The input to the map function (when it is called in "record" mode on the client) is an RpcPromise for the eventual value. That means you can't actually inspect the value, you can only queue pipelined calls on it. Since you can't inspect the value, you can't do any computation or branching on it. So any computation and branching you do perform must necessarily have the same result every time the function runs, and so can simply be recorded and replayed.
The only catch is your function needs to have no side effects (other than calling RPC methods). There are a lot of systems out there that have similar restrictions.
The only catch is your function needs to have no side effects (other than calling RPC methods). There are a lot of systems out there that have similar restrictions.