Are there any write-ups on how your error handling proposal interacts with higher-order functions and generic wrappers? That has always been a problem with "explicit everything" approach to error handling, in my experience - like, if you map() over a collection that does disk I/O as part of its implementation, then map() needs to be able to flow I/O errors through - but it can't be aware of them specifically, because it's a generic algorithm. In Java, it pretty much meant that you had to use the RuntimeException escape hatch, defeating the purpose of checked exceptions. For another example, generic collection interfaces don't reflect the fact that e.g. fetching an item can fail, making them that much less generic.

And to work around that problem, you need some kind of generics that lets you define error signatures in terms of other signatures - e.g. for map(), you want to say that it can return an error if and only if the function it maps can return an error (and ditto for error types).