Scala:

Write a function called addSub that consumes a List[Int] and produces an Int. The function should add all the elements in even position and subtract all the elements in odd position. Note that the indexes of the first element of a list is 0 so it is in even position. For example, addSub(List(10, 20, 30, 40)) should be 10 - 20 + 30 40