Functional variant of 'oneof' function in Racket

Question

I have written following function to find if one and only one of 5 variables is true:

(define (oneof v w x y z)
  (or (and v (not w) (not x) (not y)  (not z         


        

Answer 1

You can literally count how many true values you have in a list of arbitrary length, if that number is 1 then we're good (remember that in Scheme any non-false value is considered true). Also notice how to create a procedure with a variable number of arguments, using the dot notation:

(define (oneof . vars)
  (= 1
     (count (lambda (v) (not (false? v)))
            vars)))

For example:

(oneof #f #f #f #f #t)
=> #t
(oneof #f #f #f #f #f)
=> #f
(oneof #t #t #t #t #t)
=> #f