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

    Extract the elements after the head of a list, which must be non-empty.
    """
    if null(xs):
        raise IndexError("empty list")
    return xs[1:]
dataset/ETHPy150Open billpmurphy/hask/hask/Data/List.py/tail/swapped operands of `/`