As to coming up with the "simplest" representation, that's almost certainly excellent advice whether doing OO or FP. It should be noted that Hickey has a rather specific notion of "simple" that may be rather different from more typical intuitions. This is why Hickey had to differentiate between "simple" and "easy", where "simple" means not intertwined with other things, NOT what seems like the least amount of work. The least amount of work is what is "easy", not what is "simple".
If one is encapsulating the representation behind an API, this simplicity principle is much less important for the representation than it would otherwise be, however, as any complexity of the representation is fire-walled at the API. And the Law of Demeter is a good principle for helping to keep an API "simple", as functions of the API that follow The Law of Demeter should return only data and not objects.
I'm still not sure how this API business meshes with Hickey's advice, however. He seems to be rather adamant that hiding data behind an API is the wrong thing 90% of the time. I have no feel, however, for knowing if something as complex as a book falls into the 90% case or the 10% case.
If one is encapsulating the representation behind an API, this simplicity principle is much less important for the representation than it would otherwise be, however, as any complexity of the representation is fire-walled at the API. And the Law of Demeter is a good principle for helping to keep an API "simple", as functions of the API that follow The Law of Demeter should return only data and not objects.
I'm still not sure how this API business meshes with Hickey's advice, however. He seems to be rather adamant that hiding data behind an API is the wrong thing 90% of the time. I have no feel, however, for knowing if something as complex as a book falls into the 90% case or the 10% case.