-Bison News
-----------
+GNU Bison NEWS
-* Changes in version 2.5 (????-??-??):
+* Noteworthy changes in release ?.? (????-??-??) [?]
-** Named References Support
+** Future changes
+
+ The next major release of Bison will drop support for the following
+ deprecated features. Please report disagreements to bug-bison@gnu.org.
+
+*** K&C parsers
+
+ Support for generating parsers in K&R C will be removed. Parsers
+ generated for C supprt ISO C90, and are tested with ISO C99 and ISO C11
+ compilers.
+
+*** Features deprecated since Bison 1.875
+
+ The definitions of yystype and yyltype will be removed; use YYSTYPE and
+ YYLTYPE.
+
+ YYPARSE_PARAM and YYLEX_PARAM, deprecated in favor of %parse-param and
+ %lex-param, will no longer be supported.
+
+ Support for the preprocessor symbol YYERROR_VERBOSE will be removed, use
+ %error-verbose.
+
+*** The generated header will be included (yacc.c)
+
+ Instead of duplicating the content of the generated header (definition of
+ YYSTYPE, yyparse declaration etc.), the generated parser will include it,
+ as is already the case for GLR or C++ parsers. This change is deferred
+ because existing versions of ylwrap (e.g., Automake 1.12.1) do not support
+ it.
+
+** Headers
+
+*** Guards (yacc.c, glr.c, glr.cc)
+
+ The generated headers are now guarded, as is already the case for C++
+ parsers (lalr1.cc). For intance, with --defines=foo.h:
+
+ #ifndef YY_FOO_H
+ # define YY_FOO_H
+ ...
+ #endif /* !YY_FOO_H */
+
+*** New declarations (yacc.c, glr.c)
+
+ The generated header now declares yydebug and yyparse. Both honor
+ --name-prefix=bar_, and yield
+
+ int bar_parse (void);
+
+ rather than
+
+ #define yyparse bar_parse
+ int yyparse (void);
+
+ in order to facilitate the inclusion of several parser headers inside a
+ single compilation unit.
+
+*** Exported symbols in C++
+
+ The symbols YYTOKEN_TABLE and YYERROR_VERBOSE, which were defined in the
+ header, are removed, as they prevent the possibility of including several
+ generated headers from a single compilation unit.
+
+*** YYLSP_NEEDED
+
+ For the same reasons, the undocumented and unused macro YYLSP_NEEDED is no
+ longer defined.
+
+** New %define variable: api.prefix
+
+ Now that the generated headers are more complete and properly protected
+ against multiple inclusions, constant names, such as YYSTYPE are a
+ problem. While yyparse and others are properly renamed by %name-prefix,
+ YYSTYPE, YYDEBUG and others have never been affected by it. Because it
+ would introduce backward compatibility issues in projects not expecting
+ YYSTYPE to be renamed, instead of changing the behavior of %name-prefix,
+ it is deprecated in favor of a new %define variable: api.prefix.
+
+ The following examples compares both:
+
+ %name-prefix "bar_" | %define api.prefix "bar_"
+ %token <ival> FOO %token <ival> FOO
+ %union { int ival; } %union { int ival; }
+ %% %%
+ exp: 'a'; exp: 'a';
+
+ bison generates:
+
+ #ifndef BAR_FOO_H #ifndef BAR_FOO_H
+ # define BAR_FOO_H # define BAR_FOO_H
+
+ /* Enabling traces. */ /* Enabling traces. */
+ # ifndef YYDEBUG # ifndef YYDEBUG
+ # define YYDEBUG 0 # define YYDEBUG 0
+ # endif # endif
+ # if YYDEBUG # if YYDEBUG
+ extern int bar_debug; extern int bar_debug;
+ # endif # endif
+
+ /* Tokens. */ /* Tokens. */
+ # ifndef YYTOKENTYPE | # ifndef BAR_TOKENTYPE
+ # define YYTOKENTYPE | # define BAR_TOKENTYPE
+ enum yytokentype { | enum bar_tokentype {
+ FOO = 258 FOO = 258
+ }; };
+ # endif # endif
+
+ #if ! defined YYSTYPE \ | #if ! defined BAR_STYPE \
+ && ! defined YYSTYPE_IS_DECLARED | && ! defined BAR_STYPE_IS_DECLARED
+ typedef union YYSTYPE | typedef union BAR_STYPE
+ { {
+ int ival; int ival;
+ } YYSTYPE; | } BAR_STYPE;
+ # define YYSTYPE_IS_DECLARED 1 | # define BAR_STYPE_IS_DECLARED 1
+ #endif #endif
+
+ extern YYSTYPE bar_lval; | extern BAR_STYPE bar_lval;
+
+ int bar_parse (void); int bar_parse (void);
+
+ #endif /* !BAR_FOO_H */ #endif /* !BAR_FOO_H */
+
+* Noteworthy changes in release 2.5.1 (2012-06-05) [stable]
+
+** Future changes:
+
+ The next major release will drop support for generating parsers in K&R C.
+
+** yacc.c: YYBACKUP works as expected.
+
+** glr.c improvements:
+
+*** Location support is eliminated when not requested:
+
+ GLR parsers used to include location-related code even when locations were
+ not requested, and therefore not even usable.
+
+*** __attribute__ is preserved:
+
+ __attribute__ is no longer disabled when __STRICT_ANSI__ is defined (i.e.,
+ when -std is passed to GCC).
+
+** lalr1.java: several fixes:
+
+ The Java parser no longer throws ArrayIndexOutOfBoundsException if the
+ first token leads to a syntax error. Some minor clean ups.
+
+** Changes for C++:
+
+*** C++11 compatibility:
+
+ C and C++ parsers use "nullptr" instead of "0" when __cplusplus is 201103L
+ or higher.
+
+*** Header guards
+
+ The header files such as "parser.hh", "location.hh", etc. used a constant
+ name for preprocessor guards, for instance:
+
+ #ifndef BISON_LOCATION_HH
+ # define BISON_LOCATION_HH
+ ...
+ #endif // !BISON_LOCATION_HH
+
+ The inclusion guard is now computed from "PREFIX/FILE-NAME", where lower
+ case characters are converted to upper case, and series of
+ non-alphanumerical characters are converted to an underscore.
+
+ With "bison -o lang++/parser.cc", "location.hh" would now include:
+
+ #ifndef YY_LANG_LOCATION_HH
+ # define YY_LANG_LOCATION_HH
+ ...
+ #endif // !YY_LANG_LOCATION_HH
+
+*** C++ locations:
+
+ The position and location constructors (and their initialize methods)
+ accept new arguments for line and column. Several issues in the
+ documentation were fixed.
+
+** liby is no longer asking for "rpl_fprintf" on some platforms.
+
+** Changes in the manual:
+
+*** %printer is documented
+
+ The "%printer" directive, supported since at least Bison 1.50, is finally
+ documented. The "mfcalc" example is extended to demonstrate it.
+
+ For consistency with the C skeletons, the C++ parsers now also support
+ "yyoutput" (as an alias to "debug_stream ()").
+
+*** Several improvements have been made:
+
+ The layout for grammar excerpts was changed to a more compact scheme.
+ Named references are motivated. The description of the automaton
+ description file (*.output) is updated to the current format. Incorrect
+ index entries were fixed. Some other errors were fixed.
+
+** Building bison:
+
+*** Conflicting prototypes with recent/modified Flex.
+
+ Fixed build problems with the current, unreleased, version of Flex, and
+ some modified versions of 2.5.35, which have modified function prototypes.
+
+*** Warnings during the build procedure have been eliminated.
+
+*** Several portability problems in the test suite have been fixed:
+
+ This includes warnings with some compilers, unexpected behavior of tools
+ such as diff, warning messages from the test suite itself, etc.
+
+*** The install-pdf target works properly:
+
+ Running "make install-pdf" (or -dvi, -html, -info, and -ps) no longer
+ halts in the middle of its course.
+
+* Changes in version 2.5 (2011-05-14):
+
+** Grammar symbol names can now contain non-initial dashes:
+
+ Consistently with directives (such as %error-verbose) and with
+ %define variables (e.g. push-pull), grammar symbol names may contain
+ dashes in any position except the beginning. This is a GNU
+ extension over POSIX Yacc. Thus, use of this extension is reported
+ by -Wyacc and rejected in Yacc mode (--yacc).
+
+** Named references:
Historically, Yacc and Bison have supported positional references
($n, $$) to allow access to symbol values from inside of semantic
When no ambiguity is possible, original symbol names may be used
as named references:
- if_stmt : 'if' cond_expr 'then' then_stmt ';'
+ if_stmt : "if" cond_expr "then" then_stmt ';'
{ $if_stmt = mk_if_stmt($cond_expr, $then_stmt); }
In the more common case, explicit names may be declared:
- stmt[res] : 'if' expr[cond] 'then' stmt[then] 'else' stmt[else] ';'
+ stmt[res] : "if" expr[cond] "then" stmt[then] "else" stmt[else] ';'
{ $res = mk_if_stmt($cond, $then, $else); }
Location information is also accessible using @name syntax. When
These features are experimental in this version. More user feedback
will help to stabilize them.
-** IELR(1) and Canonical LR(1) Support
+** IELR(1) and canonical LR(1):
IELR(1) is a minimal LR(1) parser table generation algorithm. That
is, given any context-free grammar, IELR(1) generates parser tables
- with the full language recognition power of canonical LR(1) but with
- nearly the same number of parser states as LALR(1). This reduction in
- parser states is often an order of magnitude. More importantly,
+ with the full language-recognition power of canonical LR(1) but with
+ nearly the same number of parser states as LALR(1). This reduction
+ in parser states is often an order of magnitude. More importantly,
because canonical LR(1)'s extra parser states may contain duplicate
conflicts in the case of non-LR(1) grammars, the number of conflicts
for IELR(1) is often an order of magnitude less as well. This can
%define lr.type ielr
%define lr.type canonical-lr
- The default reduction optimization in the parser tables can also be
- adjusted using `%define lr.default-reductions'. See the documentation
- for `%define lr.type' and `%define lr.default-reductions' in the
- section `Bison Declaration Summary' in the Bison manual for the
- details.
+ The default-reduction optimization in the parser tables can also be
+ adjusted using "%define lr.default-reductions". For details on both
+ of these features, see the new section "Tuning LR" in the Bison
+ manual.
These features are experimental. More user feedback will help to
stabilize them.
-** Unrecognized %code qualifiers are now an error not a warning.
+** LAC (Lookahead Correction) for syntax error handling:
-** %define improvements.
+ Canonical LR, IELR, and LALR can suffer from a couple of problems
+ upon encountering a syntax error. First, the parser might perform
+ additional parser stack reductions before discovering the syntax
+ error. Such reductions can perform user semantic actions that are
+ unexpected because they are based on an invalid token, and they
+ cause error recovery to begin in a different syntactic context than
+ the one in which the invalid token was encountered. Second, when
+ verbose error messages are enabled (with %error-verbose or the
+ obsolete "#define YYERROR_VERBOSE"), the expected token list in the
+ syntax error message can both contain invalid tokens and omit valid
+ tokens.
-*** Unrecognized variables are now an error not a warning.
+ The culprits for the above problems are %nonassoc, default
+ reductions in inconsistent states, and parser state merging. Thus,
+ IELR and LALR suffer the most. Canonical LR can suffer only if
+ %nonassoc is used or if default reductions are enabled for
+ inconsistent states.
-*** Multiple invocations for any variable is now an error not a warning.
+ LAC is a new mechanism within the parsing algorithm that solves
+ these problems for canonical LR, IELR, and LALR without sacrificing
+ %nonassoc, default reductions, or state merging. When LAC is in
+ use, canonical LR and IELR behave almost exactly the same for both
+ syntactically acceptable and syntactically unacceptable input.
+ While LALR still does not support the full language-recognition
+ power of canonical LR and IELR, LAC at least enables LALR's syntax
+ error handling to correctly reflect LALR's language-recognition
+ power.
+
+ Currently, LAC is only supported for deterministic parsers in C.
+ You can enable LAC with the following directive:
+
+ %define parse.lac full
-*** Can now be invoked via the command line.
+ See the new section "LAC" in the Bison manual for additional
+ details including a few caveats.
+
+ LAC is an experimental feature. More user feedback will help to
+ stabilize it.
+
+** %define improvements:
+
+*** Can now be invoked via the command line:
Each of these command-line options
quietly override %define, but -D and --define do not. For further
details, see the section "Bison Options" in the Bison manual.
-*** Variables renamed.
+*** Variables renamed:
The following %define variables
The old names are now deprecated but will be maintained indefinitely
for backward compatibility.
-*** Values no longer need to be quoted in grammar file.
+*** Values no longer need to be quoted in the grammar file:
If a %define value is an identifier, it no longer needs to be placed
within quotations marks. For example,
%define api.push-pull push
-** Symbol names.
+*** Unrecognized variables are now errors not warnings.
+
+*** Multiple invocations for any variable is now an error not a warning.
+
+** Unrecognized %code qualifiers are now errors not warnings.
+
+** Character literals not of length one:
+
+ Previously, Bison quietly converted all character literals to length
+ one. For example, without warning, Bison interpreted the operators in
+ the following grammar to be the same token:
+
+ exp: exp '++'
+ | exp '+' exp
+ ;
+
+ Bison now warns when a character literal is not of length one. In
+ some future release, Bison will start reporting an error instead.
+
+** Destructor calls fixed for lookaheads altered in semantic actions:
- Consistently with directives (such as %error-verbose) and variables
- (e.g. push-pull), symbol names may include dashes in any position,
- similarly to periods and underscores. This is GNU extension over
- POSIX Yacc whose use is reported by -Wyacc, and rejected in Yacc
- mode (--yacc).
+ Previously for deterministic parsers in C, if a user semantic action
+ altered yychar, the parser in some cases used the old yychar value to
+ determine which destructor to call for the lookahead upon a syntax
+ error or upon parser return. This bug has been fixed.
-** YYFAIL now produces warnings and Java parsers no longer implement it.
+** C++ parsers use YYRHSLOC:
+
+ Similarly to the C parsers, the C++ parsers now define the YYRHSLOC
+ macro and use it in the default YYLLOC_DEFAULT. You are encouraged
+ to use it. If, for instance, your location structure has "first"
+ and "last" members, instead of
+
+ # define YYLLOC_DEFAULT(Current, Rhs, N) \
+ do \
+ if (N) \
+ { \
+ (Current).first = (Rhs)[1].location.first; \
+ (Current).last = (Rhs)[N].location.last; \
+ } \
+ else \
+ { \
+ (Current).first = (Current).last = (Rhs)[0].location.last; \
+ } \
+ while (false)
+
+ use:
+
+ # define YYLLOC_DEFAULT(Current, Rhs, N) \
+ do \
+ if (N) \
+ { \
+ (Current).first = YYRHSLOC (Rhs, 1).first; \
+ (Current).last = YYRHSLOC (Rhs, N).last; \
+ } \
+ else \
+ { \
+ (Current).first = (Current).last = YYRHSLOC (Rhs, 0).last; \
+ } \
+ while (false)
+
+** YYLLOC_DEFAULT in C++:
+
+ The default implementation of YYLLOC_DEFAULT used to be issued in
+ the header file. It is now output in the implementation file, after
+ the user %code sections so that its #ifndef guard does not try to
+ override the user's YYLLOC_DEFAULT if provided.
+
+** YYFAIL now produces warnings and Java parsers no longer implement it:
YYFAIL has existed for many years as an undocumented feature of
deterministic parsers in C generated by Bison. More recently, it was
discussion of how to suppress C preprocessor warnings about YYFAIL
being unused, see the Bison 2.4.2 NEWS entry.
-** `%prec IDENTIFIER' requires IDENTIFIER to be defined separately.
-
- As promised in Bison 2.4.2's NEWS entry, it is now an error if a token
- that appears after a %prec directive is not defined by %token, %left,
- %right, or %nonassoc. This is required by POSIX.
-
-** Temporary hack for adding a semicolon to the user action.
+** Temporary hack for adding a semicolon to the user action:
Previously, Bison appended a semicolon to every user action for
reductions when the output language defaulted to C (specifically, when
about a missing semicolon where it did not before. Future releases of
Bison will cease to append semicolons entirely.
-** Character literals not of length one.
+** Verbose syntax error message fixes:
- Previously, Bison quietly converted all character literals to length
- one. For example, without warning, Bison interpreted the operators in
- the following grammar to be the same token:
+ When %error-verbose or the obsolete "#define YYERROR_VERBOSE" is
+ specified, syntax error messages produced by the generated parser
+ include the unexpected token as well as a list of expected tokens.
+ The effect of %nonassoc on these verbose messages has been corrected
+ in two ways, but a more complete fix requires LAC, described above:
- exp: exp '++'
- | exp '+' exp
- ;
+*** When %nonassoc is used, there can exist parser states that accept no
+ tokens, and so the parser does not always require a lookahead token
+ in order to detect a syntax error. Because no unexpected token or
+ expected tokens can then be reported, the verbose syntax error
+ message described above is suppressed, and the parser instead
+ reports the simpler message, "syntax error". Previously, this
+ suppression was sometimes erroneously triggered by %nonassoc when a
+ lookahead was actually required. Now verbose messages are
+ suppressed only when all previous lookaheads have already been
+ shifted or discarded.
- Bison now warns when a character literal is not of length one. In
- some future release, Bison will report an error instead.
+*** Previously, the list of expected tokens erroneously included tokens
+ that would actually induce a syntax error because conflicts for them
+ were resolved with %nonassoc in the current parser state. Such
+ tokens are now properly omitted from the list.
-** Verbose error messages fixed for nonassociative tokens.
+*** Expected token lists are still often wrong due to state merging
+ (from LALR or IELR) and default reductions, which can both add
+ invalid tokens and subtract valid tokens. Canonical LR almost
+ completely fixes this problem by eliminating state merging and
+ default reductions. However, there is one minor problem left even
+ when using canonical LR and even after the fixes above. That is,
+ if the resolution of a conflict with %nonassoc appears in a later
+ parser state than the one at which some syntax error is
+ discovered, the conflicted token is still erroneously included in
+ the expected token list. Bison's new LAC implementation,
+ described above, eliminates this problem and the need for
+ canonical LR. However, LAC is still experimental and is disabled
+ by default.
- When %error-verbose is specified, syntax error messages produced by
- the generated parser include the unexpected token as well as a list of
- expected tokens. Previously, this list erroneously included tokens
- that would actually induce a syntax error because conflicts for them
- were resolved with %nonassoc. Such tokens are now properly omitted
- from the list.
+** Java skeleton fixes:
-** Destructor calls fixed for lookaheads altered in semantic actions.
+*** A location handling bug has been fixed.
- Previously for deterministic parsers in C, if a user semantic action
- altered yychar, the parser in some cases used the old yychar value to
- determine which destructor to call for the lookahead upon a syntax
- error or upon parser return. This bug has been fixed.
+*** The top element of each of the value stack and location stack is now
+ cleared when popped so that it can be garbage collected.
+
+*** Parser traces now print the top element of the stack.
+
+** -W/--warnings fixes:
+
+*** Bison now properly recognizes the "no-" versions of categories:
+
+ For example, given the following command line, Bison now enables all
+ warnings except warnings for incompatibilities with POSIX Yacc:
-* Changes in version 2.4.2 (????-??-??):
+ bison -Wall,no-yacc gram.y
+
+*** Bison now treats S/R and R/R conflicts like other warnings:
+
+ Previously, conflict reports were independent of Bison's normal
+ warning system. Now, Bison recognizes the warning categories
+ "conflicts-sr" and "conflicts-rr". This change has important
+ consequences for the -W and --warnings command-line options. For
+ example:
+
+ bison -Wno-conflicts-sr gram.y # S/R conflicts not reported
+ bison -Wno-conflicts-rr gram.y # R/R conflicts not reported
+ bison -Wnone gram.y # no conflicts are reported
+ bison -Werror gram.y # any conflict is an error
+
+ However, as before, if the %expect or %expect-rr directive is
+ specified, an unexpected number of conflicts is an error, and an
+ expected number of conflicts is not reported, so -W and --warning
+ then have no effect on the conflict report.
+
+*** The "none" category no longer disables a preceding "error":
+
+ For example, for the following command line, Bison now reports
+ errors instead of warnings for incompatibilities with POSIX Yacc:
+
+ bison -Werror,none,yacc gram.y
+
+*** The "none" category now disables all Bison warnings:
+
+ Previously, the "none" category disabled only Bison warnings for
+ which there existed a specific -W/--warning category. However,
+ given the following command line, Bison is now guaranteed to
+ suppress all warnings:
+
+ bison -Wnone gram.y
+
+** Precedence directives can now assign token number 0:
+
+ Since Bison 2.3b, which restored the ability of precedence
+ directives to assign token numbers, doing so for token number 0 has
+ produced an assertion failure. For example:
+
+ %left END 0
+
+ This bug has been fixed.
+
+* Changes in version 2.4.3 (2010-08-05):
+
+** Bison now obeys -Werror and --warnings=error for warnings about
+ grammar rules that are useless in the parser due to conflicts.
+
+** Problems with spawning M4 on at least FreeBSD 8 and FreeBSD 9 have
+ been fixed.
+
+** Failures in the test suite for GCC 4.5 have been fixed.
+
+** Failures in the test suite for some versions of Sun Studio C++ have
+ been fixed.
+
+** Contrary to Bison 2.4.2's NEWS entry, it has been decided that
+ warnings about undefined %prec identifiers will not be converted to
+ errors in Bison 2.5. They will remain warnings, which should be
+ sufficient for POSIX while avoiding backward compatibility issues.
+
+** Minor documentation fixes.
+
+* Changes in version 2.4.2 (2010-03-20):
** Some portability problems that resulted in failures and livelocks
in the test suite on some versions of at least Solaris, AIX, HP-UX,
- RHEL4, and Tru64 have been fixed. As part of those fixes, fatal
- Bison errors no longer cause M4 to report a broken pipe on the
+ RHEL4, and Tru64 have been addressed. As a result, fatal Bison
+ errors should no longer cause M4 to report a broken pipe on the
affected platforms.
-** `%prec IDENTIFIER' requires IDENTIFIER to be defined separately.
+** "%prec IDENTIFIER" requires IDENTIFIER to be defined separately.
POSIX specifies that an error be reported for any identifier that does
not appear on the LHS of a grammar rule and that is not defined by
%prec directive. It is now restored. However, for backward
compatibility with recent Bison releases, it is only a warning for
now. In Bison 2.5 and later, it will return to being an error.
+ [Between the 2.4.2 and 2.4.3 releases, it was decided that this
+ warning will not be converted to an error in Bison 2.5.]
** Detection of GNU M4 1.4.6 or newer during configure is improved.
that YYFAIL will automatically invoke yyerror to report the syntax
error so that you don't have to. However, there are several other
subtle differences between YYERROR and YYFAIL, and YYFAIL suffers from
- inherent flaws when %error-verbose or `#define YYERROR_VERBOSE' is
+ inherent flaws when %error-verbose or "#define YYERROR_VERBOSE" is
used. For a more detailed discussion, see:
http://lists.gnu.org/archive/html/bison-patches/2009-12/msg00024.html
Bison features compatible with it. Thus, during parser generation,
Bison 2.5 will produce a warning whenever it discovers YYFAIL in a
rule action. In a later release, YYFAIL will be disabled for
- %error-verbose and `#define YYERROR_VERBOSE'. Eventually, YYFAIL will
+ %error-verbose and "#define YYERROR_VERBOSE". Eventually, YYFAIL will
be removed altogether.
There exists at least one case where Bison 2.5's YYFAIL warning will
Bison-defined macros for the sole purpose of suppressing C
preprocessor warnings (from GCC cpp's -Wunused-macros, for example).
To avoid Bison's future warning, such YYFAIL uses can be moved to the
- epilogue (that is, after the second `%%') in the Bison input file. In
+ epilogue (that is, after the second "%%") in the Bison input file. In
this release (2.4.2), Bison already generates its own code to suppress
C preprocessor warnings for YYFAIL, so projects can remove their own
phony uses of YYFAIL if compatibility with Bison releases prior to
exp: exp "+" exp { $$ = $1 + $3; };
- Some grammars still depend on this `feature'. Bison 2.4.1 restores
+ Some grammars still depend on this "feature". Bison 2.4.1 restores
the previous behavior in the case of C output (specifically, when
neither %language or %skeleton or equivalent command-line options
are used) to leave more time for grammars depending on the old
%define NAME "VALUE"
-** The directive `%pure-parser' is now deprecated in favor of:
+** The directive "%pure-parser" is now deprecated in favor of:
%define api.pure
** Push Parsing
Bison can now generate an LALR(1) parser in C with a push interface. That
- is, instead of invoking `yyparse', which pulls tokens from `yylex', you can
- push one token at a time to the parser using `yypush_parse', which will
+ is, instead of invoking "yyparse", which pulls tokens from "yylex", you can
+ push one token at a time to the parser using "yypush_parse", which will
return to the caller after processing each token. By default, the push
interface is disabled. Either of the following directives will enable it:
%define api.push_pull "push" // Just push; does not require yylex.
%define api.push_pull "both" // Push and pull; requires yylex.
- See the new section `A Push Parser' in the Bison manual for details.
+ See the new section "A Push Parser" in the Bison manual for details.
The current push parsing interface is experimental and may evolve. More user
feedback will help to stabilize it.
** Java
Bison can now generate an LALR(1) parser in Java. The skeleton is
- `data/lalr1.java'. Consider using the new %language directive instead of
+ "data/lalr1.java". Consider using the new %language directive instead of
%skeleton to select it.
- See the new section `Java Parsers' in the Bison manual for details.
+ See the new section "Java Parsers" in the Bison manual for details.
The current Java interface is experimental and may evolve. More user
feedback will help to stabilize it.
** XML Automaton Report
Bison can now generate an XML report of the LALR(1) automaton using the new
- `--xml' option. The current XML schema is experimental and may evolve. More
+ "--xml" option. The current XML schema is experimental and may evolve. More
user feedback will help to stabilize it.
** The grammar file may now specify the name of the parser header file using
%define lr.keep_unreachable_states
- See the %define entry in the `Bison Declaration Summary' in the Bison manual
+ See the %define entry in the "Bison Declaration Summary" in the Bison manual
for further discussion.
-** Lookahead Set Correction in the `.output' Report
+** Lookahead Set Correction in the ".output" Report
- When instructed to generate a `.output' file including lookahead sets
- (using `--report=lookahead', for example), Bison now prints each reduction's
+ When instructed to generate a ".output" file including lookahead sets
+ (using "--report=lookahead", for example), Bison now prints each reduction's
lookahead set only next to the associated state's one item that (1) is
associated with the same rule as the reduction and (2) has its dot at the end
of its RHS. Previously, Bison also erroneously printed the lookahead set
next to all of the state's other items associated with the same rule. This
- bug affected only the `.output' file and not the generated parser source
+ bug affected only the ".output" file and not the generated parser source
code.
-** --report-file=FILE is a new option to override the default `.output' file
+** --report-file=FILE is a new option to override the default ".output" file
name.
-** The `=' that used to be required in the following directives is now
+** The "=" that used to be required in the following directives is now
deprecated:
%file-prefix "parser"
%name-prefix "c_"
%output "parser.c"
-** An Alternative to `%{...%}' -- `%code QUALIFIER {CODE}'
+** An Alternative to "%{...%}" -- "%code QUALIFIER {CODE}"
Bison 2.3a provided a new set of directives as a more flexible alternative to
the traditional Yacc prologue blocks. Those have now been consolidated into
the purpose of the code and thus the location(s) where Bison should generate
it:
- 1. `%code {CODE}' replaces `%after-header {CODE}'
- 2. `%code requires {CODE}' replaces `%start-header {CODE}'
- 3. `%code provides {CODE}' replaces `%end-header {CODE}'
- 4. `%code top {CODE}' replaces `%before-header {CODE}'
+ 1. "%code {CODE}" replaces "%after-header {CODE}"
+ 2. "%code requires {CODE}" replaces "%start-header {CODE}"
+ 3. "%code provides {CODE}" replaces "%end-header {CODE}"
+ 4. "%code top {CODE}" replaces "%before-header {CODE}"
- See the %code entries in section `Bison Declaration Summary' in the Bison
- manual for a summary of the new functionality. See the new section `Prologue
- Alternatives' for a detailed discussion including the advantages of %code
+ See the %code entries in section "Bison Declaration Summary" in the Bison
+ manual for a summary of the new functionality. See the new section "Prologue
+ Alternatives" for a detailed discussion including the advantages of %code
over the traditional Yacc prologues.
The prologue alternatives are experimental. More user feedback will help to
sometimes prove to be false alarms in existing grammars employing the Yacc
constructs $0 or $-N (where N is some positive integer).
- To enable these warnings, specify the option `--warnings=midrule-values' or
- `-W', which is a synonym for `--warnings=all'.
+ To enable these warnings, specify the option "--warnings=midrule-values" or
+ "-W", which is a synonym for "--warnings=all".
-** Default %destructor or %printer with `<*>' or `<>'
+** Default %destructor or %printer with "<*>" or "<>"
Bison now recognizes two separate kinds of default %destructor's and
%printer's:
- 1. Place `<*>' in a %destructor/%printer symbol list to define a default
+ 1. Place "<*>" in a %destructor/%printer symbol list to define a default
%destructor/%printer for all grammar symbols for which you have formally
declared semantic type tags.
- 2. Place `<>' in a %destructor/%printer symbol list to define a default
+ 2. Place "<>" in a %destructor/%printer symbol list to define a default
%destructor/%printer for all grammar symbols without declared semantic
type tags.
- Bison no longer supports the `%symbol-default' notation from Bison 2.3a.
- `<*>' and `<>' combined achieve the same effect with one exception: Bison no
+ Bison no longer supports the "%symbol-default" notation from Bison 2.3a.
+ "<*>" and "<>" combined achieve the same effect with one exception: Bison no
longer applies any %destructor to a mid-rule value if that mid-rule value is
not actually ever referenced using either $$ or $n in a semantic action.
feedback will help to determine whether they should become permanent
features.
- See the section `Freeing Discarded Symbols' in the Bison manual for further
+ See the section "Freeing Discarded Symbols" in the Bison manual for further
details.
** %left, %right, and %nonassoc can now declare token numbers. This is required
- by POSIX. However, see the end of section `Operator Precedence' in the Bison
+ by POSIX. However, see the end of section "Operator Precedence" in the Bison
manual for a caveat concerning the treatment of literal strings.
** The nonfunctional --no-parser, -n, and %no-parser options have been
%destructor { } <character>
guarantees that, when the parser discards any user-defined symbol that has a
- semantic type tag other than `<character>', it passes its semantic value to
- `free'. However, when the parser discards a `STRING1' or a `string1', it
- also prints its line number to `stdout'. It performs only the second
- `%destructor' in this case, so it invokes `free' only once.
+ semantic type tag other than "<character>", it passes its semantic value to
+ "free". However, when the parser discards a "STRING1" or a "string1", it
+ also prints its line number to "stdout". It performs only the second
+ "%destructor" in this case, so it invokes "free" only once.
[Although we failed to mention this here in the 2.3a release, the default
%destructor's and %printer's were experimental, and they were rewritten in
future versions.]
-** Except for LALR(1) parsers in C with POSIX Yacc emulation enabled (with `-y',
- `--yacc', or `%yacc'), Bison no longer generates #define statements for
+** Except for LALR(1) parsers in C with POSIX Yacc emulation enabled (with "-y",
+ "--yacc", or "%yacc"), Bison no longer generates #define statements for
associating token numbers with token names. Removing the #define statements
helps to sanitize the global namespace during preprocessing, but POSIX Yacc
requires them. Bison still generates an enum for token names in all cases.
potentially incompatible with previous releases of Bison.
As before, you declare prologue blocks in your grammar file with the
- `%{ ... %}' syntax. To generate the pre-prologue, Bison concatenates all
+ "%{ ... %}" syntax. To generate the pre-prologue, Bison concatenates all
prologue blocks that you've declared before the first %union. To generate
the post-prologue, Bison concatenates all prologue blocks that you've
declared after the first %union.
* the code file before the contents of the header file. It does *not*
* insert it into the header file. This is a good place to put
* #include's that you want at the top of your code file. A common
- * example is `#include "system.h"'. */
+ * example is '#include "system.h"'. */
}
%start-header {
/* Bison inserts this block into both the header file and the code file.
[Although we failed to mention this here in the 2.3a release, the prologue
alternatives were experimental, and they were rewritten in future versions.]
-** The option `--report=look-ahead' has been changed to `--report=lookahead'.
+** The option "--report=look-ahead" has been changed to "--report=lookahead".
The old spelling still works, but is not documented and may be removed
in a future release.
* Changes in version 2.3, 2006-06-05:
-** GLR grammars should now use `YYRECOVERING ()' instead of `YYRECOVERING',
+** GLR grammars should now use "YYRECOVERING ()" instead of "YYRECOVERING",
for compatibility with LALR(1) grammars.
** It is now documented that any definition of YYSTYPE or YYLTYPE should
if the symbols have destructors. For instance:
exp: exp "?" exp ":" exp { $1 ? $1 : $3; }
- | exp "+" exp
- ;
+ | exp "+" exp
+ ;
will trigger a warning about $$ and $5 in the first rule, and $3 in
the second ($1 is copied to $$ by the default rule). This example
most likely contains three errors, and could be rewritten as:
exp: exp "?" exp ":" exp
- { $$ = $1 ? $3 : $5; free ($1 ? $5 : $3); free ($1); }
- | exp "+" exp
- { $$ = $1 ? $1 : $3; if ($1) free ($3); }
- ;
+ { $$ = $1 ? $3 : $5; free ($1 ? $5 : $3); free ($1); }
+ | exp "+" exp
+ { $$ = $1 ? $1 : $3; if ($1) free ($3); }
+ ;
However, if the original actions were really intended, memory leaks
and all, the warnings can be suppressed by letting Bison believe the
values are used, e.g.:
exp: exp "?" exp ":" exp { $1 ? $1 : $3; (void) ($$, $5); }
- | exp "+" exp { $$ = $1; (void) $3; }
- ;
+ | exp "+" exp { $$ = $1; (void) $3; }
+ ;
If there are mid-rule actions, the warning is issued if no action
uses it. The following triggers no warning: $1 and $3 are used.
The %parse-params are available in the destructors (and the
experimental printers) as per the documentation.
-** Bison now warns if it finds a stray `$' or `@' in an action.
+** Bison now warns if it finds a stray "$" or "@" in an action.
** %require "VERSION"
This specifies that the grammar file depends on features implemented
** lalr1.cc: The token and value types are now class members.
The tokens were defined as free form enums and cpp macros. YYSTYPE
was defined as a free form union. They are now class members:
- tokens are enumerations of the `yy::parser::token' struct, and the
- semantic values have the `yy::parser::semantic_type' type.
+ tokens are enumerations of the "yy::parser::token" struct, and the
+ semantic values have the "yy::parser::semantic_type" type.
If you do not want or can update to this scheme, the directive
- `%define "global_tokens_and_yystype" "1"' triggers the global
+ '%define "global_tokens_and_yystype" "1"' triggers the global
definition of tokens and YYSTYPE. This change is suitable both
for previous releases of Bison, and this one.
If you wish to update, then make sure older version of Bison will
- fail using `%require "2.2"'.
+ fail using '%require "2.2"'.
** DJGPP support added.
\f
- A new directive "%expect-rr N" specifies the expected number of
reduce/reduce conflicts in GLR parsers.
- - %token numbers can now be hexadecimal integers, e.g., `%token FOO 0x12d'.
+ - %token numbers can now be hexadecimal integers, e.g., "%token FOO 0x12d".
This is a GNU extension.
- - The option `--report=lookahead' was changed to `--report=look-ahead'.
+ - The option "--report=lookahead" was changed to "--report=look-ahead".
[However, this was changed back after 2.3.]
- Experimental %destructor support has been added to lalr1.cc.
This reverts to the behavior of Bison 1.33 and earlier, and improves
compatibility with Yacc.
- - `parse error' -> `syntax error'
- Bison now uniformly uses the term `syntax error'; formerly, the code
- and manual sometimes used the term `parse error' instead. POSIX
- requires `syntax error' in diagnostics, and it was thought better to
+ - "parse error" -> "syntax error"
+ Bison now uniformly uses the term "syntax error"; formerly, the code
+ and manual sometimes used the term "parse error" instead. POSIX
+ requires "syntax error" in diagnostics, and it was thought better to
be consistent.
- The documentation now emphasizes that yylex and yyerror must be
output as "foo\\bar.y".
- Yacc command and library now available
- The Bison distribution now installs a `yacc' command, as POSIX requires.
+ The Bison distribution now installs a "yacc" command, as POSIX requires.
Also, Bison now installs a small library liby.a containing
implementations of Yacc-compatible yyerror and main functions.
This library is normally not useful, but POSIX requires it.
** Other compatibility issues
- - %union directives can now have a tag before the `{', e.g., the
- directive `%union foo {...}' now generates the C code
- `typedef union foo { ... } YYSTYPE;'; this is for Yacc compatibility.
- The default union tag is `YYSTYPE', for compatibility with Solaris 9 Yacc.
- For consistency, YYLTYPE's struct tag is now `YYLTYPE' not `yyltype'.
+ - %union directives can now have a tag before the "{", e.g., the
+ directive "%union foo {...}" now generates the C code
+ "typedef union foo { ... } YYSTYPE;"; this is for Yacc compatibility.
+ The default union tag is "YYSTYPE", for compatibility with Solaris 9 Yacc.
+ For consistency, YYLTYPE's struct tag is now "YYLTYPE" not "yyltype".
This is for compatibility with both Yacc and Bison 1.35.
- - `;' is output before the terminating `}' of an action, for
+ - ";" is output before the terminating "}" of an action, for
compatibility with Bison 1.35.
- Bison now uses a Yacc-style format for conflict reports, e.g.,
- `conflicts: 2 shift/reduce, 1 reduce/reduce'.
+ "conflicts: 2 shift/reduce, 1 reduce/reduce".
- - `yystype' and `yyltype' are now obsolescent macros instead of being
+ - "yystype" and "yyltype" are now obsolescent macros instead of being
typedefs or tags; they are no longer documented and are planned to be
withdrawn in a future release.
- GLR and inline
Users of Bison have to decide how they handle the portability of the
- C keyword `inline'.
+ C keyword "inline".
+
+ - "parsing stack overflow..." -> "parser stack overflow"
+ GLR parsers now report "parser stack overflow" as per the Bison manual.
+
+** %parse-param and %lex-param
+ The macros YYPARSE_PARAM and YYLEX_PARAM provide a means to pass
+ additional context to yyparse and yylex. They suffer from several
+ shortcomings:
+
+ - a single argument only can be added,
+ - their types are weak (void *),
+ - this context is not passed to anciliary functions such as yyerror,
+ - only yacc.c parsers support them.
+
+ The new %parse-param/%lex-param directives provide a more precise control.
+ For instance:
+
+ %parse-param {int *nastiness}
+ %lex-param {int *nastiness}
+ %parse-param {int *randomness}
+
+ results in the following signatures:
+
+ int yylex (int *nastiness);
+ int yyparse (int *nastiness, int *randomness);
+
+ or, if both %pure-parser and %locations are used:
- - `parsing stack overflow...' -> `parser stack overflow'
- GLR parsers now report `parser stack overflow' as per the Bison manual.
+ int yylex (YYSTYPE *lvalp, YYLTYPE *llocp, int *nastiness);
+ int yyparse (int *nastiness, int *randomness);
** Bison now warns if it detects conflicting outputs to the same file,
- e.g., it generates a warning for `bison -d -o foo.h foo.y' since
+ e.g., it generates a warning for "bison -d -o foo.h foo.y" since
that command outputs both code and header to foo.h.
** #line in output files
In agreement with POSIX and with other Yaccs, leaving a default
action is valid when $$ is untyped, and $1 typed:
- untyped: ... typed;
+ untyped: ... typed;
but the converse remains an error:
- typed: ... untyped;
+ typed: ... untyped;
** Values of mid-rule actions
The following code:
- foo: { ... } { $$ = $1; } ...
+ foo: { ... } { $$ = $1; } ...
was incorrectly rejected: $1 is defined in the second mid-rule
action, and is equal to the $$ of the first mid-rule action.
** Output Directory
When not in Yacc compatibility mode, when the output file was not
- specified, running `bison foo/bar.y' created `foo/bar.c'. It
- now creates `bar.c'.
+ specified, running "bison foo/bar.y" created "foo/bar.c". It
+ now creates "bar.c".
** Undefined token
The undefined token was systematically mapped to 2 which prevented
will be mapped onto another number.
** Verbose error messages
- They no longer report `..., expecting error or...' for states where
+ They no longer report "..., expecting error or..." for states where
error recovery is possible.
** End token
- Defaults to `$end' instead of `$'.
+ Defaults to "$end" instead of "$".
** Error recovery now conforms to documentation and to POSIX
When a Bison-generated parser encounters a syntax error, it now pops
Rules that can never be reduced because of conflicts are now
reported.
-** Incorrect `Token not used'
+** Incorrect "Token not used"
On a grammar such as
- %token useless useful
- %%
- exp: '0' %prec useful;
+ %token useless useful
+ %%
+ exp: '0' %prec useful;
where a token was used to set the precedence of the last rule,
- bison reported both `useful' and `useless' as useless tokens.
+ bison reported both "useful" and "useless" as useless tokens.
** Revert the C++ namespace changes introduced in 1.31
as they caused too many portability hassles.
** Token end-of-file
The token end of file may be specified by the user, in which case,
the user symbol is used in the reports, the graphs, and the verbose
- error messages instead of `$end', which remains being the default.
+ error messages instead of "$end", which remains being the default.
For instance
- %token MYEOF 0
+ %token MYEOF 0
or
- %token MYEOF 0 "end of file"
+ %token MYEOF 0 "end of file"
** Semantic parser
This old option, which has been broken for ages, is removed.
Croatian, thanks to Denis Lackovic.
** Incorrect token definitions
- When given `%token 'a' "A"', Bison used to output `#define 'a' 65'.
+ When given
+ %token 'a' "A"
+ bison used to output
+ #define 'a' 65
** Token definitions as enums
Tokens are output both as the traditional #define's, and, provided
produces additional information:
- itemset
complete the core item sets with their closure
- - lookahead [changed to `look-ahead' in 1.875e through 2.3, but changed back]
+ - lookahead [changed to "look-ahead" in 1.875e through 2.3, but changed back]
explicitly associate lookahead tokens to items
- solved
describe shift/reduce conflicts solving.
Previous versions don't complain when there is a type clash on
the default action if the rule has a mid-rule action, such as in:
- %type <foo> bar
- %%
- bar: '0' {} '0';
+ %type <foo> bar
+ %%
+ bar: '0' {} '0';
This is fixed.
** File name clashes are detected
$ bison foo.y -d -o foo.x
- fatal error: header and parser would both be named `foo.x'
+ fatal error: header and parser would both be named "foo.x"
-** A missing `;' at the end of a rule triggers a warning
+** A missing ";" at the end of a rule triggers a warning
In accordance with POSIX, and in agreement with other
Yacc implementations, Bison will mandate this semicolon in the near
future. This eases the implementation of a Bison parser of Bison
GNU Gettext asserts 10 s/r conflicts, but there are 7. Now that
Bison dies on incorrect %expectations, we fear there will be
too many bug reports for Gettext, so _for the time being_, %expect
- does not trigger an error when the input file is named `plural.y'.
+ does not trigger an error when the input file is named "plural.y".
** Use of alloca in parsers
If YYSTACK_USE_ALLOCA is defined to 0, then the parsers will use
New.
** --output
- New, aliasing `--output-file'.
+ New, aliasing "--output-file".
\f
* Changes in version 1.30, 2001-10-26:
-** `--defines' and `--graph' have now an optional argument which is the
- output file name. `-d' and `-g' do not change; they do not take any
+** "--defines" and "--graph" have now an optional argument which is the
+ output file name. "-d" and "-g" do not change; they do not take any
argument.
-** `%source_extension' and `%header_extension' are removed, failed
+** "%source_extension" and "%header_extension" are removed, failed
experiment.
** Portability fixes.
** The output file does not define const, as this caused problems when used
with common autoconfiguration schemes. If you still use ancient compilers
that lack const, compile with the equivalent of the C compiler option
- `-Dconst='. autoconf's AC_C_CONST macro provides one way to do this.
+ "-Dconst=". Autoconf's AC_C_CONST macro provides one way to do this.
-** Added `-g' and `--graph'.
+** Added "-g" and "--graph".
** The Bison manual is now distributed under the terms of the GNU FDL.
** Added the old Bison reference card.
-** Added `--locations' and `%locations'.
+** Added "--locations" and "%locations".
-** Added `-S' and `--skeleton'.
+** Added "-S" and "--skeleton".
-** `%raw', `-r', `--raw' is disabled.
+** "%raw", "-r", "--raw" is disabled.
** Special characters are escaped when output. This solves the problems
of the #line lines with path names including backslashes.
** New directives.
- `%yacc', `%fixed_output_files', `%defines', `%no_parser', `%verbose',
- `%debug', `%source_extension' and `%header_extension'.
+ "%yacc", "%fixed_output_files", "%defines", "%no_parser", "%verbose",
+ "%debug", "%source_extension" and "%header_extension".
** @$
Automatic location tracking.
\f
* Changes in version 1.26:
-** Bison now uses automake.
+** Bison now uses Automake.
** New mailing lists: <bug-bison@gnu.org> and <help-bison@gnu.org>.
** Tokens can now be specified as multiple-character strings: for
example, you could use "<=" for a token which looks like <=, instead
-of chosing a name like LESSEQ.
+of choosing a name like LESSEQ.
** The %token_table declaration says to write a table of tokens (names
and numbers) into the parser file. The yylex function can use this
Output file does not redefine const for C++.
-Local Variables:
-mode: outline
-End:
-
-----
-Copyright (C) 1995-2010 Free Software Foundation, Inc.
+Copyright (C) 1995-2012 Free Software Foundation, Inc.
This file is part of Bison, the GNU Parser Generator.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
+
+ LocalWords: yacc YYBACKUP glr GCC lalr ArrayIndexOutOfBoundsException nullptr
+ LocalWords: cplusplus liby rpl fprintf mfcalc Wyacc stmt cond expr mk sym lr
+ LocalWords: IELR ielr Lookahead YYERROR nonassoc LALR's api lookaheads yychar
+ LocalWords: destructor lookahead YYRHSLOC YYLLOC Rhs ifndef YYFAIL cpp sr rr
+ LocalWords: preprocessor initializer Wno Wnone Werror FreeBSD prec livelocks
+ LocalWords: Solaris AIX UX RHEL Tru LHS gcc's Wundef YYENABLE NLS YYLTYPE VCG
+ LocalWords: yyerror cpp's Wunused yylval yylloc prepend yyparse yylex yypush
+ LocalWords: Graphviz xml nonterminals midrule destructor's YYSTYPE typedef ly
+ LocalWords: CHR chr printf stdout namespace preprocessing enum pre include's
+ LocalWords: YYRECOVERING nonfree destructors YYABORT YYACCEPT params enums de
+ LocalWords: struct yystype DJGPP lex param Haible NUM alloca YYSTACK NUL goto
+ LocalWords: YYMAXDEPTH Unescaped UCNs YYLTYPE's yyltype typedefs inline Yaccs
+ LocalWords: Heriyanto Reenable dprec Hilfinger Eggert MYEOF Folle Menezes EOF
+ LocalWords: Lackovic define's itemset Groff Gettext malloc NEWS'ed YYDEBUG
+ LocalWords: namespaces strerror const autoconfiguration Dconst Autoconf's FDL
+ LocalWords: Automake TMPDIR LESSEQ
+
+Local Variables:
+mode: outline
+fill-column: 76
+End:
projects / bison.git / blobdiff