Task 异步执行

异步任务的实现过于复杂，我们使用folktale中的Task来演示
folktale 一个标准的函数式编程库
和lodash、ramda不同的是，他没有提供很多功能函数
只提供了一些函数式处理的操作，例如：compose、curry等，一些函子 Task、Either、MayBe等

了解folktale

const { compose, curry } = require('folktale/core/lambda')
let f = curry(2, (x, y) => {
  return x + y
})
console.log(f(4, 5))
console.log(f(1)(2))
const { toUpper, first } = require('lodash/fp')
let fc = compose(toUpper, first)
console.log(fc(['one', 'two']))

Task函子

const { task } = require('folktale/concurrency/task')
const fs = require('fs')
const { split, find } = require('lodash/fp')
function readFile(filename) {
  return task(resolver => {
    // 错误优先
    fs.readFile(filename, 'utf-8', (err, data) => {
      if (err) resolver.reject(err)
      resolver.resolve(data)
    })
  })
}

readFile('package.json')
  .map(split('\n'))
  .map(find(x => x.includes('version')))
  .run()
  .listen({
    onRejected: err => {
      console.log(err)
    },
    onResolved: value => {
      console.log(value)
    }
  })