I decided to do some archaeology of my own.

Here's the first instance of what would become Rust's `Result` type (Oct 28 2011): https://github.com/rust-lang/rust/commit/c1092fb6d88efe51e42...

Note that the type is called `t` since the convention at the time was to name the primary type of a module `t` and then refer to the type as `modulename::t` (shows how far we've come, eh?). At this initial stage the variants are named `ok` and `error`. Also note that at this point in history Rust had had an `either` type for a while (https://github.com/rust-lang/rust/blob/c1092fb6d88efe51e42df...), which would later be removed as Result gained more traction.

Here's the commit where the `error` variant is renamed to `err` (Oct 28 2011, so the same day): https://github.com/rust-lang/rust/commit/2b62a80202e2855d47f...

Here's the first instance of `std::result` being mentioned in the mailing list (Nov 14 2011): http://article.gmane.org/gmane.comp.lang.rust.devel/891

Where the type itself is renamed to `result` (Mar 13 2012): https://github.com/rust-lang/rust/commit/b968c8e6cd362567bf0...

Where the type and variant names are capitalized in accordance with the current style guide (Aug 26 2012): https://github.com/rust-lang/rust/commit/0c6e470a257fc546555...

So this convention may very well have originated with Rust.

Also interesting to note in the context of the union type discussions below is the use of the `tag` keyword as opposed to the current `enum` for declaring tagged unions.

At one point we were trying to name every part of a union type in Elm. Calling things "tags" instead of "constructors" seemed quite nice, but ultimately, it seemed like we couldn't get the perfect name.

I always did like `tag`, but I think that's a fight for another year. :)