@sig([["a"]]/ H >> ["a"] )
def concat(xss):
    """
    concat :: [[a]] -> [a]

    Concatenate a list of lists.
    """
    def __concat(xss):
        for xs in xss:
            for x in xs:
                yield x
    return L[__concat(xss)]
dataset/ETHPy150Open billpmurphy/hask/hask/Data/List.py/concat/swapped operands of `/`