text: 
  // TODO check name is a string
  function Symbol(name) {
      this.name = function () { return name; };
      this.toString = function () { return name; };
      
      this.evaluate = function (context) {
          return context.get(name);
      };
  }
  
  function createSymbol(name) {
      if (typeof name !== 'string')
          throw new Error('symbol name should be an string');
      
      return new Symbol(name);
  }
  
  function isSymbol(value) {
      return value instanceof Symbol;
  }
  
  module.exports = {
      symbol: createSymbol,
      isSymbol: isSymbol
  };
  
  