Instead of "lack of encapsulation", it's more "lack of private state". In an object oriented language, you have private instance variables and methods to manipulate them. In a functional language, you have functions which manipulate data structures.

If possible, the data structure would have straightforward fields which are public and documented. If necessary, you might make it opaque, expecting only the library which manages the data structure to manipulate it.

One way to think about this is that in functional programming, the "verbs" (functions and manipulation patterns like map) are more generic and the "nouns" (data structures) are less important than in OO languages. See http://steve-yegge.blogspot.com/2006/03/execution-in-kingdom...