I'd have said the fact that no-one's done it is pretty good evidence it's not as easy as you think. As plenty of people have pointed out, FP means different thi

I'd have said the fact that no-one's done it is pretty good evidence it's not as easy as you think. As plenty of people have pointed out, FP means different things to different people. But so does OO. In fact, I'd argue that Scala is about as close as you're going to get to your spec. Not helped by the fact that, as any Scalazzi could tell you, the requirements of 1 and 2 contain contradictory elements and make complexity shoot through the roof. (You can get fewer FP features and less complexity by going for F# instead.) Personally, I like Haskell. It's great for 1 and 3, 4 is pretty acceptable and 2 gets thrown in the bin. 5 could do with some work, though.