"Being a mathematician, I've always dreamt of a programming
language that would make use of the powerful formalism of Set
Theory. Two years ago, I started looking for an open-source
software tool to use in an elementary Set Theory class. I had a
hard time finding any on the Net, but in the end I found the object
of my dreams: a structured, general-purpose, open-source
programming language that implements as closely as possible the Set
Theory formal language. The language is called SETL (Set Language).
As I found out later, it has been around for quite a long time, 33
years to date. For some reason, though, it does not seem to be in
widespread use, at least according to the small number of related
resources available on the Net..."