In Vinyl, I can define a type alias for a record to make it easier to export to other modules:
import Data.Vinyl
name = Field :: "name" ::: String
age = Field :: "age" ::: Int
type Person = ["name" ::: String, "age" ::: Int]
Now suppose I add another field storing height.
height = Field :: "height" ::: Int
I would like to nicely construct a type alias for the record containing a Person and height. Naively, that might look something like this:
type MeasuredPerson = ("height" ::: Int) : Person
This syntax doesn't work, obviously! Is there a way to do this? Are there any good references that explain the type-level array syntax that seems to be in use here?
Turns out there's a very easy answer to this which I managed to miss:
Data.Vinyl.Rec defines both cons and append for type level lists, so the following works:
type MeasuredPerson = ("height" ::: Int) ': Person
If I had two lists, I could append them as follows:
type Other = Person ++ Address