scheme - Trying to check if all elements of a list are unique -

as title suggest trying write scheme function checks if elements of list unique. have written code think should work:

(define are-all-unique?       (lambda (v)         (if (member (car v) (cdr v))             #f             (if (pair? v)                 (are-all-unique? (cdr v))                 #t)))) 

and works fine in case false, if write:

 (are-all-unique? '(1 2 3)) 

it returns:

exception in car: () not pair 

does have clue on how fix this, , doing wrong? :)

well, error message states, you're attempting pass empty list car. why that's happening, let's take @ code.

as know, need pass cons cell car , cdr them work. check property using pair?, doing. problem when you're doing it.

the best way debug function trace through happens when pass bad input (in case '()) function. first thing run test in if statement: (member (car v) (cdr v)). now, since input we're tracing empty list, fail every time. want more this:

;; are-all-equal? poor choice of function name, way, since that's ;; not function checks (define are-all-unique?    (lambda (v)     (if (pair? v)         ; way branch ever execute         ; if (pair? v) true, know (car v) , (cdr v)         ; never raise exceptions         (and (not (member (car v) (cdr v)))              (are-all-unique? (cdr v)))         #t))) 

the thing note here control flow structure of version of function: proper list either cons cell or empty list, have 2 cases in our function (one each possibility). when writing functions deal lists, 1 should (for part) decide want in nonempty , empty cases, , make sending list argument appropriate case first thing inside of function. such approach appropriate when doing structural recursion (i.e., in words of 1 of freshman professors, 'the structure of data informs structure of code').