ENvironmentSet

module.exports = ( () => {
  const STATE = { PENDING: 0, DONE: 1, FAIL: 2};
  class Future {
    constructor(worker) {
      this.state = STATE.PENDING;
      this.value = undefined;
      this.handlers = [];
      try{
        worker(Future.resolver(this), Future.rejector(this));
      } catch (error) {