christos@zoulas.com (Christos Zoulas) writes:

[ed, ex]

>I think that the original source was taken back by USL and changes were made
>to it to handle cursor keys and to use curses. Someone with better knowledge
>should post.

McKusick's article in the open-source book is quite a nice read,
and also contains some explanation on the history of ex/vi:

http://www.openresources.com/documents/open-sources/node22.html

In there he tells that Joy and Haley as graduate students at UCB,
while working on the Pascal system that Ken Thompson had hacked
together while sitting in Berkeley's machine room as a visiting
professor, took the "em" editor from Professor George Coulouris
and turned it into ex, bundled it with the Pascal system and
shipped that software as the "Berkeley Software Distribution".
Later, Joy and Horton added the full-screen vi mode to ex,
producing the editor that we know today.
Whether "em" (reportedly "ed for mortals") was actually based
on ed (which would explain vi being "encumbered") or whether it
was written from scratch is not told in the article.
The issue with USL importing modifications into BSD vi does also
sound reasonable and I think I've read that somewhere already.

--mkb