Thinking about tree structures in Elm

tree.elm

-- A tree contains 2 kinds of nodes
-- at depths 1 through 2 you will have a node with a 'replies' field
-- at depth 3 the node is missing a 'replies' field


type alias TreeNode a =
    { a 
        | body : String
    }


type alias WithReplies a =
    { replies : List a }

type CommentTree
    = RootNode
        (TreeNode (WithReplies
            (TreeNode (WithReplies
                (TreeNode {})))
            )
        )