functional-cluster.js

'use strict'

const cluster = require('cluster')

const Cluster = cluster => {
  return {
    map (fn) {
      return Cluster(fn(cluster))
    },
    valueOf() {
      return cluster
    }
  }
}

const Empty = () => ({
  map: () => Empty()
})

const master = cluster => cluster.isMaster
const worker = cluster => cluster.isWorker

const ifCondition = condition => value => ({
  map: fn => condition(value.valueOf()) ? value.map(fn) : Empty()
})

const ifMaster = ifCondition(master)
const ifWorker = ifCondition(worker)

const fork = cluster => cluster.fork()
const listen = worker => {
  worker.on('message', msg => {
    if (msg.cmd === 'count') {
      console.log(msg.value)
    } else {
      worker.kill()
    }
  })
}

const countUntil = MAX => process => {
  return new Promise(resolve => {
    let count = 0
    setInterval(() => {
      if (count < MAX) {
        process.send({cmd: 'count', value: count })
      } else {
        process.send({})
        resolve()
      }

      count++
    }, 1000)
  })
}
const countUntil10 = countUntil(10)

const log = value => console.log(value)
const waitAndLog = wait => wait.then(() => log('Finished'))


const c = Cluster(cluster)

ifMaster(c)
  .map(fork)
  .map(listen)

ifWorker(c)
  .map(countUntil10.bind(null, process))
  .map(waitAndLog)