尝试改进haskell中处理列表的当前丑陋的一段代码 [英] Trying to improve a current ugly piece of code in haskell dealing with lists

问题描述

我试图在Haskell中实现一个函数，该函数将采用任意整数列表 xs 和一个整数 k ，并在所有可能的位置返回一组列表 k 。例如，对于 xs = [0，1] 和 k = 2 ，我们会有

  myFunction [0，1] 2 = [[2,0,1]，[0,2,1]，[0,1,2]] 
  

我将它实现为

  putOn xs xi =（take i xs）++（x：（drop i xs））
 putOnAll xs x = map（putOn xs x）[0 ..（length xs）] 
  

但是，我觉得必须有其他更聪明的方法才能达到同样的效果。我的代码好像有人试图用导弹杀死一个bug。任何人都可以通过这种方式来做出一些巧妙的做法吗？

谢谢

解决方案

摘自这个问题：

  ins x [] = [[x]] 
 ins x（y：ys）=（x ：y：ys）：[y：res | res<  -  ins x ys] 
  

I am trying to implement a function in Haskell that'll take an arbitrary integer list xs and an integer k, and returns a set of lists with k in all possible positions.

For example, for a xs = [0, 1] and k = 2, we'd have

myFunction [0, 1] 2 = [ [2, 0, 1], [0, 2, 1], [0, 1, 2] ]

I've implemented it as

putOn xs x i = (take i xs) ++ (x:(drop i xs))
putOnAll xs x = map (putOn xs x) [0..(length xs)]

yet, I feel there must be other smarter ways to achieve the same. My code seems like someone trying to kill a bug with a missile. Could anyone make sugestions on ways to do something clever than this bit of code?

Thanks

解决方案

Taken from this question:

ins x []     = [[x]]
ins x (y:ys) = (x:y:ys):[ y:res | res <- ins x ys]

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