contents of the header file. It does *not*
306 * insert it into the header file. This is a good place to declare or
307 * define internal functions or data structures that depend on the
308 * Bison-generated definitions. */
309 }
310
311 If you have multiple occurrences of any one of the above declarations, Bison
312 will concatenate the contents in declaration order.
9bc0dd67 313
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314 [Although we failed to mention this here in the 2.3a release, the prologue
315 alternatives were experimental, and they were rewritten in future versions.]
316
742e4900 317* The option `--report=look-ahead' has been changed to `--report=lookahead'.
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318 The old spelling still works, but is not documented and may be removed
319 in a future release.
742e4900 320
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321Changes in version 2.3, 2006-06-05:
322
323* GLR grammars should now use `YYRECOVERING ()' instead of `YYRECOVERING',
324 for compatibility with LALR(1) grammars.
325
326* It is now documented that any definition of YYSTYPE or YYLTYPE should
327 be to a type name that does not contain parentheses or brackets.
328
ab8d9dc5 329Changes in version 2.2, 2006-05-19:
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330
331* The distribution terms for all Bison-generated parsers now permit
332 using the parsers in nonfree programs. Previously, this permission
333 was granted only for Bison-generated LALR(1) parsers in C.
5f4236a0 334
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335* %name-prefix changes the namespace name in C++ outputs.
336
337* The C++ parsers export their token_type.
5f4236a0 338
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339* Bison now allows multiple %union declarations, and concatenates
340 their contents together.
341
affac613 342* New warning: unused values
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343 Right-hand side symbols whose values are not used are reported,
344 if the symbols have destructors. For instance:
affac613 345
8f3596a6 346 exp: exp "?" exp ":" exp { $1 ? $1 : $3; }
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347 | exp "+" exp
348 ;
affac613 349
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350 will trigger a warning about $$ and $5 in the first rule, and $3 in
351 the second ($1 is copied to $$ by the default rule). This example
4e26c69e 352 most likely contains three errors, and could be rewritten as:
affac613 353
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354 exp: exp "?" exp ":" exp
355 { $$ = $1 ? $3 : $5; free ($1 ? $5 : $3); free ($1); }
356 | exp "+" exp
357 { $$ = $1 ? $1 : $3; if ($1) free ($3); }
721be13c 358 ;
affac613 359
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360 However, if the original actions were really intended, memory leaks
361 and all, the warnings can be suppressed by letting Bison believe the
362 values are used, e.g.:
721be13c 363
8f3596a6 364 exp: exp "?" exp ":" exp { $1 ? $1 : $3; (void) ($$, $5); }
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365 | exp "+" exp { $$ = $1; (void) $3; }
366 ;
367
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368 If there are mid-rule actions, the warning is issued if no action
369 uses it. The following triggers no warning: $1 and $3 are used.
370
371 exp: exp { push ($1); } '+' exp { push ($3); sum (); };
372
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373 The warning is intended to help catching lost values and memory leaks.
374 If a value is ignored, its associated memory typically is not reclaimed.
affac613 375
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376* %destructor vs. YYABORT, YYACCEPT, and YYERROR.
377 Destructors are now called when user code invokes YYABORT, YYACCEPT,
378 and YYERROR, for all objects on the stack, other than objects
379 corresponding to the right-hand side of the current rule.
a85284cf 380
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381* %expect, %expect-rr
382 Incorrect numbers of expected conflicts are now actual errors,
383 instead of warnings.
384
4b367315 385* GLR, YACC parsers.
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386 The %parse-params are available in the destructors (and the
387 experimental printers) as per the documentation.
4b367315 388
302c0aee 389* Bison now warns if it finds a stray `$' or `@' in an action.
ad6a9b97 390
b50d2359 391* %require "VERSION"
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392 This specifies that the grammar file depends on features implemented
393 in Bison version VERSION or higher.
b50d2359 394
fb9712a9 395* lalr1.cc: The token and value types are now class members.
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396 The tokens were defined as free form enums and cpp macros. YYSTYPE
397 was defined as a free form union. They are now class members:
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398 tokens are enumerations of the `yy::parser::token' struct, and the
399 semantic values have the `yy::parser::semantic_type' type.
400
401 If you do not want or can update to this scheme, the directive
402 `%define "global_tokens_and_yystype" "1"' triggers the global
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403 definition of tokens and YYSTYPE. This change is suitable both
404 for previous releases of Bison, and this one.
fb9712a9 405
b50d2359 406 If you wish to update, then make sure older version of Bison will
ab8d9dc5 407 fail using `%require "2.2"'.
fb9712a9 408
302c0aee 409* DJGPP support added.
193d7c70 410\f
1bd0deda 411Changes in version 2.1, 2005-09-16:
1ce59070 412
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413* The C++ lalr1.cc skeleton supports %lex-param.
414
a7db4add 415* Bison-generated parsers now support the translation of diagnostics like
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416 "syntax error" into languages other than English. The default
417 language is still English. For details, please see the new
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418 Internationalization section of the Bison manual. Software
419 distributors should also see the new PACKAGING file. Thanks to
420 Bruno Haible for this new feature.
1ce59070 421
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422* Wording in the Bison-generated parsers has been changed slightly to
423 simplify translation. In particular, the message "memory exhausted"
424 has replaced "parser stack overflow", as the old message was not
425 always accurate for modern Bison-generated parsers.
426
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427* Destructors are now called when the parser aborts, for all symbols left
428 behind on the stack. Also, the start symbol is now destroyed after a
429 successful parse. In both cases, the behavior was formerly inconsistent.
430
a7db4add 431* When generating verbose diagnostics, Bison-generated parsers no longer
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432 quote the literal strings associated with tokens. For example, for
433 a syntax error associated with '%token NUM "number"' they might
434 print 'syntax error, unexpected number' instead of 'syntax error,
435 unexpected "number"'.
193d7c70 436\f
82de6b0d 437Changes in version 2.0, 2004-12-25:
efeed023 438
82de6b0d 439* Possibly-incompatible changes
d7e14fc0 440
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441 - Bison-generated parsers no longer default to using the alloca function
442 (when available) to extend the parser stack, due to widespread
443 problems in unchecked stack-overflow detection. You can "#define
444 YYSTACK_USE_ALLOCA 1" to require the use of alloca, but please read
445 the manual to determine safe values for YYMAXDEPTH in that case.
8dd162d3 446
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447 - Error token location.
448 During error recovery, the location of the syntax error is updated
449 to cover the whole sequence covered by the error token: it includes
450 the shifted symbols thrown away during the first part of the error
451 recovery, and the lookahead rejected during the second part.
18d192f0 452
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453 - Semicolon changes:
454 . Stray semicolons are no longer allowed at the start of a grammar.
455 . Semicolons are now required after in-grammar declarations.
e342c3be 456
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457 - Unescaped newlines are no longer allowed in character constants or
458 string literals. They were never portable, and GCC 3.4.0 has
459 dropped support for them. Better diagnostics are now generated if
460 forget a closing quote.
8dd162d3 461
82de6b0d 462 - NUL bytes are no longer allowed in Bison string literals, unfortunately.
f74b6f91 463
82de6b0d 464* New features
1452af69 465
82de6b0d 466 - GLR grammars now support locations.
4febdd96 467
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468 - New directive: %initial-action.
469 This directive allows the user to run arbitrary code (including
470 initializing @$) from yyparse before parsing starts.
1452af69 471
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472 - A new directive "%expect-rr N" specifies the expected number of
473 reduce/reduce conflicts in GLR parsers.
1452af69 474
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475 - %token numbers can now be hexadecimal integers, e.g., `%token FOO 0x12d'.
476 This is a GNU extension.
4febdd96 477
82de6b0d 478 - The option `--report=lookahead' was changed to `--report=look-ahead'.
9e6e7ed2 479 [However, this was changed back after 2.3.]
1452af69 480
82de6b0d 481 - Experimental %destructor support has been added to lalr1.cc.
1452af69 482
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483 - New configure option --disable-yacc, to disable installation of the
484 yacc command and -ly library introduced in 1.875 for POSIX conformance.
6040d338 485
82de6b0d 486* Bug fixes
d5a3fe37 487
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488 - For now, %expect-count violations are now just warnings, not errors.
489 This is for compatibility with Bison 1.75 and earlier (when there are
490 reduce/reduce conflicts) and with Bison 1.30 and earlier (when there
491 are too many or too few shift/reduce conflicts). However, in future
492 versions of Bison we plan to improve the %expect machinery so that
493 these violations will become errors again.
3473d0f8 494
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495 - Within Bison itself, numbers (e.g., goto numbers) are no longer
496 arbitrarily limited to 16-bit counts.
d600ee67 497
82de6b0d 498 - Semicolons are now allowed before "|" in grammar rules, as POSIX requires.
d600ee67 499\f
dc546b0f 500Changes in version 1.875, 2003-01-01:
963fcc17 501
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502* The documentation license has been upgraded to version 1.2
503 of the GNU Free Documentation License.
75eb3bc4 504
dc546b0f 505* syntax error processing
75eb3bc4 506
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507 - In Yacc-style parsers YYLLOC_DEFAULT is now used to compute error
508 locations too. This fixes bugs in error-location computation.
75eb3bc4 509
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510 - %destructor
511 It is now possible to reclaim the memory associated to symbols
512 discarded during error recovery. This feature is still experimental.
20daca06 513
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514 - %error-verbose
515 This new directive is preferred over YYERROR_VERBOSE.
74724a70 516
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517 - #defining yyerror to steal internal variables is discouraged.
518 It is not guaranteed to work forever.
d1de5372 519
dc546b0f 520* POSIX conformance
d1de5372 521
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522 - Semicolons are once again optional at the end of grammar rules.
523 This reverts to the behavior of Bison 1.33 and earlier, and improves
524 compatibility with Yacc.
74724a70 525
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526 - `parse error' -> `syntax error'
527 Bison now uniformly uses the term `syntax error'; formerly, the code
528 and manual sometimes used the term `parse error' instead. POSIX
529 requires `syntax error' in diagnostics, and it was thought better to
530 be consistent.
74724a70 531
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532 - The documentation now emphasizes that yylex and yyerror must be
533 declared before use. C99 requires this.
d1de5372 534
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535 - Bison now parses C99 lexical constructs like UCNs and
536 backslash-newline within C escape sequences, as POSIX 1003.1-2001 requires.
d1de5372 537
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538 - File names are properly escaped in C output. E.g., foo\bar.y is
539 output as "foo\\bar.y".
6780ca7a 540
dc546b0f
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541 - Yacc command and library now available
542 The Bison distribution now installs a `yacc' command, as POSIX requires.
543 Also, Bison now installs a small library liby.a containing
544 implementations of Yacc-compatible yyerror and main functions.
545 This library is normally not useful, but POSIX requires it.
6e649e65 546
dc546b0f 547 - Type clashes now generate warnings, not errors.
6e649e65 548
dc546b0f
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549 - If the user does not define YYSTYPE as a macro, Bison now declares it
550 using typedef instead of defining it as a macro.
551 For consistency, YYLTYPE is also declared instead of defined.
9501dc6e 552
dc546b0f 553* Other compatibility issues
886a425c 554
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555 - %union directives can now have a tag before the `{', e.g., the
556 directive `%union foo {...}' now generates the C code
557 `typedef union foo { ... } YYSTYPE;'; this is for Yacc compatibility.
558 The default union tag is `YYSTYPE', for compatibility with Solaris 9 Yacc.
559 For consistency, YYLTYPE's struct tag is now `YYLTYPE' not `yyltype'.
560 This is for compatibility with both Yacc and Bison 1.35.
72f889cc 561
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562 - `;' is output before the terminating `}' of an action, for
563 compatibility with Bison 1.35.
886a425c 564
dc546b0f
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565 - Bison now uses a Yacc-style format for conflict reports, e.g.,
566 `conflicts: 2 shift/reduce, 1 reduce/reduce'.
437c2d80 567
dc546b0f
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568 - `yystype' and `yyltype' are now obsolescent macros instead of being
569 typedefs or tags; they are no longer documented and are planned to be
570 withdrawn in a future release.
2a8d363a 571
dc546b0f 572* GLR parser notes
2a8d363a 573
dc546b0f
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574 - GLR and inline
575 Users of Bison have to decide how they handle the portability of the
576 C keyword `inline'.
959e5f51 577
dc546b0f
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578 - `parsing stack overflow...' -> `parser stack overflow'
579 GLR parsers now report `parser stack overflow' as per the Bison manual.
900c5db5 580
dc546b0f
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581* Bison now warns if it detects conflicting outputs to the same file,
582 e.g., it generates a warning for `bison -d -o foo.h foo.y' since
583 that command outputs both code and header to foo.h.
6e40b4eb 584
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585* #line in output files
586 - --no-line works properly.
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587
588* Bison can no longer be built by a K&R C compiler; it requires C89 or
589 later to be built. This change originally took place a few versions
590 ago, but nobody noticed until we recently asked someone to try
591 building Bison with a K&R C compiler.
d600ee67 592\f
5c16c6b1 593Changes in version 1.75, 2002-10-14:
7933f2b5
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594
595* Bison should now work on 64-bit hosts.
596
b7195100 597* Indonesian translation thanks to Tedi Heriyanto.
7933f2b5 598
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599* GLR parsers
600 Fix spurious parse errors.
601
602* Pure parsers
603 Some people redefine yyerror to steal yyparse' private variables.
604 Reenable this trick until an official feature replaces it.
605
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606* Type Clashes
607 In agreement with POSIX and with other Yaccs, leaving a default
608 action is valid when $$ is untyped, and $1 typed:
609
610 untyped: ... typed;
611
612 but the converse remains an error:
613
614 typed: ... untyped;
615
616* Values of mid-rule actions
617 The following code:
618
619 foo: { ... } { $$ = $1; } ...
620
621 was incorrectly rejected: $1 is defined in the second mid-rule
622 action, and is equal to the $$ of the first mid-rule action.
d600ee67 623\f
420f93c8 624Changes in version 1.50, 2002-10-04:
adc8c848 625
676385e2
PH
626* GLR parsing
627 The declaration
628 %glr-parser
629 causes Bison to produce a Generalized LR (GLR) parser, capable of handling
630 almost any context-free grammar, ambiguous or not. The new declarations
e8832397 631 %dprec and %merge on grammar rules allow parse-time resolution of
676385e2
PH
632 ambiguities. Contributed by Paul Hilfinger.
633
7933f2b5 634 Unfortunately Bison 1.50 does not work properly on 64-bit hosts
420f93c8
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635 like the Alpha, so please stick to 32-bit hosts for now.
636
8c165d89
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637* Output Directory
638 When not in Yacc compatibility mode, when the output file was not
e88dbdbf 639 specified, running `bison foo/bar.y' created `foo/bar.c'. It
8c165d89
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640 now creates `bar.c'.
641
007a50a4
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642* Undefined token
643 The undefined token was systematically mapped to 2 which prevented
e88dbdbf 644 the use of 2 by the user. This is no longer the case.
007a50a4 645
77714df2 646* Unknown token numbers
e88dbdbf 647 If yylex returned an out of range value, yyparse could die. This is
007a50a4
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648 no longer the case.
649
23c5a174 650* Error token
e88dbdbf 651 According to POSIX, the error token must be 256.
23c5a174
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652 Bison extends this requirement by making it a preference: *if* the
653 user specified that one of her tokens is numbered 256, then error
654 will be mapped onto another number.
655
217598da 656* Verbose error messages
e88dbdbf 657 They no longer report `..., expecting error or...' for states where
217598da
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658 error recovery is possible.
659
660* End token
661 Defaults to `$end' instead of `$'.
662
68cd8af3
PE
663* Error recovery now conforms to documentation and to POSIX
664 When a Bison-generated parser encounters a syntax error, it now pops
665 the stack until it finds a state that allows shifting the error
666 token. Formerly, it popped the stack until it found a state that
667 allowed some non-error action other than a default reduction on the
668 error token. The new behavior has long been the documented behavior,
669 and has long been required by POSIX. For more details, please see
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670 Paul Eggert, "Reductions during Bison error handling" (2002-05-20)
671 <http://lists.gnu.org/archive/html/bug-bison/2002-05/msg00038.html>.
68cd8af3 672
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673* Traces
674 Popped tokens and nonterminals are now reported.
675
a861a339
PE
676* Larger grammars
677 Larger grammars are now supported (larger token numbers, larger grammar
678 size (= sum of the LHS and RHS lengths), larger LALR tables).
679 Formerly, many of these numbers ran afoul of 16-bit limits;
680 now these limits are 32 bits on most hosts.
355e7c1c 681
77714df2 682* Explicit initial rule
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683 Bison used to play hacks with the initial rule, which the user does
684 not write. It is now explicit, and visible in the reports and
685 graphs as rule 0.
23c5a174 686
77714df2 687* Useless rules
643a5994 688 Before, Bison reported the useless rules, but, although not used,
77714df2 689 included them in the parsers. They are now actually removed.
23c5a174 690
6b98e4b5
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691* Useless rules, useless nonterminals
692 They are now reported, as a warning, with their locations.
693
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694* Rules never reduced
695 Rules that can never be reduced because of conflicts are now
696 reported.
697
77714df2 698* Incorrect `Token not used'
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699 On a grammar such as
700
701 %token useless useful
702 %%
703 exp: '0' %prec useful;
704
705 where a token was used to set the precedence of the last rule,
706 bison reported both `useful' and `useless' as useless tokens.
707
77714df2
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708* Revert the C++ namespace changes introduced in 1.31
709 as they caused too many portability hassles.
0179dd65 710
b2d52318
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711* Default locations
712 By an accident of design, the default computation of @$ was
713 performed after another default computation was performed: @$ = @1.
714 The latter is now removed: YYLLOC_DEFAULT is fully responsible of
715 the computation of @$.
adc8c848 716
b7c49edf
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717* Token end-of-file
718 The token end of file may be specified by the user, in which case,
719 the user symbol is used in the reports, the graphs, and the verbose
a861a339 720 error messages instead of `$end', which remains being the default.
b7c49edf 721 For instance
7bd6c77e 722 %token MYEOF 0
b7c49edf 723 or
7bd6c77e 724 %token MYEOF 0 "end of file"
fdbcd8e2
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725
726* Semantic parser
727 This old option, which has been broken for ages, is removed.
728
a861a339
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729* New translations
730 Brazilian Portuguese, thanks to Alexandre Folle de Menezes.
84614e13
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731 Croatian, thanks to Denis Lackovic.
732
77714df2 733* Incorrect token definitions
e88dbdbf 734 When given `%token 'a' "A"', Bison used to output `#define 'a' 65'.
b87f8b21 735
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736* Token definitions as enums
737 Tokens are output both as the traditional #define's, and, provided
738 the compiler supports ANSI C or is a C++ compiler, as enums.
e88dbdbf 739 This lets debuggers display names instead of integers.
77714df2 740
ec3bc396
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741* Reports
742 In addition to --verbose, bison supports --report=THINGS, which
743 produces additional information:
b408954b
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744 - itemset
745 complete the core item sets with their closure
9e6e7ed2
PE
746 - lookahead [changed to `look-ahead' in 1.875e through 2.3, but changed back]
747 explicitly associate lookahead tokens to items
b408954b
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748 - solved
749 describe shift/reduce conflicts solving.
750 Bison used to systematically output this information on top of
751 the report. Solved conflicts are now attached to their states.
ec3bc396 752
9af3fbce
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753* Type clashes
754 Previous versions don't complain when there is a type clash on
755 the default action if the rule has a mid-rule action, such as in:
756
757 %type <foo> bar
758 %%
759 bar: '0' {} '0';
760
761 This is fixed.
a861a339
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762
763* GNU M4 is now required when using Bison.
f987e9d2 764\f
76551463
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765Changes in version 1.35, 2002-03-25:
766
767* C Skeleton
768 Some projects use Bison's C parser with C++ compilers, and define
769 YYSTYPE as a class. The recent adjustment of C parsers for data
770 alignment and 64 bit architectures made this impossible.
771
772 Because for the time being no real solution for C++ parser
773 generation exists, kludges were implemented in the parser to
774 maintain this use. In the future, when Bison has C++ parsers, this
775 kludge will be disabled.
776
777 This kludge also addresses some C++ problems when the stack was
778 extended.
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779\f
780Changes in version 1.34, 2002-03-12:
781
782* File name clashes are detected
783 $ bison foo.y -d -o foo.x
784 fatal error: header and parser would both be named `foo.x'
785
786* A missing `;' at the end of a rule triggers a warning
787 In accordance with POSIX, and in agreement with other
788 Yacc implementations, Bison will mandate this semicolon in the near
789 future. This eases the implementation of a Bison parser of Bison
790 grammars by making this grammar LALR(1) instead of LR(2). To
791 facilitate the transition, this release introduces a warning.
792
793* Revert the C++ namespace changes introduced in 1.31, as they caused too
794 many portability hassles.
795
796* DJGPP support added.
797
798* Fix test suite portability problems.
799\f
800Changes in version 1.33, 2002-02-07:
801
802* Fix C++ issues
803 Groff could not be compiled for the definition of size_t was lacking
804 under some conditions.
805
806* Catch invalid @n
807 As is done with $n.
808\f
809Changes in version 1.32, 2002-01-23:
810
811* Fix Yacc output file names
812
813* Portability fixes
814
815* Italian, Dutch translations
816\f
52d1aeee
MA
817Changes in version 1.31, 2002-01-14:
818
819* Many Bug Fixes
820
821* GNU Gettext and %expect
822 GNU Gettext asserts 10 s/r conflicts, but there are 7. Now that
823 Bison dies on incorrect %expectations, we fear there will be
824 too many bug reports for Gettext, so _for the time being_, %expect
825 does not trigger an error when the input file is named `plural.y'.
826
827* Use of alloca in parsers
828 If YYSTACK_USE_ALLOCA is defined to 0, then the parsers will use
829 malloc exclusively. Since 1.29, but was not NEWS'ed.
830
831 alloca is used only when compiled with GCC, to avoid portability
832 problems as on AIX.
833
b47dbebe
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834* yyparse now returns 2 if memory is exhausted; formerly it dumped core.
835
52d1aeee
MA
836* When the generated parser lacks debugging code, YYDEBUG is now 0
837 (as POSIX requires) instead of being undefined.
838
839* User Actions
840 Bison has always permitted actions such as { $$ = $1 }: it adds the
841 ending semicolon. Now if in Yacc compatibility mode, the semicolon
842 is no longer output: one has to write { $$ = $1; }.
843
844* Better C++ compliance
845 The output parsers try to respect C++ namespaces.
76551463 846 [This turned out to be a failed experiment, and it was reverted later.]
52d1aeee
MA
847
848* Reduced Grammars
849 Fixed bugs when reporting useless nonterminals.
850
851* 64 bit hosts
852 The parsers work properly on 64 bit hosts.
853
854* Error messages
855 Some calls to strerror resulted in scrambled or missing error messages.
856
857* %expect
858 When the number of shift/reduce conflicts is correct, don't issue
859 any warning.
860
861* The verbose report includes the rule line numbers.
862
863* Rule line numbers are fixed in traces.
864
865* Swedish translation
866
867* Parse errors
868 Verbose parse error messages from the parsers are better looking.
869 Before: parse error: unexpected `'/'', expecting `"number"' or `'-'' or `'(''
870 Now: parse error: unexpected '/', expecting "number" or '-' or '('
871
872* Fixed parser memory leaks.
873 When the generated parser was using malloc to extend its stacks, the
874 previous allocations were not freed.
875
876* Fixed verbose output file.
877 Some newlines were missing.
878 Some conflicts in state descriptions were missing.
879
880* Fixed conflict report.
881 Option -v was needed to get the result.
882
883* %expect
884 Was not used.
885 Mismatches are errors, not warnings.
886
887* Fixed incorrect processing of some invalid input.
888
889* Fixed CPP guards: 9foo.h uses BISON_9FOO_H instead of 9FOO_H.
890
891* Fixed some typos in the documentation.
892
893* %token MY_EOF 0 is supported.
894 Before, MY_EOF was silently renumbered as 257.
895
896* doc/refcard.tex is updated.
897
898* %output, %file-prefix, %name-prefix.
899 New.
900
901* --output
902 New, aliasing `--output-file'.
903\f
76551463 904Changes in version 1.30, 2001-10-26:
342b8b6e 905
fdac0091
PE
906* `--defines' and `--graph' have now an optional argument which is the
907 output file name. `-d' and `-g' do not change; they do not take any
342b8b6e
AD
908 argument.
909
910* `%source_extension' and `%header_extension' are removed, failed
911 experiment.
912
f987e9d2
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913* Portability fixes.
914\f
9f4503d6 915Changes in version 1.29, 2001-09-07:
342b8b6e
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916
917* The output file does not define const, as this caused problems when used
918 with common autoconfiguration schemes. If you still use ancient compilers
919 that lack const, compile with the equivalent of the C compiler option
920 `-Dconst='. autoconf's AC_C_CONST macro provides one way to do this.
921
922* Added `-g' and `--graph'.
f87a2205 923
f2b5126e
PB
924* The Bison manual is now distributed under the terms of the GNU FDL.
925
f1c63ced 926* The input and the output files has automatically a similar extension.
234a3be3 927
f87a2205
JT
928* Russian translation added.
929
930* NLS support updated; should hopefully be less troublesome.
931
932* Added the old Bison reference card.
c33638bb
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933
934* Added `--locations' and `%locations'.
6deb4447 935
cd5bd6ac
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936* Added `-S' and `--skeleton'.
937
62ab6972
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938* `%raw', `-r', `--raw' is disabled.
939
cd5bd6ac
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940* Special characters are escaped when output. This solves the problems
941 of the #line lines with path names including backslashes.
942
6deb4447 943* New directives.
4ecbf796
MA
944 `%yacc', `%fixed_output_files', `%defines', `%no_parser', `%verbose',
945 `%debug', `%source_extension' and `%header_extension'.
f987e9d2
AD
946
947* @$
948 Automatic location tracking.
f87a2205 949\f
9f4503d6 950Changes in version 1.28, 1999-07-06:
d2e00347
JT
951
952* Should compile better now with K&R compilers.
953
954* Added NLS.
955
956* Fixed a problem with escaping the double quote character.
957
958* There is now a FAQ.
959\f
5c31c3c2
JT
960Changes in version 1.27:
961
962* The make rule which prevented bison.simple from being created on
963 some systems has been fixed.
964\f
965Changes in version 1.26:
4be07551
JT
966
967* Bison now uses automake.
968
969* New mailing lists: <bug-bison@gnu.org> and <help-bison@gnu.org>.
970
971* Token numbers now start at 257 as previously documented, not 258.
972
973* Bison honors the TMPDIR environment variable.
974
975* A couple of buffer overruns have been fixed.
f51dbca1
JT
976
977* Problems when closing files should now be reported.
978
979* Generated parsers should now work even on operating systems which do
980 not provide alloca().
4be07551 981\f
9f4503d6 982Changes in version 1.25, 1995-10-16:
df8878c5
RS
983
984* Errors in the input grammar are not fatal; Bison keeps reading
985the grammar file, and reports all the errors found in it.
8c44d3ec 986
df8878c5
RS
987* Tokens can now be specified as multiple-character strings: for
988example, you could use "<=" for a token which looks like <=, instead
989of chosing a name like LESSEQ.
990
991* The %token_table declaration says to write a table of tokens (names
992and numbers) into the parser file. The yylex function can use this
993table to recognize multiple-character string tokens, or for other
994purposes.
995
996* The %no_lines declaration says not to generate any #line preprocessor
997directives in the parser file.
998
999* The %raw declaration says to use internal Bison token numbers, not
1000Yacc-compatible token numbers, when token names are defined as macros.
1001
1002* The --no-parser option produces the parser tables without including
1003the parser engine; a project can now use its own parser engine.
1004The actions go into a separate file called NAME.act, in the form of
1005a switch statement body.
1006\f
6780ca7a
DM
1007Changes in version 1.23:
1008
4d019228
DM
1009The user can define YYPARSE_PARAM as the name of an argument to be
1010passed into yyparse. The argument should have type void *. It should
1011actually point to an object. Grammar actions can access the variable
1012by casting it to the proper pointer type.
6780ca7a 1013
6780ca7a 1014Line numbers in output file corrected.
6780ca7a
DM
1015\f
1016Changes in version 1.22:
1017
1018--help option added.
6780ca7a
DM
1019\f
1020Changes in version 1.20:
1021
1022Output file does not redefine const for C++.
9f4503d6
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1023
1024Local Variables:
1025mode: outline
1026End:
76551463
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1027
1028-----
1029
d6ca7905 1030Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003,
ab7f29f8 10312004, 2005, 2006, 2007, 2008 Free Software Foundation, Inc.
76551463 1032
75eb3bc4 1033This file is part of Bison, the GNU Compiler Compiler.
76551463 1034
f16b0819 1035This program is free software: you can redistribute it and/or modify
76551463 1036it under the terms of the GNU General Public License as published by
f16b0819
PE
1037the Free Software Foundation, either version 3 of the License, or
1038(at your option) any later version.
76551463 1039
f16b0819 1040This program is distributed in the hope that it will be useful,
76551463
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1041but WITHOUT ANY WARRANTY; without even the implied warranty of
1042MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
1043GNU General Public License for more details.
1044
1045You should have received a copy of the GNU General Public License
f16b0819 1046along with this program. If not, see <http://www.gnu.org/licenses/>.