Function calc_diff 

pub fn calc_diff<N, R>(
    expected: N,
    actual: N,
    diff: &[Box<dyn DiffReport<N::Leaf, R>>],
    reporter: R,
) -> Result<(), CalcDiffError<N::TraverseError, R::Error>>
where
    N: NodeTraverse + Send,
    N::Leaf: Send,
    R: Reporter + Sync,