Macro opset 

macro_rules! opset {
    (@count) => { ... };
    (@count $head:tt $(, $tail:tt)*) => { ... };
    (@op_ty $op_name:ident) => { ... };
    (@op_ty $op_name:ident = $op_path:path) => { ... };
    (@max_op_arity $op_name:ident $(= $op_path:path)?) => { ... };
    (@max_op_arity $op_name:ident $(= $op_path:path)?, $($rest:tt)+) => { ... };
    (
        $(#[$meta:meta])* $vis:vis $Ops:ident for $t:ty {
            $($op_name:ident $(= $op_path:path)?),* $(,)?
        }
    ) => { ... };
}