Not the op nor on their team but I do work at a company using Haskell for grpc services, internal cli tools, cloud web services, and heavy duty (and high performance) parallel parsing.

I'm a polyglot programmer and appreciate the features of many different languages but I couldn't imagine foregoing the benefits of Haskell's type system, reasoning about code algebraically, and leveraging the rock solid GHC RTS for some of the mission critical things we're doing. Rust would probably be my only other consideration for performance reasons but its ecosystem is more immature than Haskell's and some things are very clunky to express in rust (even with its enlightened type system) that are very clear in Haskell.

Haskell may not be the right choice for every team or project but it certainly has been for me for many years now on many (though not all) projects.

Clojure doesn't have a strong adoption within Facebook.

You can read more on Reddit: https://www.reddit.com/r/haskell/comments/68obk4/open_sourci...