Macro errmatch 

macro_rules! errmatch {
    ($err:expr, $kind:ty) => { ... };
}

any type of inside Err() can match this

if let Err(e) = some_result() {
    // errmatch!(<Unwraped Err>, <Any Type>)
    if errmatch!(e, err::MyError0) {
        // ...   
    }
}

returns boolean