> Evidently most language creators find it difficult to integrate both interactive programming and static typing.
Interactivity is one thing. Randomly redefining things is a-whole-nother thing. ML and Haskell are interactive. They just don't stuff absolutely everything in mutable cells like most dynamic languages do.
> That seems like it could be part of a potential solution, but it would require rewriting the program so that everything is implicitly wrapped in the IO monad.
You can't have it both ways: either you have effects and accept that you have effects, or don't have effects and accept that you don't have effects. (IOW, lying is bad.)
Evidently most language creators find it difficult to integrate both interactive programming and static typing, which suggests to me that the problem is not easy. Or maybe there just isn't enough overlap between the groups who value one or the other.
> just stuff all your top-level definitions into mutable cells
That seems like it could be part of a potential solution, but it would require rewriting the program so that everything is implicitly wrapped in the IO monad. And it still doesn't handle the case were you want to add to an existing data type.