Each of these functions refer to items in lists by the position
within the list. In each case the first item in the list (i.e.
the head of the list) is item zero.
index(n, l) This returns the item at position n. There
is a similar "built-in" function called nth.
takeN(n, l) This returns the first n items from the list
l.
dropN(n, l) This returns the list l with the first n
items missing.
Examples
index(2, [100,200,300,400]) = 300
takeN(3, ["one","two","three","four","five"])= ["one","two","three"]
dropN(3, ["one","two","three","four","five"])= ["four","five"]