What do you mean by serious products? There are plenty of massive projects written in purely functional languages (e.g. Facebook's Sigma) and while adoption isn

What do you mean by serious products? There are plenty of massive projects written in purely functional languages (e.g. Facebook's Sigma) and while adoption isn't as fast as it could be, things seem to be shifting towards functional/immutable, which makes sense since reasoning about highly parallel code without RT and immutability is pretty much impossible.