消息状态（MessagesState）

from langgraph.graph.message import MessagesState
from langchain_core.messages import AIMessage, HumanMessage
from langgraph.graph import StateGraph, START

def node(state: MessagesState):
  return {"messages": [AIMessage(content="你好，有什么可以帮助你吗？")]}

graph = StateGraph(MessagesState).add_node(node).add_edge(START, "node").compile()
result = graph.invoke({"messages": [HumanMessage(content="你好")]})
for message in result["messages"]:
  message.pretty_print()
  
# ================================ Human Message =================================
# 你好
# ================================== Ai Message ==================================
# 你好，有什么可以帮助你吗？

from typing_extensions import TypedDict, Annotated
from langgraph.graph.message import add_messages
from langchain_core.messages import AnyMessage, AIMessage, HumanMessage
from langgraph.graph import StateGraph, START

# 使用 add_messages 归约器追加消息
class State(TypedDict):
  messages: Annotated[list[AnyMessage], add_messages]

def node(state: State):
  return {"messages": [AIMessage(content="你好，有什么可以帮助你吗？")]}

graph = StateGraph(State).add_node(node).add_edge(START, "node").compile()
result = graph.invoke({"messages": [HumanMessage(content="你好")]})
for message in result["messages"]:
  message.pretty_print()
  
# ================================ Human Message =================================
# 你好
# ================================== Ai Message ==================================
# 你好，有什么可以帮助你吗？