Nested for loops in scheme

so.scheme

(define (SO x y)
  (let* ((x! (car x)) (y! (car y)))
    (while (< x! (car (cdr x)))
      (set! y! (car y))
      (while (< y! (car (cdr y)))
        (print (string-append (number->string x!) "-" (number->string y!)))
        (set! y! (+ y! 1))
      )
      (set! x! (+ x! 1))
    )
  )
)
(SO '(15 20) '(30 35))

this was in response to a SQ question, and tested inside Gimp's Script-fu