> Why would it be?
That's literally what they explain in the rest of the comment.
No, they don't reference any "high price to pay", only that they personally didn't need the advantages of untagged union types so far, and that Haskell (allegedly) has patterns that would play a similar role for libraries.
No, they don't reference any "high price to pay", only that they personally didn't need the advantages of untagged union types so far, and that Haskell (allegedly) has patterns that would play a similar role for libraries.