gistfile1.txt

#lang racket

(provide foo%)

(define foo%
  (class object%
    (super-new)
    
    (define (end-impl)
      (displayln "not yet"))

    (define/public (end) 
      (end-impl))
    
    (define/public (start) 
      (displayln "start")
      (set! end-impl (lambda () (displayln "end"))))))

(define f (new foo%))
(send f start)
(send f end)