use std::error::Error;
use std::fmt;

#[derive(Debug)]
enum E {
    D(Box<Error + Send>),
}

impl fmt::Display for E {
	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
		fmt::Debug::fmt(&self, f)
	}
}

impl Error for E {
    fn source(&self) -> Option<&(Error + 'static)> {
		match self {
			E::D(e) => Some(e),
			_ => None,
		}
	}
}

fn main() {
}