class Graph
{
  new make(Node[] nodes := Node[,], Edge[] edges := [,])
  {
    this.nodes = nodes
    this.edges = edges
  }
  Node[] nodes
  Edge[] edges
}

class Node
{
  Str name
  new make(Str name) { this.name = name }
  override Int hash() { name.hash }
  override Bool equals(Obj? other) { other is Node && other->name == name }
  override Str toStr() { "node($name)" }
}

class Edge
{
  Node from
  Node to
  new make(Node from, Node to) { this.from = from; this.to = to }
  override Int hash() { [from, to].hash }
  override Bool equals(Obj? other) 
  {
    other is Edge && other->from == from && other->to == to
  }
  override Str toStr() { "$from -> $to" }
}