> On Jun 19, 2021, at 6:02 AM, Marc Nieper-Wißkirchen <xxxxxx@nieper-wisskirchen.de> wrote:
>
> I have been thinking of a formulation as the following one:
>
> "Fxmappings are instances of a sealed, opaque, nongenerative record type with uid fxmapping-7a1f4d5b-a540-462b-82b1-47283c935b85 where the semantics shall be as specified by R6RS, Library Chapter 6. In particular, this means that the type defined by the record type predicate `fxmapping?' is disjoint from the base types defined in R6RS and R7RS and from any generative record type and any non-generative record type with a different uid."
>

This wording does not work for Schemes with single inheritance record types, which are a fairly simple (and very useful) extension of record types.  For example in Gambit you can define the record type bar as a subtype of the foo type like this:

  > (define-type foo
      extender: define-type-of-foo
      id: foo-B0C62CC8-F4E9-4C45-B28D-08372CE45BCE
      x)
  > (define-type-of-foo bar
      id: bar-C7C6C8CF-E107-4CA2-8AD4-04BF3D0804FB
      y)
  > (define a (make-foo 11))
  > (define b (make-bar 22 33))
  > a
  #<foo #2 x: 11>
  > b
  #<bar #3 x: 22 y: 33>
  > (map foo? (list a b))
  (#t #t)
  > (map bar? (list a b))
  (#f #t)

Note that they are both non-generative types, but even though they have different ids they are not disjoint (the object b is both a foo and a bar).

The practical implication of your proposed wording is that it would not be allowed to create a non-generative subtype of the fxmapping type.

Marc