-Bison News
-----------
+GNU Bison NEWS
-* Changes in version 2.5.1_rc2 (2012-05-23):
+* Noteworthy changes in release ?.? (????-??-??) [?]
+
+** Incompatible changes
+
+*** Obsolete features
+
+ Support for YYFAIL is removed (deprecated in Bison 2.4.2).
+ Support for yystype and yyltype (instead of YYSTYPE and YYLTYPE)
+ is removed (deprecated in Bison 1.875).
+ Support for YYPARSE_PARAM is removed (deprecated in Bison 1.875).
+
+** Warnings
+
+*** Deprecated constructs
+
+ The new 'deprecated' warning category flags obsolete constructs whose
+ support will be discontinued. It is enabled by default. These warnings
+ used to be reported as 'other' warnings.
+
+*** Warning categories are now displayed
+
+ For instance:
+
+ foo.y:4.6: warning: type clash on default action: <foo> != <bar> [-Wother]
+
+*** Useless semantic types
+
+ Bison now warns about useless (uninhabited) semantic types. Since
+ semantic types are not declared to Bison (they are defined in the opaque
+ %union structure), it is %printer/%destructor directives about useless
+ types that trigger the warning:
+
+ %token <type1> term
+ %type <type2> nterm
+ %printer {} <type1> <type3>
+ %destructor {} <type2> <type4>
+ %%
+ nterm: term { $$ = $1; };
+
+ 3.28-34: warning: type <type3> is used, but is not associated to any symbol
+ 4.28-34: warning: type <type4> is used, but is not associated to any symbol
+
+*** Undefined but unused symbols
+
+ Bison used to raise an error for undefined symbols that are not used in
+ the grammar. This is now only a warning.
+
+ %printer {} symbol1
+ %destructor {} symbol2
+ %type <type> symbol3
+ %%
+ exp: "a";
+
+*** Useless destructors or printers
+
+ Bison now warns about useless destructors or printers. In the following
+ example, the printer for <type1>, and the destructor for <type2> are
+ useless: all symbols of <type1> (token1) already have a printer, and all
+ symbols of type <type2> (token2) already have a destructor.
+
+ %token <type1> token1
+ <type2> token2
+ <type3> token3
+ <type4> token4
+ %printer {} token1 <type1> <type3>
+ %destructor {} token2 <type2> <type4>
+
+** Additional yylex/yyparse arguments
+
+ The new directive %param declares additional arguments to both yylex and
+ yyparse. The %lex-param, %parse-param, and %param directives support one
+ or more arguments. Instead of
+
+ %lex-param {arg1_type *arg1}
+ %lex-param {arg2_type *arg2}
+ %parse-param {arg1_type *arg1}
+ %parse-param {arg2_type *arg2}
+
+ one may now declare
+
+ %param {arg1_type *arg1} {arg2_type *arg2}
+
+** Java skeleton improvements
+
+ The constants for token names were moved to the Lexer interface. Also, it
+ is possible to add code to the parser's constructors using "%code init"
+ and "%define init_throws".
+
+** C++ skeletons improvements
+
+*** The parser header is no longer mandatory (lalr1.cc, glr.cc)
+
+ Using %defines is now optional. Without it, the needed support classes
+ are defined in the generated parser, instead of additional files (such as
+ location.hh, position.hh and stack.hh).
+
+*** Locations are no longer mandatory (lalr1.cc, glr.cc)
+
+ Both lalr1.cc and glr.cc no longer require %location.
+
+*** syntax_error exception (lalr1.cc)
+
+ The C++ parser features a syntax_error exception, which can be
+ thrown from the scanner or from user rules to raise syntax errors.
+ This facilitates reporting errors caught in sub-functions (e.g.,
+ rejecting too large integral literals from a conversion function
+ used by the scanner, or rejecting invalid combinations from a
+ factory invoked by the user actions).
+
+** Variable api.tokens.prefix
+
+ The variable api.tokens.prefix changes the way tokens are identified in
+ the generated files. This is especially useful to avoid collisions
+ with identifiers in the target language. For instance
+
+ %token FILE for ERROR
+ %define api.tokens.prefix "TOK_"
+ %%
+ start: FILE for ERROR;
+
+ will generate the definition of the symbols TOK_FILE, TOK_for, and
+ TOK_ERROR in the generated sources. In particular, the scanner must
+ use these prefixed token names, although the grammar itself still
+ uses the short names (as in the sample rule given above).
+
+** Variable api.namespace
+
+ The 'namespace' variable is renamed 'api.namespace'. Backward
+ compatibility is ensured, but upgrading is recommended.
+
+** Variable parse.error
+
+ This variable controls the verbosity of error messages. The use of the
+ %error-verbose directive is deprecated in favor of "%define parse.error
+ verbose".
+
+** Semantic predicates
+
+ The new, experimental, semantic-predicate feature allows actions of the
+ form "%?{ BOOLEAN-EXPRESSION }", which cause syntax errors (as for
+ YYERROR) if the expression evaluates to 0, and are evaluated immediately
+ in GLR parsers, rather than being deferred. The result is that they allow
+ the programmer to prune possible parses based on the values of run-time
+ expressions.
+
+* Noteworthy changes in release ?.? (????-??-??) [?]
+
+
+* Noteworthy changes in release 2.6.2 (2012-08-03) [stable]
+
+** Bug fixes
+
+ Buffer overruns, complaints from Flex, and portability issues in the test
+ suite have been fixed.
+
+** Spaces in %lex- and %parse-param (lalr1.cc, glr.cc)
+
+ Trailing end-of-lines in %parse-param or %lex-param would result in
+ invalid C++. This is fixed.
+
+** Spurious spaces and end-of-lines
+
+ The generated files no longer end (nor start) with empty lines.
+
+* Noteworthy changes in release 2.6.1 (2012-07-30) [stable]
+
+ Bison no longer executes user-specified M4 code when processing a grammar.
+
+** Future Changes
+
+ In addition to the removal of the features announced in Bison 2.6, the
+ next major release will remove the "Temporary hack for adding a semicolon
+ to the user action", as announced in the release 2.5. Instead of:
+
+ exp: exp "+" exp { $$ = $1 + $3 };
+
+ write:
+
+ exp: exp "+" exp { $$ = $1 + $3; };
+
+** Bug fixes
+
+*** Type names are now properly escaped.
+
+*** glr.cc: set_debug_level and debug_level work as expected.
+
+*** Stray @ or $ in actions
+
+ While Bison used to warn about stray $ or @ in action rules, it did not
+ for other actions such as printers, destructors, or initial actions. It
+ now does.
+
+** Type names in actions
+
+ For consistency with rule actions, it is now possible to qualify $$ by a
+ type-name in destructors, printers, and initial actions. For instance:
+
+ %printer { fprintf (yyo, "(%d, %f)", $<ival>$, $<fval>$); } <*> <>;
+
+ will display two values for each typed and untyped symbol (provided
+ that YYSTYPE has both "ival" and "fval" fields).
+
+* Noteworthy changes in release 2.6 (2012-07-19) [stable]
+
+** 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&R C parsers
+
+ Support for generating parsers in K&R C will be removed. Parsers
+ generated for C support 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.
+
+** Generated Parser 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 instance, 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 BAR_DEBUG
+ > # if defined YYDEBUG
+ > # if YYDEBUG
+ > # define BAR_DEBUG 1
+ > # else
+ > # define BAR_DEBUG 0
+ > # endif
+ > # else
+ # define YYDEBUG 0 | # define BAR_DEBUG 0
+ > # endif
+ # endif | # endif
+
+ # if YYDEBUG | # if BAR_DEBUG
+ 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 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
+ #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
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
+ #ifndef YY_LANG_LOCATION_HH
+ # define YY_LANG_LOCATION_HH
+ ...
+ #endif // !YY_LANG_LOCATION_HH
*** C++ locations:
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 work properly:
+*** 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.
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)
+ # 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)
+ # 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++:
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 { $$ = $1; (void) $3; }
+ ;
If there are mid-rule actions, the warning is issued if no action
uses it. The following triggers no warning: $1 and $3 are used.
- "parsing stack overflow..." -> "parser stack overflow"
GLR parsers now report "parser stack overflow" as per the Bison manual.
+** %parse-param and %lex-param
+ The macros YYPARSE_PARAM and YYLEX_PARAM provide a means to pass
+ additional context to yyparse and yylex. They suffer from several
+ shortcomings:
+
+ - a single argument only can be added,
+ - their types are weak (void *),
+ - this context is not passed to ancillary functions such as yyerror,
+ - only yacc.c parsers support them.
+
+ The new %parse-param/%lex-param directives provide a more precise control.
+ For instance:
+
+ %parse-param {int *nastiness}
+ %lex-param {int *nastiness}
+ %parse-param {int *randomness}
+
+ results in the following signatures:
+
+ int yylex (int *nastiness);
+ int yyparse (int *nastiness, int *randomness);
+
+ or, if both %pure-parser and %locations are used:
+
+ int yylex (YYSTYPE *lvalp, YYLTYPE *llocp, int *nastiness);
+ int yyparse (int *nastiness, int *randomness);
+
** Bison now warns if it detects conflicting outputs to the same file,
e.g., it generates a warning for "bison -d -o foo.h foo.y" since
that command outputs both code and header to foo.h.
In agreement with POSIX and with other Yaccs, leaving a default
action is valid when $$ 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.
** 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.
the user symbol is used in the reports, the graphs, and the verbose
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.
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.
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: Lackovic define's itemset Groff Gettext malloc NEWS'ed YYDEBUG YY
LocalWords: namespaces strerror const autoconfiguration Dconst Autoconf's FDL
- LocalWords: Automake TMPDIR LESSEQ
+ LocalWords: Automake TMPDIR LESSEQ ylwrap endif yydebug YYTOKEN YYLSP ival hh
+ LocalWords: extern YYTOKENTYPE TOKENTYPE yytokentype tokentype STYPE lval pdf
+ LocalWords: lang yyoutput dvi html ps POSIX lvalp llocp Wother nterm arg init
+ LocalWords: TOK
Local Variables:
mode: outline
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