The library I was referring to is called servant[1]. It's a library for writing backends and clients in Haskell. I mentioned it because he said something about "webscale", but it doesn't have anything to do with concurrency.

The go-to library for nice Haskell concurrency is probably async[2], which you can combine with stm[3] for very nice guarantees. If you're interested, there is a very nice, free book[4] on the subject.

[1] https://haskell-servant.github.io/ [2] https://www.stackage.org/package/async [3] https://www.stackage.org/package/stm [4] http://chimera.labs.oreilly.com/books/1230000000929/index.ht...