[] -> functor(["list", "[]"], [])
[functor(["single"], [])] -> functor(["list", "[|]"], [functor(["single"], []), functor(["list", "[]"], [])])
[functor(["1"], []), functor(["2"], []), functor(["3"], [])] -> functor(["list", "[|]"], [functor(["1"], []), functor(["list", "[|]"], [functor(["2"], []), functor(["list", "[|]"], [functor(["3"], []), functor(["list", "[]"], [])])])])