data.task.ts

Data.Task in typescript

Personal Task type class functional implementation inspired by data.task npm package. I also use monet type classes implementantion as dependency for my package because i like its simplicity.

The Task<E, R> structure represents values that depend on time. This allows one to model time-based effects explicitly, such that one can have full knowledge of when they're dealing with delayed computations, latency, or anything that can not be computed immediately.

A common use for this monad is to replace the usual [Continuation-Passing Style][cps] form of programming, in order to be able to compose and sequence time-dependent effects using the generic and powerful monadic operations.

Examples

// Simple Task, just like promises but better ;D
const getOne = new Task<Error, number>((_, res) => setTimeout(() => res(1), 500))
getOne.fork(console.error, one => console.log('this is one', one))

// Pointed Task: Task<unknown, number>
const getTwo = Task.of(2)
getTwo.fork(console.error, two => console.log('this is two', two))

// Mapping values
getOne.map(one => one + 5).fork(console.error, six => console.log('now is 6', six))

// Chaining Tasks
getOne
  .chain(one => Task.of(5 + one))
  .fork(console.error, six => console.log('now is 6', six))

// Concurrent apTo behaviour
const getOne = new Task<Error, number>((_, res) => setTimeout(() => res(1), 500))
const getTwo = new Task<Error, number>((_, res) => setTimeout(() => res(2), 1000))
const getThree = new Task<Error, number>((_, res) => setTimeout(() => res(3), 1500))

console.time('run')
Task.of((x: number) => (y: number) => (z: number) => x + z + y)
  .apTo(getOne)
  .apTo(getTwo)
  .apTo(getThree)
  .fork(console.error, r => {
    console.log(r)
    console.timeEnd('run')
  })
// you should see it run on almost 1500 ms because of concurrent execution

// Traversing an array of tasks concurrently with Task.all
const getTodo = (id: number): Task<Error, Todo> =>
  new Task((rej, res) => {
    console.time(`get-todo:${id}`)
    return axios
      .get(`https://jsonplaceholder.typicode.com/todos/${id}`)
      .then(r => {
        console.timeEnd(`get-todo:${id}`)
        return res(r.data)
      })
      .catch(rej)
  })

console.time('all')
Task.all([getTodo(1), getTodo(2), getTodo(3)]).fork(
  err => {
    console.error(err)
    console.timeEnd('all')
  },
  ([todo1, todo2, todo3, ...rest]) => {
    console.log(todo1, todo2, todo3, rest)
    console.timeEnd('all')
  },
)

Installing

The easiest way is to grab it from NPM.

$ npm install data.task.ts

Personal consideration

I'm not an experimented functional programmer or advanced typescript developer so any help with type definitions or additional features to this type class implementation is very welcome. :D