Macro helper

macro_rules! helper {
    (exists_or_zero;) => { ... };
    (exists_or_zero;$t:tt) => { ... };
    (exists;,$then:ty) => { ... };
    (exists;$t:tt, $then:ty) => { ... };
    (exists_flag;,$then:ty) => { ... };
    (exists_flag;$t:tt, $then:ty) => { ... };
    (exists_add;,$var:ident, $type:ty, $d:ident, $db:ident) => { ... };
    (exists_add;$t:tt,$var:ident, $type:ty, $d:ident, $db:ident) => { ... };
    (exists_add_flag;,$var:ident, $type:ty, $d:ident, $db:expr) => { ... };
    (exists_add_flag;$t:tt,$var:ident, $type:ty, $d:ident, $db:expr) => { ... };
    (exists_declare;,$var:ident, $type:ty) => { ... };
    (exists_declare;$t:tt,$var:ident, $type:ty) => { ... };
    (exists_declare_flag;,$var:ident, $type:ty) => { ... };
    (exists_declare_flag;$t:tt,$var:ident, $type:ty) => { ... };
}