Edward Coffin has a post that’s a nice companion to yesterday’s Irreal post on the evolution of Elisp. After much effort he managed to track down a copy of Dan Weinreb’s undergraduate thesis on the ZWEI editor and has posted a summary of the thesis on the Emacs subreddit.
ZWEI was an interactive full-screen editor written for the Lisp Machine. Like EINE, from which it was derived, it was based on Emacs (EINE is a recursive acronym for EINE is not Emacs). Like Emacs, ZWEI was written in Lisp and had features, such as the point and cursor, that today’s Emacs user would find familiar.
If you’re interested in Emacs history and seeing where your editor of choice came from, it’s worth taking a look at Coffin’s post. It’s short and won’t take much time. Also interesting and worth your time are the comments by netsettler, who worked on editors for the Lisp Machine at Symbolics. He has a nice discussion of the comparative advantages of using a linked list of lines—as ZWEI did—versus the gap structure that modern Emacs uses.