silphius/app/astride/scope.js

export default class Scope {

  context = {};
  parent = null;

  constructor(parent) {
    this.parent = parent;
  }

  allocate(key, value) {
    return this.context[key] = value;
  }

  get(key) {
    let walk = this;
    while (walk) {
      if (key in walk.context) {
        return walk.context[key];
      }
      walk = walk.parent;
    }
    return undefined;
  }

  set(key, value) {
    let walk = this;
    while (walk) {
      if (key in walk.context) {
        walk.context[key] = value;
        return value;
      }
     if (!walk.parent) {
        walk.context[key] = value;
        return value;
      }
      walk = walk.parent;
    }
  }

}