std::try!

macro_rules! try {
    ($expr:expr) => (match $expr {
        $crate::result::Result::Ok(val) => val,
        $crate::result::Result::Err(err) => {
            return $crate::result::Result::Err($crate::convert::From::from(err))
        }
    })
}

Helper macro for unwrapping Result values while returning early with an error if the value of the expression is Err.