def foldr(fn, elems, initializer=None, name=None):
    """Reduce elems using fn to combine them from right to left.

    # Arguments
        fn: Callable that will be called upon each element in elems and an
            accumulator, for instance `lambda acc, x: acc + x`
        elems: tensor
        initializer: The first value used (`elems[-1]` in case of None)
        name: A string name for the foldr node in the graph

    # Returns
        Tensor with same type and shape as `initializer`.
    """
    raise NotImplementedError(
        'MXNet Backend: foldr operator is not supported yet.')
