;Write a procedure that takes a string and returns a list of unique words in the string.  (you may assume that all the functions from homework 1 are defined)  You dont have to worry about punctuation.


;; This function takes a string and returns a list with ;; duplicate words removed
(define (rem-duplicates str) 
	(no-duplicates (split #\space str))
)

;; Helper function
;; This function takes a list and returns a new list with 
;; duplicate elements removed.
(define (no-duplicates l)

  ;; base case: an empty list has no duplicated.
  ;; just return the empty list.
  (if (null? l)
      '()      
      
      ;; get the head of the list into a local variable. 
      (let ((head (car l))
            (tail (cdr l))
           )
           
           ;; if the first element is in the rest of the list
           ;; then don't add it now.
           (if (member head tail)
               (no-duplicates tail)
               
               ;; otherwise, add the first element because it
               ;; is the only time this element occures in the 
               ;; list.
               (cons head (no-duplicates tail))
           )
      )
  )
)