Macro error_messages 

macro_rules! error_messages {
    {
        $name:ident code: $code_pfx:literal, type: $message_pfx:literal,
        $($error_name:ident $({ $($field:ident : $inner:ty),+ $(,)? })? = $code:literal: $body:literal),+ $(,)?
    } => { ... };
}