A fun esolang I haven't seen before: expressing the entire program as a directory structure!
miniblog.
Related Posts
Very readable discussion of different ways of expressing applicative and monads in ocaml. Discusses the necessary operators and new syntactic sugar:
"There's no way of expressing a complete program: there isn't even a concept textually. A sea of objects living." https://youtu.be/BDwlEJGP3Mk?t=3m40s
Understanding Taming The Meta Language https://frantic.im/meta-language (on the power of expressing things in code rather than docs)