- Have you ever heard about how Walmart handles Black Fridays?
- Do you even know what's behind Apple's payment system?
- You ever used Pandoc, Couchbase, Grammarly, CircleCI, Clubhouse.io, Pandora, Soundcloud, Spotify?
- Have you ever asked a question - what is an app like WhatsApp that was sold for $19 Billion runs on?
- or How Facebook fights spam, Cisco does malware detection or AT&T deals with abuse complains?
- How Clojure is used at NASA or how Microsoft uses Haskell?
Frankly, I don't even know what's there to debate about. Functional programming is already here and it's been used in the industry for quite awhile already and its usage growing in a quite steady pace. Almost every single programming language today has certain amount of FP idioms, either built-in or via libraries. So yeah, while you're sitting there, contemplating about if FP useful or not, people been building hundreds of awesome products.