functional/iterables.test.ts

import { expect, it } from "./deps.testing.ts";
import { at, first, fmap, last, second, third } from "./iterables.ts";

it("at", () => {
  const second = at(1);
  expect(second([1, 4, 8])).toBe(4);
  expect(second([1])).toBeUndefined();

  const second_from_end = at(-2);
  expect(second_from_end([1, 4, 6, 8])).toBe(6);
  expect(second_from_end([1])).toBeUndefined();
});

it("first", () => {
  expect(first([1, 4, 8])).toBe(1);
  expect(first([1])).toBe(1);
  expect(first([])).toBeUndefined();
});

it("second", () => {
  expect(second([1, 4, 8])).toBe(4);
  expect(second([1])).toBeUndefined();
  expect(second([])).toBeUndefined();
});

it("third", () => {
  expect(third([1, 4, 8])).toBe(8);
  expect(third([1, 4])).toBeUndefined();
  expect(third([])).toBeUndefined();
});

it("last", () => {
  expect(last([1, 4, 8])).toBe(8);
  expect(last([1])).toBe(1);
  expect(last([])).toBeUndefined();
});

it("fmap", () => {
  expect(fmap()([1, 2, 3])).toEqual([1, 2, 3]);
  expect(fmap((x: number) => x * 2)([1, 2, 3])).toEqual([2, 4, 6]);
  expect(fmap(undefined, (x: number) => x % 2 == 0)([1, 2, 3])).toEqual([2]);
  expect(fmap((x: number) => x * 2)([1, 2, 3])).toEqual([2, 4, 6]);
  expect(fmap((x: number) => x * 2, (x: number) => x < 5)([1, 2, 3])).toEqual(
    [2, 4],
  );
});