练习 4.11

以下是其中的 make-frame 的例子：

(define (make-frame vars vals)
    (list vars vals))

(define (frame-vars frame)
    (car frame))

(define (frame-vals frame)
    (cadr frame))

(define (set-frame-vars! frame new-vars)
    (set-car! frame new-vars))

(define (set-frame-vals! frame new-vals)
    (set-car! (cdr frame) new-vals))

(define (add-binding-to-frame! var val frame)
    (set-frame-vars! frame (cons var (frame-vars frame)))
    (set-frame-vals! frame (cons val (frame-vals frame))))

讨论

blog comments powered by Disqus