text: const reusable = require('../../helpers/reusable/reusable');
  
  /**
   * @function map
   * @template T, U
   * @param {Mapper<T, U>} mapper a Mapper used to determine the values in the new collection
   * @return {Operator<T, U>} a new map operation that uses mapper
   */
  module.exports = mapper => reusable(
      function *(source) {
          for (const value of source) {
              yield mapper(value);
          }
      }
  );
  