AgentAction is the agent's action to take.

AgentFinish is the agent's return value.

AgentStep is a step of the agent.

Document is the interface for interacting with a document.

ChatMessageHistory is the interface for chat history in memory/store.

Memory is the interface for memory in chains.

OutputParser is an interface for parsing the output of an LLM call.

Retriever is an interface that defines the behavior of a retriever.