Well, more attempts at this problem come along pretty often (speaking for Haskell at least, and I expect those attempts to be more mature than the other languag

Well, more attempts at this problem come along pretty often (speaking for Haskell at least, and I expect those attempts to be more mature than the other languages you mentioned), so I don't think you can say those languages have solved it. Like the other comment mentioned, it's an active area of research, and some of the research happens in languages designed to solve that problem, and some happens in languages that support solutions to the problem. (Just to add- there's a really wide range of ergonomics that you can support and it's hard to get everything right. And performance is super tricky!)