code: func (v *Vec) Set(s string) error {
  	if _, err := fmt.Sscanf(s, "(%f,%f)", &v.X, &v.Y); err != nil {
  		return fmt.Errorf("invalid syntax \"%s\"", s)
  	}
  	return nil
  }
docs: // Set sets the components of the vector from a string of the form
  // "float,float"