Extensible Records seems to be pruning fields and failing to compile

[mthiems]

Others have noticed in the past that type aliases to extensible records don’t seem to be fully supported:

Using extensible records in type aliases

I have a project with a lot of very similar but slightly different data types, so I’ve been making a lot of use of extensible records so that, for example, if I have several record types all of which have ids, I can use the same function (with a signature like List {record | id = Id } -> List {record | id = Id }) for all of them for ordering them by id. Sometimes stuff gets more complicated than that, though, and I’ve recently realized that a lot of the weird errors I’ve struggled with relating…

and are generally considered best applied in practice when used (directly, it seems, not via alias) in function type signatures.

I applied this to your Ellie and it compiles:
https://ellie-app.com/gpmHmb9bGBxa1
(I also changed your view function to confirm that it “works”.)

You can also see that the type alias is still being used, just not in the subInit signature anymore. So such type aliases are at least partly usable.

I don’t know if this should be considered a bug, or just a known limitation of how extensible records are intended to be used. But at least you can get the desired effect in your design if you avoid the alias.