Nice stuff, I'm working on something like Kaitai Struct, and it'll be very convenient to codegen to Fusion, to support multiple target languages.

However, what I like the least in all kind of software is underdocumentation. There's some reference, it's not bad, but actually it's just bunch of examples. If I want to find out exactly how a particular type or statement translates into a specific language, I'll have to dig into the code.