+ package:first-class-families

data (+)
first-class-families Fcf Fcf.Data.Nat
data (++)
first-class-families Fcf Fcf.Data.List
List catenation.

Example

>>> data Example where Ex :: a -> Example  -- Hide the type of examples to avoid brittleness in different GHC versions

>>> :kind! Ex (Eval ([1, 2] ++ [3, 4]) :: [Natural])
Ex (Eval ([1, 2] ++ [3, 4]) :: [Natural]) :: Example
= Ex [1, 2, 3, 4]