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| 1 Bison News |
| 2 ---------- |
| 3 |
| 4 * Changes in version 2.4.1 (2008-12-11): |
| 5 |
| 6 ** In the GLR defines file, unexpanded M4 macros in the yylval and yylloc |
| 7 declarations have been fixed. |
| 8 |
| 9 ** Temporary hack for adding a semicolon to the user action. |
| 10 |
| 11 Bison used to prepend a trailing semicolon at the end of the user |
| 12 action for reductions. This allowed actions such as |
| 13 |
| 14 exp: exp "+" exp { $$ = $1 + $3 }; |
| 15 |
| 16 instead of |
| 17 |
| 18 exp: exp "+" exp { $$ = $1 + $3; }; |
| 19 |
| 20 Some grammars still depend on this `feature'. Bison 2.4.1 restores |
| 21 the previous behavior in the case of C output (specifically, when |
| 22 neither %language or %skeleton or equivalent command-line options |
| 23 are used) to leave more time for grammars depending on the old |
| 24 behavior to be adjusted. Future releases of Bison will disable this |
| 25 feature. |
| 26 |
| 27 ** A few minor improvements to the Bison manual. |
| 28 |
| 29 * Changes in version 2.4 (2008-11-02): |
| 30 |
| 31 ** %language is an experimental feature. |
| 32 |
| 33 We first introduced this feature in test release 2.3b as a cleaner |
| 34 alternative to %skeleton. Since then, we have discussed the possibility of |
| 35 modifying its effect on Bison's output file names. Thus, in this release, |
| 36 we consider %language to be an experimental feature that will likely evolve |
| 37 in future releases. |
| 38 |
| 39 ** Forward compatibility with GNU M4 has been improved. |
| 40 |
| 41 ** Several bugs in the C++ skeleton and the experimental Java skeleton have been |
| 42 fixed. |
| 43 |
| 44 * Changes in version 2.3b (2008-05-27): |
| 45 |
| 46 ** The quotes around NAME that used to be required in the following directive |
| 47 are now deprecated: |
| 48 |
| 49 %define NAME "VALUE" |
| 50 |
| 51 ** The directive `%pure-parser' is now deprecated in favor of: |
| 52 |
| 53 %define api.pure |
| 54 |
| 55 which has the same effect except that Bison is more careful to warn about |
| 56 unreasonable usage in the latter case. |
| 57 |
| 58 ** Push Parsing |
| 59 |
| 60 Bison can now generate an LALR(1) parser in C with a push interface. That |
| 61 is, instead of invoking `yyparse', which pulls tokens from `yylex', you can |
| 62 push one token at a time to the parser using `yypush_parse', which will |
| 63 return to the caller after processing each token. By default, the push |
| 64 interface is disabled. Either of the following directives will enable it: |
| 65 |
| 66 %define api.push_pull "push" // Just push; does not require yylex. |
| 67 %define api.push_pull "both" // Push and pull; requires yylex. |
| 68 |
| 69 See the new section `A Push Parser' in the Bison manual for details. |
| 70 |
| 71 The current push parsing interface is experimental and may evolve. More user |
| 72 feedback will help to stabilize it. |
| 73 |
| 74 ** The -g and --graph options now output graphs in Graphviz DOT format, |
| 75 not VCG format. Like --graph, -g now also takes an optional FILE argument |
| 76 and thus cannot be bundled with other short options. |
| 77 |
| 78 ** Java |
| 79 |
| 80 Bison can now generate an LALR(1) parser in Java. The skeleton is |
| 81 `data/lalr1.java'. Consider using the new %language directive instead of |
| 82 %skeleton to select it. |
| 83 |
| 84 See the new section `Java Parsers' in the Bison manual for details. |
| 85 |
| 86 The current Java interface is experimental and may evolve. More user |
| 87 feedback will help to stabilize it. |
| 88 |
| 89 ** %language |
| 90 |
| 91 This new directive specifies the programming language of the generated |
| 92 parser, which can be C (the default), C++, or Java. Besides the skeleton |
| 93 that Bison uses, the directive affects the names of the generated files if |
| 94 the grammar file's name ends in ".y". |
| 95 |
| 96 ** XML Automaton Report |
| 97 |
| 98 Bison can now generate an XML report of the LALR(1) automaton using the new |
| 99 `--xml' option. The current XML schema is experimental and may evolve. More |
| 100 user feedback will help to stabilize it. |
| 101 |
| 102 ** The grammar file may now specify the name of the parser header file using |
| 103 %defines. For example: |
| 104 |
| 105 %defines "parser.h" |
| 106 |
| 107 ** When reporting useless rules, useless nonterminals, and unused terminals, |
| 108 Bison now employs the terms "useless in grammar" instead of "useless", |
| 109 "useless in parser" instead of "never reduced", and "unused in grammar" |
| 110 instead of "unused". |
| 111 |
| 112 ** Unreachable State Removal |
| 113 |
| 114 Previously, Bison sometimes generated parser tables containing unreachable |
| 115 states. A state can become unreachable during conflict resolution if Bison |
| 116 disables a shift action leading to it from a predecessor state. Bison now: |
| 117 |
| 118 1. Removes unreachable states. |
| 119 |
| 120 2. Does not report any conflicts that appeared in unreachable states. |
| 121 WARNING: As a result, you may need to update %expect and %expect-rr |
| 122 directives in existing grammar files. |
| 123 |
| 124 3. For any rule used only in such states, Bison now reports the rule as |
| 125 "useless in parser due to conflicts". |
| 126 |
| 127 This feature can be disabled with the following directive: |
| 128 |
| 129 %define lr.keep_unreachable_states |
| 130 |
| 131 See the %define entry in the `Bison Declaration Summary' in the Bison manual |
| 132 for further discussion. |
| 133 |
| 134 ** Lookahead Set Correction in the `.output' Report |
| 135 |
| 136 When instructed to generate a `.output' file including lookahead sets |
| 137 (using `--report=lookahead', for example), Bison now prints each reduction's |
| 138 lookahead set only next to the associated state's one item that (1) is |
| 139 associated with the same rule as the reduction and (2) has its dot at the end |
| 140 of its RHS. Previously, Bison also erroneously printed the lookahead set |
| 141 next to all of the state's other items associated with the same rule. This |
| 142 bug affected only the `.output' file and not the generated parser source |
| 143 code. |
| 144 |
| 145 ** --report-file=FILE is a new option to override the default `.output' file |
| 146 name. |
| 147 |
| 148 ** The `=' that used to be required in the following directives is now |
| 149 deprecated: |
| 150 |
| 151 %file-prefix "parser" |
| 152 %name-prefix "c_" |
| 153 %output "parser.c" |
| 154 |
| 155 ** An Alternative to `%{...%}' -- `%code QUALIFIER {CODE}' |
| 156 |
| 157 Bison 2.3a provided a new set of directives as a more flexible alternative to |
| 158 the traditional Yacc prologue blocks. Those have now been consolidated into |
| 159 a single %code directive with an optional qualifier field, which identifies |
| 160 the purpose of the code and thus the location(s) where Bison should generate |
| 161 it: |
| 162 |
| 163 1. `%code {CODE}' replaces `%after-header {CODE}' |
| 164 2. `%code requires {CODE}' replaces `%start-header {CODE}' |
| 165 3. `%code provides {CODE}' replaces `%end-header {CODE}' |
| 166 4. `%code top {CODE}' replaces `%before-header {CODE}' |
| 167 |
| 168 See the %code entries in section `Bison Declaration Summary' in the Bison |
| 169 manual for a summary of the new functionality. See the new section `Prologue |
| 170 Alternatives' for a detailed discussion including the advantages of %code |
| 171 over the traditional Yacc prologues. |
| 172 |
| 173 The prologue alternatives are experimental. More user feedback will help to |
| 174 determine whether they should become permanent features. |
| 175 |
| 176 ** Revised warning: unset or unused mid-rule values |
| 177 |
| 178 Since Bison 2.2, Bison has warned about mid-rule values that are set but not |
| 179 used within any of the actions of the parent rule. For example, Bison warns |
| 180 about unused $2 in: |
| 181 |
| 182 exp: '1' { $$ = 1; } '+' exp { $$ = $1 + $4; }; |
| 183 |
| 184 Now, Bison also warns about mid-rule values that are used but not set. For |
| 185 example, Bison warns about unset $$ in the mid-rule action in: |
| 186 |
| 187 exp: '1' { $1 = 1; } '+' exp { $$ = $2 + $4; }; |
| 188 |
| 189 However, Bison now disables both of these warnings by default since they |
| 190 sometimes prove to be false alarms in existing grammars employing the Yacc |
| 191 constructs $0 or $-N (where N is some positive integer). |
| 192 |
| 193 To enable these warnings, specify the option `--warnings=midrule-values' or |
| 194 `-W', which is a synonym for `--warnings=all'. |
| 195 |
| 196 ** Default %destructor or %printer with `<*>' or `<>' |
| 197 |
| 198 Bison now recognizes two separate kinds of default %destructor's and |
| 199 %printer's: |
| 200 |
| 201 1. Place `<*>' in a %destructor/%printer symbol list to define a default |
| 202 %destructor/%printer for all grammar symbols for which you have formally |
| 203 declared semantic type tags. |
| 204 |
| 205 2. Place `<>' in a %destructor/%printer symbol list to define a default |
| 206 %destructor/%printer for all grammar symbols without declared semantic |
| 207 type tags. |
| 208 |
| 209 Bison no longer supports the `%symbol-default' notation from Bison 2.3a. |
| 210 `<*>' and `<>' combined achieve the same effect with one exception: Bison no |
| 211 longer applies any %destructor to a mid-rule value if that mid-rule value is |
| 212 not actually ever referenced using either $$ or $n in a semantic action. |
| 213 |
| 214 The default %destructor's and %printer's are experimental. More user |
| 215 feedback will help to determine whether they should become permanent |
| 216 features. |
| 217 |
| 218 See the section `Freeing Discarded Symbols' in the Bison manual for further |
| 219 details. |
| 220 |
| 221 ** %left, %right, and %nonassoc can now declare token numbers. This is required |
| 222 by POSIX. However, see the end of section `Operator Precedence' in the Bison |
| 223 manual for a caveat concerning the treatment of literal strings. |
| 224 |
| 225 ** The nonfunctional --no-parser, -n, and %no-parser options have been |
| 226 completely removed from Bison. |
| 227 |
| 228 * Changes in version 2.3a, 2006-09-13: |
| 229 |
| 230 ** Instead of %union, you can define and use your own union type |
| 231 YYSTYPE if your grammar contains at least one <type> tag. |
| 232 Your YYSTYPE need not be a macro; it can be a typedef. |
| 233 This change is for compatibility with other Yacc implementations, |
| 234 and is required by POSIX. |
| 235 |
| 236 ** Locations columns and lines start at 1. |
| 237 In accordance with the GNU Coding Standards and Emacs. |
| 238 |
| 239 ** You may now declare per-type and default %destructor's and %printer's: |
| 240 |
| 241 For example: |
| 242 |
| 243 %union { char *string; } |
| 244 %token <string> STRING1 |
| 245 %token <string> STRING2 |
| 246 %type <string> string1 |
| 247 %type <string> string2 |
| 248 %union { char character; } |
| 249 %token <character> CHR |
| 250 %type <character> chr |
| 251 %destructor { free ($$); } %symbol-default |
| 252 %destructor { free ($$); printf ("%d", @$.first_line); } STRING1 string1 |
| 253 %destructor { } <character> |
| 254 |
| 255 guarantees that, when the parser discards any user-defined symbol that has a |
| 256 semantic type tag other than `<character>', it passes its semantic value to |
| 257 `free'. However, when the parser discards a `STRING1' or a `string1', it |
| 258 also prints its line number to `stdout'. It performs only the second |
| 259 `%destructor' in this case, so it invokes `free' only once. |
| 260 |
| 261 [Although we failed to mention this here in the 2.3a release, the default |
| 262 %destructor's and %printer's were experimental, and they were rewritten in |
| 263 future versions.] |
| 264 |
| 265 ** Except for LALR(1) parsers in C with POSIX Yacc emulation enabled (with `-y', |
| 266 `--yacc', or `%yacc'), Bison no longer generates #define statements for |
| 267 associating token numbers with token names. Removing the #define statements |
| 268 helps to sanitize the global namespace during preprocessing, but POSIX Yacc |
| 269 requires them. Bison still generates an enum for token names in all cases. |
| 270 |
| 271 ** Handling of traditional Yacc prologue blocks is now more consistent but |
| 272 potentially incompatible with previous releases of Bison. |
| 273 |
| 274 As before, you declare prologue blocks in your grammar file with the |
| 275 `%{ ... %}' syntax. To generate the pre-prologue, Bison concatenates all |
| 276 prologue blocks that you've declared before the first %union. To generate |
| 277 the post-prologue, Bison concatenates all prologue blocks that you've |
| 278 declared after the first %union. |
| 279 |
| 280 Previous releases of Bison inserted the pre-prologue into both the header |
| 281 file and the code file in all cases except for LALR(1) parsers in C. In the |
| 282 latter case, Bison inserted it only into the code file. For parsers in C++, |
| 283 the point of insertion was before any token definitions (which associate |
| 284 token numbers with names). For parsers in C, the point of insertion was |
| 285 after the token definitions. |
| 286 |
| 287 Now, Bison never inserts the pre-prologue into the header file. In the code |
| 288 file, it always inserts it before the token definitions. |
| 289 |
| 290 ** Bison now provides a more flexible alternative to the traditional Yacc |
| 291 prologue blocks: %before-header, %start-header, %end-header, and |
| 292 %after-header. |
| 293 |
| 294 For example, the following declaration order in the grammar file reflects the |
| 295 order in which Bison will output these code blocks. However, you are free to |
| 296 declare these code blocks in your grammar file in whatever order is most |
| 297 convenient for you: |
| 298 |
| 299 %before-header { |
| 300 /* Bison treats this block like a pre-prologue block: it inserts it into |
| 301 * the code file before the contents of the header file. It does *not* |
| 302 * insert it into the header file. This is a good place to put |
| 303 * #include's that you want at the top of your code file. A common |
| 304 * example is `#include "system.h"'. */ |
| 305 } |
| 306 %start-header { |
| 307 /* Bison inserts this block into both the header file and the code file. |
| 308 * In both files, the point of insertion is before any Bison-generated |
| 309 * token, semantic type, location type, and class definitions. This is a |
| 310 * good place to define %union dependencies, for example. */ |
| 311 } |
| 312 %union { |
| 313 /* Unlike the traditional Yacc prologue blocks, the output order for the |
| 314 * new %*-header blocks is not affected by their declaration position |
| 315 * relative to any %union in the grammar file. */ |
| 316 } |
| 317 %end-header { |
| 318 /* Bison inserts this block into both the header file and the code file. |
| 319 * In both files, the point of insertion is after the Bison-generated |
| 320 * definitions. This is a good place to declare or define public |
| 321 * functions or data structures that depend on the Bison-generated |
| 322 * definitions. */ |
| 323 } |
| 324 %after-header { |
| 325 /* Bison treats this block like a post-prologue block: it inserts it into |
| 326 * the code file after the contents of the header file. It does *not* |
| 327 * insert it into the header file. This is a good place to declare or |
| 328 * define internal functions or data structures that depend on the |
| 329 * Bison-generated definitions. */ |
| 330 } |
| 331 |
| 332 If you have multiple occurrences of any one of the above declarations, Bison |
| 333 will concatenate the contents in declaration order. |
| 334 |
| 335 [Although we failed to mention this here in the 2.3a release, the prologue |
| 336 alternatives were experimental, and they were rewritten in future versions.] |
| 337 |
| 338 ** The option `--report=look-ahead' has been changed to `--report=lookahead'. |
| 339 The old spelling still works, but is not documented and may be removed |
| 340 in a future release. |
| 341 |
| 342 * Changes in version 2.3, 2006-06-05: |
| 343 |
| 344 ** GLR grammars should now use `YYRECOVERING ()' instead of `YYRECOVERING', |
| 345 for compatibility with LALR(1) grammars. |
| 346 |
| 347 ** It is now documented that any definition of YYSTYPE or YYLTYPE should |
| 348 be to a type name that does not contain parentheses or brackets. |
| 349 |
| 350 * Changes in version 2.2, 2006-05-19: |
| 351 |
| 352 ** The distribution terms for all Bison-generated parsers now permit |
| 353 using the parsers in nonfree programs. Previously, this permission |
| 354 was granted only for Bison-generated LALR(1) parsers in C. |
| 355 |
| 356 ** %name-prefix changes the namespace name in C++ outputs. |
| 357 |
| 358 ** The C++ parsers export their token_type. |
| 359 |
| 360 ** Bison now allows multiple %union declarations, and concatenates |
| 361 their contents together. |
| 362 |
| 363 ** New warning: unused values |
| 364 Right-hand side symbols whose values are not used are reported, |
| 365 if the symbols have destructors. For instance: |
| 366 |
| 367 exp: exp "?" exp ":" exp { $1 ? $1 : $3; } |
| 368 | exp "+" exp |
| 369 ; |
| 370 |
| 371 will trigger a warning about $$ and $5 in the first rule, and $3 in |
| 372 the second ($1 is copied to $$ by the default rule). This example |
| 373 most likely contains three errors, and could be rewritten as: |
| 374 |
| 375 exp: exp "?" exp ":" exp |
| 376 { $$ = $1 ? $3 : $5; free ($1 ? $5 : $3); free ($1); } |
| 377 | exp "+" exp |
| 378 { $$ = $1 ? $1 : $3; if ($1) free ($3); } |
| 379 ; |
| 380 |
| 381 However, if the original actions were really intended, memory leaks |
| 382 and all, the warnings can be suppressed by letting Bison believe the |
| 383 values are used, e.g.: |
| 384 |
| 385 exp: exp "?" exp ":" exp { $1 ? $1 : $3; (void) ($$, $5); } |
| 386 | exp "+" exp { $$ = $1; (void) $3; } |
| 387 ; |
| 388 |
| 389 If there are mid-rule actions, the warning is issued if no action |
| 390 uses it. The following triggers no warning: $1 and $3 are used. |
| 391 |
| 392 exp: exp { push ($1); } '+' exp { push ($3); sum (); }; |
| 393 |
| 394 The warning is intended to help catching lost values and memory leaks. |
| 395 If a value is ignored, its associated memory typically is not reclaimed. |
| 396 |
| 397 ** %destructor vs. YYABORT, YYACCEPT, and YYERROR. |
| 398 Destructors are now called when user code invokes YYABORT, YYACCEPT, |
| 399 and YYERROR, for all objects on the stack, other than objects |
| 400 corresponding to the right-hand side of the current rule. |
| 401 |
| 402 ** %expect, %expect-rr |
| 403 Incorrect numbers of expected conflicts are now actual errors, |
| 404 instead of warnings. |
| 405 |
| 406 ** GLR, YACC parsers. |
| 407 The %parse-params are available in the destructors (and the |
| 408 experimental printers) as per the documentation. |
| 409 |
| 410 ** Bison now warns if it finds a stray `$' or `@' in an action. |
| 411 |
| 412 ** %require "VERSION" |
| 413 This specifies that the grammar file depends on features implemented |
| 414 in Bison version VERSION or higher. |
| 415 |
| 416 ** lalr1.cc: The token and value types are now class members. |
| 417 The tokens were defined as free form enums and cpp macros. YYSTYPE |
| 418 was defined as a free form union. They are now class members: |
| 419 tokens are enumerations of the `yy::parser::token' struct, and the |
| 420 semantic values have the `yy::parser::semantic_type' type. |
| 421 |
| 422 If you do not want or can update to this scheme, the directive |
| 423 `%define "global_tokens_and_yystype" "1"' triggers the global |
| 424 definition of tokens and YYSTYPE. This change is suitable both |
| 425 for previous releases of Bison, and this one. |
| 426 |
| 427 If you wish to update, then make sure older version of Bison will |
| 428 fail using `%require "2.2"'. |
| 429 |
| 430 ** DJGPP support added. |
| 431 |
| 432 * Changes in version 2.1, 2005-09-16: |
| 433 |
| 434 ** The C++ lalr1.cc skeleton supports %lex-param. |
| 435 |
| 436 ** Bison-generated parsers now support the translation of diagnostics like |
| 437 "syntax error" into languages other than English. The default |
| 438 language is still English. For details, please see the new |
| 439 Internationalization section of the Bison manual. Software |
| 440 distributors should also see the new PACKAGING file. Thanks to |
| 441 Bruno Haible for this new feature. |
| 442 |
| 443 ** Wording in the Bison-generated parsers has been changed slightly to |
| 444 simplify translation. In particular, the message "memory exhausted" |
| 445 has replaced "parser stack overflow", as the old message was not |
| 446 always accurate for modern Bison-generated parsers. |
| 447 |
| 448 ** Destructors are now called when the parser aborts, for all symbols left |
| 449 behind on the stack. Also, the start symbol is now destroyed after a |
| 450 successful parse. In both cases, the behavior was formerly inconsistent. |
| 451 |
| 452 ** When generating verbose diagnostics, Bison-generated parsers no longer |
| 453 quote the literal strings associated with tokens. For example, for |
| 454 a syntax error associated with '%token NUM "number"' they might |
| 455 print 'syntax error, unexpected number' instead of 'syntax error, |
| 456 unexpected "number"'. |
| 457 |
| 458 * Changes in version 2.0, 2004-12-25: |
| 459 |
| 460 ** Possibly-incompatible changes |
| 461 |
| 462 - Bison-generated parsers no longer default to using the alloca function |
| 463 (when available) to extend the parser stack, due to widespread |
| 464 problems in unchecked stack-overflow detection. You can "#define |
| 465 YYSTACK_USE_ALLOCA 1" to require the use of alloca, but please read |
| 466 the manual to determine safe values for YYMAXDEPTH in that case. |
| 467 |
| 468 - Error token location. |
| 469 During error recovery, the location of the syntax error is updated |
| 470 to cover the whole sequence covered by the error token: it includes |
| 471 the shifted symbols thrown away during the first part of the error |
| 472 recovery, and the lookahead rejected during the second part. |
| 473 |
| 474 - Semicolon changes: |
| 475 . Stray semicolons are no longer allowed at the start of a grammar. |
| 476 . Semicolons are now required after in-grammar declarations. |
| 477 |
| 478 - Unescaped newlines are no longer allowed in character constants or |
| 479 string literals. They were never portable, and GCC 3.4.0 has |
| 480 dropped support for them. Better diagnostics are now generated if |
| 481 forget a closing quote. |
| 482 |
| 483 - NUL bytes are no longer allowed in Bison string literals, unfortunately. |
| 484 |
| 485 ** New features |
| 486 |
| 487 - GLR grammars now support locations. |
| 488 |
| 489 - New directive: %initial-action. |
| 490 This directive allows the user to run arbitrary code (including |
| 491 initializing @$) from yyparse before parsing starts. |
| 492 |
| 493 - A new directive "%expect-rr N" specifies the expected number of |
| 494 reduce/reduce conflicts in GLR parsers. |
| 495 |
| 496 - %token numbers can now be hexadecimal integers, e.g., `%token FOO 0x12d'. |
| 497 This is a GNU extension. |
| 498 |
| 499 - The option `--report=lookahead' was changed to `--report=look-ahead'. |
| 500 [However, this was changed back after 2.3.] |
| 501 |
| 502 - Experimental %destructor support has been added to lalr1.cc. |
| 503 |
| 504 - New configure option --disable-yacc, to disable installation of the |
| 505 yacc command and -ly library introduced in 1.875 for POSIX conformance. |
| 506 |
| 507 ** Bug fixes |
| 508 |
| 509 - For now, %expect-count violations are now just warnings, not errors. |
| 510 This is for compatibility with Bison 1.75 and earlier (when there are |
| 511 reduce/reduce conflicts) and with Bison 1.30 and earlier (when there |
| 512 are too many or too few shift/reduce conflicts). However, in future |
| 513 versions of Bison we plan to improve the %expect machinery so that |
| 514 these violations will become errors again. |
| 515 |
| 516 - Within Bison itself, numbers (e.g., goto numbers) are no longer |
| 517 arbitrarily limited to 16-bit counts. |
| 518 |
| 519 - Semicolons are now allowed before "|" in grammar rules, as POSIX requires. |
| 520 |
| 521 * Changes in version 1.875, 2003-01-01: |
| 522 |
| 523 ** The documentation license has been upgraded to version 1.2 |
| 524 of the GNU Free Documentation License. |
| 525 |
| 526 ** syntax error processing |
| 527 |
| 528 - In Yacc-style parsers YYLLOC_DEFAULT is now used to compute error |
| 529 locations too. This fixes bugs in error-location computation. |
| 530 |
| 531 - %destructor |
| 532 It is now possible to reclaim the memory associated to symbols |
| 533 discarded during error recovery. This feature is still experimental. |
| 534 |
| 535 - %error-verbose |
| 536 This new directive is preferred over YYERROR_VERBOSE. |
| 537 |
| 538 - #defining yyerror to steal internal variables is discouraged. |
| 539 It is not guaranteed to work forever. |
| 540 |
| 541 ** POSIX conformance |
| 542 |
| 543 - Semicolons are once again optional at the end of grammar rules. |
| 544 This reverts to the behavior of Bison 1.33 and earlier, and improves |
| 545 compatibility with Yacc. |
| 546 |
| 547 - `parse error' -> `syntax error' |
| 548 Bison now uniformly uses the term `syntax error'; formerly, the code |
| 549 and manual sometimes used the term `parse error' instead. POSIX |
| 550 requires `syntax error' in diagnostics, and it was thought better to |
| 551 be consistent. |
| 552 |
| 553 - The documentation now emphasizes that yylex and yyerror must be |
| 554 declared before use. C99 requires this. |
| 555 |
| 556 - Bison now parses C99 lexical constructs like UCNs and |
| 557 backslash-newline within C escape sequences, as POSIX 1003.1-2001 requires. |
| 558 |
| 559 - File names are properly escaped in C output. E.g., foo\bar.y is |
| 560 output as "foo\\bar.y". |
| 561 |
| 562 - Yacc command and library now available |
| 563 The Bison distribution now installs a `yacc' command, as POSIX requires. |
| 564 Also, Bison now installs a small library liby.a containing |
| 565 implementations of Yacc-compatible yyerror and main functions. |
| 566 This library is normally not useful, but POSIX requires it. |
| 567 |
| 568 - Type clashes now generate warnings, not errors. |
| 569 |
| 570 - If the user does not define YYSTYPE as a macro, Bison now declares it |
| 571 using typedef instead of defining it as a macro. |
| 572 For consistency, YYLTYPE is also declared instead of defined. |
| 573 |
| 574 ** Other compatibility issues |
| 575 |
| 576 - %union directives can now have a tag before the `{', e.g., the |
| 577 directive `%union foo {...}' now generates the C code |
| 578 `typedef union foo { ... } YYSTYPE;'; this is for Yacc compatibility. |
| 579 The default union tag is `YYSTYPE', for compatibility with Solaris 9 Yacc. |
| 580 For consistency, YYLTYPE's struct tag is now `YYLTYPE' not `yyltype'. |
| 581 This is for compatibility with both Yacc and Bison 1.35. |
| 582 |
| 583 - `;' is output before the terminating `}' of an action, for |
| 584 compatibility with Bison 1.35. |
| 585 |
| 586 - Bison now uses a Yacc-style format for conflict reports, e.g., |
| 587 `conflicts: 2 shift/reduce, 1 reduce/reduce'. |
| 588 |
| 589 - `yystype' and `yyltype' are now obsolescent macros instead of being |
| 590 typedefs or tags; they are no longer documented and are planned to be |
| 591 withdrawn in a future release. |
| 592 |
| 593 ** GLR parser notes |
| 594 |
| 595 - GLR and inline |
| 596 Users of Bison have to decide how they handle the portability of the |
| 597 C keyword `inline'. |
| 598 |
| 599 - `parsing stack overflow...' -> `parser stack overflow' |
| 600 GLR parsers now report `parser stack overflow' as per the Bison manual. |
| 601 |
| 602 ** Bison now warns if it detects conflicting outputs to the same file, |
| 603 e.g., it generates a warning for `bison -d -o foo.h foo.y' since |
| 604 that command outputs both code and header to foo.h. |
| 605 |
| 606 ** #line in output files |
| 607 - --no-line works properly. |
| 608 |
| 609 ** Bison can no longer be built by a K&R C compiler; it requires C89 or |
| 610 later to be built. This change originally took place a few versions |
| 611 ago, but nobody noticed until we recently asked someone to try |
| 612 building Bison with a K&R C compiler. |
| 613 |
| 614 * Changes in version 1.75, 2002-10-14: |
| 615 |
| 616 ** Bison should now work on 64-bit hosts. |
| 617 |
| 618 ** Indonesian translation thanks to Tedi Heriyanto. |
| 619 |
| 620 ** GLR parsers |
| 621 Fix spurious parse errors. |
| 622 |
| 623 ** Pure parsers |
| 624 Some people redefine yyerror to steal yyparse' private variables. |
| 625 Reenable this trick until an official feature replaces it. |
| 626 |
| 627 ** Type Clashes |
| 628 In agreement with POSIX and with other Yaccs, leaving a default |
| 629 action is valid when $$ is untyped, and $1 typed: |
| 630 |
| 631 untyped: ... typed; |
| 632 |
| 633 but the converse remains an error: |
| 634 |
| 635 typed: ... untyped; |
| 636 |
| 637 ** Values of mid-rule actions |
| 638 The following code: |
| 639 |
| 640 foo: { ... } { $$ = $1; } ... |
| 641 |
| 642 was incorrectly rejected: $1 is defined in the second mid-rule |
| 643 action, and is equal to the $$ of the first mid-rule action. |
| 644 |
| 645 * Changes in version 1.50, 2002-10-04: |
| 646 |
| 647 ** GLR parsing |
| 648 The declaration |
| 649 %glr-parser |
| 650 causes Bison to produce a Generalized LR (GLR) parser, capable of handling |
| 651 almost any context-free grammar, ambiguous or not. The new declarations |
| 652 %dprec and %merge on grammar rules allow parse-time resolution of |
| 653 ambiguities. Contributed by Paul Hilfinger. |
| 654 |
| 655 Unfortunately Bison 1.50 does not work properly on 64-bit hosts |
| 656 like the Alpha, so please stick to 32-bit hosts for now. |
| 657 |
| 658 ** Output Directory |
| 659 When not in Yacc compatibility mode, when the output file was not |
| 660 specified, running `bison foo/bar.y' created `foo/bar.c'. It |
| 661 now creates `bar.c'. |
| 662 |
| 663 ** Undefined token |
| 664 The undefined token was systematically mapped to 2 which prevented |
| 665 the use of 2 by the user. This is no longer the case. |
| 666 |
| 667 ** Unknown token numbers |
| 668 If yylex returned an out of range value, yyparse could die. This is |
| 669 no longer the case. |
| 670 |
| 671 ** Error token |
| 672 According to POSIX, the error token must be 256. |
| 673 Bison extends this requirement by making it a preference: *if* the |
| 674 user specified that one of her tokens is numbered 256, then error |
| 675 will be mapped onto another number. |
| 676 |
| 677 ** Verbose error messages |
| 678 They no longer report `..., expecting error or...' for states where |
| 679 error recovery is possible. |
| 680 |
| 681 ** End token |
| 682 Defaults to `$end' instead of `$'. |
| 683 |
| 684 ** Error recovery now conforms to documentation and to POSIX |
| 685 When a Bison-generated parser encounters a syntax error, it now pops |
| 686 the stack until it finds a state that allows shifting the error |
| 687 token. Formerly, it popped the stack until it found a state that |
| 688 allowed some non-error action other than a default reduction on the |
| 689 error token. The new behavior has long been the documented behavior, |
| 690 and has long been required by POSIX. For more details, please see |
| 691 Paul Eggert, "Reductions during Bison error handling" (2002-05-20) |
| 692 <http://lists.gnu.org/archive/html/bug-bison/2002-05/msg00038.html>. |
| 693 |
| 694 ** Traces |
| 695 Popped tokens and nonterminals are now reported. |
| 696 |
| 697 ** Larger grammars |
| 698 Larger grammars are now supported (larger token numbers, larger grammar |
| 699 size (= sum of the LHS and RHS lengths), larger LALR tables). |
| 700 Formerly, many of these numbers ran afoul of 16-bit limits; |
| 701 now these limits are 32 bits on most hosts. |
| 702 |
| 703 ** Explicit initial rule |
| 704 Bison used to play hacks with the initial rule, which the user does |
| 705 not write. It is now explicit, and visible in the reports and |
| 706 graphs as rule 0. |
| 707 |
| 708 ** Useless rules |
| 709 Before, Bison reported the useless rules, but, although not used, |
| 710 included them in the parsers. They are now actually removed. |
| 711 |
| 712 ** Useless rules, useless nonterminals |
| 713 They are now reported, as a warning, with their locations. |
| 714 |
| 715 ** Rules never reduced |
| 716 Rules that can never be reduced because of conflicts are now |
| 717 reported. |
| 718 |
| 719 ** Incorrect `Token not used' |
| 720 On a grammar such as |
| 721 |
| 722 %token useless useful |
| 723 %% |
| 724 exp: '0' %prec useful; |
| 725 |
| 726 where a token was used to set the precedence of the last rule, |
| 727 bison reported both `useful' and `useless' as useless tokens. |
| 728 |
| 729 ** Revert the C++ namespace changes introduced in 1.31 |
| 730 as they caused too many portability hassles. |
| 731 |
| 732 ** Default locations |
| 733 By an accident of design, the default computation of @$ was |
| 734 performed after another default computation was performed: @$ = @1. |
| 735 The latter is now removed: YYLLOC_DEFAULT is fully responsible of |
| 736 the computation of @$. |
| 737 |
| 738 ** Token end-of-file |
| 739 The token end of file may be specified by the user, in which case, |
| 740 the user symbol is used in the reports, the graphs, and the verbose |
| 741 error messages instead of `$end', which remains being the default. |
| 742 For instance |
| 743 %token MYEOF 0 |
| 744 or |
| 745 %token MYEOF 0 "end of file" |
| 746 |
| 747 ** Semantic parser |
| 748 This old option, which has been broken for ages, is removed. |
| 749 |
| 750 ** New translations |
| 751 Brazilian Portuguese, thanks to Alexandre Folle de Menezes. |
| 752 Croatian, thanks to Denis Lackovic. |
| 753 |
| 754 ** Incorrect token definitions |
| 755 When given `%token 'a' "A"', Bison used to output `#define 'a' 65'. |
| 756 |
| 757 ** Token definitions as enums |
| 758 Tokens are output both as the traditional #define's, and, provided |
| 759 the compiler supports ANSI C or is a C++ compiler, as enums. |
| 760 This lets debuggers display names instead of integers. |
| 761 |
| 762 ** Reports |
| 763 In addition to --verbose, bison supports --report=THINGS, which |
| 764 produces additional information: |
| 765 - itemset |
| 766 complete the core item sets with their closure |
| 767 - lookahead [changed to `look-ahead' in 1.875e through 2.3, but changed back] |
| 768 explicitly associate lookahead tokens to items |
| 769 - solved |
| 770 describe shift/reduce conflicts solving. |
| 771 Bison used to systematically output this information on top of |
| 772 the report. Solved conflicts are now attached to their states. |
| 773 |
| 774 ** Type clashes |
| 775 Previous versions don't complain when there is a type clash on |
| 776 the default action if the rule has a mid-rule action, such as in: |
| 777 |
| 778 %type <foo> bar |
| 779 %% |
| 780 bar: '0' {} '0'; |
| 781 |
| 782 This is fixed. |
| 783 |
| 784 ** GNU M4 is now required when using Bison. |
| 785 |
| 786 * Changes in version 1.35, 2002-03-25: |
| 787 |
| 788 ** C Skeleton |
| 789 Some projects use Bison's C parser with C++ compilers, and define |
| 790 YYSTYPE as a class. The recent adjustment of C parsers for data |
| 791 alignment and 64 bit architectures made this impossible. |
| 792 |
| 793 Because for the time being no real solution for C++ parser |
| 794 generation exists, kludges were implemented in the parser to |
| 795 maintain this use. In the future, when Bison has C++ parsers, this |
| 796 kludge will be disabled. |
| 797 |
| 798 This kludge also addresses some C++ problems when the stack was |
| 799 extended. |
| 800 |
| 801 * Changes in version 1.34, 2002-03-12: |
| 802 |
| 803 ** File name clashes are detected |
| 804 $ bison foo.y -d -o foo.x |
| 805 fatal error: header and parser would both be named `foo.x' |
| 806 |
| 807 ** A missing `;' at the end of a rule triggers a warning |
| 808 In accordance with POSIX, and in agreement with other |
| 809 Yacc implementations, Bison will mandate this semicolon in the near |
| 810 future. This eases the implementation of a Bison parser of Bison |
| 811 grammars by making this grammar LALR(1) instead of LR(2). To |
| 812 facilitate the transition, this release introduces a warning. |
| 813 |
| 814 ** Revert the C++ namespace changes introduced in 1.31, as they caused too |
| 815 many portability hassles. |
| 816 |
| 817 ** DJGPP support added. |
| 818 |
| 819 ** Fix test suite portability problems. |
| 820 |
| 821 * Changes in version 1.33, 2002-02-07: |
| 822 |
| 823 ** Fix C++ issues |
| 824 Groff could not be compiled for the definition of size_t was lacking |
| 825 under some conditions. |
| 826 |
| 827 ** Catch invalid @n |
| 828 As is done with $n. |
| 829 |
| 830 * Changes in version 1.32, 2002-01-23: |
| 831 |
| 832 ** Fix Yacc output file names |
| 833 |
| 834 ** Portability fixes |
| 835 |
| 836 ** Italian, Dutch translations |
| 837 |
| 838 * Changes in version 1.31, 2002-01-14: |
| 839 |
| 840 ** Many Bug Fixes |
| 841 |
| 842 ** GNU Gettext and %expect |
| 843 GNU Gettext asserts 10 s/r conflicts, but there are 7. Now that |
| 844 Bison dies on incorrect %expectations, we fear there will be |
| 845 too many bug reports for Gettext, so _for the time being_, %expect |
| 846 does not trigger an error when the input file is named `plural.y'. |
| 847 |
| 848 ** Use of alloca in parsers |
| 849 If YYSTACK_USE_ALLOCA is defined to 0, then the parsers will use |
| 850 malloc exclusively. Since 1.29, but was not NEWS'ed. |
| 851 |
| 852 alloca is used only when compiled with GCC, to avoid portability |
| 853 problems as on AIX. |
| 854 |
| 855 ** yyparse now returns 2 if memory is exhausted; formerly it dumped core. |
| 856 |
| 857 ** When the generated parser lacks debugging code, YYDEBUG is now 0 |
| 858 (as POSIX requires) instead of being undefined. |
| 859 |
| 860 ** User Actions |
| 861 Bison has always permitted actions such as { $$ = $1 }: it adds the |
| 862 ending semicolon. Now if in Yacc compatibility mode, the semicolon |
| 863 is no longer output: one has to write { $$ = $1; }. |
| 864 |
| 865 ** Better C++ compliance |
| 866 The output parsers try to respect C++ namespaces. |
| 867 [This turned out to be a failed experiment, and it was reverted later.] |
| 868 |
| 869 ** Reduced Grammars |
| 870 Fixed bugs when reporting useless nonterminals. |
| 871 |
| 872 ** 64 bit hosts |
| 873 The parsers work properly on 64 bit hosts. |
| 874 |
| 875 ** Error messages |
| 876 Some calls to strerror resulted in scrambled or missing error messages. |
| 877 |
| 878 ** %expect |
| 879 When the number of shift/reduce conflicts is correct, don't issue |
| 880 any warning. |
| 881 |
| 882 ** The verbose report includes the rule line numbers. |
| 883 |
| 884 ** Rule line numbers are fixed in traces. |
| 885 |
| 886 ** Swedish translation |
| 887 |
| 888 ** Parse errors |
| 889 Verbose parse error messages from the parsers are better looking. |
| 890 Before: parse error: unexpected `'/'', expecting `"number"' or `'-'' or `'('' |
| 891 Now: parse error: unexpected '/', expecting "number" or '-' or '(' |
| 892 |
| 893 ** Fixed parser memory leaks. |
| 894 When the generated parser was using malloc to extend its stacks, the |
| 895 previous allocations were not freed. |
| 896 |
| 897 ** Fixed verbose output file. |
| 898 Some newlines were missing. |
| 899 Some conflicts in state descriptions were missing. |
| 900 |
| 901 ** Fixed conflict report. |
| 902 Option -v was needed to get the result. |
| 903 |
| 904 ** %expect |
| 905 Was not used. |
| 906 Mismatches are errors, not warnings. |
| 907 |
| 908 ** Fixed incorrect processing of some invalid input. |
| 909 |
| 910 ** Fixed CPP guards: 9foo.h uses BISON_9FOO_H instead of 9FOO_H. |
| 911 |
| 912 ** Fixed some typos in the documentation. |
| 913 |
| 914 ** %token MY_EOF 0 is supported. |
| 915 Before, MY_EOF was silently renumbered as 257. |
| 916 |
| 917 ** doc/refcard.tex is updated. |
| 918 |
| 919 ** %output, %file-prefix, %name-prefix. |
| 920 New. |
| 921 |
| 922 ** --output |
| 923 New, aliasing `--output-file'. |
| 924 |
| 925 * Changes in version 1.30, 2001-10-26: |
| 926 |
| 927 ** `--defines' and `--graph' have now an optional argument which is the |
| 928 output file name. `-d' and `-g' do not change; they do not take any |
| 929 argument. |
| 930 |
| 931 ** `%source_extension' and `%header_extension' are removed, failed |
| 932 experiment. |
| 933 |
| 934 ** Portability fixes. |
| 935 |
| 936 * Changes in version 1.29, 2001-09-07: |
| 937 |
| 938 ** The output file does not define const, as this caused problems when used |
| 939 with common autoconfiguration schemes. If you still use ancient compilers |
| 940 that lack const, compile with the equivalent of the C compiler option |
| 941 `-Dconst='. autoconf's AC_C_CONST macro provides one way to do this. |
| 942 |
| 943 ** Added `-g' and `--graph'. |
| 944 |
| 945 ** The Bison manual is now distributed under the terms of the GNU FDL. |
| 946 |
| 947 ** The input and the output files has automatically a similar extension. |
| 948 |
| 949 ** Russian translation added. |
| 950 |
| 951 ** NLS support updated; should hopefully be less troublesome. |
| 952 |
| 953 ** Added the old Bison reference card. |
| 954 |
| 955 ** Added `--locations' and `%locations'. |
| 956 |
| 957 ** Added `-S' and `--skeleton'. |
| 958 |
| 959 ** `%raw', `-r', `--raw' is disabled. |
| 960 |
| 961 ** Special characters are escaped when output. This solves the problems |
| 962 of the #line lines with path names including backslashes. |
| 963 |
| 964 ** New directives. |
| 965 `%yacc', `%fixed_output_files', `%defines', `%no_parser', `%verbose', |
| 966 `%debug', `%source_extension' and `%header_extension'. |
| 967 |
| 968 ** @$ |
| 969 Automatic location tracking. |
| 970 |
| 971 * Changes in version 1.28, 1999-07-06: |
| 972 |
| 973 ** Should compile better now with K&R compilers. |
| 974 |
| 975 ** Added NLS. |
| 976 |
| 977 ** Fixed a problem with escaping the double quote character. |
| 978 |
| 979 ** There is now a FAQ. |
| 980 |
| 981 * Changes in version 1.27: |
| 982 |
| 983 ** The make rule which prevented bison.simple from being created on |
| 984 some systems has been fixed. |
| 985 |
| 986 * Changes in version 1.26: |
| 987 |
| 988 ** Bison now uses automake. |
| 989 |
| 990 ** New mailing lists: <bug-bison@gnu.org> and <help-bison@gnu.org>. |
| 991 |
| 992 ** Token numbers now start at 257 as previously documented, not 258. |
| 993 |
| 994 ** Bison honors the TMPDIR environment variable. |
| 995 |
| 996 ** A couple of buffer overruns have been fixed. |
| 997 |
| 998 ** Problems when closing files should now be reported. |
| 999 |
| 1000 ** Generated parsers should now work even on operating systems which do |
| 1001 not provide alloca(). |
| 1002 |
| 1003 * Changes in version 1.25, 1995-10-16: |
| 1004 |
| 1005 ** Errors in the input grammar are not fatal; Bison keeps reading |
| 1006 the grammar file, and reports all the errors found in it. |
| 1007 |
| 1008 ** Tokens can now be specified as multiple-character strings: for |
| 1009 example, you could use "<=" for a token which looks like <=, instead |
| 1010 of chosing a name like LESSEQ. |
| 1011 |
| 1012 ** The %token_table declaration says to write a table of tokens (names |
| 1013 and numbers) into the parser file. The yylex function can use this |
| 1014 table to recognize multiple-character string tokens, or for other |
| 1015 purposes. |
| 1016 |
| 1017 ** The %no_lines declaration says not to generate any #line preprocessor |
| 1018 directives in the parser file. |
| 1019 |
| 1020 ** The %raw declaration says to use internal Bison token numbers, not |
| 1021 Yacc-compatible token numbers, when token names are defined as macros. |
| 1022 |
| 1023 ** The --no-parser option produces the parser tables without including |
| 1024 the parser engine; a project can now use its own parser engine. |
| 1025 The actions go into a separate file called NAME.act, in the form of |
| 1026 a switch statement body. |
| 1027 |
| 1028 * Changes in version 1.23: |
| 1029 |
| 1030 The user can define YYPARSE_PARAM as the name of an argument to be |
| 1031 passed into yyparse. The argument should have type void *. It should |
| 1032 actually point to an object. Grammar actions can access the variable |
| 1033 by casting it to the proper pointer type. |
| 1034 |
| 1035 Line numbers in output file corrected. |
| 1036 |
| 1037 * Changes in version 1.22: |
| 1038 |
| 1039 --help option added. |
| 1040 |
| 1041 * Changes in version 1.20: |
| 1042 |
| 1043 Output file does not redefine const for C++. |
| 1044 |
| 1045 Local Variables: |
| 1046 mode: outline |
| 1047 End: |
| 1048 |
| 1049 ----- |
| 1050 |
| 1051 Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, |
| 1052 2004, 2005, 2006, 2007, 2008 Free Software Foundation, Inc. |
| 1053 |
| 1054 This file is part of Bison, the GNU Compiler Compiler. |
| 1055 |
| 1056 This program is free software: you can redistribute it and/or modify |
| 1057 it under the terms of the GNU General Public License as published by |
| 1058 the Free Software Foundation, either version 3 of the License, or |
| 1059 (at your option) any later version. |
| 1060 |
| 1061 This program is distributed in the hope that it will be useful, |
| 1062 but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 1063 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 1064 GNU General Public License for more details. |
| 1065 |
| 1066 You should have received a copy of the GNU General Public License |
| 1067 along with this program. If not, see <http://www.gnu.org/licenses/>. |
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