Reading a line

input() returns Result[Option[str], IoError]. It removes a trailing LF or CRLF. Some("") means an empty line; Nothing means end-of-file. UTF-8 errors and allocation failures return Err. A failure can consume input, so retrying does not promise to repeat the same line. Input currently requires a Unix host. For a prompt, call write_stdout and flush_stdout before input().

Call echo_line()? repeatedly until it returns False to process stdin. This example’s main does not read input.

def echo_line() -> Result[bool, IoError]:
    match input()?:
        case Some(line):
            write_stdout(line)?
            write_stdout("\n")?
            Ok(True)
        case Nothing:
            Ok(False)

def main() -> Result[(), IoError]:
    print("echo_line is ready")?
    Ok(())

echo_line is ready