* Noteworthy changes in release 3.2.4 (2018-12-24) [stable]
** Bug fixes
Fix the move constructor of symbol_type.
Always provide a copy constructor for symbol_type, even in modern C++.
* Noteworthy changes in release 3.2.3 (2018-12-18) [stable]
** Bug fixes
Properly support token constructors in C++ with types that include commas
(e.g., std::pair<int, int>). A regression introduced in Bison 3.2.
* Noteworthy changes in release 3.2.2 (2018-11-21) [stable]
** Bug fixes
C++ portability issues.
* Noteworthy changes in release 3.2.1 (2018-11-09) [stable]
** Bug fixes
Several portability issues have been fixed in the build system, in the
test suite, and in the generated parsers in C++.
* Noteworthy changes in release 3.2 (2018-10-29) [stable]
** Backward incompatible changes
Support for DJGPP, which have been unmaintained and untested for years, is
obsolete. Unless there is activity to revive it, it will be removed.
** Changes
%printers should use yyo rather than yyoutput to denote the output stream.
Variant-based symbols in C++ should use emplace() rather than build().
In C++ parsers, parser::operator() is now a synonym for the parser::parse.
** Documentation
A new section, "A Simple C++ Example", is a tutorial for parsers in C++.
A comment in the generated code now emphasizes that users should not
depend upon non-documented implementation details, such as macros starting
with YY_.
** New features
*** C++: Support for move semantics (lalr1.cc)
The lalr1.cc skeleton now fully supports C++ move semantics, while
maintaining compatibility with C++98. You may now store move-only types
when using Bison's variants. For instance:
%code {
#include <memory>
#include <vector>
}
%skeleton "lalr1.cc"
%define api.value.type variant
%%
%token <int> INT "int";
%type <std::unique_ptr<int>> int;
%type <std::vector<std::unique_ptr<int>>> list;
list:
%empty {}
| list int { $$ = std::move($1); $$.emplace_back(std::move($2)); }
int: "int" { $$ = std::make_unique<int>($1); }
*** C++: Implicit move of right-hand side values (lalr1.cc)
In modern C++ (C++11 and later), you should always use 'std::move' with
the values of the right-hand side symbols ($1, $2, etc.), as they will be
popped from the stack anyway. Using 'std::move' is mandatory for
move-only types such as unique_ptr, and it provides a significant speedup
for large types such as std::string, or std::vector, etc.
If '%define api.value.automove' is set, every occurrence '$n' is replaced
by 'std::move ($n)'. The second rule in the previous grammar can be
simplified to:
list: list int { $$ = $1; $$.emplace_back($2); }
With automove enabled, the semantic values are no longer lvalues, so do
not use the swap idiom:
list: list int { std::swap($$, $1); $$.emplace_back($2); }
This idiom is anyway obsolete: it is preferable to move than to swap.
A warning is issued when automove is enabled, and a value is used several
times.
input.yy:16.31-32: warning: multiple occurrences of $2 with api.value.automove enabled [-Wother]
exp: "twice" exp { $$ = $2 + $2; }
^^
Enabling api.value.automove does not require support for modern C++. The
generated code is valid C++98/03, but will use copies instead of moves.
The new examples/c++/variant-11.yy shows these features in action.
*** C++: The implicit default semantic action is always run
When variants are enabled, the default action was not run, so
exp: "number"
was equivalent to
exp: "number" {}
It now behaves like in all the other cases, as
exp: "number" { $$ = $1; }
possibly using std::move if automove is enabled.
We do not expect backward compatibility issues. However, beware of
forward compatibility issues: if you rely on default actions with
variants, be sure to '%require "3.2"' to avoid older versions of Bison to
generate incorrect parsers.
*** C++: Renaming location.hh
When both %defines and %locations are enabled, Bison generates a
location.hh file. If you don't use locations outside of the parser, you
may avoid its creation with:
%define api.location.file none
However this file is useful if, for instance, your parser builds an AST
decorated with locations: you may use Bison's location independently of
Bison's parser. You can now give it another name, for instance:
%define api.location.file "my-location.hh"
This name can have directory components, and even be absolute. The name
under which the location file is included is controlled by
api.location.include.
This way it is possible to have several parsers share the same location
file.
For instance, in src/foo/parser.hh, generate the include/ast/loc.hh file:
%locations
%define api.namespace {foo}
%define api.location.file "include/ast/loc.hh"
%define api.location.include {<ast/loc.hh>}
and use it in src/bar/parser.hh:
%locations
%define api.namespace {bar}
%code requires {#include <ast/loc.hh>}
%define api.location.type {bar::location}
Absolute file names are supported, so in your Makefile, passing the flag
-Dapi.location.file='"$(top_srcdir)/include/ast/location.hh"' to bison is
safe.
*** C++: stack.hh and position.hh are deprecated
When asked to generate a header file (%defines), the lalr1.cc skeleton
generates a stack.hh file. This file had no interest for users; it is now
made useless: its content is included in the parser definition. It is
still generated for backward compatibility.
When in addition to %defines, location support is requested (%locations),
the file position.hh is also generated. It is now also useless: its
content is now included in location.hh.
These files are no longer generated when your grammar file requires at
least Bison 3.2 (%require "3.2").
** Bug fixes
Portability issues on MinGW and VS2015.
Portability issues in the test suite.
Portability/warning issues with Flex.
* Noteworthy changes in release 3.1 (2018-08-27) [stable]
** Backward incompatible changes
Compiling Bison now requires a C99 compiler---as announced during the
release of Bison 3.0, five years ago. Generated parsers do not require a
C99 compiler.
Support for DJGPP, which have been unmaintained and untested for years, is
obsolete. Unless there is activity to revive it, the next release of Bison
will have it removed.
** New features
*** Typed midrule actions
Because their type is unknown to Bison, the values of midrule actions are
not treated like the others: they don't have %printer and %destructor
support. It also prevents C++ (Bison) variants to handle them properly.
Typed midrule actions address these issues. Instead of:
exp: { $<ival>$ = 1; } { $<ival>$ = 2; } { $$ = $<ival>1 + $<ival>2; }
write:
exp: <ival>{ $$ = 1; } <ival>{ $$ = 2; } { $$ = $1 + $2; }
*** Reports include the type of the symbols
The sections about terminal and nonterminal symbols of the '*.output' file
now specify their declared type. For instance, for:
%token <ival> NUM
the report now shows '<ival>':
Terminals, with rules where they appear
NUM <ival> (258) 5
*** Diagnostics about useless rules
In the following grammar, the 'exp' nonterminal is trivially useless. So,
of course, its rules are useless too.
%%
input: '0' | exp
exp: exp '+' exp | exp '-' exp | '(' exp ')'
Previously all the useless rules were reported, including those whose
left-hand side is the 'exp' nonterminal:
warning: 1 nonterminal useless in grammar [-Wother]
warning: 4 rules useless in grammar [-Wother]
2.14-16: warning: nonterminal useless in grammar: exp [-Wother]
input: '0' | exp
^^^
2.14-16: warning: rule useless in grammar [-Wother]
input: '0' | exp
^^^
3.6-16: warning: rule useless in grammar [-Wother]
exp: exp '+' exp | exp '-' exp | '(' exp ')'
^^^^^^^^^^^
3.20-30: warning: rule useless in grammar [-Wother]
exp: exp '+' exp | exp '-' exp | '(' exp ')'
^^^^^^^^^^^
3.34-44: warning: rule useless in grammar [-Wother]
exp: exp '+' exp | exp '-' exp | '(' exp ')'
^^^^^^^^^^^
Now, rules whose left-hand side symbol is useless are no longer reported
as useless. The locations of the errors have also been adjusted to point
to the first use of the nonterminal as a left-hand side of a rule:
warning: 1 nonterminal useless in grammar [-Wother]
warning: 4 rules useless in grammar [-Wother]
3.1-3: warning: nonterminal useless in grammar: exp [-Wother]
exp: exp '+' exp | exp '-' exp | '(' exp ')'
^^^
2.14-16: warning: rule useless in grammar [-Wother]
input: '0' | exp
^^^
*** C++: Generated parsers can be compiled with -fno-exceptions (lalr1.cc)
When compiled with exceptions disabled, the generated parsers no longer
uses try/catch clauses.
Currently only GCC and Clang are supported.
** Documentation
*** A demonstration of variants
A new example was added (installed in .../share/doc/bison/examples),
'variant.yy', which shows how to use (Bison) variants in C++.
The other examples were made nicer to read.
*** Some features are no longer 'experimental'
The following features, mature enough, are no longer flagged as
experimental in the documentation: push parsers, default %printer and
%destructor (typed: <*> and untyped: <>), %define api.value.type union and
variant, Java parsers, XML output, LR family (lr, ielr, lalr), and
semantic predicates (%?).
** Bug fixes
*** GLR: Predicates support broken by #line directives
Predicates (%?) in GLR such as
widget:
%? {new_syntax} 'w' id new_args
| %?{!new_syntax} 'w' id old_args
were issued with #lines in the middle of C code.
*** Printer and destructor with broken #line directives
The #line directives were not properly escaped when emitting the code for
%printer/%destructor, which resulted in compiler errors if there are
backslashes or double-quotes in the grammar file name.
*** Portability on ICC
The Intel compiler claims compatibility with GCC, yet rejects its _Pragma.
Generated parsers now work around this.
*** Various
There were several small fixes in the test suite and in the build system,
many warnings in bison and in the generated parsers were eliminated. The
documentation also received its share of minor improvements.
Useless code was removed from C++ parsers, and some of the generated
constructors are more 'natural'.
Changelog:
* Noteworthy changes in release 3.0.5 (2018-05-27) [stable]
** Bug fixes
*** C++: Fix support of 'syntax_error'
One incorrect 'inline' resulted in linking errors about the constructor of
the syntax_error exception.
*** C++: Fix warnings
GCC 7.3 (with -O1 or -O2 but not -O0 or -O3) issued null-dereference
warnings about yyformat being possibly null. It also warned about the
deprecated implicit definition of copy constructors when there's a
user-defined (copy) assignment operator.
*** Location of errors
In C++ parsers, out-of-bounds errors can happen when a rule with an empty
ride-hand side raises a syntax error. The behavior of the default parser
(yacc.c) in such a condition was undefined.
Now all the parsers match the behavior of glr.c: @$ is used as the
location of the error. This handles gracefully rules with and without
rhs.
*** Portability fixes in the test suite
On some platforms, some Java and/or C++ tests were failing.
(pkgsrc)
- Add comment on patch-lib_isnan.c (from cvs log)
(upstream)
- Update devel/bison 3.0.2 to 3.0.3
Thanks obache and wiz for review.
---------------------------------
* Noteworthy changes in release 3.0.3 (2015-01-15) [stable]
** Bug fixes
*** C++ with Variants (lalr1.cc)
Problems with %destructor and '%define parse.assert' have been fixed.
*** Named %union support (yacc.c, glr.c)
Bison 3.0 introduced a regression on named %union such as
%union foo { int ival; };
The possibility to use a name was introduced "for Yacc compatibility".
It is however not required by POSIX Yacc, and its usefulness is not clear.
*** %define api.value.type union with %defines (yacc.c, glr.c)
The C parsers were broken when %defines was used together with "%define
api.value.type union".
*** Redeclarations are reported in proper order
On
%token FOO "foo"
%printer {} "foo"
%printer {} FOO
bison used to report:
/tmp/foo.yy:2.10-11: error: %printer redeclaration for FOO
%printer {} "foo"
^^
/tmp/foo.yy:3.10-11: previous declaration
%printer {} FOO
^^
Now, the "previous" declaration is always the first one.
** Documentation
Bison now installs various files in its docdir (which defaults to
'/usr/local/share/doc/bison'), including the three fully blown examples
extracted from the documentation:
- rpcalc
Reverse polish calculator, a simple introductory example.
- mfcalc
Multi-function Calc, a calculator with memory and functions and located
error messages.
- calc++
a calculator in C++ using variant support and token constructors.
* Noteworthy changes in release 3.0.2 (2013-12-05) [stable]
** Bug fixes
*** Generated source files when errors are reported
When warnings are issued and -Werror is set, bison would still generate
the source files (*.c, *.h...). As a consequence, some runs of "make"
could fail the first time, but not the second (as the files were generated
anyway).
This is fixed: bison no longer generates this source files, but, of
course, still produces the various reports (*.output, *.xml, etc.).
*** %empty is used in reports
Empty right-hand sides are denoted by '%empty' in all the reports (text,
dot, XML and formats derived from it).
*** YYERROR and variants
When C++ variant support is enabled, an error triggered via YYERROR, but
not caught via error recovery, resulted in a double deletion.
* Noteworthy changes in release 3.0.1 (2013-11-12) [stable]
** Bug fixes
*** Errors in caret diagnostics
On some platforms, some errors could result in endless diagnostics.
*** Fixes of the -Werror option
Options such as "-Werror -Wno-error=foo" were still turning "foo"
diagnostics into errors instead of warnings. This is fixed.
Actually, for consistency with GCC, "-Wno-error=foo -Werror" now also
leaves "foo" diagnostics as warnings. Similarly, with "-Werror=foo
-Wno-error", "foo" diagnostics are now errors.
*** GLR Predicates
As demonstrated in the documentation, one can now leave spaces between
"%?" and its "{".
*** Installation
The yacc.1 man page is no longer installed if --disable-yacc was
specified.
*** Fixes in the test suite
Bugs and portability issues.
* Noteworthy changes in release 3.0 (2013-07-25) [stable]
** WARNING: Future backward-incompatibilities!
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.
Missing semicolons at the end of actions are no longer added (as announced
in the release 2.5).
*** Use of YACC='bison -y'
TL;DR: With Autoconf <= 2.69, pass -Wno-yacc to (AM_)YFLAGS if you use
Bison extensions.
Traditional Yacc generates 'y.tab.c' whatever the name of the input file.
Therefore Makefiles written for Yacc expect 'y.tab.c' (and possibly
'y.tab.h' and 'y.outout') to be generated from 'foo.y'.
To this end, for ages, AC_PROG_YACC, Autoconf's macro to look for an
implementation of Yacc, was using Bison as 'bison -y'. While it does
ensure compatible output file names, it also enables warnings for
incompatibilities with POSIX Yacc. In other words, 'bison -y' triggers
warnings for Bison extensions.
Autoconf 2.70+ fixes this incompatibility by using YACC='bison -o y.tab.c'
(which also generates 'y.tab.h' and 'y.output' when needed).
Alternatively, disable Yacc warnings by passing '-Wno-yacc' to your Yacc
flags (YFLAGS, or AM_YFLAGS with Automake).
** Bug fixes
*** The epilogue is no longer affected by internal #defines (glr.c)
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 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.
*** Warnings about useless %pure-parser/%define api.pure are restored
** 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).
Some error messages that reproduced excerpts of the grammar are now using
the caret information only. For instance on:
%%
exp: 'a' | 'a';
Bison 2.7 reports:
in.y: warning: 1 reduce/reduce conflict [-Wconflicts-rr]
in.y:2.12-14: warning: rule useless in parser due to conflicts: exp: 'a' [-Wother]
Now bison reports:
in.y: warning: 1 reduce/reduce conflict [-Wconflicts-rr]
in.y:2.12-14: warning: rule useless in parser due to conflicts [-Wother]
exp: 'a' | 'a';
^^^
and "bison -fno-caret" reports:
in.y: warning: 1 reduce/reduce conflict [-Wconflicts-rr]
in.y:2.12-14: warning: rule useless in parser due to conflicts [-Wother]
*** 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
** Incompatibilities with POSIX Yacc
The 'yacc' category is no longer part of '-Wall', enable it explicitly
with '-Wyacc'.
** 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}
** Types of values for %define variables
Bison used to make no difference between '%define foo bar' and '%define
foo "bar"'. The former is now called a 'keyword value', and the latter a
'string value'. A third kind was added: 'code values', such as '%define
foo {bar}'.
Keyword variables are used for fixed value sets, e.g.,
%define lr.type lalr
Code variables are used for value in the target language, e.g.,
%define api.value.type {struct semantic_type}
String variables are used remaining cases, e.g. file names.
** 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.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.value.type
This new %define variable supersedes the #define macro YYSTYPE. The use
of YYSTYPE is discouraged. In particular, #defining YYSTYPE *and* either
using %union or %defining api.value.type results in undefined behavior.
Either define api.value.type, or use "%union":
%union
{
int ival;
char *sval;
}
%token <ival> INT "integer"
%token <sval> STRING "string"
%printer { fprintf (yyo, "%d", $$); } <ival>
%destructor { free ($$); } <sval>
/* In yylex(). */
yylval.ival = 42; return INT;
yylval.sval = "42"; return STRING;
The %define variable api.value.type supports both keyword and code values.
The keyword value 'union' means that the user provides genuine types, not
union member names such as "ival" and "sval" above (WARNING: will fail if
-y/--yacc/%yacc is enabled).
%define api.value.type union
%token <int> INT "integer"
%token <char *> STRING "string"
%printer { fprintf (yyo, "%d", $$); } <int>
%destructor { free ($$); } <char *>
/* In yylex(). */
yylval.INT = 42; return INT;
yylval.STRING = "42"; return STRING;
The keyword value variant is somewhat equivalent, but for C++ special
provision is made to allow classes to be used (more about this below).
%define api.value.type variant
%token <int> INT "integer"
%token <std::string> STRING "string"
Code values (in braces) denote user defined types. This is where YYSTYPE
used to be used.
%code requires
{
struct my_value
{
enum
{
is_int, is_string
} kind;
union
{
int ival;
char *sval;
} u;
};
}
%define api.value.type {struct my_value}
%token <u.ival> INT "integer"
%token <u.sval> STRING "string"
%printer { fprintf (yyo, "%d", $$); } <u.ival>
%destructor { free ($$); } <u.sval>
/* In yylex(). */
yylval.u.ival = 42; return INT;
yylval.u.sval = "42"; return STRING;
** 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".
** 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
** Semantic predicates
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 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.
** Tokens are numbered in their order of appearance
Contributed by Valentin Tolmer.
With '%token A B', A had a number less than the one of B. However,
precedence declarations used to generate a reversed order. This is now
fixed, and introducing tokens with any of %token, %left, %right,
%precedence, or %nonassoc yields the same result.
When mixing declarations of tokens with a litteral character (e.g., 'a')
or with an identifier (e.g., B) in a precedence declaration, Bison
numbered the litteral characters first. For example
%right A B 'c' 'd'
would lead to the tokens declared in this order: 'c' 'd' A B. Again, the
input order is now preserved.
These changes were made so that one can remove useless precedence and
associativity declarations (i.e., map %nonassoc, %left or %right to
%precedence, or to %token) and get exactly the same output.
** Useless precedence and associativity
Contributed by Valentin Tolmer.
When developing 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:
"number"
| exp '+' "number"
| 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" '=' "number";
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" '=' "number";
The warning is:
warning: useless precedence and associativity for '=' [-Wprecedence]
%nonassoc '='
^^^
** Empty rules
With help from Joel E. Denny and Gabriel Rassoul.
Empty rules (i.e., with an empty right-hand side) can now be explicitly
marked by the new %empty directive. Using %empty on a non-empty rule is
an error. The new -Wempty-rule warning reports empty rules without
%empty. On the following grammar:
%%
s: a b c;
a: ;
b: %empty;
c: 'a' %empty;
bison reports:
3.4-5: warning: empty rule without %empty [-Wempty-rule]
a: {}
^^
5.8-13: error: %empty on non-empty rule
c: 'a' %empty {};
^^^^^^
** 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 Java skeleton now supports push parsing.
Contributed by Dennis Heimbigner.
** 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).
*** %define api.value.type variant
This is based on a submission from Michiel De Wilde. With help
from Théophile Ranquet.
In this mode, complex C++ objects can be used as semantic values. For
instance:
%token <::std::string> TEXT;
%token <int> NUMBER;
%token SEMICOLON ";"
%type <::std::string> item;
%type <::std::list<std::string>> list;
%%
result:
list { std::cout << $1 << std::endl; }
;
list:
%empty { /* Generates an empty string list. */ }
| list item ";" { std::swap ($$, $1); $$.push_back ($2); }
;
item:
TEXT { std::swap ($$, $1); }
| NUMBER { $$ = string_cast ($1); }
;
*** %define api.token.constructor
When variants are enabled, Bison can generate functions to build the
tokens. This guarantees that the token type (e.g., NUMBER) is consistent
with the semantic value (e.g., int):
parser::symbol_type yylex ()
{
parser::location_type loc = ...;
...
return parser::make_TEXT ("Hello, world!", loc);
...
return parser::make_NUMBER (42, loc);
...
return parser::make_SEMICOLON (loc);
...
}
*** C++ locations
There are operator- and operator-= for 'location'. Negative line/column
increments can no longer underflow the resulting value.
* 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.
* 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 2.5.1 (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 work 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
actions code.
Starting from this version, Bison can also accept named references.
When no ambiguity is possible, original symbol names may be used
as named references:
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] ';'
{ $res = mk_if_stmt($cond, $then, $else); }
Location information is also accessible using @name syntax. When
accessing symbol names containing dots or dashes, explicit bracketing
($[sym.1]) must be used.
These features are experimental in this version. More user feedback
will help to stabilize them.
** 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,
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
significantly reduce the complexity of developing of a grammar.
Bison can now generate IELR(1) and canonical LR(1) parser tables in
place of its traditional LALR(1) parser tables, which remain the
default. You can specify the type of parser tables in the grammar
file with these directives:
%define lr.type lalr
%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'. 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.
** LAC (Lookahead Correction) for syntax error handling:
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.
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.
** %define improvements:
*** Can now be invoked via the command line:
Each of these command-line options
-D NAME[=VALUE]
--define=NAME[=VALUE]
-F NAME[=VALUE]
--force-define=NAME[=VALUE]
is equivalent to this grammar file declaration
%define NAME ["VALUE"]
except that the manner in which Bison processes multiple definitions
for the same NAME differs. Most importantly, -F and --force-define
quietly override %define, but -D and --define do not. For further
details, see the section `Bison Options' in the Bison manual.
*** Variables renamed:
The following %define variables
api.push_pull
lr.keep_unreachable_states
have been renamed to
api.push-pull
lr.keep-unreachable-states
The old names are now deprecated but will be maintained indefinitely
for backward compatibility.
*** 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"
can be rewritten as
%define api.push-pull push
*** 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)
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
a documented feature of Bison's experimental Java parsers. As
promised in Bison 2.4.2's NEWS entry, any appearance of YYFAIL in a
semantic action now produces a deprecation warning, and Java parsers
no longer implement YYFAIL at all. For further details, including a
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:
Previously, Bison appended a semicolon to every user action for
reductions when the output language defaulted to C (specifically, when
neither %yacc, %language, %skeleton, or equivalent command-line
options were specified). This allowed actions such as
exp: exp "+" exp { $$ = $1 + $3 };
instead of
exp: exp "+" exp { $$ = $1 + $3; };
As a first step in removing this misfeature, Bison now issues a
warning when it appends a semicolon. Moreover, in cases where Bison
cannot easily determine whether a semicolon is needed (for example, an
action ending with a cpp directive or a braced compound initializer),
it no longer appends one. Thus, the C compiler might now complain
about a missing semicolon where it did not before. Future releases of
Bison will cease to append semicolons entirely.
** Verbose syntax error message fixes:
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:
*** 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.
*** 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.
*** 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.
** Java skeleton fixes:
*** A location handling 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:
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 2.4.2 (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 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.
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
%token, %left, %right, or %nonassoc. Bison 2.3b and later lost this
error report for the case when an identifier appears only after a
%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.
** Detection of GNU M4 1.4.6 or newer during configure is improved.
** Warnings from gcc's -Wundef option about undefined YYENABLE_NLS,
YYLTYPE_IS_TRIVIAL, and __STRICT_ANSI__ in C/C++ parsers are now
avoided.
** %code is now a permanent feature.
A traditional Yacc prologue directive is written in the form:
%{CODE%}
To provide a more flexible alternative, Bison 2.3b introduced the
%code directive with the following forms for C/C++:
%code {CODE}
%code requires {CODE}
%code provides {CODE}
%code top {CODE}
These forms are now considered permanent features of Bison. See the
%code entries in the section "Bison Declaration Summary" in the Bison
manual for a summary of their functionality. See the section
"Prologue Alternatives" for a detailed discussion including the
advantages of %code over the traditional Yacc prologue directive.
Bison's Java feature as a whole including its current usage of %code
is still considered experimental.
** YYFAIL is deprecated and will eventually be removed.
YYFAIL has existed for many years as an undocumented feature of
deterministic parsers in C generated by Bison. Previously, it was
documented for Bison's experimental Java parsers. YYFAIL is no longer
documented for Java parsers and is formally deprecated in both cases.
Users are strongly encouraged to migrate to YYERROR, which is
specified by POSIX.
Like YYERROR, you can invoke YYFAIL from a semantic action in order to
induce a syntax error. The most obvious difference from YYERROR is
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
used. For a more detailed discussion, see:
http://lists.gnu.org/archive/html/bison-patches/2009-12/msg00024.html
The upcoming Bison 2.5 will remove YYFAIL from Java parsers, but
deterministic parsers in C will continue to implement it. However,
because YYFAIL is already flawed, it seems futile to try to make new
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
be removed altogether.
There exists at least one case where Bison 2.5's YYFAIL warning will
be a false positive. Some projects add phony uses of YYFAIL and other
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
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
2.4.2 is not necessary.
** Internationalization.
Fix a regression introduced in Bison 2.4: Under some circumstances,
message translations were not installed although supported by the
host system.
a recent enough version of gettext(3) e.g. Mac OS X or Linux. Dynamically
adjust the package list depending on the configure result.
Bump the package revisions because the package list was incorrect on
various platforms.
Changes in version 2.4 (2008-11-02):
* %language is an experimental feature.
We first introduced this feature in test release 2.3b as a cleaner
alternative to %skeleton. Since then, we have discussed the possibility of
modifying its effect on Bison's output file names. Thus, in this release,
we consider %language to be an experimental feature that will likely evolve
in future releases.
* Forward compatibility with GNU M4 has been improved.
* Several bugs in the C++ skeleton and the experimental Java skeleton have been
fixed.
Changes in version 2.3b (2008-05-27):
* The quotes around NAME that used to be required in the following directive
are now deprecated:
%define NAME "VALUE"
* The directive `%pure-parser' is now deprecated in favor of:
%define api.pure
which has the same effect except that Bison is more careful to warn about
unreasonable usage in the latter case.
* 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
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.
The current push parsing interface is experimental and may evolve. More user
feedback will help to stabilize it.
* The -g and --graph options now output graphs in Graphviz DOT format,
not VCG format. Like --graph, -g now also takes an optional FILE argument
and thus cannot be bundled with other short options.
* 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
%skeleton to select it.
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.
* %language
This new directive specifies the programming language of the generated
parser, which can be C (the default), C++, or Java. Besides the skeleton
that Bison uses, the directive affects the names of the generated files if
the grammar file's name ends in ".y".
* 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
user feedback will help to stabilize it.
* The grammar file may now specify the name of the parser header file using
%defines. For example:
%defines "parser.h"
* When reporting useless rules, useless nonterminals, and unused terminals,
Bison now employs the terms "useless in grammar" instead of "useless",
"useless in parser" instead of "never reduced", and "unused in grammar"
instead of "unused".
* Unreachable State Removal
Previously, Bison sometimes generated parser tables containing unreachable
states. A state can become unreachable during conflict resolution if Bison
disables a shift action leading to it from a predecessor state. Bison now:
1. Removes unreachable states.
2. Does not report any conflicts that appeared in unreachable states.
WARNING: As a result, you may need to update %expect and %expect-rr
directives in existing grammar files.
3. For any rule used only in such states, Bison now reports the rule as
"useless in parser due to conflicts".
This feature can be disabled with the following directive:
%define lr.keep_unreachable_states
See the %define entry in the `Bison Declaration Summary' in the Bison manual
for further discussion.
* 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
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
code.
* --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
deprecated:
%file-prefix "parser"
%name-prefix "c_"
%output "parser.c"
* 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
a single %code directive with an optional qualifier field, which identifies
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}'
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
determine whether they should become permanent features.
* Revised warning: unset or unused mid-rule values
Since Bison 2.2, Bison has warned about mid-rule values that are set but not
used within any of the actions of the parent rule. For example, Bison warns
about unused $2 in:
exp: '1' { $$ = 1; } '+' exp { $$ = $1 + $4; };
Now, Bison also warns about mid-rule values that are used but not set. For
example, Bison warns about unset $$ in the mid-rule action in:
exp: '1' { $1 = 1; } '+' exp { $$ = $2 + $4; };
However, Bison now disables both of these warnings by default since they
sometimes prove to be false alarms in existing grammars employing the Yacc
constructs $0 or $-N (where N is some positive integer).
To enable these warnings, specify the option `--warnings=midrule-values' or
`-W', which is a synonym for `--warnings=all'.
* Default %destructor or %printer with `<*>' or `<>'
Bison now recognizes two separate kinds of default %destructor's and
%printer's:
1. Place `<*>' in a %destructor/%printer symbol list to define a default
%destructor/%printer for all grammar symbols for which you have formally
declared semantic type tags.
2. Place `<>' in a %destructor/%printer symbol list to define a default
%destructor/%printer for all grammar symbols without declared semantic
type tags.
Bison no longer supports the `%symbol-default' notation from Bison 2.3a.
`<*>' and `<>' combined achieve the same effect with one exception: Bison no
longer applies any %destructor to a mid-rule value if that mid-rule value is
not actually ever referenced using either $$ or $n in a semantic action.
The default %destructor's and %printer's are experimental. More user
feedback will help to determine whether they should become permanent
features.
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
manual for a caveat concerning the treatment of literal strings.
* The nonfunctional --no-parser, -n, and %no-parser options have been
completely removed from Bison.
Changes in version 2.3a, 2006-09-13:
* Instead of %union, you can define and use your own union type
YYSTYPE if your grammar contains at least one <type> tag.
Your YYSTYPE need not be a macro; it can be a typedef.
This change is for compatibility with other Yacc implementations,
and is required by POSIX.
* Locations columns and lines start at 1.
In accordance with the GNU Coding Standards and Emacs.
* You may now declare per-type and default %destructor's and %printer's:
For example:
%union { char *string; }
%token <string> STRING1
%token <string> STRING2
%type <string> string1
%type <string> string2
%union { char character; }
%token <character> CHR
%type <character> chr
%destructor { free ($$); } %symbol-default
%destructor { free ($$); printf ("%d", @$.first_line); } STRING1 string1
%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.
[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
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.
* Handling of traditional Yacc prologue blocks is now more consistent but
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
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.
Previous releases of Bison inserted the pre-prologue into both the header
file and the code file in all cases except for LALR(1) parsers in C. In the
latter case, Bison inserted it only into the code file. For parsers in C++,
the point of insertion was before any token definitions (which associate
token numbers with names). For parsers in C, the point of insertion was
after the token definitions.
Now, Bison never inserts the pre-prologue into the header file. In the code
file, it always inserts it before the token definitions.
* Bison now provides a more flexible alternative to the traditional Yacc
prologue blocks: %before-header, %start-header, %end-header, and
%after-header.
For example, the following declaration order in the grammar file reflects the
order in which Bison will output these code blocks. However, you are free to
declare these code blocks in your grammar file in whatever order is most
convenient for you:
%before-header {
/* Bison treats this block like a pre-prologue block: it inserts it into
* 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"'. */
}
%start-header {
/* Bison inserts this block into both the header file and the code file.
* In both files, the point of insertion is before any Bison-generated
* token, semantic type, location type, and class definitions. This is a
* good place to define %union dependencies, for example. */
}
%union {
/* Unlike the traditional Yacc prologue blocks, the output order for the
* new %*-header blocks is not affected by their declaration position
* relative to any %union in the grammar file. */
}
%end-header {
/* Bison inserts this block into both the header file and the code file.
* In both files, the point of insertion is after the Bison-generated
* definitions. This is a good place to declare or define public
* functions or data structures that depend on the Bison-generated
* definitions. */
}
%after-header {
/* Bison treats this block like a post-prologue block: it inserts it into
* the code file after the contents of the header file. It does *not*
* insert it into the header file. This is a good place to declare or
* define internal functions or data structures that depend on the
* Bison-generated definitions. */
}
If you have multiple occurrences of any one of the above declarations, Bison
will concatenate the contents in declaration order.
[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 old spelling still works, but is not documented and may be removed
in a future release.
* The distribution terms for all Bison-generated parsers now permit
using the parsers in nonfree programs. Previously, this permission
was granted only for Bison-generated LALR(1) parsers in C.
* %name-prefix changes the namespace name in C++ outputs.
* The C++ parsers export their token_type.
* Bison now allows multiple %union declarations, and concatenates
their contents together.
* New warning: unused values
Right-hand side symbols whose values are not used are reported,
if the symbols have destructors. For instance:
exp: exp "?" exp ":" exp { $1 ? $1 : $3; }
| 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); }
;
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; }
;
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.
exp: exp { push ($1); } '+' exp { push ($3); sum (); };
The warning is intended to help catching lost values and memory leaks.
If a value is ignored, its associated memory typically is not reclaimed.
* %destructor vs. YYABORT, YYACCEPT, and YYERROR.
Destructors are now called when user code invokes YYABORT, YYACCEPT,
and YYERROR, for all objects on the stack, other than objects
corresponding to the right-hand side of the current rule.
* %expect, %expect-rr
Incorrect numbers of expected conflicts are now actual errors,
instead of warnings.
* GLR, YACC parsers.
The %parse-params are available in the destructors (and the
experimental printers) as per the documentation.
* Bison now warns if it finds a stray `$' or `@' in an action.
* %require "VERSION"
This specifies that the grammar file depends on features implemented
in Bison version VERSION or higher.
* 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.
If you do not want or can update to this scheme, the directive
`%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"'.
* DJGPP support added.
Changes in version 2.1, 2005-09-16:
* Bison-generated parsers now support the translation of diagnostics like
"syntax error" into languages other than English. The default
language is still English. For details, please see the new
Internationalization section of the Bison manual. Software
distributors should also see the new PACKAGING file. Thanks to
Bruno Haible for this new feature.
* Wording in the Bison-generated parsers has been changed slightly to
simplify translation. In particular, the message "memory exhausted"
has replaced "parser stack overflow", as the old message was not
always accurate for modern Bison-generated parsers.
* Destructors are now called when the parser aborts, for all symbols left
behind on the stack. Also, the start symbol is now destroyed after a
successful parse. In both cases, the behavior was formerly inconsistent.
* When generating verbose diagnostics, Bison-generated parsers no longer
quote the literal strings associated with tokens. For example, for
a syntax error associated with '%token NUM "number"' they might
print 'syntax error, unexpected number' instead of 'syntax error,
unexpected "number"'.
Differences to the plain GNU version in the packages collection:
* We do not install the shell wrapper "yacc" (it is supplied because
POSIX requires it and we already have a yacc command).
Changes since 1.75:
* Numerous bug fixes and improvements including:
+ Compatibility (with 1.35 and Solaris yacc) changes;
+ Fixes for GCC 3.2.1;
+ Use Yacc style of conflict reports;
+ Fix bug where error locations were not being recorded correctly;
+ Fix bad interaction with flex 2.5.23.
Please see the ChangeLog file supplied with the bison source code
for more details.
Changes since 1.35 (too many to mention here, please see the
ChangeLog in the bison source distribution):
* GNU m4 is now required.
* Various bug fixes.
* intl source removed.
NetBSD pkgsrc changes:
* Change of maintainer thorpej->cjep.
* C Skeleton
Some projects use Bison's C parser with C++ compilers, and define
YYSTYPE as a class. The recent adjustment of C parsers for data
alignment and 64 bit architectures made this impossible.
Because for the time being no real solution for C++ parser
generation exists, kludges were implemented in the parser to
maintain this use. In the future, when Bison has C++ parsers, this
kludge will be disabled.
This kludge also addresses some C++ problems when the stack was
extended.
* File name clashes are detected
$ bison foo.y -d -o foo.x
fatal error: header and parser would be both named `foo.x'
* A missing `;' ending a rule triggers a warning
In accordance with POSIX, and in agreement with other
Yacc implementations, Bison will mandate this semicolon in a near
future. This eases the implementation of a Bison parser of Bison
grammars by making this grammar LALR(1) instead of LR(2). To
facilitate the transition, this release introduces a warning.
* Revert the C++ namespace changes introduced in 1.31, as they caused too
many portability hassles.
* Fix test suite portability problems.
* Fix C++ issues
Groff could not be compiled for the definition of size_t was lacking
under some conditions.
* Catch invalid @n
As is done with $n.
Summary of changes:
- removal of USE_GTEXINFO
- addition of mk/texinfo.mk
- inclusion of this file in package Makefiles requiring it
- `install-info' substituted by `${INSTALL_INFO}' in PLISTs
- tuning of mk/bsd.pkg.mk:
removal of USE_GTEXINFO
INSTALL_INFO added to PLIST_SUBST
`${INSTALL_INFO}' replace `install-info' in target rules
print-PLIST target now generate `${INSTALL_INFO}' instead of `install-info'
- a couple of new patch files added for a handful of packages
- setting of the TEXINFO_OVERRIDE "switch" in packages Makefiles requiring it
- devel/cssc marked requiring texinfo 4.0
- a couple of packages Makefiles were tuned with respect of INFO_FILES and
makeinfo command usage
See -newly added by this commit- section 10.24 of Packages.txt for
further information.
* Fix Yacc output file names
* Portability fixes
* Italian, Dutch, Swedish, Russian translation
* Many Bug Fixes
* Use of alloca in parsers
* When the generated parser lacks debugging code, YYDEBUG is now 0
(as POSIX requires) instead of being undefined.
* User Actions
Bison has always permitted actions such as { $$ = $1 }: it adds the
ending semicolon. Now if in Yacc compatibility mode, the semicolon
is no longer output: one has to write { $$ = $1; }.
* Better C++ compliance
The output parsers try to respect C++ namespaces.
* Reduced Grammars
Fixed bugs when reporting useless nonterminals.
* 64 bit hosts
The parsers work properly on 64 bit hosts.
* Error messages
Some calls to strerror resulted in scrambled or missing error messages.
* The verbose report includes the rule line numbers.
* Rule line numbers are fixed in traces.
* Parse errors
Verbose parse error messages from the parsers are better looking.
* Fixed parser memory leaks.
When the generated parser was using malloc to extend its stacks, the
previous allocations were not freed.
* Fixed verbose output file.
Some newlines were missing.
Some conflicts in state descriptions were missing.
* Fixed conflict report.
Option -v was needed to get the result.
* Fixed incorrect processing of some invalid input.
* Fixed CPP guards: 9foo.h uses BISON_9FOO_H instead of 9FOO_H.
* %token MY_EOF 0 is supported.
Before, MY_EOF was silently renumbered as 257.
* doc/refcard.tex is updated.
* %output, %file-prefix, %name-prefix.
* --output
* `--defines' and `--graph' have now an optionnal argument which is the
output file name. `-d' and `-g' do not change, they do not take any
argument.
* Portability fixes.
* The output file does not define const, as this caused problems when used
with common autoconfiguration schemes. If you still use ancient compilers
that lack const, compile with the equivalent of the C compiler option
`-Dconst='. autoconf's AC_C_CONST macro provides one way to do this.
* Added `-g' and `--graph'.
* The input and the output files has automatically a similar extension.
* NLS support updated; should hopefully be less troublesome.
* Added the old Bison reference card.
* Added `--locations' and `%locations'.
* Added `-S' and `--skeleton'.
* `%raw', `-r', `--raw' is disabled.
* Special characters are escaped when output. This solves the problems
of the #line lines with path names including backslashes.
* New directives.
* @$ Automatic location tracking.
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