The released one wasn't. Its OS was written in C++ and its apps were written in Newtonscript, which was an interpreted language that loosely resembled Javascript (but well before Javascript was created).
The first Newton OS was written in Lisp (specifically in a dialect called Ralph, which was basically Scheme plus CLOS) over a C++ microkernel.
By the way, that Lisp was written by Apple Cambridge, a group in Apple that was created when Larry arranged for Apple to purchase the assets of Coral Software and hire some of its best hackers to design a new programming language.
Apple later spun out that group to create Digitool, which took with it the code and the rights to Macintosh Common Lisp. Digitool did not prosper, and one of its employees, Gary Byers, negotiated the rights to turn the MCL compiler into an open-source implementation that later became Clozure Common Lisp. So Larry is also responsible for the creation of Clozure Associates and Clozure Common Lisp.
There were some issues with the first Newton OS that led to two developments:
1. John Sculley ordered Larry Tesler to redo the OS in C++. That's the version that shipped.
2. Larry asked me and a few other Lisp hackers to see what we could do on Newton with Ralph. That resulted in the bauhaus OS, which didn't ship.
The authors of the first Newton OS were smart programmers, but they weren't Lisp hackers. Larry speculated that that had something to do with some of the early issues, and maybe it did. I think our version offered some improvements.
Another set of issues had to do with the UI design of the initial OS. Larry was critical of it on the grounds that it was basically trying to be a desktop UI in a handheld device. He thought we should try for a UI experience more suited to a new kind of device, and, in the end, both the shipping OS and the bauhaus OS did what he asked, and were better for it.
(In a final evaluation meeting for bauhaus, our managers told us that we had met and exceeded all goals of our experimental project, but Apple was of course going to ship the OS that the CEO told us to ship, and it was of course not going to ship two OSes for the device. None of this was a surprise to the bauhaus team. We were grateful to have had the support to work on the project for as long as we did, and disappointed that it was over.)
