Macro rstat::param

macro_rules! param {
    (@impl_new $name:ident<$T:ident> s.t. [$($cst:expr),*]) => { ... };
    (@impl_param $name:ident<$T:ident> s.t. [$($cst:expr),*]) => { ... };
    ($name:ident<$T:ident$(: $tc0:ident $(+ $tc:ident)*)?> s.t. [$($cst:expr),*]) => { ... };
}