-Bison News
-----------
+GNU Bison NEWS
-* Changes in version ?.? (????-??-??):
+* Noteworthy changes in release ?.? (????-??-??) [?]
+
+** WARNING: Future backward-incompatibilities!
+
+ Bison will stop adding a semicolon at the end of the actions (as announced
+ in the release 2.5):
+
+ foo.y:2.22: warning: a ';' might be needed at the end of action code
+ exp: "num" { $$ = $1 }
+ ^
+ foo.y:2.22: future versions of Bison will not add the ';'
+
+ Like other GNU packages, Bison will start using some of the C99 features
+ for its own code, especially the definition of variables after statements.
+ The generated C parsers still aim at C90.
+
+** Backward incompatible changes
+
+*** Obsolete features
+
+ Support for YYFAIL is removed (deprecated in Bison 2.4.2): use YYERROR.
+
+ Support for yystype and yyltype is removed (deprecated in Bison 1.875):
+ use YYSTYPE and YYLTYPE.
+
+ Support for YYLEX_PARAM and YYPARSE_PARAM is removed (deprecated in Bison
+ 1.875): use %lex-param, %parse-param, or %param.
+
+** Bug fixes
+
+*** The epilogue is no longer affected by internal #defines
+
+ The glr.c skeleton uses defines such as #define yylval (yystackp->yyval) in
+ generated code. These weren't properly undefined before the inclusion of
+ the user epilogue, so functions such as the following were butchered by the
+ preprocessor expansion:
+
+ int yylex (YYSTYPE *yylval);
+
+ This is has been fixed: yylval, yynerrs, yychar, and yylloc are now valid
+ identifiers for user-provided variables.
+
+*** stdio.h is no longer needed when locations are enabled (yacc.c)
+
+ Changes in Bison 2.7 introduced a dependency on FILE and fprintf when
+ locations are enabled. This is fixed.
+
+** Diagnostics reported by Bison
+
+ Most of these features were contributed by Théophile Ranquet and Victor
+ Santet.
+
+*** Carets
+
+ Version 2.7 introduced caret errors, for a prettier output. These are now
+ activated by default. The old format can still be used by invoking Bison
+ with -fno-caret (or -fnone).
+
+*** Enhancements of the -Werror option
+
+ The -Werror=CATEGORY option is now recognized, and will treat specified
+ warnings as errors. The warnings need not have been explicitly activated
+ using the -W option, this is similar to what GCC 4.7 does.
+
+ For example, given the following command line, Bison will treat both
+ warnings related to POSIX Yacc incompatibilities and S/R conflicts as
+ errors (and only those):
+
+ $ bison -Werror=yacc,error=conflicts-sr input.y
+
+ If no categories are specified, -Werror will make all active warnings into
+ errors. For example, the following line does the same the previous example:
+
+ $ bison -Werror -Wnone -Wyacc -Wconflicts-sr input.y
+
+ (By default -Wconflicts-sr,conflicts-rr,deprecated,other is enabled.)
+
+ Note that the categories in this -Werror option may not be prefixed with
+ "no-". However, -Wno-error[=CATEGORY] is valid.
+
+ Note that -y enables -Werror=yacc. Therefore it is now possible to require
+ Yacc-like behavior (e.g., always generate y.tab.c), but to report
+ incompatibilities as warnings: "-y -Wno-error=yacc".
+
+*** The display of warnings is now richer
+
+ The option that controls a given warning is now displayed:
+
+ foo.y:4.6: warning: type clash on default action: <foo> != <bar> [-Wother]
+
+ In the case of warnings treated as errors, the prefix is changed from
+ "warning: " to "error: ", and the suffix is displayed, in a manner similar
+ to GCC, as [-Werror=CATEGORY].
+
+ For instance, where the previous version of Bison would report (and exit
+ with failure):
+
+ bison: warnings being treated as errors
+ input.y:1.1: warning: stray ',' treated as white space
+
+ it now reports:
+
+ input.y:1.1: error: stray ',' treated as white space [-Werror=other]
+
+*** 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.
+
+*** 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>
+
+*** Conflicts
+
+ The warnings and error messages about shift/reduce and reduce/reduce
+ conflicts have been normalized. For instance on the following foo.y file:
+
+ %glr-parser
+ %%
+ exp: exp '+' exp | '0' | '0';
+
+ compare the previous version of bison:
+
+ $ bison foo.y
+ foo.y: conflicts: 1 shift/reduce, 2 reduce/reduce
+ $ bison -Werror foo.y
+ bison: warnings being treated as errors
+ foo.y: conflicts: 1 shift/reduce, 2 reduce/reduce
+
+ with the new behavior:
+
+ $ bison foo.y
+ foo.y: warning: 1 shift/reduce conflict [-Wconflicts-sr]
+ foo.y: warning: 2 reduce/reduce conflicts [-Wconflicts-rr]
+ $ bison -Werror foo.y
+ foo.y: error: 1 shift/reduce conflict [-Werror=conflicts-sr]
+ foo.y: error: 2 reduce/reduce conflicts [-Werror=conflicts-rr]
+
+ When %expect or %expect-rr is used, such as with bar.y:
+
+ %expect 0
+ %glr-parser
+ %%
+ exp: exp '+' exp | '0' | '0';
+
+ Former behavior:
+
+ $ bison bar.y
+ bar.y: conflicts: 1 shift/reduce, 2 reduce/reduce
+ bar.y: expected 0 shift/reduce conflicts
+ bar.y: expected 0 reduce/reduce conflicts
+
+ New one:
+
+ $ bison bar.y
+ bar.y: error: shift/reduce conflicts: 1 found, 0 expected
+ bar.y: error: reduce/reduce conflicts: 2 found, 0 expected
** Additional yylex/yyparse arguments
- The new directive %param declare additional argument to both yylex
- and yyparse. The %lex-param, %parse-param, and %param directives
- support one or more arguments. Instead of
+ 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}
+ %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}
+ %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".
+ Contributed by Paolo Bonzini.
+
+ 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.
-** Variable api.tokens.prefix
+*** syntax_error exception (lalr1.cc)
- The variable api.tokens.prefix changes the way tokens are identified in
+ 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).
+
+** Renamed %define variables
+
+ The following variables have been renamed for consistency. Backward
+ compatibility is ensured, but upgrading is recommended.
+
+ lr.default-reductions -> lr.default-reduction
+ lr.keep-unreachable-states -> lr.keep-unreachable-state
+ namespace -> api.namespace
+ stype -> api.value.type
+
+** Variable api.token.prefix
+
+ The variable api.token.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;
+ %token FILE for ERROR
+ %define api.token.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
- The variable error controls the verbosity of error messages. The
- use of the %error-verbose directive is deprecated in favor of
- %define parse.error "verbose".
+ 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
+ Contributed by Paul Hilfinger.
+
+ 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
- runtime expressions.
+ 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.
+
+** The directive %expect-rr is now an error in non GLR mode
+
+ It used to be an error only if used in non GLR mode, _and_ if there are
+ reduce/reduce conflicts.
+
+** Token numbering has changed to preserve the user-defined order
+
+ When declaring %token A B, the numbering for A is inferior to B. Up to now,
+ when declaring associativity at the same time, with %left (or %right,
+ %precedence, %nonassoc), B was inferior to A.
+
+** Useless precedence and associativity
+
+ When developping and maintaining a grammar, useless associativity and
+ precedence directives are common. They can be a nuisance: new ambiguities
+ arising are sometimes masked because their conflicts are resolved due to
+ the extra precedence or associativity information. Furthermore, it can
+ hinder the comprehension of a new grammar: one will wonder about the role
+ of a precedence, where in fact it is useless. The following changes aim
+ at detecting and reporting these extra directives.
+
+*** Precedence warning category
+
+ A new category of warning, -Wprecedence, was introduced. It flags the
+ useless precedence and associativity directives.
+
+*** Useless associativity
+
+ Bison now warns about symbols with a declared associativity that is never
+ used to resolve conflicts. In that case, using %precedence is sufficient;
+ the parsing tables will remain unchanged. Solving these warnings may raise
+ useless precedence warnings, as the symbols no longer have associativity.
+ For example:
+
+ %left '+'
+ %left '*'
+ %%
+ exp:
+ "num"
+ | exp '+' "num"
+ | exp '*' exp
+ ;
+
+ will produce a
+
+ warning: useless associativity for '+', use %precedence [-Wprecedence]
+ %left '+'
+ ^^^
+
+*** Useless precedence
+
+ Bison now warns about symbols with a declared precedence and no declared
+ associativity (i.e., declared with %precedence), and whose precedence is
+ never used. In that case, the symbol can be safely declared with %token
+ instead, without modifying the parsing tables. For example:
+
+ %precedence '='
+ %%
+ exp: "var" '=' "num";
+
+ will produce a
+
+ warning: useless precedence for '=' [-Wprecedence]
+ %precedence '='
+ ^^^
+
+*** Useless precedence and associativity
+
+ In case of both useless precedence and associativity, the issue is flagged
+ as follows:
+
+ %nonassoc '='
+ %%
+ exp: "var" '=' "num";
+
+ The warning is:
+
+ warning: useless precedence and associativity for '=' [-Wprecedence]
+ %nonassoc '='
+ ^^^
+
+* Noteworthy changes in release 2.7 (2012-12-12) [stable]
+
+** Bug fixes
+
+ Warnings about uninitialized yylloc in yyparse have been fixed.
+
+ Restored C90 compliance (yet no report was ever made).
+
+** Diagnostics are improved
+
+ Contributed by Théophile Ranquet.
+
+*** Changes in the format of error messages
+
+ This used to be the format of many error reports:
+
+ input.y:2.7-12: %type redeclaration for exp
+ input.y:1.7-12: previous declaration
+
+ It is now:
+
+ input.y:2.7-12: error: %type redeclaration for exp
+ input.y:1.7-12: previous declaration
+
+*** New format for error reports: carets
+
+ Caret errors have been added to Bison:
+
+ input.y:2.7-12: error: %type redeclaration for exp
+ %type <sval> exp
+ ^^^^^^
+ input.y:1.7-12: previous declaration
+ %type <ival> exp
+ ^^^^^^
+
+ or
+
+ input.y:3.20-23: error: ambiguous reference: '$exp'
+ exp: exp '+' exp { $exp = $1 + $3; };
+ ^^^^
+ input.y:3.1-3: refers to: $exp at $$
+ exp: exp '+' exp { $exp = $1 + $3; };
+ ^^^
+ input.y:3.6-8: refers to: $exp at $1
+ exp: exp '+' exp { $exp = $1 + $3; };
+ ^^^
+ input.y:3.14-16: refers to: $exp at $3
+ exp: exp '+' exp { $exp = $1 + $3; };
+ ^^^
+
+ The default behaviour for now is still not to display these unless
+ explictly asked with -fcaret (or -fall). However, in a later release, it
+ will be made the default behavior (but may still be deactivated with
+ -fno-caret).
+
+** New value for %define variable: api.pure full
+
+ The %define variable api.pure requests a pure (reentrant) parser. However,
+ for historical reasons, using it in a location-tracking Yacc parser
+ resulted in a yyerror function that did not take a location as a
+ parameter. With this new value, the user may request a better pure parser,
+ where yyerror does take a location as a parameter (in location-tracking
+ parsers).
+
+ The use of "%define api.pure true" is deprecated in favor of this new
+ "%define api.pure full".
+
+** New %define variable: api.location.type (glr.cc, lalr1.cc, lalr1.java)
+
+ The %define variable api.location.type defines the name of the type to use
+ for locations. When defined, Bison no longer generates the position.hh
+ and location.hh files, nor does the parser will include them: the user is
+ then responsible to define her type.
+
+ This can be used in programs with several parsers to factor their location
+ and position files: let one of them generate them, and the others just use
+ them.
+
+ This feature was actually introduced, but not documented, in Bison 2.5,
+ under the name "location_type" (which is maintained for backward
+ compatibility).
+
+ For consistency, lalr1.java's %define variables location_type and
+ position_type are deprecated in favor of api.location.type and
+ api.position.type.
+
+** Exception safety (lalr1.cc)
+
+ The parse function now catches exceptions, uses the %destructors to
+ release memory (the lookahead symbol and the symbols pushed on the stack)
+ before re-throwing the exception.
+
+ This feature is somewhat experimental. User feedback would be
+ appreciated.
+
+** Graph improvements in DOT and XSLT
+
+ Contributed by Théophile Ranquet.
+
+ The graphical presentation of the states is more readable: their shape is
+ now rectangular, the state number is clearly displayed, and the items are
+ numbered and left-justified.
+
+ The reductions are now explicitly represented as transitions to other
+ diamond shaped nodes.
+
+ These changes are present in both --graph output and xml2dot.xsl XSLT
+ processing, with minor (documented) differences.
+
+** %language is no longer an experimental feature.
+
+ The introduction of this feature, in 2.4, was four years ago. The
+ --language option and the %language directive are no longer experimental.
+
+** Documentation
+
+ The sections about shift/reduce and reduce/reduce conflicts resolution
+ have been fixed and extended.
+
+ Although introduced more than four years ago, XML and Graphviz reports
+ were not properly documented.
+
+ The translation of mid-rule actions is now described.
+
+* Noteworthy changes in release 2.6.5 (2012-11-07) [stable]
+
+ We consider compiler warnings about Bison generated parsers to be bugs.
+ Rather than working around them in your own project, please consider
+ reporting them to us.
+
+** Bug fixes
+
+ Warnings about uninitialized yylval and/or yylloc for push parsers with a
+ pure interface have been fixed for GCC 4.0 up to 4.8, and Clang 2.9 to
+ 3.2.
+
+ Other issues in the test suite have been addressed.
+
+ Nul characters are correctly displayed in error messages.
+
+ When possible, yylloc is correctly initialized before calling yylex. It
+ is no longer necessary to initialize it in the %initial-action.
+
+* Noteworthy changes in release 2.6.4 (2012-10-23) [stable]
+
+ Bison 2.6.3's --version was incorrect. This release fixes this issue.
+
+* Noteworthy changes in release 2.6.3 (2012-10-22) [stable]
+
+** Bug fixes
+
+ Bugs and portability issues in the test suite have been fixed.
+
+ Some errors in translations have been addressed, and --help now directs
+ users to the appropriate place to report them.
+
+ Stray Info files shipped by accident are removed.
+
+ Incorrect definitions of YY_, issued by yacc.c when no parser header is
+ generated, are removed.
+
+ All the generated headers are self-contained.
+
+** Header guards (yacc.c, glr.c, glr.cc)
+
+ In order to avoid collisions, the header guards are now
+ YY_<PREFIX>_<FILE>_INCLUDED, instead of merely <PREFIX>_<FILE>.
+ For instance the header generated from
+
+ %define api.prefix "calc"
+ %defines "lib/parse.h"
+
+ will use YY_CALC_LIB_PARSE_H_INCLUDED as guard.
+
+** Fix compiler warnings in the generated parser (yacc.c, glr.c)
+
+ The compilation of pure parsers (%define api.pure) can trigger GCC
+ warnings such as:
+
+ input.c: In function 'yyparse':
+ input.c:1503:12: warning: 'yylval' may be used uninitialized in this
+ function [-Wmaybe-uninitialized]
+ *++yyvsp = yylval;
+ ^
+
+ This is now fixed; pragmas to avoid these warnings are no longer needed.
+
+ Warnings from clang ("equality comparison with extraneous parentheses" and
+ "function declared 'noreturn' should not return") have also been
+ addressed.
+
+* 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
-* Changes in version 2.5 (????-??-??):
+ # if YYDEBUG | # if BAR_DEBUG
+ extern int bar_debug; extern int bar_debug;
+ # endif # endif
-** Named References Support
+ /* 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.
+ Contributed by Alex Rozenman.
-** 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.
+ Contributed by Joel E. Denny.
-*** Unrecognized variables are now an error not a warning.
+ 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.
-*** Multiple invocations for any variable is 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.
+
+ 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
+
+ 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.
-*** Can now be invoked via the command line.
+** %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:
+
+ 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.
+
+** 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)
- 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).
+ use:
-** YYFAIL now produces warnings and Java parsers no longer implement it.
+ # 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.
-** 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.
-** C++ parsers use YYRHSLOC
+*** Parser traces now print the top element of the stack.
- 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
+** -W/--warnings fixes:
- # 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)
+*** Bison now properly recognizes the "no-" versions of categories:
- use:
+ For example, given the following command line, Bison now enables all
+ warnings except warnings for incompatibilities with POSIX Yacc:
- # 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++
+ bison -Wall,no-yacc gram.y
- 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.
+*** 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:
-* Changes in version 2.4.3 (????-??-??):
+ 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.
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
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.
+ Contributed by Paolo Bonzini.
** %language
** 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.
+ Contributed by Wojciech Polak.
** The grammar file may now specify the name of the parser header file using
%defines. For example:
%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 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:
- - `parsing stack overflow...' -> `parser stack overflow'
- GLR parsers now report `parser stack overflow' as per the Bison manual.
+ 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
+ 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, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003,
-2004, 2005, 2006, 2007, 2008, 2009, 2010 Free Software Foundation,
-Inc.
+Copyright (C) 1995-2013 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 YY
+ LocalWords: namespaces strerror const autoconfiguration Dconst Autoconf's FDL
+ 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 calc yyo fval Wconflicts
+
+Local Variables:
+mode: outline
+fill-column: 76
+End:
projects / bison.git / blobdiff