This looks great. I have recently started a simple physics-based rope swinging game in Elm. It's a lovely language to use, but I have found the workflow quite frustrating. I love the "try elm" editor on the website for the quick feedback loop, however the text editor itself is basic. For this reason I find myself writing larger blocks of code in emacs, and then copying and pasting between the browser for debugging. Not ideal.

I will try this program later, and even if it's not currently quite there feature wise, it definitely looks like it has a lot of potential facilitate a great development experience.