Am Mo., 31. Okt. 2022 um 13:00 Uhr schrieb Marc Feeley
<xxxxxx@iro.umontreal.ca>:

> However I’m not arguing that nongenerative record definitions should be the default even though in the Gambit codebase most if not all of the record type definitions are nongenerative.  Due to the presence of a UID the nongenerative record definitions are a bit more verbose and visually inelegant than generative ones.  Note that I think R6RS has a design error in allowing nongenerative record definitions without a UID (it just slightly shifts the meaning of type instantiation and will not work in the above use cases and most people will not fully grasp the meaning of a UID-less nongenerative record type definition).

A nongenerative clause without a UID has a defined meaning, sitting in
between generative record types and non-generative ones with a UID:
In the case of "global" library definitions, It means that a record
type is generated per visit of a library, not one per instance of a
library (as would be a generative record-type) and not one per big
bang (as would be a non-generative record-type with a UID).

I think this part of R6RS is okay; the actual problem is the library
system of R6RS is not strict about the number of visits to a library,
presumably so that, at that time, the module system of MzScheme was a
faithful implementation.  (Notable, Racket does not allow a
nongenerative clause without a UID.)  As we have agreed upon implicit
phasing, we can remove this problematic part of R6RS (which makes it
hard to write portable programs despite that this was a design goal of
R6RS), by enforcing that libraries must only be expanded once per
program run.  (This still needs UIDs in portable code for
communication between different instances of the program if
portability is required.)  In a sense, one can think of each visit
having its own UID, and this being prepended to auto-generated UIDs of
record-types.

If we can't agree to change the default from generative to
non-generative, what we can do instead is to allow the non-generative
clause to be of the form "(nongenerative #f)" and to advise
implementations to issue a warning when it sees a record type without
a non-generative clause of either form.

Marc