A huge chunk of the site integrity bits (e.g. general spam prevention and application of this technology to other problem spaces like instant messages, etc.) for Facebook are done in Haskell and if you know Haskell and fancy working in London I am fairly certain that team is always on the lookout for new people.
And also happen to employ Simon Peyton Jones and Simon Marlow, respectively, two of the originators of the GHC project.
Yes, please note that BigTechCo using something in production is not an endorsement that it's production-ready. Ironically, more often than not, it means the opposite. BigTechCo employs the best computer scientists in the world to make all of that stuff work together, frequently including the project's founders/BDFLs so they can get whatever changes they need rammed through. Your company does not have this luxury.
It is definitely an endorsement that it is ready, although maybe not we-search-code-monkeys ready.
A large part of our jobs is figuring things out.
People looking for so-called production-grade tech are usually looking for ready-for-managers tech in my experience.
I'm pretty sure Simon Peyton Jones is still at Microsoft Research.
I know about FB (Haxl, spam filtering etc) but what exactly is MS using Haskell "in production" for?