Structure
Left/right 'digits' (1-4 elements) + inner spine that's a finger tree of 2-3 nodes. Recursive definition.
Advertisement
Amortized bounds
Push/pop: amortized O(1). Split/append: O(log N). Random access: O(log N).
Advertisement
Monoidal cache
Each spine node caches monoid measurement of its contents. Enables position-based indexing.
Persistent
Fully functional — old versions preserved. Sharing keeps space reasonable.