[Compose] 11. Use Task for Asynchronous Actions

We refactor a standard node callback style workflow into a composed task-based workflow.

For example we have the code as following:

We want to wrap async functions (readFile and writeFile) into Task. Therefore it becomes composeable.

const Task = require('data.task')
const fs = require('fs')

const readFile = name => 
  new Task((rej, res) => 
          fs.readFile(name, 'utf-8',
                      (err, contents) => err ? rej(err) : res(contents)));

const writeFile = (name, content) => 
  new Task((rej, res) => 
          fs.writeFile(name, contents, 
                       (err, _) => err ? rej(err): res(content)));

const app = () => 
  readFile('config.json') //return Task()
    .map(contents => contents.replace(/8/g, '6'))
    .chain(replaced => wirteFile('config.json',  replaced));  //flat Task(Task()) --> Task()

app.fork(console.error, console.log);