data Node a = NodeEmpty | NodeSome (Node a) a (Node a)
data Root a = RootEmpty | RootSome (Node a) a (Node a)
data Tree = Root | Node

whatNode :: Tree -> String
whatNode RootEmpty = "empty root"
whatNode RootSome {} = "some root"
whatNode NodeEmpty = "empty node"
whatNode NodeSome {} = "some node"