I'd wager that in most programming ecosystems (the non-FP ones in particular), "persistent" means "sticks around after a crash/restart/etc", i.e. in practice, t

I'd wager that in most programming ecosystems (the non-FP ones in particular), "persistent" means "sticks around after a crash/restart/etc", i.e. in practice, that it's saved to disk. Sure, some academics used the term for a class of in-memory data structures too, and it got taken over in some programming circles, but it's a niche term at best. Now, so far so good, but using that term for databases might be maximally confusing. After all, isn't a database's primary purpose to persist data? Then, aren't all databases persistent? Oh, no, the author meant that other meaning of "persistent" that many people aren't familiar with. I think the author made the right call :-) (I know that immutable and persistent aren't the same thing: you can make an immutable data structure that isn't persistent in that it doesn't reuse data - but it's the best we got)