code: func (n *Join) Accept(v Visitor) (Node, bool) {
  	newNode, skipChildren := v.Enter(n)
  	if skipChildren {
  		return v.Leave(newNode)
  	}
  	n = newNode.(*Join)
  	node, ok := n.Left.Accept(v)
  	if !ok {
  		return n, false
  	}
  	n.Left = node.(ResultSetNode)
  	if n.Right != nil {
  		node, ok = n.Right.Accept(v)
  		if !ok {
  			return n, false
  		}
  		n.Right = node.(ResultSetNode)
  	}
  	if n.On != nil {
  		node, ok = n.On.Accept(v)
  		if !ok {
  			return n, false
  		}
  		n.On = node.(*OnCondition)
  	}
  	return v.Leave(n)
  }
docs: // Accept implements Node Accept interface.