no-repeat

gistfile1.txt

(define (is-already-present? val lst)
    (if(null? lst)
        #f
        (if(= val (car lst))
            #t
            (is-already-present? val (cdr lst))
        )
    )
)

(define (no-repeats s)
    (define (process-s rest tracker)
        (if(null? rest)
            nil
            (if (is-already-present? (car rest) tracker)
                (process-s (cdr rest) tracker)
                (begin
                    (define tracker (append tracker (list (car rest))))
                    (cons (car rest) (process-s (cdr rest) tracker))
                )
            )
        )
    )
    (cons (car s) (process-s (cdr s) (cons (car s) nil)))
)