You can make a basic type system that wraps your language like c#, and add support for union types. The nodes and the nodes values(slots) will each have a type which could be a union. Then you can define operators(also typed nodes) that work on typed params. Add -> FoF<ret, args>. Then evaluate
Probably compile it into an ast and keep it updated on any change. The tree can be simplified and evaluated based on its language rules. Serialization should be just two flat lists of nodes and edges. For connection types, I ended up writing a minimal type system with primivites map to language
