[hnlmorg]

> Some operating systems as you point out are PLs

None that immediately spring to my mind. There are operating systems that incorporate programming languages as their default user interface (like UNIX that drops into a Borne shell and LISP machines) and there are computers that have programming languages baked into their firmware (like the 70s and 80s micro computers did with BASIC). But in neither instance is the language itself the operating system.

The micro computer instance is definitely nuanced though. Some do argue that Microsoft BASIC et al were an operating system. Some don't. I'm in the latter category because I think "BIOS" more closely describes the function of the software on those old micro computers.

[ModernMech]

Others in this thread have mentioned some good ones: Smalltalk, Lisp Machines, and the JVM. Some others I would add:

- Pilot was an OS that was essentially bare metal Mesa. It was written in Mesa, only runs Mesa programs, and used Mesa language features for OS capabilities like safety: https://courses.cs.washington.edu/courses/cse550/20au/papers...

- Cedar was both a PL and an OS: https://www.ics.uci.edu/~andre/ics228s2006/swinehartzellwege...

- The Oberon OS and Oberon PL are highly coupled https://people.inf.ethz.ch/wirth/ProjectOberon1992.pdf

- Here's a Scheme OS called MrEd: https://www2.ccs.neu.edu/racket/pubs/icfp99-ffkf.pdf

[rjsw]

For a Lisp Machine the operating system was written in the language itself, this included a network stack and the filesystem interface for local disks.

[lispm]

The filesystem(s) and the disk driver(s) were written in Lisp, too.