Question

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

Answer 1

Taken from this question:

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