I think a Brett Victor like dev tool would be a good companion to pure functional languages, and help improve their standing.
Shared state code does not respond well to running functions in a tight loop while changing the code. Mutations accumulate and the results become meaningless very quickly.
There have been some minor attempts that may even predate Brett's work, especially around trying to run unit tests on every edit. Those tend to be slow so some people have done work on using code coverage tools to figure out which code changes affect which tests, but I suspect they ran into problems since I haven't heard about any of those in some time now.
Shared state code does not respond well to running functions in a tight loop while changing the code. Mutations accumulate and the results become meaningless very quickly.
There have been some minor attempts that may even predate Brett's work, especially around trying to run unit tests on every edit. Those tend to be slow so some people have done work on using code coverage tools to figure out which code changes affect which tests, but I suspect they ran into problems since I haven't heard about any of those in some time now.