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

A functional programming library.

import __ from '../../src/Function/__'
/**
 * Functor f => (a -> f b) -> f a -> f b
 */
import chain from '../../src/Functor/chain'
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('chain(not using __), array', () => {
  expect(
    chain(x => [x, x + 1])([1, 2, 3])
  ).toEqual([1, 2, 2, 3, 3, 4])
})

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

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