Macro ertrace::ertrace

macro_rules! ertrace {
    ($cause:expr => $struct_name:ident($variant:expr)) => { ... };
    ($cause:expr => $struct_name:ident) => { ... };
    ($cause:expr =>) => { ... };
    ($struct_name:ident($variant:expr)) => { ... };
    ($struct_name:ident) => { ... };
}