[wheatBread]

We discussed this to death on the mailing list, and this was definitely a consideration!

People searching for it online will very likely be searching for "elm union type" where they'll quickly find examples and docs. Furthermore, you can prefix the term "union type" with stuff like "closed/open" and "tagged/untagged" to start making finer grained distinctions as need higher degrees of precision. In Elm it is always tagged and closed, so in discussions within the community, adding those prefixes is redundant. Finally, if you start with the term "union type" it becomes easier to think about what an "anonymous union type" might look like (like OCaml's polymorphic variants or open variants) ;)

More broadly, if people do run into the term "union type" in other languages they will be building intuition in exactly the way I'd like: it's a way to use different types in the same place. Things happen to have this extra tag thing in Elm, but it's not so different than anything people do in JS or Clojure or Racket or TypeScript or C or whatever else. I think bringing that connection out is a major benefit of this naming choice. The goal is to feel really welcoming and friendly, and my personal preference is to build on people's existing intuition as much as possible. If someone comes from JS and does not see all the subtleties of this discussion immediately on day one, they are actually having a better experience because they can learn the info as it becomes relevant to their daily usage. Hopefully a much nicer learning curve!

I realize I am making a somewhat controversial choice, but the idea is that statically typed FP people are building artificial barriers by being sticklers about this, rather than just prefixing for precision. You may not agree with all this, but we thought it through pretty extensively, and that is the reasoning!