`if err != nil` is the easiest example. Sum types allow you to express type-level OR. Structs/tuples etc are AND (product types). I like to be able to use both

`if err != nil` is the easiest example. Sum types allow you to express type-level OR. Structs/tuples etc are AND (product types). I like to be able to use both OR and AND at both the expression and type level.