How to move an element in a list in Haskell?

Question

I'm reading through Learn You a Haskell and reached a spot where I'm trying to move an element in a list to the head. I've come up with what I think is the naive way and I'm curious if someone can show me what the experienced Haskell programmer would do instead. In this example, I have a list of Integers and I want to move the element '4', which would be index '3', to the head of the list. ``` let nums = [1, 2, 3, 4, 5] (nums !! 3) : delete (nums !! 3) nums ``` returns [4, 1, 2, 3, 5]. What do you think?

Accepted Answer

I would do it this way:

```
move n as = head ts : (hs ++ tail ts)
   where (hs, ts) = splitAt n as
```

`splitAt` splits a list at the given position, it returns the two parts that are created by the splitting (here `hs` and `ts`). The element that should be moved to the front is now at the beginning of `ts`. `head ts` returns just this first element of `ts`, `tail ts` returns everything but that first element. The result of the function are just these parts combined in the right order: `hs` concatenated with `tail ts` and prepended by the element `head ts`.

How to move an element in a list in Haskell?

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