declare-a-list.rkt

#lang racket/base

(require (for-syntax racket/base
                     racket/sequence
                     racket/provide-transform))

(provide (except-out (all-defined-out)
                     (all-in-private-list)))

(define-for-syntax private-list '())
(define-syntax (declare-as-private stx)
  (syntax-case stx ()
    [(_ id ...)
     (let ()
       (for ([an-id (in-syntax #'(id ...))])
         (set! private-list (cons an-id private-list)))
       (syntax/loc stx (begin)))]))
(define-syntax all-in-private-list
  (make-provide-transformer
   (λ (stx modes)
     (expand-export #`(combine-out . #,private-list) modes))))
  

(define (fib n)
  (do-fib 0 1 n))

(declare-as-private do-fib)
(define (do-fib a b n)
  (cond [(zero? n) a]
        [else (do-fib b (+ a b) (sub1 n))]))