Swap two elements in a list by its indices

Question

Is there any way to swap two elements in a list if the only thing I know about the elements is the position at which they occur in the list.

To be more specific, I a

Answer 1

For positional swapping, using a more complex fold function I have changed the value of the smalest (min) index with the value of the greates (xs!!(y-ii)) and then keep the value for the greatest index in the temp, until find it, the index(max).

I used min and max to make sure I encounter in proper order the indices otherwise I would have to put more checks and conditions in the folds function.

folds _ _ _ _ [] = []
folds i z y tmp (x:xs)
    | i == z = (xs!!(y-ii)):folds ii z y x xs
    | i == y = tmp:folds ii z y 0 xs
    | otherwise = x:folds ii z y tmp xs
    where 
        ii = i+1

swapElementsAt x y xs = folds 0 a b 0 xs
    where
        a = min x y
        b = max x y

Results

> swapElementsAt 0 1 [1,1,1,3,4,9]
[1,1,1,3,4,9]
> swapElementsAt 0 5 [1,1,1,3,4,9]
[9,1,1,3,4,1]
> swapElementsAt 3 1 [1,1,1,3,4,5]
[1,3,1,1,4,5]
> swapElementsAt 1 3 [1,1,1,3,4,5]
[1,3,1,1,4,5]
> swapElementsAt 5 4 [1,1,1,3,4,5]
[1,1,1,3,5,4]