code: function promisify_value(result_transformer) {
      result_transformer = result_transformer || identity;
  
      var transformer = function (promise) {
          result_transformer(promise);
      };
  
      transformer.for_property = function (obj_promise, prop) {
          return when(obj_promise, function (obj) {
              result_transformer(obj[prop]);
          });
      };
  
      return transformer;
  }
docs: Produces a transformer that takes a value and simply returns it.