Lexical binding (was: JDEE)

Mats Lidell writes:

 > I saw in the mail list archives that the new lexical binding in Emacs
 > is considered a culprit for keeping XEmacs support. I'm not a lisp
 > language expert but I would expect that to be true. 
 > 
 > I also assume that type of feature is something we really need to have
 > or all major elisp packages will sooner or later stop working for
 > us.

Yes, yes, and yes (but I doubt that most of the major packages will
move to lexical binding for several years; they want to support
non-lexbind Emacs versions as well as XEmacsen).

 > Am I right? How hard would it be to implement?

I don't know, except that it's not something I know how to do.  Adrian
and Mike would both be able to do it, but I imagine it's a pretty big
job, and time will be a factor.  There may be others who can help.

We'd have to use the strategy that GNU used of allowing individual
libraries to be compiled with lexical binding or not.  They used a
magic cookie of "*lexbind*" or something like that in a comment at the
top.  I think that's a pretty horrible hack, but we might need to
support it somehow anyway.  I'm not sure what the alternatives might
be (explicitly specifying the mode of compilation in the byte compile
function call?)