A couple of months ago, at the
Lightweight Languages Workshop 2002, Matthew Flat made a premise in his talk:
Operating system and programming language are the same thing (at least "mathematically speaking"). I find this interesting and has a lot of truth in it. Both OS and PL are platforms on which other programs run. Both are virtualizing machines. Both make it easier for people to write applications (by providing API, abtractions, frameworks, etc.)