Aren't those the same things? i.e. 2. are just read-only data structures with functions to create new read-only data structures based on them. (e.g. immutable l

Aren't those the same things? i.e. 2. are just read-only data structures with functions to create new read-only data structures based on them. (e.g. immutable linked lists that you can filter, concat, etc. with) Or are you talking about something more specific, like mutable data structures that provide immutable snapshots of the backing data?