text: 'use strict';
  
  function _typeof(obj) { if (typeof Symbol === "function" && typeof Symbol.iterator === "symbol") { _typeof = function _typeof(obj) { return typeof obj; }; } else { _typeof = function _typeof(obj) { return obj && typeof Symbol === "function" && obj.constructor === Symbol && obj !== Symbol.prototype ? "symbol" : typeof obj; }; } return _typeof(obj); }
  
  function _classCallCheck(instance, Constructor) { if (!(instance instanceof Constructor)) { throw new TypeError("Cannot call a class as a function"); } }
  
  function _defineProperties(target, props) { for (var i = 0; i < props.length; i++) { var descriptor = props[i]; descriptor.enumerable = descriptor.enumerable || false; descriptor.configurable = true; if ("value" in descriptor) descriptor.writable = true; Object.defineProperty(target, descriptor.key, descriptor); } }
  
  function _createClass(Constructor, protoProps, staticProps) { if (protoProps) _defineProperties(Constructor.prototype, protoProps); if (staticProps) _defineProperties(Constructor, staticProps); return Constructor; }
  
  function _possibleConstructorReturn(self, call) { if (call && (_typeof(call) === "object" || typeof call === "function")) { return call; } return _assertThisInitialized(self); }
  
  function _assertThisInitialized(self) { if (self === void 0) { throw new ReferenceError("this hasn't been initialised - super() hasn't been called"); } return self; }
  
  function _getPrototypeOf(o) { _getPrototypeOf = Object.setPrototypeOf ? Object.getPrototypeOf : function _getPrototypeOf(o) { return o.__proto__ || Object.getPrototypeOf(o); }; return _getPrototypeOf(o); }
  
  function _inherits(subClass, superClass) { if (typeof superClass !== "function" && superClass !== null) { throw new TypeError("Super expression must either be null or a function"); } subClass.prototype = Object.create(superClass && superClass.prototype, { constructor: { value: subClass, writable: true, configurable: true } }); if (superClass) _setPrototypeOf(subClass, superClass); }
  
  function _setPrototypeOf(o, p) { _setPrototypeOf = Object.setPrototypeOf || function _setPrototypeOf(o, p) { o.__proto__ = p; return o; }; return _setPrototypeOf(o, p); }
  
  var BlankNode = require('./blank-node');
  
  var ClassOrder = require('./class-order');
  
  var Node = require('./node');
  
  var Collection =
  /*#__PURE__*/
  function (_Node) {
    _inherits(Collection, _Node);
  
    function Collection(initial) {
      var _this;
  
      _classCallCheck(this, Collection);
  
      _this = _possibleConstructorReturn(this, _getPrototypeOf(Collection).call(this));
      _this.termType = Collection.termType;
      _this.id = BlankNode.nextId++;
      _this.elements = [];
      _this.closed = false;
  
      if (initial && initial.length > 0) {
        initial.forEach(function (element) {
          _this.elements.push(Node.fromValue(element));
        });
      }
  
      return _this;
    }
  
    _createClass(Collection, [{
      key: "append",
      value: function append(element) {
        return this.elements.push(element);
      }
    }, {
      key: "close",
      value: function close() {
        this.closed = true;
        return this.closed;
      }
    }, {
      key: "shift",
      value: function shift() {
        return this.elements.shift();
      }
    }, {
      key: "substitute",
      value: function substitute(bindings) {
        var elementsCopy = this.elements.map(function (ea) {
          ea.substitute(bindings);
        });
        return new Collection(elementsCopy);
      }
    }, {
      key: "toNT",
      value: function toNT() {
        return BlankNode.NTAnonymousNodePrefix + this.id;
      }
    }, {
      key: "toString",
      value: function toString() {
        return '(' + this.elements.join(' ') + ')';
      }
    }, {
      key: "unshift",
      value: function unshift(element) {
        return this.elements.unshift(element);
      }
    }]);
  
    return Collection;
  }(Node);
  
  Collection.termType = 'Collection';
  Collection.prototype.classOrder = ClassOrder['Collection'];
  Collection.prototype.compareTerm = BlankNode.prototype.compareTerm;
  Collection.prototype.isVar = 0;
  module.exports = Collection;