> You need a PhD in type theory to get anywhere.

That is extremely false. Haskell isn't even a good playground for academic type theory -- you'd want Agda etc. for that. The development of the language over the last few years has been characterized by pragmatism and a focus on backwards-compatibility, which is why you can take code from something like ten years ago and have it run without issues on modern versions of the Haskell compiler with little to no modifications. (Let's not talk about how long code written in "modern" JS lasts.)

And I'd really like to see type class constraint resolution with functional dependencies, or Hindley-Milner type checking, or something of that sort implemented in "5-10 lines" of JS.

"There he goes again with his mumbo-jumbo," you say. That's right, you don't need to care about those things to write Haskell. What you meant is implementations of typeclasses ("interfaces") like Monad, Functor, and so on: they don't take much more code in Haskell.

  Array.prototype.chain = function (f) {
    return this.reduce((acc, it) => acc.concat(f(it)), [])
  }

  instance Monad [] where
    xs >>= f = concat (map f xs)
    return = pure

And we didn't even have to go the "this" route! Notice that your 5 - 10 lines of JS don't let you write code that works in any monad, whereas I can easily write

  whenM :: Monad m => m Bool -> m () -> m ()
  whenM cond action = do
    condition <- cond
    if cond then action else pure ()

In Elm, you'd have List.whenM, Array.whenM, Maybe.whenM, ... or a straight-up false type signature like their Eq ones, and in JS, a bunch of prototype methods with no unifying threads.

--

As for an example of why I think Haskell has the right ideas (few of us will say it's the "best language evar"):

I'd really like to see a JS version of the Servant library, which takes an API spec for a server and actually generates a fully functional server from that. Here's a description:

https://news.ycombinator.com/item?id=14149200

Does this strike you as idle theoretical self-enjoyment?

You certainly would need a PhD to fully understand Monads from that small JavaScript snippet. The Haskell link you gave gives Phil Wadler's original paper as the first link. It is easy to read, explains everything beautifully and full of many examples. Learn some basic Haskell for no other reason than to read seminal papers such as these. To favour some random JavaScript hacker on the internet and steer others away from the original work is anti-intellectualism.

> Basically every obscure overly complicated concept that Haskell throws at you (all the while pretending to be the only true FP language out there) can be explained in 5 to 10 lines of JavaScript

So presumably the same concepts can be explained in 5 to 10 lines of Haskell too.

I think you're confusing the refinement and polishing of ideas that's taken place in Haskell over the last two decades with the succinct presentation of those ideas once they've been worked out.