Look at how you'd do it in f#, ocaml, or elm first imo. The type systems of those languages allow for a very tight approach with no confounding factors. The way rust does it is the same, but with more details leaked in from the constraints rust imposes. Which is fine, but I think it's valuable to see the "pure" stripped back form in a language almost perfectly suited to it first.

I don't have much Rust-specific experience, but I wonder if you need a library for this when the language/compiler is doing all the heavy lifting. When working with Elm, for example, that uses that a lot for the Model-View-Update framework, you just define your model states and pattern match them to build the view and update functions.