Hacker News Reader

Yeah it's really hard to introduce, let alone completely stick with, FP in a non-FP language. I started to introduce some into our Ruby/Rails project, but halfway through, the code was more procedural than functional (which admittedly is more concise and cogent than OO); it's really hard to remember to treat everything as immutable all the time.

Scala's for-comprehensions (and Haskell's do-notation) help quite a lot as well.

Also F#'s computational expressions.

When combined with flow or typescript, Javascript absolutely supports sum types. Also, it's trivial to encode the Option and Either monad using Objects to get the same functionality.