Haskell 快速检查生成器-自定义类型的任意元素

我正在尝试为自定义数据类型生成任意大小的元素：

newtype ZippList a = ZPL ([a], [a])
    deriving (Show)

这就是我得到的：

instance Arbitrary a => Arbitrary (ZippList a) where
arbitrary = sized zipplist where
    zipplist n = do
        firstLength <- choose(0,n)
        secondLength <- n - firstLength
        firstList <- [arbitrary :: Gen a | [1..firstLength]]
        secondList <- [arbitrary :: Gen a | [1..secondLength]]
        return $ ZPL (firstList, secondList)

instance arbitral a=>arbitral（ZippList a）其中
任意=列表大小，其中
zipplist n=do
firstLength这对我很有效

instance Arbitrary a => Arbitrary (ZippList a) where
  arbitrary = sized zipplist where
    zipplist n = do
        firstLength <- choose (0, n)
        let secondLength = n - firstLength
        firstList <- sequence [arbitrary | _ <- [1..firstLength]]
        secondList <- sequence [arbitrary | _ <- [1..secondLength]]
        return $ ZPL (firstList, secondList)

instance arbitral a=>arbitral（ZippList a）其中
任意=列表大小，其中
zipplist n=do
firstLength
sequence[Arbitral |@epsilonhalbe我也喜欢你的方式，但是理解方法在quickstart中似乎是惯用的，因为某些原因，见鬼，我有点忘记了用
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