moy-fp/test/Functor/ap.test.js

A functional programming library.

import __ from '../../src/Function/__'
/**
 * Functor f => f (a -> b) -> f a -> f b
 */
import ap from '../../src/Functor/ap'
import Identity from '../../src/Functor/Identity/index'

/**
 * you should not use this similar funciton to get value anywhere in your application
 * if you must need the inner value, you may need Comonad
 * here is just simple for test
 */
const inspect = x => `Identity(${x.value})`

test('ap(not using __), array', () => {
  expect(
    ap([x => x + 1, x => x * 2])([1, 2, 3])
  ).toEqual([2, 3, 4, 2, 4, 6])
})

test('ap(not using __), identity', () => {
  expect(
    inspect(ap(Identity.of(x => x + 1))(Identity.of(4)))
  ).toBe('Identity(5)')
})

test('ap(using __), identity', () => {
  expect(
    inspect(ap(__, Identity.of(4))(Identity.of(x => x + 1)))
  ).toBe('Identity(5)')
})