closure.rkt

#lang racket
(define (my_closure x) ;Return a fcn which adds x to its input.
  (define copy-of-x x)
  (lambda (y)
    (set! copy-of-x (+ copy-of-x y))
    copy-of-x
    )
  )

(define copy-of-my-closure (my_closure 4))

((my_closure 4) 5) ;9
((my_closure 4) 5) ;9

(copy-of-my-closure 5) ;9
(copy-of-my-closure 5) ;14