Macro with_scalar 

macro_rules! with_scalar {
    ($tensor:expr, all, backend = $backend:expr, op = $op:expr, |$typed:ident| $(-> $ret:ty)? $body:block) => { ... };
    ($tensor:expr, numeric, backend = $backend:expr, op = $op:expr, |$typed:ident| $(-> $ret:ty)? $body:block) => { ... };
    ($tensor:expr, float_complex, backend = $backend:expr, op = $op:expr, |$typed:ident| $(-> $ret:ty)? $body:block) => { ... };
    ($tensor:expr, float_only, backend = $backend:expr, op = $op:expr, |$typed:ident| $(-> $ret:ty)? $body:block) => { ... };
}