I would use the term "wrapped-up" where you've used "encapsulated", and in fact I specifically avoided talking about wrappers for this exact reason :) Maybe my

I would use the term "wrapped-up" where you've used "encapsulated", and in fact I specifically avoided talking about wrappers for this exact reason :) Maybe my terminology could have been better, but I meant "encapsulated" in analogy to OOP, which advocates "encapsulating" all data via methods. The OOP definition of encapsulation includes using getters/setters, which is like having "wrapped-up" properties, but the idea is that we can go beyond this to calculate the data in arbitrary ways without our clients having to know about the implementation. That's what I was trying to get at here; for example, the implementation of IO involves horrible imperative yukiness, but we (the client) don't need to know that: we just use the interface, and if our functions ever get called, they will be given an appropriate argument.