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;;; fakespace.el --- fake namespaces with defpackage
;; This is free and unencumbered software released into the public domain.
;; Author: Christopher Wellons <>
;; URL:
;; Version: 1.0
;;; Commentary:
;; Provides fake namespaces through a very rudimentary `defpackage',
;; familiar to Common Lisp users. The developer declares which symbols
;; are to be exported outside the package. All other symbols are
;; hidden away (by `end-package') where no other package can trample
;; on them.
;; See example.el for an example of using this package.
;; It works by comparing the symbol table before any declarations to
;; the symbol table afterward, then uninterning any symbols that were
;; created and not exported. This will work even on byte-compiled
;; files. In fact, everything is determined at compile-time, so there
;; is practically no load-time penalty from using these fake
;; namespaces.
;; Generally you will not want to actively use these fake namespaces
;; during development because there is no `in-package' function. You
;; will always been in the main namespace unable to access your
;; private functions. Later, when you're finishing up and want to test
;; out your namespace, make sure your code is unloaded from Emacs
;; (i.e. none of your symbols is in the symbol table) before applying
;; your namespace. The same applies to compilation: the package must
;; not be loaded before compilation or the `defpackage' will not hide
;; any symbols.
;; Unfortunately, due to the downright ugly implementation of obarrays
;; in Emacs, it's currently not possible to implement
;; `in-package'. Uninterned symbols cannot be added back to the global
;; obarray (or any other obarray). Symbols are invisibly chained as
;; linked lists in the obarray so it's not possible to put a symbol
;; into two obarrays at the same time -- the chains would
;; conflict. Not only is the required functionality not provided
;; (intentionally), trying to hack it in would break everything.
;;; Code:
(defun fakespace--atom-list (&optional ob)
"Return given obarray OB as a list. Defaults to obarray."
(let ((lst ()))
(mapatoms (lambda (s) (push s lst)) ob)
(defun fakespace--atom-difference (a b)
"Like set-difference, but, for performance reasons, requires
specially formed lists (i.e. from `fakespace--atom-list'). Returns
items that are in B and not A."
(let ((diff))
(while (and (not (null a)) (not (null b)))
(while (not (eq (car a) (car b)))
(push (car b) diff)
(setq b (cdr b)))
(setq a (cdr a))
(setq b (cdr b)))
(defvar fakespace--obarray ()
"Snapshot of the obarray before interning the package's symbols.")
(defmacro defpackage (name &rest args)
(dolist (arg args)
(let ((type (car arg)))
(cond ((eq type :exports) t) ; interning the symbols is enough
((eq type :use) (mapc (lambda (s) (require s)) (cdr arg))))))
(setq fakespace--obarray (fakespace--atom-list) )
`(provide (quote ,name)))
(defmacro end-package ()
(cons 'progn
(mapcar (lambda (s) `(unintern (quote ,s) nil))
(fakespace--atom-difference fakespace--obarray
(provide 'fakespace)
;;; fakespace.el ends here
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