streaming effection chatbot resource

chat.ts

import type { Result, Stream } from "effection"
import { Ok, Err } from "effection";

function chat(history: Array<Message>): Stream<string, Result<void>> {
  return resource<{
    channel: Signal<string, void>;
    await: Operation<E.Either<Error, void>>;
  }>(function* (provide) {
    const signal = yield* useAbortSignal();
    const channel = createSignal<string, Result<void>>();

    const result = streamText({
      system: prompt,
      messages: history,
      abortSignal: signal,
      model: openai("gpt-4o-mini"),
      onError({ error }) {
        let e: Error;

        if (error instanceof Error) {
          e = error;
        } else {
          e = new Error("Uknown error");
          e.cause = error;
        }

        channel.close(Err(e));
      },
      onFinish(_) {
        channel.close(Ok();
      },
    });

    result.consumeStream();

    yield* spawn(function* () {
      yield* call(async () => {
        for await (const chunk of result.textStream) {
          channel.send(chunk);
        }
      });
    });

    try {
      yield* provide(yield* channel);
    } finally {
      channel.close(Ok());
    }
  });
}