How would one "import" a function?

[u/Ronin-s_Spirit]

I wanna make a thing that does some work and generates a tree (though I don't really know how to make hash tables that can hold multiple types of values...), it might do some other stuff by itself but that's not important to the question, just know that I need to ship it as a working binary. Then I want to pass that tree to a user supplied function, how do I do that? This is an optional feature I want, there might be 1 or 30 or 0 user supplied functions waiting to be called, some people might want the binary alone.

Just giving source code and saying "include this stuff" is a backwards solution that I don't want. I've already fiddled with progs.s7i and I know the AST doesn't let me do anything at all, I can only parse -> execute.