# Abstract tree map structure
# * `K`: tree node key
# * `E`: tree node value
abstract class TreeMap[K: Comparable, E]
	super Map[K, E]

	# Type of nodes used in this tree implementation
	protected type N: TreeNode[K, E]

	# The `root` node of the tree (null if tree is empty)
	protected var root: nullable N = null is protected writable

	# Display the tree in a gaphical windows
	# Graphviz with a working -Txlib is expected
	# Used for debugging
	fun show_dot is abstract
end