Macro mk

macro_rules! mk {
    (struct $state:ident<$($glts:lifetime),*> {$($field:ident : {$($lts:lifetime),*} $field_type:ty),*$(,)?}) => { ... };
    (@$state:ident {$($acc:tt)*} $fields:tt {
        $field:ident : $lts:tt $field_type:tt
        $(,$($rest:tt)*)?
    }) => { ... };
    (@$state:ident $body:tt $fields:tt {$(,)?}) => { ... };
    (@@$state:ident {$({$($fields:tt)*} $field:ident : {$($lts:lifetime)*} {$($field_type:tt)+},)*}) => { ... };
}