如何组合列表列表和列表列表

Question

我有列表列表，需要将它与另一个列表列表组合在一起。示例输入: A：[1,2,3,4,5,6,7,8] B：[1,2,3,4,5,6,7,8]

输出示例：[1,2,1,2,1,2,3,4，..,7,8,5,6,7,8,7,8]

包含4个列表的2个列表将返回一个列表大小为4*4 = 16的列表

我尝试过递归地组合列表，但我知道即使可以通过，它也不会起作用。

  mergeAll [[]] [[]] = [[]]
  mergeAll [[]] b = b
  mergeAll a [[]] = a
  mergeAll xs ys = mergeAll (merge xs ys) (drop 1 ys) 

  merge :: [[a]] -> [[a]] -> [[a]]
  merge [[]] [[]] = [[]]
  merge xs [[]] = xs
  merge [[]] ys = ys
  merge (x:xs) (y:ys)  = ((x++y):xs)

Answer 1

您可以使用列表理解：

[ xs ++ ys | xs <- listOfLists1, ys <- listOfLists2 ]

Answer 2

你可以这样做

Prelude> let doit = \as bs -> as >>= \a -> bs >>= \b -> pure (a ++ b)
Prelude> doit [[1,2],[3,4],[5,6],[7,8]] [[1,2],[3,4],[5,6],[7,8]]
[[1,2,1,2],[1,2,3,4],[1,2,5,6],[1,2,7,8],[3,4,1,2],[3,4,3,4],[3,4,5,6],[3,4,7,8],[5,6,1,2],[5,6,3,4],[5,6,5,6],[5,6,7,8],[7,8,1,2],[7,8,3,4],[7,8,5,6],[7,8,7,8]]

Answer 3

正如Robin在评论中所说，你也可以这样做：

liftA2 (++)

我问我的self a question，试图理解为什么这等同于：

[xs ++ ys | xs <- xss, ys <- yss]