code: func (c Call) MarshalText() ([]byte, error) {
  	if c.frame == (runtime.Frame{}) {
  		return nil, ErrNoFunc
  	}
  
  	buf := bytes.Buffer{}
  	fmt.Fprint(&buf, c)
  	return buf.Bytes(), nil
  }
docs: // MarshalText implements encoding.TextMarshaler. It formats the Call the same
  // as fmt.Sprintf("%v", c).