(define (make-numbers-property numbers)
  (let* ((vec (list->u32vector numbers))
         (len (u32vector-length vec))
         (lvec ((foreign-lambda* c-pointer ((u32vector s) (int length))
                  "unsigned long * lvec = malloc(sizeof(unsigned long) * length);"
                  "int i;"
                  "for (i = 0; i < length; i++) {"
                  "    lvec[i] = s[i];"
                  "}"
                  "C_return(lvec);")
                vec len)))
    (set-finalizer! lvec free)
    (make-window-property "CARDINAL" 32 lvec len)))