Proper way of doing opaque external types?

[sirlan-ff00ff]

So, for some time I've been trying to write raylib bindings for koka for testing things out, and one thing that most stops me - among other things - is trying to wrap raylib types in ones to use from koka and converting between the two

For simple things like colors, or enums is quite trivial to write a koka representation and convert between them in the C glue code, but then for more complex ones that for example uses void*s, there doesn't seem to be a good solution to represent those

The ideal would be opaque types, that carry/point to data that is not representable in koka and only interacted with using external functions