[CM] emacs support for s7 repl?

[bil at ccrma.Stanford.EDU]

The Snd repl (xen_repl in the scheme section in xen.c)
uses the function stdin_check_for_full_expression (snd-xen.c)
to get a full expression from emacs.  It might be more
straightforward in s7 to use the missing-close-paren-hook or
the underlying error to do something similar.  But currently
the s7 emacs repl is dumb.

I looked at geiser briefly, but my recollection is that
it insisted on r6rs library ("module") handling.  Maybe
they have removed that requirement, or someone could hack
around it.  It would be great to have that capability
in emacs.

The other possibility is LSP (Miscrosoft's Language
Server Protocol).  Again my memory is fading, but I
think it uses JSON to communicate both ways.  I started
json.scm, but lost interest (I guess XML would have been
worse, but geez...).  There is emacs support for LSP.