It's true that here the data type was just a tag. There's always a decision to be made about how much structure you want to enforce by the construction of the d

It's true that here the data type was just a tag. There's always a decision to be made about how much structure you want to enforce by the construction of the data type. You'd still consider it to be "parsing" because you now statically know that an Email is valid according to the rules of the parser - in a loose sense, it's a "conversion" between a type you know nothing about, and one you know a lot about. If you wanted to go further you could start going the "correct by construction" route - having a data type that enforces more invariants. For example, you might store the recipient name, domain name, and tld of your email in separate fields. Then your parser would more obviously be a parser. I think of the "mere tag" type as a kind of degenerate case of this, rather than something totally separate.