RE: Multiple M-x shells sharing input ring

[Drew Adams]

> > There are not only two alternatives: permanent-local and global.
> > The normal way to handle what you describe is to make the variable
> > local in each buffer where it should be local.  It can even be
> > made automatically local everywhere (`make-variable-buffer-local').
> >
> > And any mode derived from comint mode that happens to want a
> > separate history can easily obtain that, even if the variable
> > is not declared automatically local.  Nothing prevents scheme
> > mode or whatever from doing `make-buffer-local' in its buffers.  
> > That's the usual way these things are done.
> 
> Yes, but if you want to have a shared input history for all shell
> buffers, and another shared history for all interactive scheme
> buffers, using a global var is not good enough either.

True.  But nothing says that scheme mode cannot use a different
global variable.  Just because it is derived from comint mode does
not mean that it needs to stay in lockstep with other comint-mode
(or derived-p) buffers.

> >  Permanent locals are appropriate for...
>
> It doesn't say that it's inappropriate for all other cases ;-)

Oh, come on.

> > And even if it does that, that just makes the variable buffer-
> > local.  What prevents one from then killing that local variable
> > and using the global one instead?
> 
> Nothing, but I just think a per-mode input history could be more
> useful.

OK.  But see above.  I don't disagree with the per-mode part.

But starting with per-comint-mode is not a bad start.  Any mode
derived from comint-mode could then, if it needed, use its own
separate variable - for all of its buffers (shared).  Or it
could use a separate history for each of its buffers, as is the
case now.  (Or for some but not others.)

Anyway, I think we've probably beat this request to death. ;-)
It should be clear now that Joseph can get any combination of
behaviors he wants, and there are different ways to do that.