@sig(H/ ["a"] >> bool)
def null(xs):
    """
    null :: [a] -> bool

    Test whether the structure is empty.
    """
    return ~(caseof(xs)
                | m(m.y ^ m.ys) >> False
                | m(m.ys)       >> True)
dataset/ETHPy150Open billpmurphy/hask/hask/Data/List.py/null/original