message: comment about spans
diff: @@ -56,6 +56,7 @@ fn main() {
  },
  ) = (source_file, &e)
  {
  + // TODO delegate this to a crate that uses spans?
  let mut lines = f.split('\n');
  eprintln!("error: {e}");
  eprintln!("{}", lines.nth((pos.row - 1) as usize).unwrap());
  