class Arel::Visitors::Dot

def visit(o) 

def visit(o)
  if node = @seen[o.object_id]
    @edge_stack.last.to = node
    return
  end
  node = Node.new(o.class.name, o.object_id)
  @seen[node.id] = node
  @nodes << node
  with_node node do
    super
  end
end