Background
Last quarter I took a course called Principles of Safe Software which had a lot to do with program correctness, compile time guarantees, etc. We specifically explored this through Haskell and its type system. Haskell is a pure, statically typed functional language. Almost all of my programming experience has been with 'impure', dynamically typed, imperative languages so this was quite the trip for me! While I haven't had much time to master Haskell as much as I'd like, an opportunity in class has come up for me to play with Haskell-like things, namely Elm!
Elm
Recently I've been playing a lot with Elm and by playing I mean actually playing! Elm is a language with similar syntax to Haskell that compiles to HTML and JS. Elm is tons of fun and really easy to write. I don't (and don't necessarily want to) know a whole lot of JavaScript, so Elm has been a good way for me to build some fun UI stuff with a syntax and idioms that are very similar to those of Haskell. It's really neat what you can do with a couple lines of code sometimes(hint: click and drag)!