;This function returns #t iff
;  mylist is a list of atoms, and
;  none of the atoms are repeated.


(define listOfUniqueAtoms? 
  (lambda (mylist)
    (define sublist '())
    (define firstMember '()) 
    (cond 
      ((null? mylist) #t)
      ((not (list? mylist)) #f)
      (else
        (begin
          (set! firstMember (car mylist))
          (set! sublist (cdr mylist))
          (cond 
            ((not (atom? firstMember)) #f)
            ;memq: Buildin Scheme function:
            ;  (memq 'a '(a b c)) ===>  (a b c)
            ;  (memq 'b '(a b c)) ===>  (b c)
            ;  (memq 'a '(b c d)) ===>  #f
            ((not (eq? (memq (car mylist) sublist) #f)) #f)
            (else (listOfUniqueAtoms? sublist))
          )
        )
      )
    )
  )
)


;============== Unit Tests ======================
(load "atom.scm")
(load "test.scm")
(define msg "listOfUniqueAtoms?")
(test  msg (listOfUniqueAtoms? '(a b c d)) #t)
(test  msg (listOfUniqueAtoms? '(a)) #t)
(test  msg (listOfUniqueAtoms? '()) #t)
(test  msg (listOfUniqueAtoms? '(a b c b)) #f)
(test  msg (listOfUniqueAtoms? '(a (b) c d)) #f)