There's no way to update state with updates that are different from the state type

[davidfant]

Moving from Slack: https://langchainpart-saq4831.slack.com/archives/C06PTQF6MCK/p1714034843538009

Current types for the state:

export type BinaryOperator<Value> = (a: Value, b: Value) => Value;

export interface StateGraphArgs<Channels extends Record<string, any>> {
    channels: {
        [K in keyof Channels]: {
            value: BinaryOperator<Channels[K]> | null;
            default?: () => Channels[K];
        } | string;
    } | {
        value: BinaryOperator<unknown> | null;
        default?: () => unknown;
    };
}

What I want to do:

interface AgentState {
  messages: Messages[];
}

// this looks like how you suggest managing msgs in examples
const channels = {
  messages: (oldMsgs, newMsgs) => [...oldMsgs, ...newMsgs],
}

// to add a message, i'd return a state update like
return { messages: [newMessage] };

However, if I want to update messages in a different way than just appending (say e.g. clearing all msgs) I can't do that bc the BinaryOperator type requires a (curr value) and b (the update value, which could in theory have a different shape) to be the same

[davidfant]

@functorism might have some good ideas on typing for this