The trouble is, I would love to have a language with properly controlled side effects and the basic functional goodies, but for real world use I'm not aware of any functional language that doesn't also make something basic much harder than imperative languages do.

If I could have a language with the functional toys of an ML or a Haskell, but where the impure side of things was as easy to write as the pure computations, that would be great. But for that to happen, I suspect there needs to be a dramatic shift in the way effectful code is written, in the same way that type inference practically eliminated all the syntactic overheads we might otherwise have assumed were necessary with a static type system.

I've seen a lot of research in this area, and there's huge potential in some of the ideas being tried out in languages like Haskell, but to my knowledge no-one has really hit anywhere near the sweet spot I'm looking for in a production language yet.