Scheme

● 有点像面向对象的写法^-^

● 闭包？

(define counter
  (let ([next 0])
    (lambda ()
      (set! next (+ next 1))
      next)))

(counter)

(counter)

(define make-counter
  (lambda ()
    (let ([count 0])
      (lambda ()
        (set! count (+ count 1))
        count))))

(define counter (make-counter))
(counter)
(counter)
(counter)