15 lines
450 B
Scheme
15 lines
450 B
Scheme
(define (make-stack)
|
|
(let ((st '()))
|
|
(lambda (message . args)
|
|
(case message
|
|
((empty?) (null? st))
|
|
((top) (if (null? st)
|
|
'empty
|
|
(car st)))
|
|
((push) (set! st (cons (car args) st)))
|
|
((pop) (if (null? st)
|
|
'empty
|
|
(let ((result (car st)))
|
|
(set! st (cdr st))
|
|
result)))
|
|
(else 'badmsg)))))
|