taskeither

test.ts

import { array } from "fp-ts/lib/Array";
import { left2v, taskEither, tryCatch } from "fp-ts/lib/TaskEither";

const t1 = tryCatch<Error, string>(
  // some function that returns a promise or an either
  async () => "someValue1",
  // "catch" handler
  () => Error("t1 error")
);

// no need to type tryCatch, type is inferred from returned values
const t2 = tryCatch(async () => "anotherValue2", () => Error("t2 error"));

const t3 = tryCatch(async () => "anotherValue3", () => Error("t3 error"));

array
  .sequence(taskEither)([t1, t2, t3])
  .run()
  // tslint:disable-next-line: no-console
  .then(console.log)
  // tslint:disable-next-line: no-console
  .catch(e => console.error("*ERR", e)); // --> right(["someValue1", "anotherValue2", "anotherValue3"])

// suppose t2 throws / reject
const t2exp = tryCatch(
  async () => {
    throw new Error("t2 exception");
  },
  e => e
);

array
  .sequence(taskEither)([t1, t2exp, t3])
  .run()
  // tslint:disable-next-line: no-console
  .then(console.log)
  // tslint:disable-next-line: no-console
  .catch(e => console.error("*ERR", e)); // --> left(Error: t2 exception)

// suppose t2 returns a left
const t2left = left2v(Error("some left error"));

array
  .sequence(taskEither)([t1, t2left, t3])
  .run()
  // tslint:disable-next-line: no-console
  .then(console.log)
  // tslint:disable-next-line: no-console
  .catch(e => console.error("*ERR", e)); // --> left(Error: some left error)