No experience with Rust, but for a couple of personal projects I’ve written the logic in Haskell and the GUI in C++ (e.g. https://github.com/bradrn/brassica/blob/master/ARCHITECTURE....). It works pretty well, at least for smaller projects — the basic idea is that the Haskell code gets compiled into a library (static on Windows, dynamic on Linux) which the C++ side can link to. I’d imagine doing the same with Rust would be even easier, since it’s less of a pain to marshal stuff across the language barrier.