fp-ts traverse examples

import * as Task from "fp-ts/Task";
import * as TaskEither from "fp-ts/TaskEither";
import * as ReadonlyArray from "fp-ts/ReadonlyArray";
import { pipe } from "fp-ts/function";

const example = async () => {
  const getUserPreferences = (
    userId: string
  ): TaskEither.TaskEither<string, string> => {
    if (userId.includes("invalid")) {
      return TaskEither.left("No preferences found");
    }
    return TaskEither.right(userId);
  };

  const userIds = ["a", "b", "c"];

  const mapTaskEither = TaskEither.traverseArray(
    getUserPreferences
  );
  const result = await mapTaskEither(userIds)();
  console.log(`Result: ${JSON.stringify(result)}`);

  const validAndInvalidUserIds = ["a", "invalid", "c"];
  const anotherResult = await mapTaskEither(validAndInvalidUserIds)();
  console.log(
    `If there's at least one Left, the whole result is a Left: ${JSON.stringify(
      anotherResult
    )}`
  );

  const onlyRightResults = await pipe(
    validAndInvalidUserIds,
    Task.traverseArray(getUserPreferences),
    Task.map(ReadonlyArray.separate),
    Task.map(({ right }) => right)
  )();
  console.log(
    `Updated function to get all Right results: ${JSON.stringify(
      onlyRightResults
    )}`
  );
};

example();