As I understand, the more "up-to-date" 2017 version is not as comprehensive
as the 2014 version. I got in contact with Bruce Ravel (2014 author) and he
says he's standing by, but I told him to wait to see what the org-mode side
can do first about the :session issue. So in general I'm supposing that
when a language's REPL session is not started, babel sometimes goes
straight the executable on the system and comes back with results. But then
others specifically need a :session named and started -- or at least start
a session.

I guess I'm being manic about this due to the overall difficulty of
producing graphs and diagrams in general in the STEM world. If you're good,
you can transcribe JIT, say, a math lecture on your laptop with org-mode --
prose and LaTeX formulae. But if you need diagrams you're blown away. . .

I've got a copy of Martin Weissman's *An Illustrated Theory of Numbers *which
utilizes LaTeX Tufte with diagrams in TikZ/PGF. Quite a beautiful book. In
general, it's just too damned hard to produce diagrams relative to prose
and formulae. . .  My two farthings. . . .

On Tue, Apr 30, 2019 at 12:10 PM Fraga, Eric <e.fraga@ucl.ac.uk> wrote:

> For the list: Lawrence and I have followed this through a bit more.  The
> solution, for those that have a newer version of gnuplot-mode (2017
> version instead of the 2014 version), is to set :session to "none".
>
> I would suggest that there is a bug in ob-gnuplot.el.  Specifically,
> :session is initialized to nil but all the code that checks for session
> assumes that it has to be set to "none" to not use a session.
>
> What hasn't been resolved is how to get sessions to work with the more
> up-to-date gnuplot-mode.
> --
> Eric S Fraga via Emacs 27.0.50, Org release_9.2.3-327-g3375f0
>