Convert node async functions into most.js streams

example.js

import { readFile } from 'fs'

// Create a stream-returning version of fs.readFile
const readFileS = fromNode(readFile)

// Use it to create a stream containing the files contents
// map(String) to convert Buffer to string
const s = readFileS('./a/file.txt').map(String)

// Observe the contents
s.observe(x => console.log('Stream', x))

fromNode.js

import { Stream } from 'most'

// Take a node async function like fs.readFile, and give back
// a Stream-returning function
const fromNode = f =>
	function (...args) {
		return new Stream(new NodeCallback(f, this, args))
	}

// Make a node callback (i.e. function(e, value)) that
// will emit its outcome into a Sink
const nodeCallback = (sink, scheduler) =>
	function (e, ...args) {
		if(e != null) {
			return sink.error(scheduler.now(), e)
		}

		sink.event(scheduler.now(), args.length < 2 ? args[0] : args)
		sink.end(scheduler.now(), undefined)
	}

// Source for node async functions
class NodeCallback {
	constructor (f, context, args) {
		this.f = f
		this.context = context
		this.args = args
	}

	run (sink, scheduler) {
		this.f.call(this.context, ...this.args, nodeCallback(sink, scheduler))
	}
}