code: function eval$call(params) {
    var func = typeof params.$call == 'string'
                ? this.getFunc(params.$call)
                : params.$call;
    // TODO params.$args is object
    return Promise.resolve(func.apply(null, params.$args));
  }
docs: Function definition
  @this   Evaluation
  @param  {Object} params instruction keywords ($call, $args)
  @return {any}    result of the function call