for line in lines {
  match Indentation::parse_line(&line) {
      Ok(Some(Indentation::Spaces(size))) => { *spaces.entry(size).or_insert(0) += 1; }, // Derp
      Ok(Some(Indentation::Tabs)) => tabs = true,
      Ok(None) => continue,
      Err(e) => return Err(e),
  }
}