[cryptica]

My view on FP is that one of its main benefits in terms of avoiding bugs is that it forces you to turn all your 'movable state' into raw messages. The fact that it also abolishes 'unmovable state' is just a quirk of it, not necessarily a benefit.

My main point in support of OOP is that OOP doesn't prevent you from making all your 'movable state' into raw messages too. Properly encapsulated instance state is not dangerous. What I like about OOP is that it offers some additional benefits in terms of high cohesion and loose coupling because co-locating logic with related state helps to write high cohesion, loosely coupled modules. It reduces the amount and complexity of state that needs to be transferred between modules. It allows my messages and function/method signatures to be even leaner than FP allows.

If you want to catch a taxi to the airport, FP still requires that you bring a jerrycan of fuel and steering wheel to give to your taxi driver, the only restriction is that he cannot alter them (no mutations). The benefit of this is that you can fully trust that the integrity of your jerrycan and steering wheel has been maintained after the trip and you can then confidently re-use them for your airplane as well... Anyway, as elegant as that seems in theory, it's not quite how the world works.