"The idea of the app logic producing an explicit tree mutation while holding an immutable reference to the old state of the tree feels very functional, though the app state itself is mutable. Even so, I haven’t seen this particular pattern in the functional programming UI literature (hopefully readers can fill me in). "
IIUC, this sounds a lot like what MWeststrate does with Mobx-State-Tree^1
"The idea of the app logic producing an explicit tree mutation while holding an immutable reference to the old state of the tree feels very functional, though the app state itself is mutable. Even so, I haven’t seen this particular pattern in the functional programming UI literature (hopefully readers can fill me in). "
IIUC, this sounds a lot like what MWeststrate does with Mobx-State-Tree^1
1. https://github.com/mobxjs/mobx-state-tree