General comments are very welcome although I was p...

# codereview

[Dmitry Kandalov]

General comments are very welcome although I was particularly interested in two things:
1) is it a good decision to model “no node" as End object? Or should it be null or may be a class?
2) what is the best way to model Nodes with XY position? I decided to wrap node value into object which has coordinates, unlike for example this solution http://aperiodic.net/phil/scala/s-99/p64.scala where they define PositionedNode class.