Alias `mixed` as `one-of`

[bugcounting]

In the student languages' signature (type) annotations, function
mixed is used to describe mixed data or, as they are sometimes
called in HtDP, itemizations:

(define StringOrInteger (signature (mixed String Integer)))

An itemization is usually described in HtDP with the structured
natural language form:

A StringOrInteger is one of:
  - a String
  - an Integer

Having one-of as a synonym of mixed would help make formal type
declarations closer to the structured natural language form used in
HtDP:

(define (StringOrInteger (signature (one-of String Integer))

[racket-discourse-github-bot]

This issue has been mentioned on Racket Discourse. There might be relevant details there:

https://racket.discourse.group/t/signatures-in-student-languages/4166/4

[mikesperber]

That's easily done, but I'm a little hazy on what the currently used terminology with HtDP is. With HtDP/1e, it used to be "mixed data", hence the name. If HtDP/2e uses "itemization", wouldn't that be a better word?

@mfelleisen?

[mfelleisen]

Agreed. 2e updates this. (Having said that it still uses "mixed" in a couple of places.)