tomberek: I was working on a PR to use immutable lists (https://github.com/NixOS/nix/pull/11767) and was working on shrinking the size of the Value structure (https://github.com/ConnorBaker/nix/commits/feat/tagged-values/). Both of them are what made me want to give my talk.

I don’t have a PR for the primitives — I think the first step would be to survey the ways we most commonly interact (or want to interact) with the data structures. Then, choosing primitives that enable those interactions and compose well. Then, choosing implementations for the data structures that make those primitives fast.