being immutable and being functional aren't even close to the same thing. It just so happens that git's object db is immutable, although even then it depends what you're talking about.<p>It's most interesting property is that it's content-addressable, but still has tons of mutable elements, refs, symbolic refs, config keys, the notes infrastructure (kinda).
Isn't the word he's looking for 'persistent' ?
<a href="http://en.wikipedia.org/wiki/Persistent_data_structure" rel="nofollow">http://en.wikipedia.org/wiki/Persistent_data_structure</a>