This made me immediately think of the Elm architecture. To an extent this is how react works internally. There is a function which takes state and produces UI.

This made me immediately think of the Elm architecture. To an extent this is how react works internally. There is a function which takes state and produces UI. In order not to have to re-render the whole UI if only a small part of the state changes, there is a diffing algorithm and "virtual dom" that is diffed against. Maybe it doesn't work exactly like that anymore but that's the gist of it.