Actually, the short-circuiting nature of the current structure makes the most sense. We don't need `result` unless there's a `default` and don't need `param` unless there's a `result`. I guess leave it as-is or fix up the formatting a little. I'm not sure what the preferred style in Rails is, perhaps:

```ruby
define_method :to_param do
  if (default = super()) && 
       (result = send(method_name).to_s).present? &&
         (param = result.squish.truncate(20, separator: /\s/, omission: nil).parameterize).present?
    "#{default}-#{param}"
  else
    default
  end
end
```