Well, Twitter didn't backed away from Scala, but it doesn't qualify as purely functional. Turing completeness ensures there's no "true way", but some languages

Well, Twitter didn't backed away from Scala, but it doesn't qualify as purely functional. Turing completeness ensures there's no "true way", but some languages offer better abstractions than others. In my experience, once you learn the abstractions, the functional paradigm has an edge about the ability to reason about the code. Of course, the adoption of new ideas and technologies takes time, they need to be explored and fully developed. But even right now, you see many mainstream languages adopting functional flavors. I believe that eventually, there will be enough successful large scale projects build with pure functional languages to convince skeptics, there's nothing wrong with "playing it safe" and wait. If Scala is good enough as an example, I see an increasing adoption. As an anecdote, one of the biggest and Very Serious(tm) investment bank, is using Scala for most of their new initiatives, with a big team spread across the world. And the language itself was selected by a committee. You can't get more serious than that...