Types `Posn` and `PosnOf`

[bugcounting]

In the student languages' signature (type) annotations, a
define-struct with name struct also defines signature forms
Struct and StructOf. For example:

(define-struct name [first last])

; name-full inputs instances of `name` where both fields are strings
(: name-full ((NameOf String String) -> String))
(define (name-full n) (string-append (name-first n) " " (name-last n)))

; the constructor of `name` returns an instance of type `Name`
(: make-name (Any Any -> Name))

In the student languages, there is a predefined struct called
posn. However, the type names Posn and PosnOf are not
defined. Can we provide these definitions as part of the student
languages?

[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]

You're right: posn never made the transition to capitalized signature names.

(Oddly, you can access the plain signature as posn.)