Simple Task implementation

task.js

const Task = fork => ({
    map: f => Task((reject, resolve)=>{ fork(reject, x => { resolve(f(x)) })  }),
    chain: f => Task((reject, resolve)=>{ fork(reject, x => { f(x).fork(reject, resolve) })  }),
    join: () => Task(fork).chain(i=>i),
    ap: A => A.map(a => Task(fork).map(f => f(a))).join(),
    fork
})
Task.of = x => Task((_,resolve)=>{ resolve(x)})