Macro gstore::slice

macro_rules! slice {
    (
        $state:ident {
            $($state_field:ident: $state_field_type:ty = $state_field_initializer:expr),*
        }
        $action:ident {
        $(
            $action_field:ident $( ( $($action_field_arg:ty),*) )?
        ),*
        }
    ) => { ... };
}