It's on the bottom half of the page about enumerations. Typically languages have product types, but lack true sum types. Swift's enums provide such leverage. T

It's on the bottom half of the page about enumerations. Typically languages have product types, but lack true sum types. Swift's enums provide such leverage. That said, Swift's types are a bit less than recursive, so there's a bit of niggling still before you get to the affordances of something like Haskell's `data`.