Question: I want to be able to loop every second element of a given list. I can do this recursively as so:

```
check validate (x:xs) = check (validate x) (tail xs)

```

But the problem is that I need a function that accepts a list as parameter, then returns a list consisting of only every second element in the list, starting with (and including) the first element of the list, and I do not think this is possible recursively.

Can someone show me how to this using list comprehension? This would probably be the best approach.

Answer: 
```
second (x:y:xs) = y : second xs;
second _ = []

```

List comprehension may not be useful.
One of the Haskellish approaches would be something with `map`, `filter`, and `zip`.

```
second xs = map fst $ filter (odd . snd) $ zip xs [1..]

```

If you really wanted to use list comprehension, you could use the parallel list comprehension extension.

```
{-# LANGUAGE ParallelListComp #-}
second xs = [ x | (x, n) <- [ (x, n) | x <- xs | n <- [1..] ], odd n ]

```

I think that the former is concise, though.