Macro json

macro_rules! json {
    (null) => { ... };
    ([ $($elems:tt),* $(,)? ]) => { ... };
    ({ $($key:tt : $value:tt),* $(,)? }) => { ... };
    ($other:expr) => { ... };
    (private_quote_property $key:ident) => { ... };
    (private_quote_property $key:expr) => { ... };
}