(author here)

Well, I haven't used Haskell in a few years, so I could absolutely be wrong. That being said, I'm almost sure that I saw a presentation by Simon Marlowe 15-20 years ago demonstrating GHC with a multicore scheduler (alongside `seq` and `par`). Also, from the very same Simon Marlowe, there's a package called `async` https://hackage.haskell.org/package/async which basically provides async (no await, though).