* 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
*** 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
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.
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