Macro impl_enum 

macro_rules! impl_enum {
    (
        impl Serialize,
        impl Deserialize,
        $enum_name:ident $tree:tt,
    ) => { ... };
    (
        impl From<$enum_name:ident>,
        impl TryFrom<$( $type:tt ),*>,
        $error_type:ty,
        $pairs:tt,
    ) => { ... };
}