flow.js

function flow(makeGenerator) {
  // Return a function that constructs an Observable.
  return function(...args) {
    return Observable.create(observer => {
      // This function won't be called until the observable is subscribed.
      const generator = makeGenerator.apply(this, args)
      generator.next = action(generator.next)
      generator.throw = action(generator.throw)
      generator.return = action(generator.return)
      return new GeneratorSubscriber(observer, generator)
    })
  }
}