Arrow is a Kotlin library that has brought support for HKTs and type classes into the language. On top of that we have ported a good chunk of the FP stack including comprehensions, lenses, recursion schemes, and a blazing fast effects system. This enables experimenting with Haskell papers that you can seamlessly run on your phone.
The other aspect of Arrow is that it’s already widespread in the industry and is being used by startups and banks. It works on top of the vanilla Kotlin toolset, so it is safe to bring into your JVM programs. Bring your favorite FP constructs onto your day-to-day job!