Macro bail 

macro_rules! bail {
    ($($arg:tt)*) => { ... };
}

Macro for one time errors.

example:

use std::env;
use idc::*;

fn main() -> Result<()> {
    let args: Vec<String> = env::args().collect();
    if args.len() < 2 {
        bail!("no argument provided!");
    }
    //...
    Ok(())
}