Add MessageGraph

langgraph/graph/message.py

@@ -0,0 +1,24 @@
+from typing import Annotated, Union
+
+from langchain_core.messages import AnyMessage
+
+from langgraph.graph.state import StateGraph
+
+Messages = Union[list[AnyMessage], AnyMessage]
+
+
+def add_messages(left: Messages, right: Messages) -> Messages:
+    if not isinstance(left, list):
+        left = [left]
+    if not isinstance(right, list):
+        right = [right]
+    return left + right
+
+
+class MessageGraph(StateGraph):
+    """A StateGraph where every node
+    - receives a list of messages as input
+    - returns one or more messages as output."""
+
+    def __init__(self) -> None:
+        super().__init__(Annotated[list[AnyMessage], add_messages])