I've made my peace with those aspects of the libraries. I'm happy to wrap the standard classes in MyOption, MyStream, etc. Then I can extend FlatMappable myse

I've made my peace with those aspects of the libraries. I'm happy to wrap the standard classes in MyOption, MyStream, etc. Then I can extend FlatMappable myself. I just don't know how to declare and implement FlatMappable in a sane way (preserving type information, not needing casts, etc.)