A happy new year to all the Haskell community. My current role involves an app with a Scala backend and a React/Redux Javascript frontend. What should be quite simple tasks are made difficult/impossible, firstly by the fact if you even touch a Javascript codebase in any significant way you break the code in weird and wonderful ways, which may only be apparent as random runtime errors days, weeks or months in the future, but another issue is that tracking some bug back from the browser to the backend and the database is a nightmare because it's far from obvious what's going on across the language boundary between Scala and Javascript, particularly as everything is being flattened to JSON across that boundary. Anyway, I was thinking of a better way of doing this, and I thought it would be nice if much of the code was shared between the browser frontend and backend server though a common datatype, with the frontend just compiled with GHCJS. Some of the state to the client could be readonly, and some writable. The actual details of pushing the data back and forth would be abstracted away (as much as possible). When the client does writes, it wouldn't need to wait for the server to process these writes, it could just save these on the client side state, and send them off to the server to record, but otherwise continue on. There's quite a few nuances here I've started to think about (and there's likely more I haven't thought about) and given that I don't think this idea is particularly novel, are there any libraries out there that already do roughly what I'm talking about here? If someone has already thought this through I don't want to reinvent the wheel.