I stumbled across this a few times while writing Elixir code. I separated the code into processes that return actions, and processes that execute actions… I did not go further because it was a application that integrated GitHub and Slack and what really broke purity was HTTP calls. And writing a framework for doing it went well beyond the scope of the project.
That said I think Elm has a great approach to managing effects purely and could be a good inspiration 
I would love to collaborate on something similar for the backend
Now from a theoretical perspective, recursive types offer a basis for purely functional processes, that might be a solid starting point for more academic work, so I thought it is worth mentioning.
Roughly, a process is a function that takes a message and returns a reply and a new process (which is again a function that takes a message and … all the way down):
process :: message -> (message, process)
Does anyone know if dyalizer can check this kind of types?
