callback monad.js

class Callback {
  constructor(f) {
    this.run = (...args) => {
      f(...args)
    }
    
    this.map = g => new Callback((...args) => {
      const nArgs = R.init(args)
      const callback = R.last(args)
      
      nArgs.push((error, ...args)  => {
        if(!!error) {
          callback(error, null)
        } else {
          callback(null, g(...args))
        }
      })
      
      f(...nArgs)
    })
    
    this.bind = g => new Callback((...args) => {
      const nArgs = R.init(args)
      const callback = R.last(args)
      
      nArgs.push((error, ...args)  => {
        if(!!error) {
          callback(error, null)
        } else {
          g(...args).run(null, callback) 
        }
      })
      
      f(...nArgs)
    })
  }
}

new Callback((x, cb) => cb(null, x))
.map(x => x * 3)
.bind(x => new Callback((y, cb) => cb(null, x - 1)))
.run(6, (error, result) => console.log(error, result))