fn main() { 
      if let Err(e) = real_main() {
        let status = status_from_error(e);
        // print the error message, or whatever
        std::process:exit(status);
      }
    }

    fn real_main() -> Result<(), TopErrorType> {
      // ...
    }

I believe that in a recent stable version of Rust, you can make this even simpler and have `main()` return a Result directly.

edit: not quite as simple as I described, but maybe more powerful because of the Termination trait: https://github.com/rust-lang/rfcs/blob/master/text/1937-ques... see: https://github.com/rust-lang/rfcs/blob/master/text/1937-ques...

    fn main() -> Result<(), io::Error> {
      let mut stdin = io::stdin();
      let mut raw_stdout = io::stdout();
      let mut stdout = raw_stdout.lock();
      for line in stdin.lock().lines() {
        stdout.write(line?.trim().as_bytes())?;
        stdout.write(b"\n")?;
      }
      stdout.flush()
    }