[ESS] show wd in mode-line?

[Martin Maechler]

>>>>> Vitalie Spinu <spinuvit at gmail.com>
>>>>>     on Wed, 22 Aug 2012 17:27:07 +0200 writes:

    >>> What ESS can potentially do, is to reset on idle time
    >>> the emacs's wd to that of R. I guess, this would be
    >>> useful in general, and is pretty easy, as ESS has to
    >>> synchronize some other stuff as well. So if there are no
    >>> objections, I will implement that.

    SE> Have a look at `ess-dirs' bound to M-RET -- doing it in
    SE> idle time could work, but never bothered me enough.

    > Oh, right, I forgot about that. There are a bunch of
    > similar functions in ESS ess-change-directory, ess-dirs
    > and ess-use-this-dir. I can sense a confusing redundancy
    > on the first glance.

    >>> Kasper Daniel Hansen <kasperdanielhansen at gmail.com> on
    >>> Wed, 22 Aug 2012 10:49:34 -0400 wrote:

    KDH> Vitalie, You need to think about what happens when you
    KDH> run multiple R's with different working directories.  I
    KDH> do that frequently.

    > Correct, but you don't run two different processes in the
    > same buffer, do you? So, there is no conflict. Otherwise I
    > am really curious how you manage that :-).

Aah you are right indeed.  Kasper:
the good ole   default-directory  has become a buffer local
variable at some point in time during the last twenty years.
I'm pretty sure it was not, when I started using S-mode, the
precursor of ESS, in 1989, 1990 or so, and Emacs version 18.59

Martin