I'd like to write a small module using Data.TypeLevel.Num.
It has type level constants, variables, addition, and maximum, which is pretty much
all I need. But I've never used it before, and there's one thing I want to do that
I don't understand how to do.
val :: Nat t => t -> Int
val _ = t as an Int
e.g., if x :: D8 then val x = 8.
The "value-level reflection functions" in Data.TypeLevel.Num.Ops all seem to be
'undefined'.
