(use callable-hash-tables)

(define +none+
  (list 'none))

(define (nested-get callable path #!optional default)
  (let loop ((path path)
             (callable/val callable))
    (if (null? path)
        (if (eq? callable/val +none+)
            default
            callable/val)
        (if (procedure? callable/val)
            (let* ((key (car path))
                   (val (callable/val key +none+)))
              (if (eq? val +none+)
                  default
                  (loop (cdr path) val)))
            default))))

(define ^ make-callable-hash-table)

(define silly-list
  (^ `((car . 0)
       (cdr . ,(^ `((car . 1)
                    (cdr . ,(^ `((car . 2)
                                 (cdr))))))))))

(print (nested-get silly-list '(cdr cdr car)))