Comment by ackfoobar

> Sum types: For example, Kotlin and Java (and de facto C#) use a construct associated with inheritance relations called sealing.

This has the benefit of giving you the ability to refer to a case as its own type.

> the expression of sums verbose and, in my view, harder to reason about.

You declare the sum type once, and use it many times. Slightly more verbose sum type declaration is worth it when it makes using the cases cleaner.