I don't know TECO, as I have never used it.  But I know James Gosling (yeah,
THAT James Gosling) wrote the original Emacs (NOT GNU Emacs, but the
original Emacs) using TECO macros.

GNU Emacs, of course, was written originally almost entirely by Richard
Stallman (yeah, THAT Richard Stallman) using a little C and a lot of LISP.
After version 0.8, it has been added to by a lot of people.

Richard now mostly spends his time whining against the Open Source
Initiative. ;-)

He says open source != free software (how's that for a holy war?)

Later,
Cranky