moy-fp/src/Functor/Task/index.js

A functional programming library.

/**
 * Task is a Functor, Monad and Applicative
 * can map
 * can join
 * can chain
 * can ap
 * always use for asynchronous task and side effects
 * can also handle synchronous task if you'd like
 * a super Functor, can't convert to other Functor, but other Functor can easy convert to Task
 * you may not need it if you are not sensitive in functional programming
 */
const Task = fork => Object.seal(
  Object.create(null, {
    fork: {
      value: fork,
    },
    [Symbol.toStringTag]: {
      value: 'Task',
    },
    map: {
      value: function map(fn){
        return Task(
          (reject, resolve) => this.fork(
            reject,
            x => resolve(fn(x))
          )
        )
      },
    },
    join: {
      value: function join(){
        return this.chain(x => x)
      },
    },
    chain: {
      value: function chain(fn){
        return Task(
          (reject, resolve) => this.fork(
            reject,
            x => fn(x).fork(
              reject,
              resolve,
            )
          )
        )
      },
    },
    ap: {
      value: function ap(T){
        return this.chain(fn => T.map(fn))
      },
    },
  })
)

/**
 * Functor Task => a -> Task a
 */
Task.of = x => Task(
  (_, resolve) => resolve(x)
)

export default Task