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- (define (empty-stack) (box '()))
- (define (make-stack lst) (box lst))
- (define (stack-top s)
- (let ((stk (unbox s)))
- (if (null? stk)
- (error 'stack-top/null 0 0)
- (car stk))))
- (define (stack-pop! s)
- (let ((stk (unbox s)))
- (if (null? stk)
- (error 'stack-pop/null 0 0)
- (begin
- (set-box! s (cdr stk))
- (car stk)))))
- (define (stack-push! s v) (set-box! s (cons v (unbox s))))
- (define (stack-get s) (unbox s))
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