closed vs open types

Both sum and product types have closed and open variations:

	Product	Sum
Closed	structs/record types	coproducts / variants / enums
Open	row types (i.e. extensible records)	polymorphic variants

Interestingly I don’t think it is possible to define open variants of the dependent product / dependent sum. Without a specific domain to scope over, dependent types seem fairly ill scoped.