Macro an_err 

macro_rules! an_err {
    ($kind:expr) => { ... };
    ($fmt:literal $(, $arg:expr)* => $inner:expr $(,)?) => { ... };
    ($kind:expr, $fmt:literal $(, $arg:expr)* $(,)?) => { ... };
}

Ergonomic constructor and chaining macro for AnErr.

Forms

Form	Equivalent to
an_err!(Kind)	AnErr::new(Kind)
an_err!(Kind, "reason")	AnErr::with_fmt(Kind, ...)
an_err!(Kind, "reason {}", arg, ...)	AnErr::with_fmt(Kind, ...)
an_err!("reason" => inner)	inner.context(...) (appends to reason only)
an_err!("reason {}", arg => inner)	inner.context_fmt(...) (appends to reason only)