@sig(["a"]/ H[(Eq, "a")] >> ["a"] >> ["a"])
def diff(xs, ys):
    """
    diff :: :: Eq a => [a] -> [a] -> [a]

    List difference.
    """
    raise NotImplementedError()
dataset/ETHPy150Open billpmurphy/hask/hask/Data/List.py/diff/swapped operands of `/`