This is what I like about FP. As in math, you're expressing ideas about relationships that must always hold true, regardless of time. You think less about how state changes over time and more about what the fundamental "truths" of your program have to be. For me -- and for many problems but certainly not all -- this is an easier way to think.

yeah "regardless of time and space", as one observes in the resulting time and space usage. By the time the purely functional program has been tweaked for better (time and space) performance, said readability has greatly suffered ;D and I say that as an enthusiastic FPer