use std::error::Error;
use std::{io, io::Write};

fn prompt() -> Result<(), Box<dyn Error>> {
    print!("> ");
    io::stdout().flush()?;
    Ok(())
}

fn read_stdin() -> Result<String, Box<dyn Error>> {
    let mut buffer = String::new();
    io::stdin().read_line(&mut buffer)?;
    Ok(buffer)
}

fn main() -> Result<(), Box<dyn Error>> {
    loop {
        prompt()?;
        let user_input = read_stdin()?;

        if user_input.len() == 0 {
            // control-d or end of input. Needs to be specially handled before
            // the match because this is identical to whitespace after the trim.
            break;
        }

        match user_input.trim() {
            "" => {}
            "exit" => {
                break;
            }
            other_input => {
                println!("Unknown input {}", other_input);
            }
        }
    }
    Ok(())
}