Returning last element of a list in drracket

Question

I need help with my computer science homework. I've been trying to return the last element of a list but I keep failing. This is what I have so far:

(check-expect (last empty) "Error! The list is empty!")
(check-expect (last (list "apple" "banana" "pear" "orange")) "orange")

(define (last loe)
  (cond
    [(empty? loe) "Error! The list is empty!"]
    []))

I do not know where to go from here. I know i am missing a base case but i cannot figure it out. please help!

Answer 1

The last procedure is already included in Racket, you don't need to implement it. But if you have to write it from scratch it's a simple matter of knowing where to stop - right before the list ends! like this:

(define (last loe)
  (cond
    [(empty? loe) "Error! The list is empty!"] ; we don't allow empty lists
    [(empty? (rest loe)) (first loe)]          ; stop right before last
    [else (last (rest loe))]))                 ; advance recursion