;; How modules work in Racket

(require fruits)        => "fruits/main.rkt"
(require fruits/banana) => "fruits/banana.rkt"
#lang fruits            => "fruits/lang/reader.rkt" OR (submod "fruits/main.rkt" reader)
#lang fruits/apple      => "fruits/apple/lang/reader.rkt" OR (submod "fruits/apple.rkt" reader)

fruits
|
+- main.rkt        (require fruits)
|
+- apple.rkt       (require fruits/apple)
|
+- banana.rkt      (require fruits/banana)
|
+- pineapple
   |
   +- main.rkt     (require fruits/pineapple/main)


================================================================================

;;; Publicly provide a private lang with a default reader:

;; collection/private/lingua.rkt
#lang racket/base
(provide #%module-begin)

;; collection/lingua.rkt
#lang racket/base
(module reader syntax/module-reader collection/private/lingua)


================================================================================

;;; Publicly provide a private lang with its own reader:

;; collection/private/lingua/reader.rkt
#lang racket/base
(provide read read-syntax)
(define (read-syntax src in)
  #'(module whatever collection/private/lingua/expander
      parse-tree-from-in))

;; collection/private/lingua/expander.rkt
#lang racket/base
(provide #%module-begin)

;; collection/lingua.rkt
#lang racket/base
(module reader racket/base
  (provide (all-from-out collection/private/lingua/reader))
  (require collection/private/lingua/reader))
;; OR
(module reader reprovide collection/private/lingua/reader)