I looked at your code. Very, very nice!! (Listened to the demo as well). I think in most respects you are farther along with an Elm version of Euterpea than am I. I’ve been working on this for a short while – it grew out of my wacky drum language project – first commit on June 27.
About a library – this is most definitely what should happen. Let’s talk some more. There is plenty to do to make a really good Elm Euterpea, and collaboration might be a good way to accomplish that. I’m interested. I think that @Lucas_Payr would be also. He’s helped me several times already.
Oh – one more point. Despite my experiments, I agree that it is desirable to stay as close to Hudak’s design as possible while writing idiomatic Elm. He has put a lot of thought into this.
PS. Here is the latest version of my test app: https://jxxcarlson.github.io/app/euterpia-test.html – not very impressive. It really only plays one voice at the moment. I’m using Tone.js as the backend.