code: func (re *JSRE) Evaluate(code string, w io.Writer) error {
  	var fail error
  
  	re.Do(func(vm *otto.Otto) {
  		val, err := vm.Run(code)
  		if err != nil {
  			prettyError(vm, err, w)
  		} else {
  			prettyPrint(vm, val, w)
  		}
  		fmt.Fprintln(w)
  	})
  	return fail
  }
docs: // Evaluate executes code and pretty prints the result to the specified output
  // stream.