This is false. Well, it may be true in Erlang, but its false in Haskell, where there is always clear separation between equations and effects/state no matter th

This is false. Well, it may be true in Erlang, but its false in Haskell, where there is always clear separation between equations and effects/state no matter the source (IO to other services or local state). Not to mention that there are tools such as STM that let you deal with state in a much safer and less error-prone way. Separating the state between multiple communicating services is basically the same strategy as OOP (objects that communicate via messages and encapsulate state) but with stronger encapsulation requirements (access only via API, you can't just "reuse" methods willy-nilly all over the place but you have to come up with a sensible library or a third service, etc etc). It works, yes but it works about just as much as OO does. Which is... not very much. And it also comes with its own tradeoffs (good luck getting atomic changes over multiple microservices)