new_features

伯克利的语法分析器的创建工具

     This version of Berkeley Yacc has been extensively reorganized and
contains many new features.  It is an amalgam of three earlier versions
of Berkeley Yacc.  It is largely untested, so expect it to contain bugs.
When bugs are found report them to [e-mail].  Please
include small examples if possible.

     Despite my pleas not to be told of undocumented features of AT&T Yacc,
I have received unsolicited descriptions of such features.  Telling me of
such features places the public-domain status of Berkeley Yacc at risk.
Please do not send me descriptions of undocumented features.  On the
other hand, I would be very interested in learning of documented
features I have not implemented.

     The -l and -t options have been implemented.  The -l option tells
Yacc not to include #line directives in the code it produces.  The -t
option causes debugging code to be included in the compiled parser.

     The code for error recovery has been changed to implement the same
algorithm as AT&T Yacc.  There will still be differences in the way
error recovery works because AT&T Yacc uses more default reductions
than Berekeley Yacc.

     The environment variable TMPDIR determines the directory where
temporary files will be created.  If TMPDIR is defined, temporary files
will be created in the directory whose pathname is the value of TMPDIR.
By default, temporary files are created in /tmp.

     The keywords are now case-insensitive.  For example, %nonassoc,
%NONASSOC, %NonAssoc, and %nOnAsSoC are all equivalent.

     Commas and semicolons that are not part of C code are treated as
commentary.

     Line-end comments, as in BCPL, are permitted.  Line-end comments
begin with // and end at the next end-of-line.  Line-end comments are
permitted in C code; they are converted to C comments on output.

     The form of y.output files has been changed to look more like
those produced by AT&T Yacc.

     A new kind of declaration has been added.  The form of the declaration
is

	  %ident string

where string is a sequence of characters begining with a double quote
and ending with either a double quote or the next end-of-line, whichever
comes first.  The declaration will cause a #ident directive to be written
near the start of the output file.

     If a parser has been compiled with debugging code, that code can be
enabled by setting an environment variable.  If the environment variable
YYDEBUG is set to 0, debugging output is suppressed.  If it is set to 1,
debugging output is written to standard output.