Something that takes PL theory concepts and puts them into practice:
- dependent types
- algebraic effects
- linear types
- algebraic data types
- higher kinded types
- homoiconicity (so it'd have to be Lisp-like, but typed)
- borrow checking, and beyond, such as region borrow checking
- cross-platform, JITed, as well as ahead of time compilation in release mode
- static metaprogramming