* Changes in version 2.5 (????-??-??):
-** Named References Support
+** Named references:
Historically, Yacc and Bison have supported positional references
($n, $$) to allow access to symbol values from inside of semantic
These features are experimental in this version. More user feedback
will help to stabilize them.
-** IELR(1) and Canonical LR(1) Support
+** IELR(1) and canonical LR(1):
IELR(1) is a minimal LR(1) parser table generation algorithm. That
is, given any context-free grammar, IELR(1) generates parser tables
with the full language recognition power of canonical LR(1) but with
- nearly the same number of parser states as LALR(1). This reduction in
- parser states is often an order of magnitude. More importantly,
+ 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
LAC is an experimental feature. More user feedback will help to
stabilize it.
-** Unrecognized %code qualifiers are now an error not a warning.
+** Unrecognized %code qualifiers are now errors not warnings.
-** %define improvements.
+** %define improvements:
-*** Unrecognized variables are now an error not a warning.
+*** Unrecognized variables are now errors not warnings.
*** Multiple invocations for any variable is now an error not a warning.
-*** Can now be invoked via the command line.
+*** 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 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.
+** Grammar symbol names can now contain dashes:
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).
+ (e.g. push-pull), grammar 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).
-** YYFAIL now produces warnings and Java parsers no longer implement it.
+** 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.
+** 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
;
Bison now warns when a character literal is not of length one. In
- some future release, Bison will report an error instead.
+ some future release, Bison will start reporting an error instead.
** Verbose syntax error message fixes:
canonical LR. However, LAC is still experimental and is disabled
by default.
-** Destructor calls fixed for lookaheads altered in semantic actions.
+** 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
+** 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
} \
while (false)
-** YYLLOC_DEFAULT in C++
+** 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
restrictions of @acronym{LALR}(1), which is hard to explain simply.
@xref{Mystery Conflicts, ,Mysterious Reduce/Reduce Conflicts}, for
more information on this.
-To escape these additional restrictions, you can request
-@acronym{IELR}(1) or canonical @acronym{LR}(1) parser tables.
+As an experimental feature, you can escape these additional restrictions by
+requesting @acronym{IELR}(1) or canonical @acronym{LR}(1) parser tables.
@xref{Decl Summary,,lr.type}, to learn how.
@cindex @acronym{GLR} parsing
@itemize @bullet
@item Language(s): C (deterministic parsers only)
-@item Purpose: Requests a pull parser, a push parser, or both.
+@item Purpose: Request a pull parser, a push parser, or both.
@xref{Push Decl, ,A Push Parser}.
(The current push parsing interface is experimental and may evolve.
More user feedback will help to stabilize it.)
@itemize @bullet
@item Language(s): all
-@item Purpose: Requests that Bison allow unreachable parser states to remain in
-the parser tables.
+@item Purpose: Request that Bison allow unreachable parser states to
+remain in the parser tables.
Bison considers a state to be unreachable if there exists no sequence of
transitions from the start state to that state.
A state can become unreachable during conflict resolution if Bison disables a
@itemize @bullet
@item Language(s): all
-@item Purpose: Specifies the type of parser tables within the
+@item Purpose: Specify the type of parser tables within the
@acronym{LR}(1) family.
(This feature is experimental.
More user feedback will help to stabilize it.)
to alter the language accepted by the parser.
@acronym{LALR} parser tables are the smallest parser tables Bison can
currently generate, so they may be preferable.
+Nevertheless, once you begin to resolve conflicts statically,
+@acronym{GLR} begins to behave more like a deterministic parser, and so
+@acronym{IELR} and canonical @acronym{LR} can be helpful to avoid
+@acronym{LALR}'s mysterious behavior.
@item Occasionally during development, an especially malformed grammar
with a major recurring flaw may severely impede the @acronym{IELR} or
@itemize
@item Languages(s): C++
-@item Purpose: Specifies the namespace for the parser class.
+@item Purpose: Specify the namespace for the parser class.
For example, if you specify:
@smallexample
projects / bison.git / commitdiff
