The real modern question for programmers is what we can do, given that we actually have computers. Editors as flexible paper won't cut it.
So of course I like TermKit:
It brings back memories of Apple Dylan:
It's simple: replace plain text files with collections, and lines with objects, and you get Good Things for free!
For example: Scott McKay describes the DEUCE editor:
The editor for FunO's Dylan product -- Deuce -- is the next generation of Zwei in many ways. It has first class polymorphic lines, first class BPs [buffer pointers], and introduces the idea first class "source containers" and "source sections". A buffer is then dynamically composed of "section nodes". This extra generality costs in space (it takes about 2 bytes of storage for every byte in a source file, whereas gnuemacs and the LW editor takes about 1 byte), and it costs a little in performance, but in return it's much easier to build some cool features:
- Multiple fonts and colors fall right out (it took me about 1 day to get this working, and most of the work for fonts was because FunO Dylan doesn't have built-in support for "rich characters", so I had to roll my own).
- Graphics display falls right out (e.g., the display of a buffer can show lines that separate sections, and there is a column of icons that show where breakpoints are set, where there are compiler warnings, etc. Doing both these things took less than 1 day, but a comparable feature in Zwei took a week. I wonder how long it took to do the icons in Lucid's C/C++ environment, whose name I can't recall.)
- "Composite buffers" (buffers built by generating functions such as "callers of 'foo'" or "subclasses of 'window') fall right out of this design, and again, it took less than a day to do this. It took a very talented hacker more than a month to build a comparable (but non-extensible) version in Zwei for an in-house VC system, and it never really worked right.
Of course, the Deuce design was driven by knowing about the sorts of things that gnuemacs and Zwei didn't get right (*). It's so much easier to stand on other people shoulders...