glue Rec's

[Pitometsu]

glue Rec's

[dwincort]

Are you looking for something like:

type family (l :: *) .* (r :: *) :: * where
  Rec l .* Rec r = Rec (l .+ r)
  x .* y =  TypeError (TL.Text "Tried to .* non-records")

No, I haven't included anything like this in row-types because .+ seemed general enough, and having another operator just for records seemed unnecessary. Do you have a particular use-case in mind?

[Pitometsu]

Do you have a particular use-case in mind?

Yes, following steps.
Create alias to record, to use it everywhere.
Now it's expected to have an ability to create type alias to helper record with additional fields without defining intermediate type alias of rows of original type.

[dwincort]

I suppose I can see the usefulness of this — I've definitely made a row-type synonym called FooRow just so I can then define Rec FooRow — but I think it may make things more confusing overall because now different row-types type families will work on different kinds of arguments. That is, other type functions like .\, .!, .-, Extend, etc, all work on row-types themselves, and not on Recs over row-types, and .* won't play nicely with them. One might argue that we should add special Rec versions of all of those type functions too, but I'm not ready to go there (maybe if they were all in a separate module, e.g. Data.Row.Record.TypeFamilies, but still, I'm not sure it's sensible).

For now, I encourage you to use the 3-line .* I suggested above in your own row-types code. If you find that it's actually super-useful and you're using it a lot, maybe we can discuss upstreaming it later.