[slime-devel] presentations

[Matthias Koeppe]

Helmut Eller <heller at common-lisp.net> writes:

> I've some questions about the presentation stuff:
>
> 1. now that we have explicit messages for presentations in the
>    protocol, can we remove the bridge thing?  Yes, I know that
>    presentations will then not work with the dedicated output stream,
>    but that's a efficiency hack and layerying the bridge kludge on top
>    of the efficiency hack is so ugly, it makes me cry.  I'll remove
>    it, if there are no objections.

The bridge code has never worked cleanly for me (sometimes I see
partial escape sequences in the output).  Also, I think that the
method of signalling presentations by printing escape sequences is
inherently broken because it messes up the character position, which
disturbs the pretty printer layout.  Hence I agree with your
suggestion to remove the bridge code.

I would suggest to automatically turn off the dedicated output stream
when presentations are in use.

Alan's point about the speed of the bridge-less presentation code is
valid, of course.  I think we should try to speed up this code; I do
not have time to work on this, though.

> 2. is there another way to handle presentations than with
>    after-change-functions?  Our after-change-functions are totally
>    broken in Emacs20.  Could we use overlays instead of text
>    properties for presentations?

We definitely need text properties for associating presentation _data_
with the text, because overlays do not get copied.  For implementing
the visual mark-up, I am currently using text properties (which do get
copied) and overlays (which allow highlighting of nested presentations).
(Try (describe 'standard-object) in CMUCL and mouse over the
#<Wrapper...> object.)  Again the problem is that overlays do not get
copied with the text.  I have been thinking about using overlays only
for the visual markup; then the after-change function will need to be
extended to create overlays for marking up presentations and to delete
them when the presentations become invalid.  I don't know whether this
technique will work better for Emacs 20, but it will be worth a try.

> 3. is *can-print-presentation* still needed?  It seems to me that
>    slime-stream-p serves about the same purpose, but it is much
>    cleaner.  It's also ugly the we need to bind
>    *can-print-presentation* in a lot of unrelated/random places.

I would think it is not needed any more.

-- 
Matthias Köppe -- http://www.math.uni-magdeburg.de/~mkoeppe