fn print_help(&mut self) {
        let help_message = "Press Ctrl+C to abort current expression, Ctrl+D to exit the REPL";

        println!("{}", help_message);
    }
/// Print out a help message.
Print out a help message.
Print out a help message .
fn print_help(&mut self) {
        let help_message = "Press Ctrl+C to abort current expression, Ctrl+D to exit the REPL";
        println!("{}", help_message);
    }
fn print_help ( & mut self ) { let help_message = " " ; println ! ( " " help_message ) ; }
Print out a help message.
Print out a help message .
&mut self