3 * Noteworthy changes in release ?.? (????-??-??) [?]
5 Fixed portability issues of bison on Cygwin.
7 Improvements in glr2.cc: add support for custom error messages (`%define
8 parse.error custom`), allow linking several parsers together.
10 * Noteworthy changes in release 3.8.1 (2021-09-11) [stable]
12 The generation of prototypes for yylex and yyerror in Yacc mode is
13 breaking existing grammar files. To avoid breaking too many grammars, the
14 prototypes are now generated when `-y/--yacc` is used *and* the
15 `POSIXLY_CORRECT` environment variable is defined.
17 Avoid using `-y`/`--yacc` simply to comply with Yacc's file name
18 conventions, rather, use `-o y.tab.c`. Autoconf's AC_PROG_YACC macro uses
19 `-y`. Avoid it if possible, for instance by using gnulib's gl_PROG_BISON.
21 * Noteworthy changes in release 3.8 (2021-09-07) [stable]
23 ** Backward incompatible changes
25 In conformance with the recommendations of the Graphviz team
26 (https://marc.info/?l=graphviz-devel&m=129418103126092), `-g`/`--graph`
27 now generates a *.gv file by default, instead of *.dot. A transition
30 To comply with the latest POSIX standard, in Yacc compatibility mode
31 (options `-y`/`--yacc`) Bison now generates prototypes for yyerror and
32 yylex. In some situations, this is breaking compatibility: if the user
33 has already declared these functions but with some differences (e.g., to
34 declare them as static, or to use specific attributes), the generated
35 parser will fail to compile. To disable these prototypes, #define yyerror
36 (to `yyerror`), and likewise for yylex.
38 ** Deprecated features
40 Support for the YYPRINT macro is removed. It worked only with yacc.c and
41 only for tokens. It was obsoleted by %printer, introduced in Bison 1.50
44 It has always been recommended to prefer `%define api.value.type foo` to
45 `#define YYSTYPE foo`. The latter is supported in C for compatibility
46 with Yacc, but not in C++. Warnings are now issued if `#define YYSTYPE`
47 is used in C++, and eventually support will be removed.
49 In C++ code, prefer value_type to semantic_type to denote the semantic
50 value type, which is specified by the `api.value.type` %define variable.
54 *** A skeleton for the D programming language
56 The "lalr1.d" skeleton is now officially part of Bison.
58 It was originally contributed by Oliver Mangold, based on Paolo Bonzini's
59 lalr1.java, and was improved by H. S. Teoh. Adela Vais then took over
60 maintenance and invested a lot of efforts to complete, test and document
63 It now supports all the bells and whistles of the other deterministic
64 parsers, which include: pull/push interfaces, verbose and custom error
65 messages, lookahead correction, token constructors, internationalization,
66 locations, printers, token and symbol prefixes, etc.
68 Two examples demonstrate the D parsers: a basic one (examples/d/simple),
69 and an advanced one (examples/d/calc).
71 *** Option -H, --header and directive %header
73 The option `-H`/`--header` supersedes the option `--defines`, and the
74 directive %header supersedes %defines. Both `--defines` and `%defines`
75 are, of course, maintained for backward compatibility.
79 Since version 2.4 Bison can be used to generate HTML reports. However it
80 was a two-step process: first bison must be invoked with option `--xml`,
81 and then xsltproc must be run to the convert the XML reports into HTML.
83 The new option `--html` combines these steps. The xsltproc program must
86 *** A C++ native GLR parser
88 A new version of the C++ GLR parser was added: "glr2.cc". It generates
89 "true C++11", instead of a C++ wrapper around a C parser as does the
90 existing "glr.cc" parser. As a first significant consequence, it supports
91 `%define api.value.type variant`, contrary to glr.cc.
93 It should be upward compatible in terms of interface, feature and
94 performance to "glr.cc". To try it out, simply use
98 It will eventually replace "glr.cc". However we need user feedback on
99 this skeleton. _Please_ report your results and comments about it.
103 Counterexamples now show the rule numbers, and always show ε for rules
104 with an empty right-hand side. For instance
116 *** Lookahead correction in Java
118 The Java skeleton (lalr1.java) now supports LAC, via the `parse.lac`
121 *** Abort parsing for memory exhaustion (C)
123 User actions may now use `YYNOMEM` (similar to `YYACCEPT` and `YYABORT`)
124 to abort the current parse with memory exhaustion.
126 *** Printing locations in debug traces (C)
128 The `YYLOCATION_PRINT(File, Loc)` macro prints a location. It is defined
129 when (i) locations are enabled, (ii) the default type for locations is
130 used, (iii) debug traces are enabled, and (iv) `YYLOCATION_PRINT` is not
133 Users may define `YYLOCATION_PRINT` to cover other cases.
137 There were no debug traces for deferred calls to user actions. They are
141 * Noteworthy changes in release 3.7.6 (2021-03-08) [stable]
145 *** Reused Push Parsers
147 When a push-parser state structure is used for multiple parses, it was
148 possible for some state to leak from one run into the following one.
150 *** Fix Table Generation
152 In some very rare conditions, when there are many useless tokens, it was
153 possible to generate incorrect parsers.
156 * Noteworthy changes in release 3.7.5 (2021-01-24) [stable]
160 *** Counterexample Generation
162 In some cases counterexample generation could crash. This is fixed.
164 *** Fix Table Generation
166 In some very rare conditions, when there are many useless tokens, it was
167 possible to generate incorrect parsers.
169 *** GLR parsers now support %merge together with api.value.type=union.
171 *** C++ parsers use noexcept in more places.
173 *** Generated parsers avoid some warnings about signedness issues.
175 *** C-language parsers now avoid warnings from pedantic clang.
177 *** C-language parsers now work around quirks of HP-UX 11.23 (2003).
180 * Noteworthy changes in release 3.7.4 (2020-11-14) [stable]
184 *** Bug fixes in yacc.c
186 In Yacc mode, all the tokens are defined twice: once as an enum, and then
187 as a macro. YYEMPTY was missing its macro.
189 *** Bug fixes in lalr1.cc
191 The lalr1.cc skeleton used to emit internal assertions (using YY_ASSERT)
192 even when the `parse.assert` %define variable is not enabled. It no
195 The private internal macro YY_ASSERT now obeys the `api.prefix` %define
198 When there is a very large number of tokens, some assertions could be long
199 enough to hit arbitrary limits in Visual C++. They have been rewritten to
200 work around this limitation.
204 The YYBISON macro in generated "regular C parsers" (from the "yacc.c"
205 skeleton) used to be defined to 1. It is now defined to the version of
206 Bison as an integer (e.g., 30704 for version 3.7.4).
209 * Noteworthy changes in release 3.7.3 (2020-10-13) [stable]
213 Fix concurrent build issues.
215 The bison executable is no longer linked uselessly against libreadline.
217 Fix incorrect use of yytname in glr.cc.
220 * Noteworthy changes in release 3.7.2 (2020-09-05) [stable]
222 This release of Bison fixes all known bugs reported for Bison in MITRE's
223 Common Vulnerabilities and Exposures (CVE) system. These vulnerabilities
224 are only about bison-the-program itself, not the generated code.
226 Although these bugs are typically irrelevant to how Bison is used, they
227 are worth fixing if only to give users peace of mind.
229 There is no known vulnerability in the generated parsers.
233 Fix concurrent build issues (introduced in Bison 3.5).
235 Push parsers always use YYMALLOC/YYFREE (no direct calls to malloc/free).
237 Fix portability issues of the test suite, and of bison itself.
239 Some unlikely crashes found by fuzzing have been fixed. This is only
240 about bison itself, not the generated parsers.
243 * Noteworthy changes in release 3.7.1 (2020-08-02) [stable]
247 Crash when a token alias contains a NUL byte.
249 Portability issues with libtextstyle.
251 Portability issues of Bison itself with MSVC.
255 Improvements and fixes in the documentation.
257 More precise location about symbol type redefinitions.
260 * Noteworthy changes in release 3.7 (2020-07-23) [stable]
262 ** Deprecated features
264 The YYPRINT macro, which works only with yacc.c and only for tokens, was
265 obsoleted long ago by %printer, introduced in Bison 1.50 (November 2002).
266 It is deprecated and its support will be removed eventually.
268 In conformance with the recommendations of the Graphviz team, in the next
269 version Bison the option `--graph` will generate a *.gv file by default,
270 instead of *.dot. A transition started in Bison 3.4.
274 *** Counterexample Generation
276 Contributed by Vincent Imbimbo.
278 When given `-Wcounterexamples`/`-Wcex`, bison will now output
279 counterexamples for conflicts.
281 **** Unifying Counterexamples
283 Unifying counterexamples are strings which can be parsed in two ways due
284 to the conflict. For example on a grammar that contains the usual
285 "dangling else" ambiguity:
288 else.y: warning: 1 shift/reduce conflict [-Wconflicts-sr]
289 else.y: note: rerun with option '-Wcounterexamples' to generate conflict counterexamples
292 else.y: warning: 1 shift/reduce conflict [-Wconflicts-sr]
293 else.y: warning: shift/reduce conflict on token "else" [-Wcounterexamples]
294 Example: "if" exp "then" "if" exp "then" exp • "else" exp
297 ↳ "if" exp "then" exp
298 ↳ "if" exp "then" exp • "else" exp
299 Example: "if" exp "then" "if" exp "then" exp • "else" exp
302 ↳ "if" exp "then" exp "else" exp
303 ↳ "if" exp "then" exp •
305 When text styling is enabled, colors are used in the examples and the
306 derivations to highlight the structure of both analyses. In this case,
308 "if" exp "then" [ "if" exp "then" exp • ] "else" exp
312 "if" exp "then" [ "if" exp "then" exp • "else" exp ]
315 The counterexamples are "focused", in two different ways. First, they do
316 not clutter the output with all the derivations from the start symbol,
317 rather they start on the "conflicted nonterminal". They go straight to the
318 point. Second, they don't "expand" nonterminal symbols uselessly.
320 **** Nonunifying Counterexamples
322 In the case of the dangling else, Bison found an example that can be
323 parsed in two ways (therefore proving that the grammar is ambiguous).
324 When it cannot find such an example, it instead generates two examples
325 that are the same up until the dot:
328 foo.y: warning: 1 shift/reduce conflict [-Wconflicts-sr]
329 foo.y: note: rerun with option '-Wcounterexamples' to generate conflict counterexamples
330 foo.y:4.4-7: warning: rule useless in parser due to conflicts [-Wother]
335 foo.y: warning: 1 shift/reduce conflict [-Wconflicts-sr]
336 foo.y: warning: shift/reduce conflict on token ID [-Wcounterexamples]
337 First example: expr • ID ',' ID $end
344 Second example: expr • ID $end
350 foo.y:4.4-7: warning: rule useless in parser due to conflicts [-Wother]
354 In these cases, the parser usually doesn't have enough lookahead to
355 differentiate the two given examples.
359 Counterexamples are also included in the report when given
360 `--report=counterexamples`/`-rcex` (or `--report=all`), with more
365 1 exp: "if" exp "then" exp • [$end, "then", "else"]
366 2 | "if" exp "then" exp • "else" exp
368 "else" shift, and go to state 8
370 "else" [reduce using rule 1 (exp)]
371 $default reduce using rule 1 (exp)
373 shift/reduce conflict on token "else":
374 1 exp: "if" exp "then" exp •
375 2 exp: "if" exp "then" exp • "else" exp
376 Example: "if" exp "then" "if" exp "then" exp • "else" exp
379 ↳ "if" exp "then" exp
380 ↳ "if" exp "then" exp • "else" exp
381 Example: "if" exp "then" "if" exp "then" exp • "else" exp
384 ↳ "if" exp "then" exp "else" exp
385 ↳ "if" exp "then" exp •
387 *** File prefix mapping
389 Contributed by Joshua Watt.
391 Bison learned a new argument, `--file-prefix-map OLD=NEW`. Any file path
392 in the output (specifically `#line` directives and `#ifdef` header guards)
393 that begins with the prefix OLD will have it replaced with the prefix NEW,
394 similar to the `-ffile-prefix-map` in GCC. This option can be used to
395 make bison output reproducible.
401 When text styling is enabled and the terminal supports it, the warnings
402 now include hyperlinks to the documentation.
404 *** Relocatable installation
406 When installed to be relocatable (via `configure --enable-relocatable`),
407 bison will now also look for a relocated m4.
411 The `filename_type` %define variable was renamed `api.filename.type`.
414 %define filename_type "symbol"
418 %define api.filename.type {symbol}
420 (Or let `bison --update` do it for you).
422 It now defaults to `const std::string` instead of `std::string`.
424 *** Deprecated %define variable names
426 The following variables have been renamed for consistency. Backward
427 compatibility is ensured, but upgrading is recommended.
429 filename_type -> api.filename.type
430 package -> api.package
432 *** Push parsers no longer clear their state when parsing is finished
434 Previously push-parsers cleared their state when parsing was finished (on
435 success and on failure). This made it impossible to check if there were
436 parse errors, since `yynerrs` was also reset. This can be especially
437 troublesome when used in autocompletion, since a parser with error
438 recovery would suggest (irrelevant) expected tokens even if there were
441 Now the parser state can be examined when parsing is finished. The parser
442 state is reset when starting a new parse.
448 The bistromathic demonstrates %param and how to quote sources in the error
452 1.5-7: syntax error: expected end of file or + or - or * or / or ^ before number
458 *** Include the generated header (yacc.c)
460 Historically, when --defines was used, bison generated a header and pasted
461 an exact copy of it into the generated parser implementation file. Since
462 Bison 3.4 it is possible to specify that the header should be `#include`d,
463 and how. For instance
465 %define api.header.include {"parse.h"}
469 %define api.header.include {<parser/parse.h>}
471 Now api.header.include defaults to `"header-basename"`, as was intended in
472 Bison 3.4, where `header-basename` is the basename of the generated
473 header. This is disabled when the generated header is `y.tab.h`, to
474 comply with Automake's ylwrap.
476 *** String aliases are faithfully propagated
478 Bison used to interpret user strings (i.e., decoding backslash escapes)
479 when reading them, and to escape them (i.e., issue non-printable
480 characters as backslash escapes, taking the locale into account) when
481 outputting them. As a consequence non-ASCII strings (say in UTF-8) ended
482 up "ciphered" as sequences of backslash escapes. This happened not only
483 in the generated sources (where the compiler will reinterpret them), but
484 also in all the generated reports (text, xml, html, dot, etc.). Reports
485 were therefore not readable when string aliases were not pure ASCII.
486 Worse yet: the output depended on the user's locale.
488 Now Bison faithfully treats the string aliases exactly the way the user
489 spelled them. This fixes all the aforementioned problems. However, now,
490 string aliases semantically equivalent but syntactically different (e.g.,
491 "A", "\x41", "\101") are considered to be different.
493 *** Crash when generating IELR
495 An old, well hidden, bug in the generation of IELR parsers was fixed.
498 * Noteworthy changes in release 3.6.4 (2020-06-15) [stable]
502 In glr.cc some internal macros leaked in the user's code, and could damage
503 access to the token kinds.
506 * Noteworthy changes in release 3.6.3 (2020-06-03) [stable]
510 Incorrect comments in the generated parsers.
512 Warnings in push parsers (yacc.c).
514 Incorrect display of gotos in LAC traces (lalr1.cc).
517 * Noteworthy changes in release 3.6.2 (2020-05-17) [stable]
521 Some tests were fixed.
523 When token aliases contain comment delimiters:
525 %token FOO "/* foo */"
527 bison used to emit "nested" comments, which is invalid C.
530 * Noteworthy changes in release 3.6.1 (2020-05-10) [stable]
534 Restored ANSI-C compliance in yacc.c.
536 GNU readline portability issues.
538 In C++, yy::parser::symbol_name is now a public member, as was intended.
542 In C++, yy::parser::symbol_type now has a public name() member function.
545 * Noteworthy changes in release 3.6 (2020-05-08) [stable]
547 ** Backward incompatible changes
549 TL;DR: replace "#define YYERROR_VERBOSE 1" by "%define parse.error verbose".
551 The YYERROR_VERBOSE macro is no longer supported; the parsers that still
552 depend on it will now produce Yacc-like error messages (just "syntax
553 error"). It was superseded by the "%error-verbose" directive in Bison
554 1.875 (2003-01-01). Bison 2.6 (2012-07-19) clearly announced that support
555 for YYERROR_VERBOSE would be removed. Note that since Bison 3.0
556 (2013-07-25), "%error-verbose" is deprecated in favor of "%define
557 parse.error verbose".
559 ** Deprecated features
561 The YYPRINT macro, which works only with yacc.c and only for tokens, was
562 obsoleted long ago by %printer, introduced in Bison 1.50 (November 2002).
563 It is deprecated and its support will be removed eventually.
567 *** Improved syntax error messages
569 Two new values for the %define parse.error variable offer more control to
570 the user. Available in all the skeletons (C, C++, Java).
572 **** %define parse.error detailed
574 The behavior of "%define parse.error detailed" is closely resembling that
575 of "%define parse.error verbose" with a few exceptions. First, it is safe
576 to use non-ASCII characters in token aliases (with 'verbose', the result
577 depends on the locale with which bison was run). Second, a yysymbol_name
578 function is exposed to the user, instead of the yytnamerr function and the
579 yytname table. Third, token internationalization is supported (see
582 **** %define parse.error custom
584 With this directive, the user forges and emits the syntax error message
585 herself by defining the yyreport_syntax_error function. A new type,
586 yypcontext_t, captures the circumstances of the error, and provides the
587 user with functions to get details, such as yypcontext_expected_tokens to
588 get the list of expected token kinds.
590 A possible implementation of yyreport_syntax_error is:
593 yyreport_syntax_error (const yypcontext_t *ctx)
596 YY_LOCATION_PRINT (stderr, *yypcontext_location (ctx));
597 fprintf (stderr, ": syntax error");
598 // Report the tokens expected at this point.
600 enum { TOKENMAX = 10 };
601 yysymbol_kind_t expected[TOKENMAX];
602 int n = yypcontext_expected_tokens (ctx, expected, TOKENMAX);
604 // Forward errors to yyparse.
607 for (int i = 0; i < n; ++i)
608 fprintf (stderr, "%s %s",
609 i == 0 ? ": expected" : " or", yysymbol_name (expected[i]));
611 // Report the unexpected token.
613 yysymbol_kind_t lookahead = yypcontext_token (ctx);
614 if (lookahead != YYSYMBOL_YYEMPTY)
615 fprintf (stderr, " before %s", yysymbol_name (lookahead));
617 fprintf (stderr, "\n");
621 **** Token aliases internationalization
623 When the %define variable parse.error is set to `custom` or `detailed`,
624 one may specify which token aliases are to be translated using _(). For
636 In that case the user must define _() and N_(), and yysymbol_name returns
637 the translated symbol (i.e., it returns '_("variable")' rather that
638 '"variable"'). In Java, the user must provide an i18n() function.
640 *** List of expected tokens (yacc.c)
642 Push parsers may invoke yypstate_expected_tokens at any point during
643 parsing (including even before submitting the first token) to get the list
644 of possible tokens. This feature can be used to propose autocompletion
645 (see below the "bistromathic" example).
647 It makes little sense to use this feature without enabling LAC (lookahead
650 *** Returning the error token
652 When the scanner returns an invalid token or the undefined token
653 (YYUNDEF), the parser generates an error message and enters error
654 recovery. Because of that error message, most scanners that find lexical
655 errors generate an error message, and then ignore the invalid input
656 without entering the error-recovery.
658 The scanners may now return YYerror, the error token, to enter the
659 error-recovery mode without triggering an additional error message. See
660 the bistromathic for an example.
662 *** Deep overhaul of the symbol and token kinds
664 To avoid the confusion with types in programming languages, we now refer
665 to token and symbol "kinds" instead of token and symbol "types". The
666 documentation and error messages have been revised.
668 All the skeletons have been updated to use dedicated enum types rather
669 than integral types. Special symbols are now regular citizens, instead of
670 being declared in ad hoc ways.
674 The "token kind" is what is returned by the scanner, e.g., PLUS, NUMBER,
675 LPAREN, etc. While backward compatibility is of course ensured, users are
676 nonetheless invited to replace their uses of "enum yytokentype" by
679 This type now also includes tokens that were previously hidden: YYEOF (end
680 of input), YYUNDEF (undefined token), and YYerror (error token). They
681 now have string aliases, internationalized when internationalization is
682 enabled. Therefore, by default, error messages now refer to "end of file"
683 (internationalized) rather than the cryptic "$end", or to "invalid token"
684 rather than "$undefined".
686 Therefore in most cases it is now useless to define the end-of-line token
689 %token T_EOF 0 "end of file"
691 Rather simply use "YYEOF" in your scanner.
695 The "symbol kinds" is what the parser actually uses. (Unless the
696 api.token.raw %define variable is used, the symbol kind of a terminal
697 differs from the corresponding token kind.)
699 They are now exposed as a enum, "yysymbol_kind_t".
701 This allows users to tailor the error messages the way they want, or to
702 process some symbols in a specific way in autocompletion (see the
703 bistromathic example below).
705 *** Modernize display of explanatory statements in diagnostics
707 Since Bison 2.7, output was indented four spaces for explanatory
708 statements. For example:
710 input.y:2.7-13: error: %type redeclaration for exp
711 input.y:1.7-11: previous declaration
713 Since the introduction of caret-diagnostics, it became less clear. This
714 indentation has been removed and submessages are displayed similarly as in
717 input.y:2.7-13: error: %type redeclaration for exp
718 2 | %type <float> exp
720 input.y:1.7-11: note: previous declaration
724 Contributed by Victor Morales Cayuela.
728 The token and symbol kinds are yy::parser::token_kind_type and
729 yy::parser::symbol_kind_type.
731 The symbol_type::kind() member function allows to get the kind of a
732 symbol. This can be used to write unit tests for scanners, e.g.,
734 yy::parser::symbol_type t = make_NUMBER ("123");
735 assert (t.kind () == yy::parser::symbol_kind::S_NUMBER);
736 assert (t.value.as<int> () == 123);
742 In order to avoid ambiguities with "type" as in "typing", we now refer to
743 the "token kind" (e.g., `PLUS`, `NUMBER`, etc.) rather than the "token
744 type". We now also refer to the "symbol type" (e.g., `PLUS`, `expr`,
749 There are now examples/java: a very simple calculator, and a more complete
750 one (push-parser, location tracking, and debug traces).
752 The lexcalc example (a simple example in C based on Flex and Bison) now
753 also demonstrates location tracking.
756 A new C example, bistromathic, is a fully featured interactive calculator
757 using many Bison features: pure interface, push parser, autocompletion
758 based on the current parser state (using yypstate_expected_tokens),
759 location tracking, internationalized custom error messages, lookahead
760 correction, rich debug traces, etc.
762 It shows how to depend on the symbol kinds to tailor autocompletion. For
763 instance it recognizes the symbol kind "VARIABLE" to propose
764 autocompletion on the existing variables, rather than of the word
768 * Noteworthy changes in release 3.5.4 (2020-04-05) [stable]
770 ** WARNING: Future backward-incompatibilities!
772 TL;DR: replace "#define YYERROR_VERBOSE 1" by "%define parse.error verbose".
774 Bison 3.6 will no longer support the YYERROR_VERBOSE macro; the parsers
775 that still depend on it will produce Yacc-like error messages (just
776 "syntax error"). It was superseded by the "%error-verbose" directive in
777 Bison 1.875 (2003-01-01). Bison 2.6 (2012-07-19) clearly announced that
778 support for YYERROR_VERBOSE would be removed. Note that since Bison 3.0
779 (2013-07-25), "%error-verbose" is deprecated in favor of "%define
780 parse.error verbose".
784 Fix portability issues of the package itself on old compilers.
786 Fix api.token.raw support in Java.
789 * Noteworthy changes in release 3.5.3 (2020-03-08) [stable]
793 Error messages could quote lines containing zero-width characters (such as
794 \005) with incorrect styling. Fixes for similar issues with unexpectedly
795 short lines (e.g., the file was changed between parsing and diagnosing).
797 Some unlikely crashes found by fuzzing have been fixed. This is only
798 about bison itself, not the generated parsers.
801 * Noteworthy changes in release 3.5.2 (2020-02-13) [stable]
805 Portability issues and minor cosmetic issues.
807 The lalr1.cc skeleton properly rejects unsupported values for parse.lac
811 * Noteworthy changes in release 3.5.1 (2020-01-19) [stable]
817 Fix compiler warnings.
820 * Noteworthy changes in release 3.5 (2019-12-11) [stable]
822 ** Backward incompatible changes
824 Lone carriage-return characters (aka \r or ^M) in the grammar files are no
825 longer treated as end-of-lines. This changes the diagnostics, and in
826 particular their locations.
828 In C++, line numbers and columns are now represented as 'int' not
829 'unsigned', so that integer overflow on positions is easily checkable via
830 'gcc -fsanitize=undefined' and the like. This affects the API for
831 positions. The default position and location classes now expose
832 'counter_type' (int), used to define line and column numbers.
834 ** Deprecated features
836 The YYPRINT macro, which works only with yacc.c and only for tokens, was
837 obsoleted long ago by %printer, introduced in Bison 1.50 (November 2002).
838 It is deprecated and its support will be removed eventually.
842 *** Lookahead correction in C++
844 Contributed by Adrian Vogelsgesang.
846 The C++ deterministic skeleton (lalr1.cc) now supports LAC, via the
847 %define variable parse.lac.
849 *** Variable api.token.raw: Optimized token numbers (all skeletons)
851 In the generated parsers, tokens have two numbers: the "external" token
852 number as returned by yylex (which starts at 257), and the "internal"
853 symbol number (which starts at 3). Each time yylex is called, a table
854 lookup maps the external token number to the internal symbol number.
856 When the %define variable api.token.raw is set, tokens are assigned their
857 internal number, which saves one table lookup per token, and also saves
858 the generation of the mapping table.
860 The gain is typically moderate, but in extreme cases (very simple user
861 actions), a 10% improvement can be observed.
863 *** Generated parsers use better types for states
865 Stacks now use the best integral type for state numbers, instead of always
866 using 15 bits. As a result "small" parsers now have a smaller memory
867 footprint (they use 8 bits), and there is support for large automata (16
868 bits), and extra large (using int, i.e., typically 31 bits).
870 *** Generated parsers prefer signed integer types
872 Bison skeletons now prefer signed to unsigned integer types when either
873 will do, as the signed types are less error-prone and allow for better
874 checking with 'gcc -fsanitize=undefined'. Also, the types chosen are now
875 portable to unusual machines where char, short and int are all the same
876 width. On non-GNU platforms this may entail including <limits.h> and (if
877 available) <stdint.h> to define integer types and constants.
879 *** A skeleton for the D programming language
881 For the last few releases, Bison has shipped a stealth experimental
882 skeleton: lalr1.d. It was first contributed by Oliver Mangold, based on
883 Paolo Bonzini's lalr1.java, and was cleaned and improved thanks to
886 However, because nobody has committed to improving, testing, and
887 documenting this skeleton, it is not clear that it will be supported in
890 The lalr1.d skeleton *is functional*, and works well, as demonstrated in
891 examples/d/calc.d. Please try it, enjoy it, and... commit to support it.
893 *** Debug traces in Java
895 The Java backend no longer emits code and data for parser tracing if the
896 %define variable parse.trace is not defined.
900 *** New diagnostic: -Wdangling-alias
902 String literals, which allow for better error messages, are (too)
903 liberally accepted by Bison, which might result in silent errors. For
906 %type <exVal> cond "condition"
908 does not define "condition" as a string alias to 'cond' (nonterminal
909 symbols do not have string aliases). It is rather equivalent to
912 %token <exVal> "condition"
914 i.e., it gives the type 'exVal' to the "condition" token, which was
915 clearly not the intention.
917 Also, because string aliases need not be defined, typos such as "baz"
918 instead of "bar" will be not reported.
920 The option `-Wdangling-alias` catches these situations. On
923 %type <ival> foo "foo"
927 bison -Wdangling-alias reports
929 warning: string literal not attached to a symbol
930 | %type <ival> foo "foo"
932 warning: string literal not attached to a symbol
936 The `-Wall` option does not (yet?) include `-Wdangling-alias`.
938 *** Better POSIX Yacc compatibility diagnostics
940 POSIX Yacc restricts %type to nonterminals. This is now diagnosed by
944 %type <ival> TOKEN1 TOKEN2 't'
951 input.y:2.15-20: warning: POSIX yacc reserves %type to nonterminals [-Wyacc]
952 2 | %type <ival> TOKEN1 TOKEN2 't'
954 input.y:2.29-31: warning: POSIX yacc reserves %type to nonterminals [-Wyacc]
955 2 | %type <ival> TOKEN1 TOKEN2 't'
957 input.y:2.22-27: warning: POSIX yacc reserves %type to nonterminals [-Wyacc]
958 2 | %type <ival> TOKEN1 TOKEN2 't'
961 *** Diagnostics with insertion
963 The diagnostics now display the suggestion below the underlined source.
964 Replacement for undeclared symbols are now also suggested.
971 foo.y:2.7-9: error: symbol 'lis' is used, but is not defined as a token and has no rules; did you mean 'list'?
975 foo.y:2.16: warning: empty rule without %empty [-Wempty-rule]
979 foo.y: warning: fix-its can be applied. Rerun with option '--update'. [-Wother]
981 *** Diagnostics about long lines
983 Quoted sources may now be truncated to fit the screen. For instance, on a
984 30-column wide terminal:
991 foo.y:1.34-36: warning: symbol FOO redeclared [-Wother]
994 foo.y:1.8-10: previous declaration
997 foo.y:1.62-64: warning: symbol FOO redeclared [-Wother]
1000 foo.y:1.8-10: previous declaration
1006 *** Debugging glr.c and glr.cc
1008 The glr.c skeleton always had asserts to check its own behavior (not the
1009 user's). These assertions are now under the control of the parse.assert
1010 %define variable (disabled by default).
1014 Several new compiler warnings in the generated output have been avoided.
1015 Some unused features are no longer emitted. Cleaner generated code in
1020 Portability issues in the test suite.
1022 In theory, parsers using %nonassoc could crash when reporting verbose
1023 error messages. This unlikely bug has been fixed.
1025 In Java, %define api.prefix was ignored. It now behaves as expected.
1028 * Noteworthy changes in release 3.4.2 (2019-09-12) [stable]
1032 In some cases, when warnings are disabled, bison could emit tons of white
1033 spaces as diagnostics.
1035 When running out of memory, bison could crash (found by fuzzing).
1037 When defining twice the EOF token, bison would crash.
1039 New warnings from recent compilers have been addressed in the generated
1040 parsers (yacc.c, glr.c, glr.cc).
1042 When lone carriage-return characters appeared in the input file,
1043 diagnostics could hang forever.
1046 * Noteworthy changes in release 3.4.1 (2019-05-22) [stable]
1053 * Noteworthy changes in release 3.4 (2019-05-19) [stable]
1055 ** Deprecated features
1057 The %pure-parser directive is deprecated in favor of '%define api.pure'
1058 since Bison 2.3b (2008-05-27), but no warning was issued; there is one
1059 now. Note that since Bison 2.7 you are strongly encouraged to use
1060 '%define api.pure full' instead of '%define api.pure'.
1064 *** Colored diagnostics
1066 As an experimental feature, diagnostics are now colored, controlled by the
1067 new options --color and --style.
1069 To use them, install the libtextstyle library before configuring Bison.
1070 It is available from
1072 https://alpha.gnu.org/gnu/gettext/
1076 https://alpha.gnu.org/gnu/gettext/libtextstyle-0.8.tar.gz
1078 The option --color supports the following arguments:
1079 - always, yes: Enable colors.
1080 - never, no: Disable colors.
1081 - auto, tty (default): Enable colors if the output device is a tty.
1083 To customize the styles, create a CSS file similar to
1087 .error { font-weight: 800; text-decoration: underline; }
1090 then invoke bison with --style=bison-bw.css, or set the BISON_STYLE
1091 environment variable to "bison-bw.css".
1093 *** Disabling output
1095 When given -fsyntax-only, the diagnostics are reported, but no output is
1098 The name of this option is somewhat misleading as bison does more than
1099 just checking the syntax: every stage is run (including checking for
1100 conflicts for instance), except the generation of the output files.
1102 *** Include the generated header (yacc.c)
1104 Before, when --defines is used, bison generated a header, and pasted an
1105 exact copy of it into the generated parser implementation file. If the
1106 header name is not "y.tab.h", it is now #included instead of being
1109 To use an '#include' even if the header name is "y.tab.h" (which is what
1110 happens with --yacc, or when using the Autotools' ylwrap), define
1111 api.header.include to the exact argument to pass to #include. For
1114 %define api.header.include {"parse.h"}
1118 %define api.header.include {<parser/parse.h>}
1120 *** api.location.type is now supported in C (yacc.c, glr.c)
1122 The %define variable api.location.type defines the name of the type to use
1123 for locations. When defined, Bison no longer defines YYLTYPE.
1125 This can be used in programs with several parsers to factor their
1126 definition of locations: let one of them generate them, and the others
1133 In conformance with the recommendations of the Graphviz team, if %require
1134 "3.4" (or better) is specified, the option --graph generates a *.gv file
1135 by default, instead of *.dot.
1137 *** Diagnostics overhaul
1139 Column numbers were wrong with multibyte characters, which would also
1140 result in skewed diagnostics with carets. Beside, because we were
1141 indenting the quoted source with a single space, lines with tab characters
1142 were incorrectly underlined.
1144 To address these issues, and to be clearer, Bison now issues diagnostics
1145 as GCC9 does. For instance it used to display (there's a tab before the
1148 foo.y:3.37-38: error: $2 of ‘expr’ has no declared type
1149 expr: expr '+' "number" { $$ = $1 + $2; }
1153 foo.y:3.37-38: error: $2 of ‘expr’ has no declared type
1154 3 | expr: expr '+' "number" { $$ = $1 + $2; }
1157 Other constructs now also have better locations, resulting in more precise
1160 *** Fix-it hints for %empty
1162 Running Bison with -Wempty-rules and --update will remove incorrect %empty
1163 annotations, and add the missing ones.
1165 *** Generated reports
1167 The format of the reports (parse.output) was improved for readability.
1169 *** Better support for --no-line.
1171 When --no-line is used, the generated files are now cleaner: no lines are
1172 generated instead of empty lines. Together with using api.header.include,
1173 that should help people saving the generated files into version control
1174 systems get smaller diffs.
1178 A new example in C shows an simple infix calculator with a hand-written
1179 scanner (examples/c/calc).
1181 A new example in C shows a reentrant parser (capable of recursive calls)
1182 built with Flex and Bison (examples/c/reccalc).
1184 There is a new section about the history of Yaccs and Bison.
1188 A few obscure bugs were fixed, including the second oldest (known) bug in
1189 Bison: it was there when Bison was entered in the RCS version control
1190 system, in December 1987. See the NEWS of Bison 3.3 for the previous
1194 * Noteworthy changes in release 3.3.2 (2019-02-03) [stable]
1198 Bison 3.3 failed to generate parsers for grammars with unused nonterminal
1202 * Noteworthy changes in release 3.3.1 (2019-01-27) [stable]
1206 The option -y/--yacc used to imply -Werror=yacc, which turns uses of Bison
1207 extensions into errors. It now makes them simple warnings (-Wyacc).
1210 * Noteworthy changes in release 3.3 (2019-01-26) [stable]
1212 A new mailing list was created, Bison Announce. It is low traffic, and is
1213 only about announcing new releases and important messages (e.g., polls
1214 about major decisions to make).
1216 https://lists.gnu.org/mailman/listinfo/bison-announce
1218 ** Backward incompatible changes
1220 Support for DJGPP, which has been unmaintained and untested for years, is
1223 ** Deprecated features
1225 A new feature, --update (see below) helps adjusting existing grammars to
1228 *** Deprecated directives
1230 The %error-verbose directive is deprecated in favor of '%define
1231 parse.error verbose' since Bison 3.0, but no warning was issued.
1233 The '%name-prefix "xx"' directive is deprecated in favor of '%define
1234 api.prefix {xx}' since Bison 3.0, but no warning was issued. These
1235 directives are slightly different, you might need to adjust your code.
1236 %name-prefix renames only symbols with external linkage, while api.prefix
1237 also renames types and macros, including YYDEBUG, YYTOKENTYPE,
1238 yytokentype, YYSTYPE, YYLTYPE, etc.
1240 Users of Flex that move from '%name-prefix "xx"' to '%define api.prefix
1241 {xx}' will typically have to update YY_DECL from
1243 #define YY_DECL int xxlex (YYSTYPE *yylval, YYLTYPE *yylloc)
1247 #define YY_DECL int xxlex (XXSTYPE *yylval, XXLTYPE *yylloc)
1249 *** Deprecated %define variable names
1251 The following variables, mostly related to parsers in Java, have been
1252 renamed for consistency. Backward compatibility is ensured, but upgrading
1255 abstract -> api.parser.abstract
1256 annotations -> api.parser.annotations
1257 extends -> api.parser.extends
1258 final -> api.parser.final
1259 implements -> api.parser.implements
1260 parser_class_name -> api.parser.class
1261 public -> api.parser.public
1262 strictfp -> api.parser.strictfp
1266 *** Generation of fix-its for IDEs/Editors
1268 When given the new option -ffixit (aka -fdiagnostics-parseable-fixits),
1269 bison now generates machine readable editing instructions to fix some
1270 issues. Currently, this is mostly limited to updating deprecated
1271 directives and removing duplicates. For instance:
1275 %define parser_class_name "Parser"
1276 %define api.parser.class "Parser"
1280 See the "fix-it:" lines below:
1282 $ bison -ffixit foo.y
1283 foo.y:1.1-14: warning: deprecated directive, use '%define parse.error verbose' [-Wdeprecated]
1286 fix-it:"foo.y":{1:1-1:15}:"%define parse.error verbose"
1287 foo.y:2.1-34: warning: deprecated directive, use '%define api.parser.class {Parser}' [-Wdeprecated]
1288 %define parser_class_name "Parser"
1289 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1290 fix-it:"foo.y":{2:1-2:35}:"%define api.parser.class {Parser}"
1291 foo.y:3.1-33: error: %define variable 'api.parser.class' redefined
1292 %define api.parser.class "Parser"
1293 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1294 foo.y:2.1-34: previous definition
1295 %define parser_class_name "Parser"
1296 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1297 fix-it:"foo.y":{3:1-3:34}:""
1298 foo.y: warning: fix-its can be applied. Rerun with option '--update'. [-Wother]
1300 This uses the same output format as GCC and Clang.
1302 *** Updating grammar files
1304 Fixes can be applied on the fly. The previous example ends with the
1305 suggestion to re-run bison with the option -u/--update, which results in a
1306 cleaner grammar file.
1308 $ bison --update foo.y
1310 bison: file 'foo.y' was updated (backup: 'foo.y~')
1313 %define parse.error verbose
1314 %define api.parser.class {Parser}
1318 *** Bison is now relocatable
1320 If you pass '--enable-relocatable' to 'configure', Bison is relocatable.
1322 A relocatable program can be moved or copied to a different location on
1323 the file system. It can also be used through mount points for network
1324 sharing. It is possible to make symbolic links to the installed and moved
1325 programs, and invoke them through the symbolic link.
1327 *** %expect and %expect-rr modifiers on individual rules
1329 One can now document (and check) which rules participate in shift/reduce
1330 and reduce/reduce conflicts. This is particularly important GLR parsers,
1331 where conflicts are a normal occurrence. For example,
1347 | argument_list ',' expression
1352 Looking at the output from -v, one can see that the shift/reduce conflict
1353 here is due to the fact that the parser does not know whether to reduce
1354 arguments to argument_list until it sees the token _after_ the following
1355 ','. By marking the rule with %expect 1 (because there is a conflict in
1356 one state), we document the source of the 1 overall shift/reduce conflict.
1358 In GLR parsers, we can use %expect-rr in a rule for reduce/reduce
1359 conflicts. In this case, we mark each of the conflicting rules. For
1368 target_list '=' expr ';'
1374 | target ',' target_list
1383 | expr ',' expr_list
1391 In a statement such as
1395 the parser must reduce x to a target or an expr, but does not know which
1396 until it sees the '='. So we notate the two possible reductions to
1397 indicate that each conflicts in one rule.
1399 This feature needs user feedback, and might evolve in the future.
1401 *** C++: Actual token constructors
1403 When variants and token constructors are enabled, in addition to the
1404 type-safe named token constructors (make_ID, make_INT, etc.), we now
1405 generate genuine constructors for symbol_type.
1407 For instance with these declarations
1413 you may use these constructors:
1415 symbol_type (int token, const std::string&);
1416 symbol_type (int token, const int&);
1417 symbol_type (int token);
1419 Correct matching between token types and value types is checked via
1420 'assert'; for instance, 'symbol_type (ID, 42)' would abort. Named
1421 constructors are preferable, as they offer better type safety (for
1422 instance 'make_ID (42)' would not even compile), but symbol_type
1423 constructors may help when token types are discovered at run-time, e.g.,
1426 if (auto i = lookup_keyword (yytext))
1427 return yy::parser::symbol_type (i);
1429 return yy::parser::make_ID (yytext);
1432 *** C++: Variadic emplace
1434 If your application requires C++11 and you don't use symbol constructors,
1435 you may now use a variadic emplace for semantic values:
1437 %define api.value.type variant
1438 %token <std::pair<int, int>> PAIR
1442 int yylex (parser::semantic_type *lvalp)
1444 lvalp->emplace <std::pair<int, int>> (1, 2);
1445 return parser::token::PAIR;
1448 *** C++: Syntax error exceptions in GLR
1450 The glr.cc skeleton now supports syntax_error exceptions thrown from user
1451 actions, or from the scanner.
1453 *** More POSIX Yacc compatibility warnings
1455 More Bison specific directives are now reported with -y or -Wyacc. This
1456 change was ready since the release of Bison 3.0 in September 2015. It was
1457 delayed because Autoconf used to define YACC as `bison -y`, which resulted
1458 in numerous warnings for Bison users that use the GNU Build System.
1460 If you still experience that problem, either redefine YACC as `bison -o
1461 y.tab.c`, or pass -Wno-yacc to Bison.
1463 *** The tables yyrhs and yyphrs are back
1465 Because no Bison skeleton uses them, these tables were removed (no longer
1466 passed to the skeletons, not even computed) in 2008. However, some users
1467 have expressed interest in being able to use them in their own skeletons.
1471 *** Incorrect number of reduce/reduce conflicts
1473 On a grammar such as
1475 exp: "num" | "num" | "num"
1477 bison used to report a single RR conflict, instead of two. This is now
1478 fixed. This was the oldest (known) bug in Bison: it was there when Bison
1479 was entered in the RCS version control system, in December 1987.
1481 Some grammar files might have to adjust their %expect-rr.
1483 *** Parser directives that were not careful enough
1485 Passing invalid arguments to %nterm, for instance character literals, used
1486 to result in unclear error messages.
1490 The examples/ directory (installed in .../share/doc/bison/examples) has
1491 been restructured per language for clarity. The examples come with a
1492 README and a Makefile. Not only can they be used to toy with Bison, they
1493 can also be starting points for your own grammars.
1495 There is now a Java example, and a simple example in C based on Flex and
1496 Bison (examples/c/lexcalc/).
1502 They now use noexcept and constexpr. Please, report missing annotations.
1504 *** Symbol Declarations
1506 The syntax of the variation directives to declare symbols was overhauled
1507 for more consistency, and also better POSIX Yacc compliance (which, for
1508 instance, allows "%type" without actually providing a type). The %nterm
1509 directive, supported by Bison since its inception, is now documented and
1510 officially supported.
1512 The syntax is now as follows:
1514 %token TAG? ( ID NUMBER? STRING? )+ ( TAG ( ID NUMBER? STRING? )+ )*
1515 %left TAG? ( ID NUMBER? )+ ( TAG ( ID NUMBER? )+ )*
1516 %type TAG? ( ID | CHAR | STRING )+ ( TAG ( ID | CHAR | STRING )+ )*
1517 %nterm TAG? ID+ ( TAG ID+ )*
1519 where TAG denotes a type tag such as ‘<ival>’, ID denotes an identifier
1520 such as ‘NUM’, NUMBER a decimal or hexadecimal integer such as ‘300’ or
1521 ‘0x12d’, CHAR a character literal such as ‘'+'’, and STRING a string
1522 literal such as ‘"number"’. The post-fix quantifiers are ‘?’ (zero or
1523 one), ‘*’ (zero or more) and ‘+’ (one or more).
1526 * Noteworthy changes in release 3.2.4 (2018-12-24) [stable]
1530 Fix the move constructor of symbol_type.
1532 Always provide a copy constructor for symbol_type, even in modern C++.
1535 * Noteworthy changes in release 3.2.3 (2018-12-18) [stable]
1539 Properly support token constructors in C++ with types that include commas
1540 (e.g., std::pair<int, int>). A regression introduced in Bison 3.2.
1543 * Noteworthy changes in release 3.2.2 (2018-11-21) [stable]
1547 C++ portability issues.
1550 * Noteworthy changes in release 3.2.1 (2018-11-09) [stable]
1554 Several portability issues have been fixed in the build system, in the
1555 test suite, and in the generated parsers in C++.
1558 * Noteworthy changes in release 3.2 (2018-10-29) [stable]
1560 ** Backward incompatible changes
1562 Support for DJGPP, which has been unmaintained and untested for years, is
1563 obsolete. Unless there is activity to revive it, it will be removed.
1567 %printers should use yyo rather than yyoutput to denote the output stream.
1569 Variant-based symbols in C++ should use emplace() rather than build().
1571 In C++ parsers, parser::operator() is now a synonym for the parser::parse.
1575 A new section, "A Simple C++ Example", is a tutorial for parsers in C++.
1577 A comment in the generated code now emphasizes that users should not
1578 depend upon non-documented implementation details, such as macros starting
1583 *** C++: Support for move semantics (lalr1.cc)
1585 The lalr1.cc skeleton now fully supports C++ move semantics, while
1586 maintaining compatibility with C++98. You may now store move-only types
1587 when using Bison's variants. For instance:
1594 %skeleton "lalr1.cc"
1595 %define api.value.type variant
1599 %token <int> INT "int";
1600 %type <std::unique_ptr<int>> int;
1601 %type <std::vector<std::unique_ptr<int>>> list;
1605 | list int { $$ = std::move($1); $$.emplace_back(std::move($2)); }
1607 int: "int" { $$ = std::make_unique<int>($1); }
1609 *** C++: Implicit move of right-hand side values (lalr1.cc)
1611 In modern C++ (C++11 and later), you should always use 'std::move' with
1612 the values of the right-hand side symbols ($1, $2, etc.), as they will be
1613 popped from the stack anyway. Using 'std::move' is mandatory for
1614 move-only types such as unique_ptr, and it provides a significant speedup
1615 for large types such as std::string, or std::vector, etc.
1617 If '%define api.value.automove' is set, every occurrence '$n' is replaced
1618 by 'std::move ($n)'. The second rule in the previous grammar can be
1621 list: list int { $$ = $1; $$.emplace_back($2); }
1623 With automove enabled, the semantic values are no longer lvalues, so do
1624 not use the swap idiom:
1626 list: list int { std::swap($$, $1); $$.emplace_back($2); }
1628 This idiom is anyway obsolete: it is preferable to move than to swap.
1630 A warning is issued when automove is enabled, and a value is used several
1633 input.yy:16.31-32: warning: multiple occurrences of $2 with api.value.automove enabled [-Wother]
1634 exp: "twice" exp { $$ = $2 + $2; }
1637 Enabling api.value.automove does not require support for modern C++. The
1638 generated code is valid C++98/03, but will use copies instead of moves.
1640 The new examples/c++/variant-11.yy shows these features in action.
1642 *** C++: The implicit default semantic action is always run
1644 When variants are enabled, the default action was not run, so
1652 It now behaves like in all the other cases, as
1654 exp: "number" { $$ = $1; }
1656 possibly using std::move if automove is enabled.
1658 We do not expect backward compatibility issues. However, beware of
1659 forward compatibility issues: if you rely on default actions with
1660 variants, be sure to '%require "3.2"' to avoid older versions of Bison to
1661 generate incorrect parsers.
1663 *** C++: Renaming location.hh
1665 When both %defines and %locations are enabled, Bison generates a
1666 location.hh file. If you don't use locations outside of the parser, you
1667 may avoid its creation with:
1669 %define api.location.file none
1671 However this file is useful if, for instance, your parser builds an AST
1672 decorated with locations: you may use Bison's location independently of
1673 Bison's parser. You can now give it another name, for instance:
1675 %define api.location.file "my-location.hh"
1677 This name can have directory components, and even be absolute. The name
1678 under which the location file is included is controlled by
1679 api.location.include.
1681 This way it is possible to have several parsers share the same location
1684 For instance, in src/foo/parser.hh, generate the include/ast/loc.hh file:
1687 %define api.namespace {foo}
1688 %define api.location.file "include/ast/loc.hh"
1689 %define api.location.include {<ast/loc.hh>}
1691 and use it in src/bar/parser.hh:
1694 %define api.namespace {bar}
1695 %code requires {#include <ast/loc.hh>}
1696 %define api.location.type {bar::location}
1698 Absolute file names are supported, so in your Makefile, passing the flag
1699 -Dapi.location.file='"$(top_srcdir)/include/ast/location.hh"' to bison is
1702 *** C++: stack.hh and position.hh are deprecated
1704 When asked to generate a header file (%defines), the lalr1.cc skeleton
1705 generates a stack.hh file. This file had no interest for users; it is now
1706 made useless: its content is included in the parser definition. It is
1707 still generated for backward compatibility.
1709 When in addition to %defines, location support is requested (%locations),
1710 the file position.hh is also generated. It is now also useless: its
1711 content is now included in location.hh.
1713 These files are no longer generated when your grammar file requires at
1714 least Bison 3.2 (%require "3.2").
1718 Portability issues on MinGW and VS2015.
1720 Portability issues in the test suite.
1722 Portability/warning issues with Flex.
1725 * Noteworthy changes in release 3.1 (2018-08-27) [stable]
1727 ** Backward incompatible changes
1729 Compiling Bison now requires a C99 compiler---as announced during the
1730 release of Bison 3.0, five years ago. Generated parsers do not require a
1733 Support for DJGPP, which has been unmaintained and untested for years, is
1734 obsolete. Unless there is activity to revive it, the next release of Bison
1735 will have it removed.
1739 *** Typed midrule actions
1741 Because their type is unknown to Bison, the values of midrule actions are
1742 not treated like the others: they don't have %printer and %destructor
1743 support. It also prevents C++ (Bison) variants to handle them properly.
1745 Typed midrule actions address these issues. Instead of:
1747 exp: { $<ival>$ = 1; } { $<ival>$ = 2; } { $$ = $<ival>1 + $<ival>2; }
1751 exp: <ival>{ $$ = 1; } <ival>{ $$ = 2; } { $$ = $1 + $2; }
1753 *** Reports include the type of the symbols
1755 The sections about terminal and nonterminal symbols of the '*.output' file
1756 now specify their declared type. For instance, for:
1760 the report now shows '<ival>':
1762 Terminals, with rules where they appear
1766 *** Diagnostics about useless rules
1768 In the following grammar, the 'exp' nonterminal is trivially useless. So,
1769 of course, its rules are useless too.
1773 exp: exp '+' exp | exp '-' exp | '(' exp ')'
1775 Previously all the useless rules were reported, including those whose
1776 left-hand side is the 'exp' nonterminal:
1778 warning: 1 nonterminal useless in grammar [-Wother]
1779 warning: 4 rules useless in grammar [-Wother]
1780 2.14-16: warning: nonterminal useless in grammar: exp [-Wother]
1783 2.14-16: warning: rule useless in grammar [-Wother]
1786 3.6-16: warning: rule useless in grammar [-Wother]
1787 exp: exp '+' exp | exp '-' exp | '(' exp ')'
1789 3.20-30: warning: rule useless in grammar [-Wother]
1790 exp: exp '+' exp | exp '-' exp | '(' exp ')'
1792 3.34-44: warning: rule useless in grammar [-Wother]
1793 exp: exp '+' exp | exp '-' exp | '(' exp ')'
1796 Now, rules whose left-hand side symbol is useless are no longer reported
1797 as useless. The locations of the errors have also been adjusted to point
1798 to the first use of the nonterminal as a left-hand side of a rule:
1800 warning: 1 nonterminal useless in grammar [-Wother]
1801 warning: 4 rules useless in grammar [-Wother]
1802 3.1-3: warning: nonterminal useless in grammar: exp [-Wother]
1803 exp: exp '+' exp | exp '-' exp | '(' exp ')'
1805 2.14-16: warning: rule useless in grammar [-Wother]
1809 *** C++: Generated parsers can be compiled with -fno-exceptions (lalr1.cc)
1811 When compiled with exceptions disabled, the generated parsers no longer
1812 uses try/catch clauses.
1814 Currently only GCC and Clang are supported.
1818 *** A demonstration of variants
1820 A new example was added (installed in .../share/doc/bison/examples),
1821 'variant.yy', which shows how to use (Bison) variants in C++.
1823 The other examples were made nicer to read.
1825 *** Some features are no longer 'experimental'
1827 The following features, mature enough, are no longer flagged as
1828 experimental in the documentation: push parsers, default %printer and
1829 %destructor (typed: <*> and untyped: <>), %define api.value.type union and
1830 variant, Java parsers, XML output, LR family (lr, ielr, lalr), and
1831 semantic predicates (%?).
1835 *** GLR: Predicates support broken by #line directives
1837 Predicates (%?) in GLR such as
1840 %? {new_syntax} 'w' id new_args
1841 | %?{!new_syntax} 'w' id old_args
1843 were issued with #lines in the middle of C code.
1845 *** Printer and destructor with broken #line directives
1847 The #line directives were not properly escaped when emitting the code for
1848 %printer/%destructor, which resulted in compiler errors if there are
1849 backslashes or double-quotes in the grammar file name.
1851 *** Portability on ICC
1853 The Intel compiler claims compatibility with GCC, yet rejects its _Pragma.
1854 Generated parsers now work around this.
1858 There were several small fixes in the test suite and in the build system,
1859 many warnings in bison and in the generated parsers were eliminated. The
1860 documentation also received its share of minor improvements.
1862 Useless code was removed from C++ parsers, and some of the generated
1863 constructors are more 'natural'.
1866 * Noteworthy changes in release 3.0.5 (2018-05-27) [stable]
1870 *** C++: Fix support of 'syntax_error'
1872 One incorrect 'inline' resulted in linking errors about the constructor of
1873 the syntax_error exception.
1875 *** C++: Fix warnings
1877 GCC 7.3 (with -O1 or -O2 but not -O0 or -O3) issued null-dereference
1878 warnings about yyformat being possibly null. It also warned about the
1879 deprecated implicit definition of copy constructors when there's a
1880 user-defined (copy) assignment operator.
1882 *** Location of errors
1884 In C++ parsers, out-of-bounds errors can happen when a rule with an empty
1885 ride-hand side raises a syntax error. The behavior of the default parser
1886 (yacc.c) in such a condition was undefined.
1888 Now all the parsers match the behavior of glr.c: @$ is used as the
1889 location of the error. This handles gracefully rules with and without
1892 *** Portability fixes in the test suite
1894 On some platforms, some Java and/or C++ tests were failing.
1897 * Noteworthy changes in release 3.0.4 (2015-01-23) [stable]
1901 *** C++ with Variants (lalr1.cc)
1903 Fix a compiler warning when no %destructor use $$.
1907 Several portability issues in tests were fixed.
1910 * Noteworthy changes in release 3.0.3 (2015-01-15) [stable]
1914 *** C++ with Variants (lalr1.cc)
1916 Problems with %destructor and '%define parse.assert' have been fixed.
1918 *** Named %union support (yacc.c, glr.c)
1920 Bison 3.0 introduced a regression on named %union such as
1922 %union foo { int ival; };
1924 The possibility to use a name was introduced "for Yacc compatibility".
1925 It is however not required by POSIX Yacc, and its usefulness is not clear.
1927 *** %define api.value.type union with %defines (yacc.c, glr.c)
1929 The C parsers were broken when %defines was used together with "%define
1930 api.value.type union".
1932 *** Redeclarations are reported in proper order
1940 bison used to report:
1942 foo.yy:2.10-11: error: %printer redeclaration for FOO
1945 foo.yy:3.10-11: previous declaration
1949 Now, the "previous" declaration is always the first one.
1954 Bison now installs various files in its docdir (which defaults to
1955 '/usr/local/share/doc/bison'), including the three fully blown examples
1956 extracted from the documentation:
1959 Reverse Polish Calculator, a simple introductory example.
1961 Multi-function Calc, a calculator with memory and functions and located
1964 a calculator in C++ using variant support and token constructors.
1967 * Noteworthy changes in release 3.0.2 (2013-12-05) [stable]
1971 *** Generated source files when errors are reported
1973 When warnings are issued and -Werror is set, bison would still generate
1974 the source files (*.c, *.h...). As a consequence, some runs of "make"
1975 could fail the first time, but not the second (as the files were generated
1978 This is fixed: bison no longer generates this source files, but, of
1979 course, still produces the various reports (*.output, *.xml, etc.).
1981 *** %empty is used in reports
1983 Empty right-hand sides are denoted by '%empty' in all the reports (text,
1984 dot, XML and formats derived from it).
1986 *** YYERROR and variants
1988 When C++ variant support is enabled, an error triggered via YYERROR, but
1989 not caught via error recovery, resulted in a double deletion.
1992 * Noteworthy changes in release 3.0.1 (2013-11-12) [stable]
1996 *** Errors in caret diagnostics
1998 On some platforms, some errors could result in endless diagnostics.
2000 *** Fixes of the -Werror option
2002 Options such as "-Werror -Wno-error=foo" were still turning "foo"
2003 diagnostics into errors instead of warnings. This is fixed.
2005 Actually, for consistency with GCC, "-Wno-error=foo -Werror" now also
2006 leaves "foo" diagnostics as warnings. Similarly, with "-Werror=foo
2007 -Wno-error", "foo" diagnostics are now errors.
2011 As demonstrated in the documentation, one can now leave spaces between
2016 The yacc.1 man page is no longer installed if --disable-yacc was
2019 *** Fixes in the test suite
2021 Bugs and portability issues.
2024 * Noteworthy changes in release 3.0 (2013-07-25) [stable]
2026 ** WARNING: Future backward-incompatibilities!
2028 Like other GNU packages, Bison will start using some of the C99 features
2029 for its own code, especially the definition of variables after statements.
2030 The generated C parsers still aim at C90.
2032 ** Backward incompatible changes
2034 *** Obsolete features
2036 Support for YYFAIL is removed (deprecated in Bison 2.4.2): use YYERROR.
2038 Support for yystype and yyltype is removed (deprecated in Bison 1.875):
2039 use YYSTYPE and YYLTYPE.
2041 Support for YYLEX_PARAM and YYPARSE_PARAM is removed (deprecated in Bison
2042 1.875): use %lex-param, %parse-param, or %param.
2044 Missing semicolons at the end of actions are no longer added (as announced
2045 in the release 2.5).
2047 *** Use of YACC='bison -y'
2049 TL;DR: With Autoconf <= 2.69, pass -Wno-yacc to (AM_)YFLAGS if you use
2052 Traditional Yacc generates 'y.tab.c' whatever the name of the input file.
2053 Therefore Makefiles written for Yacc expect 'y.tab.c' (and possibly
2054 'y.tab.h' and 'y.output') to be generated from 'foo.y'.
2056 To this end, for ages, AC_PROG_YACC, Autoconf's macro to look for an
2057 implementation of Yacc, was using Bison as 'bison -y'. While it does
2058 ensure compatible output file names, it also enables warnings for
2059 incompatibilities with POSIX Yacc. In other words, 'bison -y' triggers
2060 warnings for Bison extensions.
2062 Autoconf 2.70+ fixes this incompatibility by using YACC='bison -o y.tab.c'
2063 (which also generates 'y.tab.h' and 'y.output' when needed).
2064 Alternatively, disable Yacc warnings by passing '-Wno-yacc' to your Yacc
2065 flags (YFLAGS, or AM_YFLAGS with Automake).
2069 *** The epilogue is no longer affected by internal #defines (glr.c)
2071 The glr.c skeleton uses defines such as #define yylval (yystackp->yyval) in
2072 generated code. These weren't properly undefined before the inclusion of
2073 the user epilogue, so functions such as the following were butchered by the
2074 preprocessor expansion:
2076 int yylex (YYSTYPE *yylval);
2078 This is fixed: yylval, yynerrs, yychar, and yylloc are now valid
2079 identifiers for user-provided variables.
2081 *** stdio.h is no longer needed when locations are enabled (yacc.c)
2083 Changes in Bison 2.7 introduced a dependency on FILE and fprintf when
2084 locations are enabled. This is fixed.
2086 *** Warnings about useless %pure-parser/%define api.pure are restored
2088 ** Diagnostics reported by Bison
2090 Most of these features were contributed by Théophile Ranquet and Victor
2095 Version 2.7 introduced caret errors, for a prettier output. These are now
2096 activated by default. The old format can still be used by invoking Bison
2097 with -fno-caret (or -fnone).
2099 Some error messages that reproduced excerpts of the grammar are now using
2100 the caret information only. For instance on:
2107 in.y: warning: 1 reduce/reduce conflict [-Wconflicts-rr]
2108 in.y:2.12-14: warning: rule useless in parser due to conflicts: exp: 'a' [-Wother]
2112 in.y: warning: 1 reduce/reduce conflict [-Wconflicts-rr]
2113 in.y:2.12-14: warning: rule useless in parser due to conflicts [-Wother]
2117 and "bison -fno-caret" reports:
2119 in.y: warning: 1 reduce/reduce conflict [-Wconflicts-rr]
2120 in.y:2.12-14: warning: rule useless in parser due to conflicts [-Wother]
2122 *** Enhancements of the -Werror option
2124 The -Werror=CATEGORY option is now recognized, and will treat specified
2125 warnings as errors. The warnings need not have been explicitly activated
2126 using the -W option, this is similar to what GCC 4.7 does.
2128 For example, given the following command line, Bison will treat both
2129 warnings related to POSIX Yacc incompatibilities and S/R conflicts as
2130 errors (and only those):
2132 $ bison -Werror=yacc,error=conflicts-sr input.y
2134 If no categories are specified, -Werror will make all active warnings into
2135 errors. For example, the following line does the same the previous example:
2137 $ bison -Werror -Wnone -Wyacc -Wconflicts-sr input.y
2139 (By default -Wconflicts-sr,conflicts-rr,deprecated,other is enabled.)
2141 Note that the categories in this -Werror option may not be prefixed with
2142 "no-". However, -Wno-error[=CATEGORY] is valid.
2144 Note that -y enables -Werror=yacc. Therefore it is now possible to require
2145 Yacc-like behavior (e.g., always generate y.tab.c), but to report
2146 incompatibilities as warnings: "-y -Wno-error=yacc".
2148 *** The display of warnings is now richer
2150 The option that controls a given warning is now displayed:
2152 foo.y:4.6: warning: type clash on default action: <foo> != <bar> [-Wother]
2154 In the case of warnings treated as errors, the prefix is changed from
2155 "warning: " to "error: ", and the suffix is displayed, in a manner similar
2156 to GCC, as [-Werror=CATEGORY].
2158 For instance, where the previous version of Bison would report (and exit
2161 bison: warnings being treated as errors
2162 input.y:1.1: warning: stray ',' treated as white space
2166 input.y:1.1: error: stray ',' treated as white space [-Werror=other]
2168 *** Deprecated constructs
2170 The new 'deprecated' warning category flags obsolete constructs whose
2171 support will be discontinued. It is enabled by default. These warnings
2172 used to be reported as 'other' warnings.
2174 *** Useless semantic types
2176 Bison now warns about useless (uninhabited) semantic types. Since
2177 semantic types are not declared to Bison (they are defined in the opaque
2178 %union structure), it is %printer/%destructor directives about useless
2179 types that trigger the warning:
2183 %printer {} <type1> <type3>
2184 %destructor {} <type2> <type4>
2186 nterm: term { $$ = $1; };
2188 3.28-34: warning: type <type3> is used, but is not associated to any symbol
2189 4.28-34: warning: type <type4> is used, but is not associated to any symbol
2191 *** Undefined but unused symbols
2193 Bison used to raise an error for undefined symbols that are not used in
2194 the grammar. This is now only a warning.
2197 %destructor {} symbol2
2198 %type <type> symbol3
2202 *** Useless destructors or printers
2204 Bison now warns about useless destructors or printers. In the following
2205 example, the printer for <type1>, and the destructor for <type2> are
2206 useless: all symbols of <type1> (token1) already have a printer, and all
2207 symbols of type <type2> (token2) already have a destructor.
2209 %token <type1> token1
2213 %printer {} token1 <type1> <type3>
2214 %destructor {} token2 <type2> <type4>
2218 The warnings and error messages about shift/reduce and reduce/reduce
2219 conflicts have been normalized. For instance on the following foo.y file:
2223 exp: exp '+' exp | '0' | '0';
2225 compare the previous version of bison:
2228 foo.y: conflicts: 1 shift/reduce, 2 reduce/reduce
2229 $ bison -Werror foo.y
2230 bison: warnings being treated as errors
2231 foo.y: conflicts: 1 shift/reduce, 2 reduce/reduce
2233 with the new behavior:
2236 foo.y: warning: 1 shift/reduce conflict [-Wconflicts-sr]
2237 foo.y: warning: 2 reduce/reduce conflicts [-Wconflicts-rr]
2238 $ bison -Werror foo.y
2239 foo.y: error: 1 shift/reduce conflict [-Werror=conflicts-sr]
2240 foo.y: error: 2 reduce/reduce conflicts [-Werror=conflicts-rr]
2242 When %expect or %expect-rr is used, such as with bar.y:
2247 exp: exp '+' exp | '0' | '0';
2252 bar.y: conflicts: 1 shift/reduce, 2 reduce/reduce
2253 bar.y: expected 0 shift/reduce conflicts
2254 bar.y: expected 0 reduce/reduce conflicts
2259 bar.y: error: shift/reduce conflicts: 1 found, 0 expected
2260 bar.y: error: reduce/reduce conflicts: 2 found, 0 expected
2262 ** Incompatibilities with POSIX Yacc
2264 The 'yacc' category is no longer part of '-Wall', enable it explicitly
2267 ** Additional yylex/yyparse arguments
2269 The new directive %param declares additional arguments to both yylex and
2270 yyparse. The %lex-param, %parse-param, and %param directives support one
2271 or more arguments. Instead of
2273 %lex-param {arg1_type *arg1}
2274 %lex-param {arg2_type *arg2}
2275 %parse-param {arg1_type *arg1}
2276 %parse-param {arg2_type *arg2}
2280 %param {arg1_type *arg1} {arg2_type *arg2}
2282 ** Types of values for %define variables
2284 Bison used to make no difference between '%define foo bar' and '%define
2285 foo "bar"'. The former is now called a 'keyword value', and the latter a
2286 'string value'. A third kind was added: 'code values', such as '%define
2289 Keyword variables are used for fixed value sets, e.g.,
2291 %define lr.type lalr
2293 Code variables are used for value in the target language, e.g.,
2295 %define api.value.type {struct semantic_type}
2297 String variables are used remaining cases, e.g. file names.
2299 ** Variable api.token.prefix
2301 The variable api.token.prefix changes the way tokens are identified in
2302 the generated files. This is especially useful to avoid collisions
2303 with identifiers in the target language. For instance
2305 %token FILE for ERROR
2306 %define api.token.prefix {TOK_}
2308 start: FILE for ERROR;
2310 will generate the definition of the symbols TOK_FILE, TOK_for, and
2311 TOK_ERROR in the generated sources. In particular, the scanner must
2312 use these prefixed token names, although the grammar itself still
2313 uses the short names (as in the sample rule given above).
2315 ** Variable api.value.type
2317 This new %define variable supersedes the #define macro YYSTYPE. The use
2318 of YYSTYPE is discouraged. In particular, #defining YYSTYPE *and* either
2319 using %union or %defining api.value.type results in undefined behavior.
2321 Either define api.value.type, or use "%union":
2328 %token <ival> INT "integer"
2329 %token <sval> STRING "string"
2330 %printer { fprintf (yyo, "%d", $$); } <ival>
2331 %destructor { free ($$); } <sval>
2334 yylval.ival = 42; return INT;
2335 yylval.sval = "42"; return STRING;
2337 The %define variable api.value.type supports both keyword and code values.
2339 The keyword value 'union' means that the user provides genuine types, not
2340 union member names such as "ival" and "sval" above (WARNING: will fail if
2341 -y/--yacc/%yacc is enabled).
2343 %define api.value.type union
2344 %token <int> INT "integer"
2345 %token <char *> STRING "string"
2346 %printer { fprintf (yyo, "%d", $$); } <int>
2347 %destructor { free ($$); } <char *>
2350 yylval.INT = 42; return INT;
2351 yylval.STRING = "42"; return STRING;
2353 The keyword value variant is somewhat equivalent, but for C++ special
2354 provision is made to allow classes to be used (more about this below).
2356 %define api.value.type variant
2357 %token <int> INT "integer"
2358 %token <std::string> STRING "string"
2360 Code values (in braces) denote user defined types. This is where YYSTYPE
2378 %define api.value.type {struct my_value}
2379 %token <u.ival> INT "integer"
2380 %token <u.sval> STRING "string"
2381 %printer { fprintf (yyo, "%d", $$); } <u.ival>
2382 %destructor { free ($$); } <u.sval>
2385 yylval.u.ival = 42; return INT;
2386 yylval.u.sval = "42"; return STRING;
2388 ** Variable parse.error
2390 This variable controls the verbosity of error messages. The use of the
2391 %error-verbose directive is deprecated in favor of "%define parse.error
2394 ** Deprecated %define variable names
2396 The following variables have been renamed for consistency. Backward
2397 compatibility is ensured, but upgrading is recommended.
2399 lr.default-reductions -> lr.default-reduction
2400 lr.keep-unreachable-states -> lr.keep-unreachable-state
2401 namespace -> api.namespace
2402 stype -> api.value.type
2404 ** Semantic predicates
2406 Contributed by Paul Hilfinger.
2408 The new, experimental, semantic-predicate feature allows actions of the
2409 form "%?{ BOOLEAN-EXPRESSION }", which cause syntax errors (as for
2410 YYERROR) if the expression evaluates to 0, and are evaluated immediately
2411 in GLR parsers, rather than being deferred. The result is that they allow
2412 the programmer to prune possible parses based on the values of run-time
2415 ** The directive %expect-rr is now an error in non GLR mode
2417 It used to be an error only if used in non GLR mode, _and_ if there are
2418 reduce/reduce conflicts.
2420 ** Tokens are numbered in their order of appearance
2422 Contributed by Valentin Tolmer.
2424 With '%token A B', A had a number less than the one of B. However,
2425 precedence declarations used to generate a reversed order. This is now
2426 fixed, and introducing tokens with any of %token, %left, %right,
2427 %precedence, or %nonassoc yields the same result.
2429 When mixing declarations of tokens with a literal character (e.g., 'a') or
2430 with an identifier (e.g., B) in a precedence declaration, Bison numbered
2431 the literal characters first. For example
2435 would lead to the tokens declared in this order: 'c' 'd' A B. Again, the
2436 input order is now preserved.
2438 These changes were made so that one can remove useless precedence and
2439 associativity declarations (i.e., map %nonassoc, %left or %right to
2440 %precedence, or to %token) and get exactly the same output.
2442 ** Useless precedence and associativity
2444 Contributed by Valentin Tolmer.
2446 When developing and maintaining a grammar, useless associativity and
2447 precedence directives are common. They can be a nuisance: new ambiguities
2448 arising are sometimes masked because their conflicts are resolved due to
2449 the extra precedence or associativity information. Furthermore, it can
2450 hinder the comprehension of a new grammar: one will wonder about the role
2451 of a precedence, where in fact it is useless. The following changes aim
2452 at detecting and reporting these extra directives.
2454 *** Precedence warning category
2456 A new category of warning, -Wprecedence, was introduced. It flags the
2457 useless precedence and associativity directives.
2459 *** Useless associativity
2461 Bison now warns about symbols with a declared associativity that is never
2462 used to resolve conflicts. In that case, using %precedence is sufficient;
2463 the parsing tables will remain unchanged. Solving these warnings may raise
2464 useless precedence warnings, as the symbols no longer have associativity.
2478 warning: useless associativity for '+', use %precedence [-Wprecedence]
2482 *** Useless precedence
2484 Bison now warns about symbols with a declared precedence and no declared
2485 associativity (i.e., declared with %precedence), and whose precedence is
2486 never used. In that case, the symbol can be safely declared with %token
2487 instead, without modifying the parsing tables. For example:
2491 exp: "var" '=' "number";
2495 warning: useless precedence for '=' [-Wprecedence]
2499 *** Useless precedence and associativity
2501 In case of both useless precedence and associativity, the issue is flagged
2506 exp: "var" '=' "number";
2510 warning: useless precedence and associativity for '=' [-Wprecedence]
2516 With help from Joel E. Denny and Gabriel Rassoul.
2518 Empty rules (i.e., with an empty right-hand side) can now be explicitly
2519 marked by the new %empty directive. Using %empty on a non-empty rule is
2520 an error. The new -Wempty-rule warning reports empty rules without
2521 %empty. On the following grammar:
2531 3.4-5: warning: empty rule without %empty [-Wempty-rule]
2534 5.8-13: error: %empty on non-empty rule
2538 ** Java skeleton improvements
2540 The constants for token names were moved to the Lexer interface. Also, it
2541 is possible to add code to the parser's constructors using "%code init"
2542 and "%define init_throws".
2543 Contributed by Paolo Bonzini.
2545 The Java skeleton now supports push parsing.
2546 Contributed by Dennis Heimbigner.
2548 ** C++ skeletons improvements
2550 *** The parser header is no longer mandatory (lalr1.cc, glr.cc)
2552 Using %defines is now optional. Without it, the needed support classes
2553 are defined in the generated parser, instead of additional files (such as
2554 location.hh, position.hh and stack.hh).
2556 *** Locations are no longer mandatory (lalr1.cc, glr.cc)
2558 Both lalr1.cc and glr.cc no longer require %location.
2560 *** syntax_error exception (lalr1.cc)
2562 The C++ parser features a syntax_error exception, which can be
2563 thrown from the scanner or from user rules to raise syntax errors.
2564 This facilitates reporting errors caught in sub-functions (e.g.,
2565 rejecting too large integral literals from a conversion function
2566 used by the scanner, or rejecting invalid combinations from a
2567 factory invoked by the user actions).
2569 *** %define api.value.type variant
2571 This is based on a submission from Michiel De Wilde. With help
2572 from Théophile Ranquet.
2574 In this mode, complex C++ objects can be used as semantic values. For
2577 %token <::std::string> TEXT;
2578 %token <int> NUMBER;
2579 %token SEMICOLON ";"
2580 %type <::std::string> item;
2581 %type <::std::list<std::string>> list;
2584 list { std::cout << $1 << std::endl; }
2588 %empty { /* Generates an empty string list. */ }
2589 | list item ";" { std::swap ($$, $1); $$.push_back ($2); }
2593 TEXT { std::swap ($$, $1); }
2594 | NUMBER { $$ = string_cast ($1); }
2597 *** %define api.token.constructor
2599 When variants are enabled, Bison can generate functions to build the
2600 tokens. This guarantees that the token type (e.g., NUMBER) is consistent
2601 with the semantic value (e.g., int):
2603 parser::symbol_type yylex ()
2605 parser::location_type loc = ...;
2607 return parser::make_TEXT ("Hello, world!", loc);
2609 return parser::make_NUMBER (42, loc);
2611 return parser::make_SEMICOLON (loc);
2617 There are operator- and operator-= for 'location'. Negative line/column
2618 increments can no longer underflow the resulting value.
2621 * Noteworthy changes in release 2.7.1 (2013-04-15) [stable]
2625 *** Fix compiler attribute portability (yacc.c)
2627 With locations enabled, __attribute__ was used unprotected.
2629 *** Fix some compiler warnings (lalr1.cc)
2632 * Noteworthy changes in release 2.7 (2012-12-12) [stable]
2636 Warnings about uninitialized yylloc in yyparse have been fixed.
2638 Restored C90 compliance (yet no report was ever made).
2640 ** Diagnostics are improved
2642 Contributed by Théophile Ranquet.
2644 *** Changes in the format of error messages
2646 This used to be the format of many error reports:
2648 input.y:2.7-12: %type redeclaration for exp
2649 input.y:1.7-12: previous declaration
2653 input.y:2.7-12: error: %type redeclaration for exp
2654 input.y:1.7-12: previous declaration
2656 *** New format for error reports: carets
2658 Caret errors have been added to Bison:
2660 input.y:2.7-12: error: %type redeclaration for exp
2663 input.y:1.7-12: previous declaration
2669 input.y:3.20-23: error: ambiguous reference: '$exp'
2670 exp: exp '+' exp { $exp = $1 + $3; };
2672 input.y:3.1-3: refers to: $exp at $$
2673 exp: exp '+' exp { $exp = $1 + $3; };
2675 input.y:3.6-8: refers to: $exp at $1
2676 exp: exp '+' exp { $exp = $1 + $3; };
2678 input.y:3.14-16: refers to: $exp at $3
2679 exp: exp '+' exp { $exp = $1 + $3; };
2682 The default behavior for now is still not to display these unless
2683 explicitly asked with -fcaret (or -fall). However, in a later release, it
2684 will be made the default behavior (but may still be deactivated with
2687 ** New value for %define variable: api.pure full
2689 The %define variable api.pure requests a pure (reentrant) parser. However,
2690 for historical reasons, using it in a location-tracking Yacc parser
2691 resulted in a yyerror function that did not take a location as a
2692 parameter. With this new value, the user may request a better pure parser,
2693 where yyerror does take a location as a parameter (in location-tracking
2696 The use of "%define api.pure true" is deprecated in favor of this new
2697 "%define api.pure full".
2699 ** New %define variable: api.location.type (glr.cc, lalr1.cc, lalr1.java)
2701 The %define variable api.location.type defines the name of the type to use
2702 for locations. When defined, Bison no longer generates the position.hh
2703 and location.hh files, nor does the parser will include them: the user is
2704 then responsible to define her type.
2706 This can be used in programs with several parsers to factor their location
2707 and position files: let one of them generate them, and the others just use
2710 This feature was actually introduced, but not documented, in Bison 2.5,
2711 under the name "location_type" (which is maintained for backward
2714 For consistency, lalr1.java's %define variables location_type and
2715 position_type are deprecated in favor of api.location.type and
2718 ** Exception safety (lalr1.cc)
2720 The parse function now catches exceptions, uses the %destructors to
2721 release memory (the lookahead symbol and the symbols pushed on the stack)
2722 before re-throwing the exception.
2724 This feature is somewhat experimental. User feedback would be
2727 ** Graph improvements in DOT and XSLT
2729 Contributed by Théophile Ranquet.
2731 The graphical presentation of the states is more readable: their shape is
2732 now rectangular, the state number is clearly displayed, and the items are
2733 numbered and left-justified.
2735 The reductions are now explicitly represented as transitions to other
2736 diamond shaped nodes.
2738 These changes are present in both --graph output and xml2dot.xsl XSLT
2739 processing, with minor (documented) differences.
2741 ** %language is no longer an experimental feature.
2743 The introduction of this feature, in 2.4, was four years ago. The
2744 --language option and the %language directive are no longer experimental.
2748 The sections about shift/reduce and reduce/reduce conflicts resolution
2749 have been fixed and extended.
2751 Although introduced more than four years ago, XML and Graphviz reports
2752 were not properly documented.
2754 The translation of midrule actions is now described.
2757 * Noteworthy changes in release 2.6.5 (2012-11-07) [stable]
2759 We consider compiler warnings about Bison generated parsers to be bugs.
2760 Rather than working around them in your own project, please consider
2761 reporting them to us.
2765 Warnings about uninitialized yylval and/or yylloc for push parsers with a
2766 pure interface have been fixed for GCC 4.0 up to 4.8, and Clang 2.9 to
2769 Other issues in the test suite have been addressed.
2771 Null characters are correctly displayed in error messages.
2773 When possible, yylloc is correctly initialized before calling yylex. It
2774 is no longer necessary to initialize it in the %initial-action.
2777 * Noteworthy changes in release 2.6.4 (2012-10-23) [stable]
2779 Bison 2.6.3's --version was incorrect. This release fixes this issue.
2782 * Noteworthy changes in release 2.6.3 (2012-10-22) [stable]
2786 Bugs and portability issues in the test suite have been fixed.
2788 Some errors in translations have been addressed, and --help now directs
2789 users to the appropriate place to report them.
2791 Stray Info files shipped by accident are removed.
2793 Incorrect definitions of YY_, issued by yacc.c when no parser header is
2794 generated, are removed.
2796 All the generated headers are self-contained.
2798 ** Header guards (yacc.c, glr.c, glr.cc)
2800 In order to avoid collisions, the header guards are now
2801 YY_<PREFIX>_<FILE>_INCLUDED, instead of merely <PREFIX>_<FILE>.
2802 For instance the header generated from
2804 %define api.prefix "calc"
2805 %defines "lib/parse.h"
2807 will use YY_CALC_LIB_PARSE_H_INCLUDED as guard.
2809 ** Fix compiler warnings in the generated parser (yacc.c, glr.c)
2811 The compilation of pure parsers (%define api.pure) can trigger GCC
2814 input.c: In function 'yyparse':
2815 input.c:1503:12: warning: 'yylval' may be used uninitialized in this
2816 function [-Wmaybe-uninitialized]
2820 This is now fixed; pragmas to avoid these warnings are no longer needed.
2822 Warnings from clang ("equality comparison with extraneous parentheses" and
2823 "function declared 'noreturn' should not return") have also been
2827 * Noteworthy changes in release 2.6.2 (2012-08-03) [stable]
2831 Buffer overruns, complaints from Flex, and portability issues in the test
2832 suite have been fixed.
2834 ** Spaces in %lex- and %parse-param (lalr1.cc, glr.cc)
2836 Trailing end-of-lines in %parse-param or %lex-param would result in
2837 invalid C++. This is fixed.
2839 ** Spurious spaces and end-of-lines
2841 The generated files no longer end (nor start) with empty lines.
2844 * Noteworthy changes in release 2.6.1 (2012-07-30) [stable]
2846 Bison no longer executes user-specified M4 code when processing a grammar.
2850 In addition to the removal of the features announced in Bison 2.6, the
2851 next major release will remove the "Temporary hack for adding a semicolon
2852 to the user action", as announced in the release 2.5. Instead of:
2854 exp: exp "+" exp { $$ = $1 + $3 };
2858 exp: exp "+" exp { $$ = $1 + $3; };
2862 *** Type names are now properly escaped.
2864 *** glr.cc: set_debug_level and debug_level work as expected.
2866 *** Stray @ or $ in actions
2868 While Bison used to warn about stray $ or @ in action rules, it did not
2869 for other actions such as printers, destructors, or initial actions. It
2872 ** Type names in actions
2874 For consistency with rule actions, it is now possible to qualify $$ by a
2875 type-name in destructors, printers, and initial actions. For instance:
2877 %printer { fprintf (yyo, "(%d, %f)", $<ival>$, $<fval>$); } <*> <>;
2879 will display two values for each typed and untyped symbol (provided
2880 that YYSTYPE has both "ival" and "fval" fields).
2883 * Noteworthy changes in release 2.6 (2012-07-19) [stable]
2887 The next major release of Bison will drop support for the following
2888 deprecated features. Please report disagreements to bug-bison@gnu.org.
2892 Support for generating parsers in K&R C will be removed. Parsers
2893 generated for C support ISO C90, and are tested with ISO C99 and ISO C11
2896 *** Features deprecated since Bison 1.875
2898 The definitions of yystype and yyltype will be removed; use YYSTYPE and
2901 YYPARSE_PARAM and YYLEX_PARAM, deprecated in favor of %parse-param and
2902 %lex-param, will no longer be supported.
2904 Support for the preprocessor symbol YYERROR_VERBOSE will be removed, use
2907 *** The generated header will be included (yacc.c)
2909 Instead of duplicating the content of the generated header (definition of
2910 YYSTYPE, yyparse declaration etc.), the generated parser will include it,
2911 as is already the case for GLR or C++ parsers. This change is deferred
2912 because existing versions of ylwrap (e.g., Automake 1.12.1) do not support
2915 ** Generated Parser Headers
2917 *** Guards (yacc.c, glr.c, glr.cc)
2919 The generated headers are now guarded, as is already the case for C++
2920 parsers (lalr1.cc). For instance, with --defines=foo.h:
2925 #endif /* !YY_FOO_H */
2927 *** New declarations (yacc.c, glr.c)
2929 The generated header now declares yydebug and yyparse. Both honor
2930 --name-prefix=bar_, and yield
2932 int bar_parse (void);
2936 #define yyparse bar_parse
2939 in order to facilitate the inclusion of several parser headers inside a
2940 single compilation unit.
2942 *** Exported symbols in C++
2944 The symbols YYTOKEN_TABLE and YYERROR_VERBOSE, which were defined in the
2945 header, are removed, as they prevent the possibility of including several
2946 generated headers from a single compilation unit.
2950 For the same reasons, the undocumented and unused macro YYLSP_NEEDED is no
2953 ** New %define variable: api.prefix
2955 Now that the generated headers are more complete and properly protected
2956 against multiple inclusions, constant names, such as YYSTYPE are a
2957 problem. While yyparse and others are properly renamed by %name-prefix,
2958 YYSTYPE, YYDEBUG and others have never been affected by it. Because it
2959 would introduce backward compatibility issues in projects not expecting
2960 YYSTYPE to be renamed, instead of changing the behavior of %name-prefix,
2961 it is deprecated in favor of a new %define variable: api.prefix.
2963 The following examples compares both:
2965 %name-prefix "bar_" | %define api.prefix "bar_"
2966 %token <ival> FOO %token <ival> FOO
2967 %union { int ival; } %union { int ival; }
2973 #ifndef BAR_FOO_H #ifndef BAR_FOO_H
2974 # define BAR_FOO_H # define BAR_FOO_H
2976 /* Enabling traces. */ /* Enabling traces. */
2977 # ifndef YYDEBUG | # ifndef BAR_DEBUG
2978 > # if defined YYDEBUG
2980 > # define BAR_DEBUG 1
2982 > # define BAR_DEBUG 0
2985 # define YYDEBUG 0 | # define BAR_DEBUG 0
2989 # if YYDEBUG | # if BAR_DEBUG
2990 extern int bar_debug; extern int bar_debug;
2993 /* Tokens. */ /* Tokens. */
2994 # ifndef YYTOKENTYPE | # ifndef BAR_TOKENTYPE
2995 # define YYTOKENTYPE | # define BAR_TOKENTYPE
2996 enum yytokentype { | enum bar_tokentype {
3001 #if ! defined YYSTYPE \ | #if ! defined BAR_STYPE \
3002 && ! defined YYSTYPE_IS_DECLARED | && ! defined BAR_STYPE_IS_DECLARED
3003 typedef union YYSTYPE | typedef union BAR_STYPE
3006 } YYSTYPE; | } BAR_STYPE;
3007 # define YYSTYPE_IS_DECLARED 1 | # define BAR_STYPE_IS_DECLARED 1
3010 extern YYSTYPE bar_lval; | extern BAR_STYPE bar_lval;
3012 int bar_parse (void); int bar_parse (void);
3014 #endif /* !BAR_FOO_H */ #endif /* !BAR_FOO_H */
3017 * Noteworthy changes in release 2.5.1 (2012-06-05) [stable]
3021 The next major release will drop support for generating parsers in K&R C.
3023 ** yacc.c: YYBACKUP works as expected.
3025 ** glr.c improvements:
3027 *** Location support is eliminated when not requested:
3029 GLR parsers used to include location-related code even when locations were
3030 not requested, and therefore not even usable.
3032 *** __attribute__ is preserved:
3034 __attribute__ is no longer disabled when __STRICT_ANSI__ is defined (i.e.,
3035 when -std is passed to GCC).
3037 ** lalr1.java: several fixes:
3039 The Java parser no longer throws ArrayIndexOutOfBoundsException if the
3040 first token leads to a syntax error. Some minor clean ups.
3044 *** C++11 compatibility:
3046 C and C++ parsers use "nullptr" instead of "0" when __cplusplus is 201103L
3051 The header files such as "parser.hh", "location.hh", etc. used a constant
3052 name for preprocessor guards, for instance:
3054 #ifndef BISON_LOCATION_HH
3055 # define BISON_LOCATION_HH
3057 #endif // !BISON_LOCATION_HH
3059 The inclusion guard is now computed from "PREFIX/FILE-NAME", where lower
3060 case characters are converted to upper case, and series of
3061 non-alphanumerical characters are converted to an underscore.
3063 With "bison -o lang++/parser.cc", "location.hh" would now include:
3065 #ifndef YY_LANG_LOCATION_HH
3066 # define YY_LANG_LOCATION_HH
3068 #endif // !YY_LANG_LOCATION_HH
3072 The position and location constructors (and their initialize methods)
3073 accept new arguments for line and column. Several issues in the
3074 documentation were fixed.
3076 ** liby is no longer asking for "rpl_fprintf" on some platforms.
3078 ** Changes in the manual:
3080 *** %printer is documented
3082 The "%printer" directive, supported since at least Bison 1.50, is finally
3083 documented. The "mfcalc" example is extended to demonstrate it.
3085 For consistency with the C skeletons, the C++ parsers now also support
3086 "yyoutput" (as an alias to "debug_stream ()").
3088 *** Several improvements have been made:
3090 The layout for grammar excerpts was changed to a more compact scheme.
3091 Named references are motivated. The description of the automaton
3092 description file (*.output) is updated to the current format. Incorrect
3093 index entries were fixed. Some other errors were fixed.
3097 *** Conflicting prototypes with recent/modified Flex.
3099 Fixed build problems with the current, unreleased, version of Flex, and
3100 some modified versions of 2.5.35, which have modified function prototypes.
3102 *** Warnings during the build procedure have been eliminated.
3104 *** Several portability problems in the test suite have been fixed:
3106 This includes warnings with some compilers, unexpected behavior of tools
3107 such as diff, warning messages from the test suite itself, etc.
3109 *** The install-pdf target works properly:
3111 Running "make install-pdf" (or -dvi, -html, -info, and -ps) no longer
3112 halts in the middle of its course.
3115 * Noteworthy changes in release 2.5 (2011-05-14)
3117 ** Grammar symbol names can now contain non-initial dashes:
3119 Consistently with directives (such as %error-verbose) and with
3120 %define variables (e.g. push-pull), grammar symbol names may contain
3121 dashes in any position except the beginning. This is a GNU
3122 extension over POSIX Yacc. Thus, use of this extension is reported
3123 by -Wyacc and rejected in Yacc mode (--yacc).
3125 ** Named references:
3127 Historically, Yacc and Bison have supported positional references
3128 ($n, $$) to allow access to symbol values from inside of semantic
3131 Starting from this version, Bison can also accept named references.
3132 When no ambiguity is possible, original symbol names may be used
3133 as named references:
3135 if_stmt : "if" cond_expr "then" then_stmt ';'
3136 { $if_stmt = mk_if_stmt($cond_expr, $then_stmt); }
3138 In the more common case, explicit names may be declared:
3140 stmt[res] : "if" expr[cond] "then" stmt[then] "else" stmt[else] ';'
3141 { $res = mk_if_stmt($cond, $then, $else); }
3143 Location information is also accessible using @name syntax. When
3144 accessing symbol names containing dots or dashes, explicit bracketing
3145 ($[sym.1]) must be used.
3147 These features are experimental in this version. More user feedback
3148 will help to stabilize them.
3149 Contributed by Alex Rozenman.
3151 ** IELR(1) and canonical LR(1):
3153 IELR(1) is a minimal LR(1) parser table generation algorithm. That
3154 is, given any context-free grammar, IELR(1) generates parser tables
3155 with the full language-recognition power of canonical LR(1) but with
3156 nearly the same number of parser states as LALR(1). This reduction
3157 in parser states is often an order of magnitude. More importantly,
3158 because canonical LR(1)'s extra parser states may contain duplicate
3159 conflicts in the case of non-LR(1) grammars, the number of conflicts
3160 for IELR(1) is often an order of magnitude less as well. This can
3161 significantly reduce the complexity of developing of a grammar.
3163 Bison can now generate IELR(1) and canonical LR(1) parser tables in
3164 place of its traditional LALR(1) parser tables, which remain the
3165 default. You can specify the type of parser tables in the grammar
3166 file with these directives:
3168 %define lr.type lalr
3169 %define lr.type ielr
3170 %define lr.type canonical-lr
3172 The default-reduction optimization in the parser tables can also be
3173 adjusted using "%define lr.default-reductions". For details on both
3174 of these features, see the new section "Tuning LR" in the Bison
3177 These features are experimental. More user feedback will help to
3180 ** LAC (Lookahead Correction) for syntax error handling
3182 Contributed by Joel E. Denny.
3184 Canonical LR, IELR, and LALR can suffer from a couple of problems
3185 upon encountering a syntax error. First, the parser might perform
3186 additional parser stack reductions before discovering the syntax
3187 error. Such reductions can perform user semantic actions that are
3188 unexpected because they are based on an invalid token, and they
3189 cause error recovery to begin in a different syntactic context than
3190 the one in which the invalid token was encountered. Second, when
3191 verbose error messages are enabled (with %error-verbose or the
3192 obsolete "#define YYERROR_VERBOSE"), the expected token list in the
3193 syntax error message can both contain invalid tokens and omit valid
3196 The culprits for the above problems are %nonassoc, default
3197 reductions in inconsistent states, and parser state merging. Thus,
3198 IELR and LALR suffer the most. Canonical LR can suffer only if
3199 %nonassoc is used or if default reductions are enabled for
3200 inconsistent states.
3202 LAC is a new mechanism within the parsing algorithm that solves
3203 these problems for canonical LR, IELR, and LALR without sacrificing
3204 %nonassoc, default reductions, or state merging. When LAC is in
3205 use, canonical LR and IELR behave almost exactly the same for both
3206 syntactically acceptable and syntactically unacceptable input.
3207 While LALR still does not support the full language-recognition
3208 power of canonical LR and IELR, LAC at least enables LALR's syntax
3209 error handling to correctly reflect LALR's language-recognition
3212 Currently, LAC is only supported for deterministic parsers in C.
3213 You can enable LAC with the following directive:
3215 %define parse.lac full
3217 See the new section "LAC" in the Bison manual for additional
3218 details including a few caveats.
3220 LAC is an experimental feature. More user feedback will help to
3223 ** %define improvements:
3225 *** Can now be invoked via the command line:
3227 Each of these command-line options
3230 --define=NAME[=VALUE]
3233 --force-define=NAME[=VALUE]
3235 is equivalent to this grammar file declaration
3237 %define NAME ["VALUE"]
3239 except that the manner in which Bison processes multiple definitions
3240 for the same NAME differs. Most importantly, -F and --force-define
3241 quietly override %define, but -D and --define do not. For further
3242 details, see the section "Bison Options" in the Bison manual.
3244 *** Variables renamed:
3246 The following %define variables
3249 lr.keep_unreachable_states
3251 have been renamed to
3254 lr.keep-unreachable-states
3256 The old names are now deprecated but will be maintained indefinitely
3257 for backward compatibility.
3259 *** Values no longer need to be quoted in the grammar file:
3261 If a %define value is an identifier, it no longer needs to be placed
3262 within quotations marks. For example,
3264 %define api.push-pull "push"
3268 %define api.push-pull push
3270 *** Unrecognized variables are now errors not warnings.
3272 *** Multiple invocations for any variable is now an error not a warning.
3274 ** Unrecognized %code qualifiers are now errors not warnings.
3276 ** Character literals not of length one:
3278 Previously, Bison quietly converted all character literals to length
3279 one. For example, without warning, Bison interpreted the operators in
3280 the following grammar to be the same token:
3286 Bison now warns when a character literal is not of length one. In
3287 some future release, Bison will start reporting an error instead.
3289 ** Destructor calls fixed for lookaheads altered in semantic actions:
3291 Previously for deterministic parsers in C, if a user semantic action
3292 altered yychar, the parser in some cases used the old yychar value to
3293 determine which destructor to call for the lookahead upon a syntax
3294 error or upon parser return. This bug has been fixed.
3296 ** C++ parsers use YYRHSLOC:
3298 Similarly to the C parsers, the C++ parsers now define the YYRHSLOC
3299 macro and use it in the default YYLLOC_DEFAULT. You are encouraged
3300 to use it. If, for instance, your location structure has "first"
3301 and "last" members, instead of
3303 # define YYLLOC_DEFAULT(Current, Rhs, N) \
3307 (Current).first = (Rhs)[1].location.first; \
3308 (Current).last = (Rhs)[N].location.last; \
3312 (Current).first = (Current).last = (Rhs)[0].location.last; \
3318 # define YYLLOC_DEFAULT(Current, Rhs, N) \
3322 (Current).first = YYRHSLOC (Rhs, 1).first; \
3323 (Current).last = YYRHSLOC (Rhs, N).last; \
3327 (Current).first = (Current).last = YYRHSLOC (Rhs, 0).last; \
3331 ** YYLLOC_DEFAULT in C++:
3333 The default implementation of YYLLOC_DEFAULT used to be issued in
3334 the header file. It is now output in the implementation file, after
3335 the user %code sections so that its #ifndef guard does not try to
3336 override the user's YYLLOC_DEFAULT if provided.
3338 ** YYFAIL now produces warnings and Java parsers no longer implement it:
3340 YYFAIL has existed for many years as an undocumented feature of
3341 deterministic parsers in C generated by Bison. More recently, it was
3342 a documented feature of Bison's experimental Java parsers. As
3343 promised in Bison 2.4.2's NEWS entry, any appearance of YYFAIL in a
3344 semantic action now produces a deprecation warning, and Java parsers
3345 no longer implement YYFAIL at all. For further details, including a
3346 discussion of how to suppress C preprocessor warnings about YYFAIL
3347 being unused, see the Bison 2.4.2 NEWS entry.
3349 ** Temporary hack for adding a semicolon to the user action:
3351 Previously, Bison appended a semicolon to every user action for
3352 reductions when the output language defaulted to C (specifically, when
3353 neither %yacc, %language, %skeleton, or equivalent command-line
3354 options were specified). This allowed actions such as
3356 exp: exp "+" exp { $$ = $1 + $3 };
3360 exp: exp "+" exp { $$ = $1 + $3; };
3362 As a first step in removing this misfeature, Bison now issues a
3363 warning when it appends a semicolon. Moreover, in cases where Bison
3364 cannot easily determine whether a semicolon is needed (for example, an
3365 action ending with a cpp directive or a braced compound initializer),
3366 it no longer appends one. Thus, the C compiler might now complain
3367 about a missing semicolon where it did not before. Future releases of
3368 Bison will cease to append semicolons entirely.
3370 ** Verbose syntax error message fixes:
3372 When %error-verbose or the obsolete "#define YYERROR_VERBOSE" is
3373 specified, syntax error messages produced by the generated parser
3374 include the unexpected token as well as a list of expected tokens.
3375 The effect of %nonassoc on these verbose messages has been corrected
3376 in two ways, but a more complete fix requires LAC, described above:
3378 *** When %nonassoc is used, there can exist parser states that accept no
3379 tokens, and so the parser does not always require a lookahead token
3380 in order to detect a syntax error. Because no unexpected token or
3381 expected tokens can then be reported, the verbose syntax error
3382 message described above is suppressed, and the parser instead
3383 reports the simpler message, "syntax error". Previously, this
3384 suppression was sometimes erroneously triggered by %nonassoc when a
3385 lookahead was actually required. Now verbose messages are
3386 suppressed only when all previous lookaheads have already been
3387 shifted or discarded.
3389 *** Previously, the list of expected tokens erroneously included tokens
3390 that would actually induce a syntax error because conflicts for them
3391 were resolved with %nonassoc in the current parser state. Such
3392 tokens are now properly omitted from the list.
3394 *** Expected token lists are still often wrong due to state merging
3395 (from LALR or IELR) and default reductions, which can both add
3396 invalid tokens and subtract valid tokens. Canonical LR almost
3397 completely fixes this problem by eliminating state merging and
3398 default reductions. However, there is one minor problem left even
3399 when using canonical LR and even after the fixes above. That is,
3400 if the resolution of a conflict with %nonassoc appears in a later
3401 parser state than the one at which some syntax error is
3402 discovered, the conflicted token is still erroneously included in
3403 the expected token list. Bison's new LAC implementation,
3404 described above, eliminates this problem and the need for
3405 canonical LR. However, LAC is still experimental and is disabled
3408 ** Java skeleton fixes:
3410 *** A location handling bug has been fixed.
3412 *** The top element of each of the value stack and location stack is now
3413 cleared when popped so that it can be garbage collected.
3415 *** Parser traces now print the top element of the stack.
3417 ** -W/--warnings fixes:
3419 *** Bison now properly recognizes the "no-" versions of categories:
3421 For example, given the following command line, Bison now enables all
3422 warnings except warnings for incompatibilities with POSIX Yacc:
3424 bison -Wall,no-yacc gram.y
3426 *** Bison now treats S/R and R/R conflicts like other warnings:
3428 Previously, conflict reports were independent of Bison's normal
3429 warning system. Now, Bison recognizes the warning categories
3430 "conflicts-sr" and "conflicts-rr". This change has important
3431 consequences for the -W and --warnings command-line options. For
3434 bison -Wno-conflicts-sr gram.y # S/R conflicts not reported
3435 bison -Wno-conflicts-rr gram.y # R/R conflicts not reported
3436 bison -Wnone gram.y # no conflicts are reported
3437 bison -Werror gram.y # any conflict is an error
3439 However, as before, if the %expect or %expect-rr directive is
3440 specified, an unexpected number of conflicts is an error, and an
3441 expected number of conflicts is not reported, so -W and --warning
3442 then have no effect on the conflict report.
3444 *** The "none" category no longer disables a preceding "error":
3446 For example, for the following command line, Bison now reports
3447 errors instead of warnings for incompatibilities with POSIX Yacc:
3449 bison -Werror,none,yacc gram.y
3451 *** The "none" category now disables all Bison warnings:
3453 Previously, the "none" category disabled only Bison warnings for
3454 which there existed a specific -W/--warning category. However,
3455 given the following command line, Bison is now guaranteed to
3456 suppress all warnings:
3460 ** Precedence directives can now assign token number 0:
3462 Since Bison 2.3b, which restored the ability of precedence
3463 directives to assign token numbers, doing so for token number 0 has
3464 produced an assertion failure. For example:
3468 This bug has been fixed.
3471 * Noteworthy changes in release 2.4.3 (2010-08-05)
3473 ** Bison now obeys -Werror and --warnings=error for warnings about
3474 grammar rules that are useless in the parser due to conflicts.
3476 ** Problems with spawning M4 on at least FreeBSD 8 and FreeBSD 9 have
3479 ** Failures in the test suite for GCC 4.5 have been fixed.
3481 ** Failures in the test suite for some versions of Sun Studio C++ have
3484 ** Contrary to Bison 2.4.2's NEWS entry, it has been decided that
3485 warnings about undefined %prec identifiers will not be converted to
3486 errors in Bison 2.5. They will remain warnings, which should be
3487 sufficient for POSIX while avoiding backward compatibility issues.
3489 ** Minor documentation fixes.
3492 * Noteworthy changes in release 2.4.2 (2010-03-20)
3494 ** Some portability problems that resulted in failures and livelocks
3495 in the test suite on some versions of at least Solaris, AIX, HP-UX,
3496 RHEL4, and Tru64 have been addressed. As a result, fatal Bison
3497 errors should no longer cause M4 to report a broken pipe on the
3500 ** "%prec IDENTIFIER" requires IDENTIFIER to be defined separately.
3502 POSIX specifies that an error be reported for any identifier that does
3503 not appear on the LHS of a grammar rule and that is not defined by
3504 %token, %left, %right, or %nonassoc. Bison 2.3b and later lost this
3505 error report for the case when an identifier appears only after a
3506 %prec directive. It is now restored. However, for backward
3507 compatibility with recent Bison releases, it is only a warning for
3508 now. In Bison 2.5 and later, it will return to being an error.
3509 [Between the 2.4.2 and 2.4.3 releases, it was decided that this
3510 warning will not be converted to an error in Bison 2.5.]
3512 ** Detection of GNU M4 1.4.6 or newer during configure is improved.
3514 ** Warnings from gcc's -Wundef option about undefined YYENABLE_NLS,
3515 YYLTYPE_IS_TRIVIAL, and __STRICT_ANSI__ in C/C++ parsers are now
3518 ** %code is now a permanent feature.
3520 A traditional Yacc prologue directive is written in the form:
3524 To provide a more flexible alternative, Bison 2.3b introduced the
3525 %code directive with the following forms for C/C++:
3528 %code requires {CODE}
3529 %code provides {CODE}
3532 These forms are now considered permanent features of Bison. See the
3533 %code entries in the section "Bison Declaration Summary" in the Bison
3534 manual for a summary of their functionality. See the section
3535 "Prologue Alternatives" for a detailed discussion including the
3536 advantages of %code over the traditional Yacc prologue directive.
3538 Bison's Java feature as a whole including its current usage of %code
3539 is still considered experimental.
3541 ** YYFAIL is deprecated and will eventually be removed.
3543 YYFAIL has existed for many years as an undocumented feature of
3544 deterministic parsers in C generated by Bison. Previously, it was
3545 documented for Bison's experimental Java parsers. YYFAIL is no longer
3546 documented for Java parsers and is formally deprecated in both cases.
3547 Users are strongly encouraged to migrate to YYERROR, which is
3550 Like YYERROR, you can invoke YYFAIL from a semantic action in order to
3551 induce a syntax error. The most obvious difference from YYERROR is
3552 that YYFAIL will automatically invoke yyerror to report the syntax
3553 error so that you don't have to. However, there are several other
3554 subtle differences between YYERROR and YYFAIL, and YYFAIL suffers from
3555 inherent flaws when %error-verbose or "#define YYERROR_VERBOSE" is
3556 used. For a more detailed discussion, see:
3558 https://lists.gnu.org/r/bison-patches/2009-12/msg00024.html
3560 The upcoming Bison 2.5 will remove YYFAIL from Java parsers, but
3561 deterministic parsers in C will continue to implement it. However,
3562 because YYFAIL is already flawed, it seems futile to try to make new
3563 Bison features compatible with it. Thus, during parser generation,
3564 Bison 2.5 will produce a warning whenever it discovers YYFAIL in a
3565 rule action. In a later release, YYFAIL will be disabled for
3566 %error-verbose and "#define YYERROR_VERBOSE". Eventually, YYFAIL will
3567 be removed altogether.
3569 There exists at least one case where Bison 2.5's YYFAIL warning will
3570 be a false positive. Some projects add phony uses of YYFAIL and other
3571 Bison-defined macros for the sole purpose of suppressing C
3572 preprocessor warnings (from GCC cpp's -Wunused-macros, for example).
3573 To avoid Bison's future warning, such YYFAIL uses can be moved to the
3574 epilogue (that is, after the second "%%") in the Bison input file. In
3575 this release (2.4.2), Bison already generates its own code to suppress
3576 C preprocessor warnings for YYFAIL, so projects can remove their own
3577 phony uses of YYFAIL if compatibility with Bison releases prior to
3578 2.4.2 is not necessary.
3580 ** Internationalization.
3582 Fix a regression introduced in Bison 2.4: Under some circumstances,
3583 message translations were not installed although supported by the
3587 * Noteworthy changes in release 2.4.1 (2008-12-11)
3589 ** In the GLR defines file, unexpanded M4 macros in the yylval and yylloc
3590 declarations have been fixed.
3592 ** Temporary hack for adding a semicolon to the user action.
3594 Bison used to prepend a trailing semicolon at the end of the user
3595 action for reductions. This allowed actions such as
3597 exp: exp "+" exp { $$ = $1 + $3 };
3601 exp: exp "+" exp { $$ = $1 + $3; };
3603 Some grammars still depend on this "feature". Bison 2.4.1 restores
3604 the previous behavior in the case of C output (specifically, when
3605 neither %language or %skeleton or equivalent command-line options
3606 are used) to leave more time for grammars depending on the old
3607 behavior to be adjusted. Future releases of Bison will disable this
3610 ** A few minor improvements to the Bison manual.
3613 * Noteworthy changes in release 2.4 (2008-11-02)
3615 ** %language is an experimental feature.
3617 We first introduced this feature in test release 2.3b as a cleaner
3618 alternative to %skeleton. Since then, we have discussed the possibility of
3619 modifying its effect on Bison's output file names. Thus, in this release,
3620 we consider %language to be an experimental feature that will likely evolve
3623 ** Forward compatibility with GNU M4 has been improved.
3625 ** Several bugs in the C++ skeleton and the experimental Java skeleton have been
3629 * Noteworthy changes in release 2.3b (2008-05-27)
3631 ** The quotes around NAME that used to be required in the following directive
3634 %define NAME "VALUE"
3636 ** The directive "%pure-parser" is now deprecated in favor of:
3640 which has the same effect except that Bison is more careful to warn about
3641 unreasonable usage in the latter case.
3645 Bison can now generate an LALR(1) parser in C with a push interface. That
3646 is, instead of invoking "yyparse", which pulls tokens from "yylex", you can
3647 push one token at a time to the parser using "yypush_parse", which will
3648 return to the caller after processing each token. By default, the push
3649 interface is disabled. Either of the following directives will enable it:
3651 %define api.push_pull "push" // Just push; does not require yylex.
3652 %define api.push_pull "both" // Push and pull; requires yylex.
3654 See the new section "A Push Parser" in the Bison manual for details.
3656 The current push parsing interface is experimental and may evolve. More user
3657 feedback will help to stabilize it.
3659 ** The -g and --graph options now output graphs in Graphviz DOT format,
3660 not VCG format. Like --graph, -g now also takes an optional FILE argument
3661 and thus cannot be bundled with other short options.
3665 Bison can now generate an LALR(1) parser in Java. The skeleton is
3666 "data/lalr1.java". Consider using the new %language directive instead of
3667 %skeleton to select it.
3669 See the new section "Java Parsers" in the Bison manual for details.
3671 The current Java interface is experimental and may evolve. More user
3672 feedback will help to stabilize it.
3673 Contributed by Paolo Bonzini.
3677 This new directive specifies the programming language of the generated
3678 parser, which can be C (the default), C++, or Java. Besides the skeleton
3679 that Bison uses, the directive affects the names of the generated files if
3680 the grammar file's name ends in ".y".
3682 ** XML Automaton Report
3684 Bison can now generate an XML report of the LALR(1) automaton using the new
3685 "--xml" option. The current XML schema is experimental and may evolve. More
3686 user feedback will help to stabilize it.
3687 Contributed by Wojciech Polak.
3689 ** The grammar file may now specify the name of the parser header file using
3690 %defines. For example:
3694 ** When reporting useless rules, useless nonterminals, and unused terminals,
3695 Bison now employs the terms "useless in grammar" instead of "useless",
3696 "useless in parser" instead of "never reduced", and "unused in grammar"
3697 instead of "unused".
3699 ** Unreachable State Removal
3701 Previously, Bison sometimes generated parser tables containing unreachable
3702 states. A state can become unreachable during conflict resolution if Bison
3703 disables a shift action leading to it from a predecessor state. Bison now:
3705 1. Removes unreachable states.
3707 2. Does not report any conflicts that appeared in unreachable states.
3708 WARNING: As a result, you may need to update %expect and %expect-rr
3709 directives in existing grammar files.
3711 3. For any rule used only in such states, Bison now reports the rule as
3712 "useless in parser due to conflicts".
3714 This feature can be disabled with the following directive:
3716 %define lr.keep_unreachable_states
3718 See the %define entry in the "Bison Declaration Summary" in the Bison manual
3719 for further discussion.
3721 ** Lookahead Set Correction in the ".output" Report
3723 When instructed to generate a ".output" file including lookahead sets
3724 (using "--report=lookahead", for example), Bison now prints each reduction's
3725 lookahead set only next to the associated state's one item that (1) is
3726 associated with the same rule as the reduction and (2) has its dot at the end
3727 of its RHS. Previously, Bison also erroneously printed the lookahead set
3728 next to all of the state's other items associated with the same rule. This
3729 bug affected only the ".output" file and not the generated parser source
3732 ** --report-file=FILE is a new option to override the default ".output" file
3735 ** The "=" that used to be required in the following directives is now
3738 %file-prefix "parser"
3742 ** An Alternative to "%{...%}" -- "%code QUALIFIER {CODE}"
3744 Bison 2.3a provided a new set of directives as a more flexible alternative to
3745 the traditional Yacc prologue blocks. Those have now been consolidated into
3746 a single %code directive with an optional qualifier field, which identifies
3747 the purpose of the code and thus the location(s) where Bison should generate
3750 1. "%code {CODE}" replaces "%after-header {CODE}"
3751 2. "%code requires {CODE}" replaces "%start-header {CODE}"
3752 3. "%code provides {CODE}" replaces "%end-header {CODE}"
3753 4. "%code top {CODE}" replaces "%before-header {CODE}"
3755 See the %code entries in section "Bison Declaration Summary" in the Bison
3756 manual for a summary of the new functionality. See the new section "Prologue
3757 Alternatives" for a detailed discussion including the advantages of %code
3758 over the traditional Yacc prologues.
3760 The prologue alternatives are experimental. More user feedback will help to
3761 determine whether they should become permanent features.
3763 ** Revised warning: unset or unused midrule values
3765 Since Bison 2.2, Bison has warned about midrule values that are set but not
3766 used within any of the actions of the parent rule. For example, Bison warns
3769 exp: '1' { $$ = 1; } '+' exp { $$ = $1 + $4; };
3771 Now, Bison also warns about midrule values that are used but not set. For
3772 example, Bison warns about unset $$ in the midrule action in:
3774 exp: '1' { $1 = 1; } '+' exp { $$ = $2 + $4; };
3776 However, Bison now disables both of these warnings by default since they
3777 sometimes prove to be false alarms in existing grammars employing the Yacc
3778 constructs $0 or $-N (where N is some positive integer).
3780 To enable these warnings, specify the option "--warnings=midrule-values" or
3781 "-W", which is a synonym for "--warnings=all".
3783 ** Default %destructor or %printer with "<*>" or "<>"
3785 Bison now recognizes two separate kinds of default %destructor's and
3788 1. Place "<*>" in a %destructor/%printer symbol list to define a default
3789 %destructor/%printer for all grammar symbols for which you have formally
3790 declared semantic type tags.
3792 2. Place "<>" in a %destructor/%printer symbol list to define a default
3793 %destructor/%printer for all grammar symbols without declared semantic
3796 Bison no longer supports the "%symbol-default" notation from Bison 2.3a.
3797 "<*>" and "<>" combined achieve the same effect with one exception: Bison no
3798 longer applies any %destructor to a midrule value if that midrule value is
3799 not actually ever referenced using either $$ or $n in a semantic action.
3801 The default %destructor's and %printer's are experimental. More user
3802 feedback will help to determine whether they should become permanent
3805 See the section "Freeing Discarded Symbols" in the Bison manual for further
3808 ** %left, %right, and %nonassoc can now declare token numbers. This is required
3809 by POSIX. However, see the end of section "Operator Precedence" in the Bison
3810 manual for a caveat concerning the treatment of literal strings.
3812 ** The nonfunctional --no-parser, -n, and %no-parser options have been
3813 completely removed from Bison.
3816 * Noteworthy changes in release 2.3a (2006-09-13)
3818 ** Instead of %union, you can define and use your own union type
3819 YYSTYPE if your grammar contains at least one <type> tag.
3820 Your YYSTYPE need not be a macro; it can be a typedef.
3821 This change is for compatibility with other Yacc implementations,
3822 and is required by POSIX.
3824 ** Locations columns and lines start at 1.
3825 In accordance with the GNU Coding Standards and Emacs.
3827 ** You may now declare per-type and default %destructor's and %printer's:
3831 %union { char *string; }
3832 %token <string> STRING1
3833 %token <string> STRING2
3834 %type <string> string1
3835 %type <string> string2
3836 %union { char character; }
3837 %token <character> CHR
3838 %type <character> chr
3839 %destructor { free ($$); } %symbol-default
3840 %destructor { free ($$); printf ("%d", @$.first_line); } STRING1 string1
3841 %destructor { } <character>
3843 guarantees that, when the parser discards any user-defined symbol that has a
3844 semantic type tag other than "<character>", it passes its semantic value to
3845 "free". However, when the parser discards a "STRING1" or a "string1", it
3846 also prints its line number to "stdout". It performs only the second
3847 "%destructor" in this case, so it invokes "free" only once.
3849 [Although we failed to mention this here in the 2.3a release, the default
3850 %destructor's and %printer's were experimental, and they were rewritten in
3853 ** Except for LALR(1) parsers in C with POSIX Yacc emulation enabled (with "-y",
3854 "--yacc", or "%yacc"), Bison no longer generates #define statements for
3855 associating token numbers with token names. Removing the #define statements
3856 helps to sanitize the global namespace during preprocessing, but POSIX Yacc
3857 requires them. Bison still generates an enum for token names in all cases.
3859 ** Handling of traditional Yacc prologue blocks is now more consistent but
3860 potentially incompatible with previous releases of Bison.
3862 As before, you declare prologue blocks in your grammar file with the
3863 "%{ ... %}" syntax. To generate the pre-prologue, Bison concatenates all
3864 prologue blocks that you've declared before the first %union. To generate
3865 the post-prologue, Bison concatenates all prologue blocks that you've
3866 declared after the first %union.
3868 Previous releases of Bison inserted the pre-prologue into both the header
3869 file and the code file in all cases except for LALR(1) parsers in C. In the
3870 latter case, Bison inserted it only into the code file. For parsers in C++,
3871 the point of insertion was before any token definitions (which associate
3872 token numbers with names). For parsers in C, the point of insertion was
3873 after the token definitions.
3875 Now, Bison never inserts the pre-prologue into the header file. In the code
3876 file, it always inserts it before the token definitions.
3878 ** Bison now provides a more flexible alternative to the traditional Yacc
3879 prologue blocks: %before-header, %start-header, %end-header, and
3882 For example, the following declaration order in the grammar file reflects the
3883 order in which Bison will output these code blocks. However, you are free to
3884 declare these code blocks in your grammar file in whatever order is most
3888 /* Bison treats this block like a pre-prologue block: it inserts it into
3889 * the code file before the contents of the header file. It does *not*
3890 * insert it into the header file. This is a good place to put
3891 * #include's that you want at the top of your code file. A common
3892 * example is '#include "system.h"'. */
3895 /* Bison inserts this block into both the header file and the code file.
3896 * In both files, the point of insertion is before any Bison-generated
3897 * token, semantic type, location type, and class definitions. This is a
3898 * good place to define %union dependencies, for example. */
3901 /* Unlike the traditional Yacc prologue blocks, the output order for the
3902 * new %*-header blocks is not affected by their declaration position
3903 * relative to any %union in the grammar file. */
3906 /* Bison inserts this block into both the header file and the code file.
3907 * In both files, the point of insertion is after the Bison-generated
3908 * definitions. This is a good place to declare or define public
3909 * functions or data structures that depend on the Bison-generated
3913 /* Bison treats this block like a post-prologue block: it inserts it into
3914 * the code file after the contents of the header file. It does *not*
3915 * insert it into the header file. This is a good place to declare or
3916 * define internal functions or data structures that depend on the
3917 * Bison-generated definitions. */
3920 If you have multiple occurrences of any one of the above declarations, Bison
3921 will concatenate the contents in declaration order.
3923 [Although we failed to mention this here in the 2.3a release, the prologue
3924 alternatives were experimental, and they were rewritten in future versions.]
3926 ** The option "--report=look-ahead" has been changed to "--report=lookahead".
3927 The old spelling still works, but is not documented and may be removed
3928 in a future release.
3931 * Noteworthy changes in release 2.3 (2006-06-05)
3933 ** GLR grammars should now use "YYRECOVERING ()" instead of "YYRECOVERING",
3934 for compatibility with LALR(1) grammars.
3936 ** It is now documented that any definition of YYSTYPE or YYLTYPE should
3937 be to a type name that does not contain parentheses or brackets.
3940 * Noteworthy changes in release 2.2 (2006-05-19)
3942 ** The distribution terms for all Bison-generated parsers now permit
3943 using the parsers in nonfree programs. Previously, this permission
3944 was granted only for Bison-generated LALR(1) parsers in C.
3946 ** %name-prefix changes the namespace name in C++ outputs.
3948 ** The C++ parsers export their token_type.
3950 ** Bison now allows multiple %union declarations, and concatenates
3951 their contents together.
3953 ** New warning: unused values
3954 Right-hand side symbols whose values are not used are reported,
3955 if the symbols have destructors. For instance:
3957 exp: exp "?" exp ":" exp { $1 ? $1 : $3; }
3961 will trigger a warning about $$ and $5 in the first rule, and $3 in
3962 the second ($1 is copied to $$ by the default rule). This example
3963 most likely contains three errors, and could be rewritten as:
3965 exp: exp "?" exp ":" exp
3966 { $$ = $1 ? $3 : $5; free ($1 ? $5 : $3); free ($1); }
3968 { $$ = $1 ? $1 : $3; if ($1) free ($3); }
3971 However, if the original actions were really intended, memory leaks
3972 and all, the warnings can be suppressed by letting Bison believe the
3973 values are used, e.g.:
3975 exp: exp "?" exp ":" exp { $1 ? $1 : $3; (void) ($$, $5); }
3976 | exp "+" exp { $$ = $1; (void) $3; }
3979 If there are midrule actions, the warning is issued if no action
3980 uses it. The following triggers no warning: $1 and $3 are used.
3982 exp: exp { push ($1); } '+' exp { push ($3); sum (); };
3984 The warning is intended to help catching lost values and memory leaks.
3985 If a value is ignored, its associated memory typically is not reclaimed.
3987 ** %destructor vs. YYABORT, YYACCEPT, and YYERROR.
3988 Destructors are now called when user code invokes YYABORT, YYACCEPT,
3989 and YYERROR, for all objects on the stack, other than objects
3990 corresponding to the right-hand side of the current rule.
3992 ** %expect, %expect-rr
3993 Incorrect numbers of expected conflicts are now actual errors,
3994 instead of warnings.
3996 ** GLR, YACC parsers.
3997 The %parse-params are available in the destructors (and the
3998 experimental printers) as per the documentation.
4000 ** Bison now warns if it finds a stray "$" or "@" in an action.
4002 ** %require "VERSION"
4003 This specifies that the grammar file depends on features implemented
4004 in Bison version VERSION or higher.
4006 ** lalr1.cc: The token and value types are now class members.
4007 The tokens were defined as free form enums and cpp macros. YYSTYPE
4008 was defined as a free form union. They are now class members:
4009 tokens are enumerations of the "yy::parser::token" struct, and the
4010 semantic values have the "yy::parser::semantic_type" type.
4012 If you do not want or can update to this scheme, the directive
4013 '%define "global_tokens_and_yystype" "1"' triggers the global
4014 definition of tokens and YYSTYPE. This change is suitable both
4015 for previous releases of Bison, and this one.
4017 If you wish to update, then make sure older version of Bison will
4018 fail using '%require "2.2"'.
4020 ** DJGPP support added.
4023 * Noteworthy changes in release 2.1 (2005-09-16)
4025 ** The C++ lalr1.cc skeleton supports %lex-param.
4027 ** Bison-generated parsers now support the translation of diagnostics like
4028 "syntax error" into languages other than English. The default
4029 language is still English. For details, please see the new
4030 Internationalization section of the Bison manual. Software
4031 distributors should also see the new PACKAGING file. Thanks to
4032 Bruno Haible for this new feature.
4034 ** Wording in the Bison-generated parsers has been changed slightly to
4035 simplify translation. In particular, the message "memory exhausted"
4036 has replaced "parser stack overflow", as the old message was not
4037 always accurate for modern Bison-generated parsers.
4039 ** Destructors are now called when the parser aborts, for all symbols left
4040 behind on the stack. Also, the start symbol is now destroyed after a
4041 successful parse. In both cases, the behavior was formerly inconsistent.
4043 ** When generating verbose diagnostics, Bison-generated parsers no longer
4044 quote the literal strings associated with tokens. For example, for
4045 a syntax error associated with '%token NUM "number"' they might
4046 print 'syntax error, unexpected number' instead of 'syntax error,
4047 unexpected "number"'.
4050 * Noteworthy changes in release 2.0 (2004-12-25)
4052 ** Possibly-incompatible changes
4054 - Bison-generated parsers no longer default to using the alloca function
4055 (when available) to extend the parser stack, due to widespread
4056 problems in unchecked stack-overflow detection. You can "#define
4057 YYSTACK_USE_ALLOCA 1" to require the use of alloca, but please read
4058 the manual to determine safe values for YYMAXDEPTH in that case.
4060 - Error token location.
4061 During error recovery, the location of the syntax error is updated
4062 to cover the whole sequence covered by the error token: it includes
4063 the shifted symbols thrown away during the first part of the error
4064 recovery, and the lookahead rejected during the second part.
4066 - Semicolon changes:
4067 . Stray semicolons are no longer allowed at the start of a grammar.
4068 . Semicolons are now required after in-grammar declarations.
4070 - Unescaped newlines are no longer allowed in character constants or
4071 string literals. They were never portable, and GCC 3.4.0 has
4072 dropped support for them. Better diagnostics are now generated if
4073 forget a closing quote.
4075 - NUL bytes are no longer allowed in Bison string literals, unfortunately.
4079 - GLR grammars now support locations.
4081 - New directive: %initial-action.
4082 This directive allows the user to run arbitrary code (including
4083 initializing @$) from yyparse before parsing starts.
4085 - A new directive "%expect-rr N" specifies the expected number of
4086 reduce/reduce conflicts in GLR parsers.
4088 - %token numbers can now be hexadecimal integers, e.g., "%token FOO 0x12d".
4089 This is a GNU extension.
4091 - The option "--report=lookahead" was changed to "--report=look-ahead".
4092 [However, this was changed back after 2.3.]
4094 - Experimental %destructor support has been added to lalr1.cc.
4096 - New configure option --disable-yacc, to disable installation of the
4097 yacc command and -ly library introduced in 1.875 for POSIX conformance.
4101 - For now, %expect-count violations are now just warnings, not errors.
4102 This is for compatibility with Bison 1.75 and earlier (when there are
4103 reduce/reduce conflicts) and with Bison 1.30 and earlier (when there
4104 are too many or too few shift/reduce conflicts). However, in future
4105 versions of Bison we plan to improve the %expect machinery so that
4106 these violations will become errors again.
4108 - Within Bison itself, numbers (e.g., goto numbers) are no longer
4109 arbitrarily limited to 16-bit counts.
4111 - Semicolons are now allowed before "|" in grammar rules, as POSIX requires.
4114 * Noteworthy changes in release 1.875 (2003-01-01)
4116 ** The documentation license has been upgraded to version 1.2
4117 of the GNU Free Documentation License.
4119 ** syntax error processing
4121 - In Yacc-style parsers YYLLOC_DEFAULT is now used to compute error
4122 locations too. This fixes bugs in error-location computation.
4125 It is now possible to reclaim the memory associated to symbols
4126 discarded during error recovery. This feature is still experimental.
4129 This new directive is preferred over YYERROR_VERBOSE.
4131 - #defining yyerror to steal internal variables is discouraged.
4132 It is not guaranteed to work forever.
4134 ** POSIX conformance
4136 - Semicolons are once again optional at the end of grammar rules.
4137 This reverts to the behavior of Bison 1.33 and earlier, and improves
4138 compatibility with Yacc.
4140 - "parse error" -> "syntax error"
4141 Bison now uniformly uses the term "syntax error"; formerly, the code
4142 and manual sometimes used the term "parse error" instead. POSIX
4143 requires "syntax error" in diagnostics, and it was thought better to
4146 - The documentation now emphasizes that yylex and yyerror must be
4147 declared before use. C99 requires this.
4149 - Bison now parses C99 lexical constructs like UCNs and
4150 backslash-newline within C escape sequences, as POSIX 1003.1-2001 requires.
4152 - File names are properly escaped in C output. E.g., foo\bar.y is
4153 output as "foo\\bar.y".
4155 - Yacc command and library now available
4156 The Bison distribution now installs a "yacc" command, as POSIX requires.
4157 Also, Bison now installs a small library liby.a containing
4158 implementations of Yacc-compatible yyerror and main functions.
4159 This library is normally not useful, but POSIX requires it.
4161 - Type clashes now generate warnings, not errors.
4163 - If the user does not define YYSTYPE as a macro, Bison now declares it
4164 using typedef instead of defining it as a macro.
4165 For consistency, YYLTYPE is also declared instead of defined.
4167 ** Other compatibility issues
4169 - %union directives can now have a tag before the "{", e.g., the
4170 directive "%union foo {...}" now generates the C code
4171 "typedef union foo { ... } YYSTYPE;"; this is for Yacc compatibility.
4172 The default union tag is "YYSTYPE", for compatibility with Solaris 9 Yacc.
4173 For consistency, YYLTYPE's struct tag is now "YYLTYPE" not "yyltype".
4174 This is for compatibility with both Yacc and Bison 1.35.
4176 - ";" is output before the terminating "}" of an action, for
4177 compatibility with Bison 1.35.
4179 - Bison now uses a Yacc-style format for conflict reports, e.g.,
4180 "conflicts: 2 shift/reduce, 1 reduce/reduce".
4182 - "yystype" and "yyltype" are now obsolescent macros instead of being
4183 typedefs or tags; they are no longer documented and are planned to be
4184 withdrawn in a future release.
4189 Users of Bison have to decide how they handle the portability of the
4192 - "parsing stack overflow..." -> "parser stack overflow"
4193 GLR parsers now report "parser stack overflow" as per the Bison manual.
4195 ** %parse-param and %lex-param
4196 The macros YYPARSE_PARAM and YYLEX_PARAM provide a means to pass
4197 additional context to yyparse and yylex. They suffer from several
4200 - a single argument only can be added,
4201 - their types are weak (void *),
4202 - this context is not passed to ancillary functions such as yyerror,
4203 - only yacc.c parsers support them.
4205 The new %parse-param/%lex-param directives provide a more precise control.
4208 %parse-param {int *nastiness}
4209 %lex-param {int *nastiness}
4210 %parse-param {int *randomness}
4212 results in the following signatures:
4214 int yylex (int *nastiness);
4215 int yyparse (int *nastiness, int *randomness);
4217 or, if both %pure-parser and %locations are used:
4219 int yylex (YYSTYPE *lvalp, YYLTYPE *llocp, int *nastiness);
4220 int yyparse (int *nastiness, int *randomness);
4222 ** Bison now warns if it detects conflicting outputs to the same file,
4223 e.g., it generates a warning for "bison -d -o foo.h foo.y" since
4224 that command outputs both code and header to foo.h.
4226 ** #line in output files
4227 - --no-line works properly.
4229 ** Bison can no longer be built by a K&R C compiler; it requires C89 or
4230 later to be built. This change originally took place a few versions
4231 ago, but nobody noticed until we recently asked someone to try
4232 building Bison with a K&R C compiler.
4235 * Noteworthy changes in release 1.75 (2002-10-14)
4237 ** Bison should now work on 64-bit hosts.
4239 ** Indonesian translation thanks to Tedi Heriyanto.
4242 Fix spurious parse errors.
4245 Some people redefine yyerror to steal yyparse' private variables.
4246 Reenable this trick until an official feature replaces it.
4249 In agreement with POSIX and with other Yaccs, leaving a default
4250 action is valid when $$ is untyped, and $1 typed:
4254 but the converse remains an error:
4258 ** Values of midrule actions
4261 foo: { ... } { $$ = $1; } ...
4263 was incorrectly rejected: $1 is defined in the second midrule
4264 action, and is equal to the $$ of the first midrule action.
4267 * Noteworthy changes in release 1.50 (2002-10-04)
4272 causes Bison to produce a Generalized LR (GLR) parser, capable of handling
4273 almost any context-free grammar, ambiguous or not. The new declarations
4274 %dprec and %merge on grammar rules allow parse-time resolution of
4275 ambiguities. Contributed by Paul Hilfinger.
4277 Unfortunately Bison 1.50 does not work properly on 64-bit hosts
4278 like the Alpha, so please stick to 32-bit hosts for now.
4281 When not in Yacc compatibility mode, when the output file was not
4282 specified, running "bison foo/bar.y" created "foo/bar.c". It
4283 now creates "bar.c".
4286 The undefined token was systematically mapped to 2 which prevented
4287 the use of 2 by the user. This is no longer the case.
4289 ** Unknown token numbers
4290 If yylex returned an out of range value, yyparse could die. This is
4294 According to POSIX, the error token must be 256.
4295 Bison extends this requirement by making it a preference: *if* the
4296 user specified that one of her tokens is numbered 256, then error
4297 will be mapped onto another number.
4299 ** Verbose error messages
4300 They no longer report "..., expecting error or..." for states where
4301 error recovery is possible.
4304 Defaults to "$end" instead of "$".
4306 ** Error recovery now conforms to documentation and to POSIX
4307 When a Bison-generated parser encounters a syntax error, it now pops
4308 the stack until it finds a state that allows shifting the error
4309 token. Formerly, it popped the stack until it found a state that
4310 allowed some non-error action other than a default reduction on the
4311 error token. The new behavior has long been the documented behavior,
4312 and has long been required by POSIX. For more details, please see
4313 Paul Eggert, "Reductions during Bison error handling" (2002-05-20)
4314 <https://lists.gnu.org/r/bug-bison/2002-05/msg00038.html>.
4317 Popped tokens and nonterminals are now reported.
4320 Larger grammars are now supported (larger token numbers, larger grammar
4321 size (= sum of the LHS and RHS lengths), larger LALR tables).
4322 Formerly, many of these numbers ran afoul of 16-bit limits;
4323 now these limits are 32 bits on most hosts.
4325 ** Explicit initial rule
4326 Bison used to play hacks with the initial rule, which the user does
4327 not write. It is now explicit, and visible in the reports and
4331 Before, Bison reported the useless rules, but, although not used,
4332 included them in the parsers. They are now actually removed.
4334 ** Useless rules, useless nonterminals
4335 They are now reported, as a warning, with their locations.
4337 ** Rules never reduced
4338 Rules that can never be reduced because of conflicts are now
4341 ** Incorrect "Token not used"
4342 On a grammar such as
4344 %token useless useful
4346 exp: '0' %prec useful;
4348 where a token was used to set the precedence of the last rule,
4349 bison reported both "useful" and "useless" as useless tokens.
4351 ** Revert the C++ namespace changes introduced in 1.31
4352 as they caused too many portability hassles.
4354 ** Default locations
4355 By an accident of design, the default computation of @$ was
4356 performed after another default computation was performed: @$ = @1.
4357 The latter is now removed: YYLLOC_DEFAULT is fully responsible of
4358 the computation of @$.
4360 ** Token end-of-file
4361 The token end of file may be specified by the user, in which case,
4362 the user symbol is used in the reports, the graphs, and the verbose
4363 error messages instead of "$end", which remains being the default.
4367 %token MYEOF 0 "end of file"
4370 This old option, which has been broken for ages, is removed.
4373 Brazilian Portuguese, thanks to Alexandre Folle de Menezes.
4374 Croatian, thanks to Denis Lackovic.
4376 ** Incorrect token definitions
4379 bison used to output
4382 ** Token definitions as enums
4383 Tokens are output both as the traditional #define's, and, provided
4384 the compiler supports ANSI C or is a C++ compiler, as enums.
4385 This lets debuggers display names instead of integers.
4388 In addition to --verbose, bison supports --report=THINGS, which
4389 produces additional information:
4391 complete the core item sets with their closure
4392 - lookahead [changed to "look-ahead" in 1.875e through 2.3, but changed back]
4393 explicitly associate lookahead tokens to items
4395 describe shift/reduce conflicts solving.
4396 Bison used to systematically output this information on top of
4397 the report. Solved conflicts are now attached to their states.
4400 Previous versions don't complain when there is a type clash on
4401 the default action if the rule has a midrule action, such as in:
4409 ** GNU M4 is now required when using Bison.
4412 * Noteworthy changes in release 1.35 (2002-03-25)
4415 Some projects use Bison's C parser with C++ compilers, and define
4416 YYSTYPE as a class. The recent adjustment of C parsers for data
4417 alignment and 64 bit architectures made this impossible.
4419 Because for the time being no real solution for C++ parser
4420 generation exists, kludges were implemented in the parser to
4421 maintain this use. In the future, when Bison has C++ parsers, this
4422 kludge will be disabled.
4424 This kludge also addresses some C++ problems when the stack was
4428 * Noteworthy changes in release 1.34 (2002-03-12)
4430 ** File name clashes are detected
4431 $ bison foo.y -d -o foo.x
4432 fatal error: header and parser would both be named "foo.x"
4434 ** A missing ";" at the end of a rule triggers a warning
4435 In accordance with POSIX, and in agreement with other
4436 Yacc implementations, Bison will mandate this semicolon in the near
4437 future. This eases the implementation of a Bison parser of Bison
4438 grammars by making this grammar LALR(1) instead of LR(2). To
4439 facilitate the transition, this release introduces a warning.
4441 ** Revert the C++ namespace changes introduced in 1.31, as they caused too
4442 many portability hassles.
4444 ** DJGPP support added.
4446 ** Fix test suite portability problems.
4449 * Noteworthy changes in release 1.33 (2002-02-07)
4452 Groff could not be compiled for the definition of size_t was lacking
4453 under some conditions.
4459 * Noteworthy changes in release 1.32 (2002-01-23)
4461 ** Fix Yacc output file names
4463 ** Portability fixes
4465 ** Italian, Dutch translations
4468 * Noteworthy changes in release 1.31 (2002-01-14)
4472 ** GNU Gettext and %expect
4473 GNU Gettext asserts 10 s/r conflicts, but there are 7. Now that
4474 Bison dies on incorrect %expectations, we fear there will be
4475 too many bug reports for Gettext, so _for the time being_, %expect
4476 does not trigger an error when the input file is named "plural.y".
4478 ** Use of alloca in parsers
4479 If YYSTACK_USE_ALLOCA is defined to 0, then the parsers will use
4480 malloc exclusively. Since 1.29, but was not NEWS'ed.
4482 alloca is used only when compiled with GCC, to avoid portability
4485 ** yyparse now returns 2 if memory is exhausted; formerly it dumped core.
4487 ** When the generated parser lacks debugging code, YYDEBUG is now 0
4488 (as POSIX requires) instead of being undefined.
4491 Bison has always permitted actions such as { $$ = $1 }: it adds the
4492 ending semicolon. Now if in Yacc compatibility mode, the semicolon
4493 is no longer output: one has to write { $$ = $1; }.
4495 ** Better C++ compliance
4496 The output parsers try to respect C++ namespaces.
4497 [This turned out to be a failed experiment, and it was reverted later.]
4500 Fixed bugs when reporting useless nonterminals.
4503 The parsers work properly on 64 bit hosts.
4506 Some calls to strerror resulted in scrambled or missing error messages.
4509 When the number of shift/reduce conflicts is correct, don't issue
4512 ** The verbose report includes the rule line numbers.
4514 ** Rule line numbers are fixed in traces.
4516 ** Swedish translation
4519 Verbose parse error messages from the parsers are better looking.
4520 Before: parse error: unexpected `'/'', expecting `"number"' or `'-'' or `'(''
4521 Now: parse error: unexpected '/', expecting "number" or '-' or '('
4523 ** Fixed parser memory leaks.
4524 When the generated parser was using malloc to extend its stacks, the
4525 previous allocations were not freed.
4527 ** Fixed verbose output file.
4528 Some newlines were missing.
4529 Some conflicts in state descriptions were missing.
4531 ** Fixed conflict report.
4532 Option -v was needed to get the result.
4536 Mismatches are errors, not warnings.
4538 ** Fixed incorrect processing of some invalid input.
4540 ** Fixed CPP guards: 9foo.h uses BISON_9FOO_H instead of 9FOO_H.
4542 ** Fixed some typos in the documentation.
4544 ** %token MY_EOF 0 is supported.
4545 Before, MY_EOF was silently renumbered as 257.
4547 ** doc/refcard.tex is updated.
4549 ** %output, %file-prefix, %name-prefix.
4553 New, aliasing "--output-file".
4556 * Noteworthy changes in release 1.30 (2001-10-26)
4558 ** "--defines" and "--graph" have now an optional argument which is the
4559 output file name. "-d" and "-g" do not change; they do not take any
4562 ** "%source_extension" and "%header_extension" are removed, failed
4565 ** Portability fixes.
4568 * Noteworthy changes in release 1.29 (2001-09-07)
4570 ** The output file does not define const, as this caused problems when used
4571 with common autoconfiguration schemes. If you still use ancient compilers
4572 that lack const, compile with the equivalent of the C compiler option
4573 "-Dconst=". Autoconf's AC_C_CONST macro provides one way to do this.
4575 ** Added "-g" and "--graph".
4577 ** The Bison manual is now distributed under the terms of the GNU FDL.
4579 ** The input and the output files has automatically a similar extension.
4581 ** Russian translation added.
4583 ** NLS support updated; should hopefully be less troublesome.
4585 ** Added the old Bison reference card.
4587 ** Added "--locations" and "%locations".
4589 ** Added "-S" and "--skeleton".
4591 ** "%raw", "-r", "--raw" is disabled.
4593 ** Special characters are escaped when output. This solves the problems
4594 of the #line lines with path names including backslashes.
4597 "%yacc", "%fixed_output_files", "%defines", "%no_parser", "%verbose",
4598 "%debug", "%source_extension" and "%header_extension".
4601 Automatic location tracking.
4604 * Noteworthy changes in release 1.28 (1999-07-06)
4606 ** Should compile better now with K&R compilers.
4610 ** Fixed a problem with escaping the double quote character.
4612 ** There is now a FAQ.
4615 * Noteworthy changes in release 1.27
4617 ** The make rule which prevented bison.simple from being created on
4618 some systems has been fixed.
4621 * Noteworthy changes in release 1.26
4623 ** Bison now uses Automake.
4625 ** New mailing lists: <bug-bison@gnu.org> and <help-bison@gnu.org>.
4627 ** Token numbers now start at 257 as previously documented, not 258.
4629 ** Bison honors the TMPDIR environment variable.
4631 ** A couple of buffer overruns have been fixed.
4633 ** Problems when closing files should now be reported.
4635 ** Generated parsers should now work even on operating systems which do
4636 not provide alloca().
4639 * Noteworthy changes in release 1.25 (1995-10-16)
4641 ** Errors in the input grammar are not fatal; Bison keeps reading
4642 the grammar file, and reports all the errors found in it.
4644 ** Tokens can now be specified as multiple-character strings: for
4645 example, you could use "<=" for a token which looks like <=, instead
4646 of choosing a name like LESSEQ.
4648 ** The %token_table declaration says to write a table of tokens (names
4649 and numbers) into the parser file. The yylex function can use this
4650 table to recognize multiple-character string tokens, or for other
4653 ** The %no_lines declaration says not to generate any #line preprocessor
4654 directives in the parser file.
4656 ** The %raw declaration says to use internal Bison token numbers, not
4657 Yacc-compatible token numbers, when token names are defined as macros.
4659 ** The --no-parser option produces the parser tables without including
4660 the parser engine; a project can now use its own parser engine.
4661 The actions go into a separate file called NAME.act, in the form of
4662 a switch statement body.
4665 * Noteworthy changes in release 1.23
4667 The user can define YYPARSE_PARAM as the name of an argument to be
4668 passed into yyparse. The argument should have type void *. It should
4669 actually point to an object. Grammar actions can access the variable
4670 by casting it to the proper pointer type.
4672 Line numbers in output file corrected.
4675 * Noteworthy changes in release 1.22
4677 --help option added.
4680 * Noteworthy changes in release 1.20
4682 Output file does not redefine const for C++.
4686 LocalWords: yacc YYBACKUP glr GCC lalr ArrayIndexOutOfBoundsException nullptr
4687 LocalWords: cplusplus liby rpl fprintf mfcalc Wyacc stmt cond expr mk sym lr
4688 LocalWords: IELR ielr Lookahead YYERROR nonassoc LALR's api lookaheads yychar
4689 LocalWords: destructor lookahead YYRHSLOC YYLLOC Rhs ifndef YYFAIL cpp sr rr
4690 LocalWords: preprocessor initializer Wno Wnone Werror FreeBSD prec livelocks
4691 LocalWords: Solaris AIX UX RHEL Tru LHS gcc's Wundef YYENABLE NLS YYLTYPE VCG
4692 LocalWords: yyerror cpp's Wunused yylval yylloc prepend yyparse yylex yypush
4693 LocalWords: Graphviz xml nonterminals midrule destructor's YYSTYPE typedef ly
4694 LocalWords: CHR chr printf stdout namespace preprocessing enum pre include's
4695 LocalWords: YYRECOVERING nonfree destructors YYABORT YYACCEPT params enums de
4696 LocalWords: struct yystype DJGPP lex param Haible NUM alloca YYSTACK NUL goto
4697 LocalWords: YYMAXDEPTH Unescaped UCNs YYLTYPE's yyltype typedefs inline Yaccs
4698 LocalWords: Heriyanto Reenable dprec Hilfinger Eggert MYEOF Folle Menezes EOF
4699 LocalWords: Lackovic define's itemset Groff Gettext malloc NEWS'ed YYDEBUG YY
4700 LocalWords: namespaces strerror const autoconfiguration Dconst Autoconf's FDL
4701 LocalWords: Automake TMPDIR LESSEQ ylwrap endif yydebug YYTOKEN YYLSP ival hh
4702 LocalWords: extern YYTOKENTYPE TOKENTYPE yytokentype tokentype STYPE lval pdf
4703 LocalWords: lang yyoutput dvi html ps POSIX lvalp llocp Wother nterm arg init
4704 LocalWords: TOK calc yyo fval Wconflicts parsers yystackp yyval yynerrs
4705 LocalWords: Théophile Ranquet Santet fno fnone stype associativity Tolmer
4706 LocalWords: Wprecedence Rassoul Wempty Paolo Bonzini parser's Michiel loc
4707 LocalWords: redeclaration sval fcaret reentrant XSLT xsl Wmaybe yyvsp Tedi
4708 LocalWords: pragmas noreturn untyped Rozenman unexpanded Wojciech Polak
4709 LocalWords: Alexandre MERCHANTABILITY yytype emplace ptr automove lvalues
4710 LocalWords: nonterminal yy args Pragma dereference yyformat rhs docdir bw
4711 LocalWords: Redeclarations rpcalc Autoconf YFLAGS Makefiles PROG DECL num
4712 LocalWords: Heimbigner AST src ast Makefile srcdir MinGW xxlex XXSTYPE CVE
4713 LocalWords: XXLTYPE strictfp IDEs ffixit fdiagnostics parseable fixits
4714 LocalWords: Wdeprecated yytext Variadic variadic yyrhs yyphrs RCS README
4715 LocalWords: noexcept constexpr ispell american deprecations backend Teoh
4716 LocalWords: YYPRINT Mangold Bonzini's Wdangling exVal baz checkable gcc
4717 LocalWords: fsanitize Vogelsgesang lis redeclared stdint automata yytname
4718 LocalWords: yysymbol yytnamerr yyreport ctx ARGMAX yysyntax stderr LPAREN
4719 LocalWords: symrec yypcontext TOKENMAX yyexpected YYEMPTY yypstate YYEOF
4720 LocalWords: autocompletion bistromathic submessages Cayuela lexcalc hoc
4721 LocalWords: yytoken YYUNDEF YYerror basename Automake's UTF ifdef ffile
4722 LocalWords: gotos readline Imbimbo Wcounterexamples Wcex Nonunifying rcex
4723 LocalWords: Vais xsltproc YYNOMEM YYLOCATION signedness YYBISON MITRE's
4724 LocalWords: libreadline YYMALLOC YYFREE MSVC redefinitions POSIXLY
4727 ispell-dictionary: "american"
4732 Copyright (C) 1995-2015, 2018-2021 Free Software Foundation, Inc.
4734 This file is part of Bison, the GNU Parser Generator.
4736 Permission is granted to copy, distribute and/or modify this document
4737 under the terms of the GNU Free Documentation License, Version 1.3 or
4738 any later version published by the Free Software Foundation; with no
4739 Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
4740 Texts. A copy of the license is included in the "GNU Free
4741 Documentation License" file as part of this distribution.