code: func (p *Promise) Peek() (interface{}, error) {
  	select {
  	case <-p.signalC:
  		return p.data, p.err
  
  	default:
  		return nil, ErrNoData
  	}
  }
docs: // Peek returns the promise's current value. If the value isn't set, Peek will
  // return immediately with ErrNoData.