How to recur over extensible records? - recursion

Question

I am a relative beginner in Elm. I learned how to recur over records, and to create extensible records. My target application has tree-shaped data, that is to be rendered in several tree views.
In order for Elm to allow recursive models, one needs
a Union type for the children field,
a Maybe in that type definition, and
the lazy anonymous function construct if Json decoding is needed.
So far so good, but I cannot combine recursion with extension. Here below is a minimized version of how far I got. This program is capable of rendering either one of the two example types (Folder and Note), but not both. (see lines commented with -- NOTE and -- FOLDER).
The problem is with the kids function. Elm doesn't allow it to produce two different output types. I am stuck with either duplicating the code, or do without record extensions. Both seems like show-stoppers.
Is there a way to get this working with both, extension and recursion, and without code duplication?
Run on Ellie
module Main exposing (main)
import Html exposing (..)
import Maybe
-- MAIN
main = Html.beginnerProgram
{ model = init
, update = update
, view = view
}
-- MODEL
type alias Model =
{ folder : Folder
, note : Note
}
type alias Node a =
{ a | name : String
, children : Children a
}
type alias Folder =
{ name : String
, children : ChildFolders
}
type alias Note =
{ name : String
, children : ChildNotes
}
type Children a = Children a (Maybe (List (Node a)))
type ChildFolders = ChildFolders (Maybe (List Folder))
type ChildNotes = ChildNotes (Maybe (List Note))
-- INIT
init : Model
init = Model
(Folder "Parent F" someFolders)
(Note "Parent N" (ChildNotes Nothing))
someFolders : ChildFolders
someFolders = ChildFolders
( Just
( [ Folder "Child F1" (ChildFolders Nothing)
, Folder "Child F2" (ChildFolders Nothing)
, Folder "Child F3" (ChildFolders Nothing)
]
)
)
-- UPDATE
type Msg = NoOp
update : Msg -> Model -> Model
update msg model =
case msg of
NoOp -> model
-- VIEW
view : Model -> Html msg
view model =
div []
[ viewBranch model.folder -- FOLDER
-- , viewBranch model.note -- NOTE
]
-- viewBranch : (?) -> Html msg
viewBranch node =
uli
( text node.name
:: ( node
|> kids
|> List.map viewBranch
)
)
uli : List (Html msg) -> Html msg
uli items = ul [] [ li [] items ]
-- kids : (?) -> (?)
kids { children } =
case children of
(ChildFolders data) -> Maybe.withDefault [] data -- FOLDER
-- (ChildNotes data) -> Maybe.withDefault [] data -- NOTE