I think the problem is that the Box / Map / any stuff and all the explicit declarations that Go requires makes it harder.

In Haskell as well, you can let the compiler infer a lot of things but that doesn’t appear to be the case with this example.

I’d want the compiler to infer things, but that - I think - is at odds with Go desiring a fast compiler, which I also understand.

I was about to mention Haskell as well, I feel like it also avoids this sort of cognitive load. Maybe it's something to do with the languages being designed as functional languages instead of languages with functional components.