Old but good. I've had this in my bookmarks for years but I can't not upvote this. A really valuable reference resource.

I'm going to point the next person who says "you mean immutable data structure, not persistent data structure. A persistent data structure is one that survives across process boundaries" to this.

Indeed, here's the direct link:

http://www.itl.nist.gov/div897/sqg/dads/HTML/persistentDataS...