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Emacs Lisp container

From: Etienne Prud’homme
Subject: Emacs Lisp container
Date: Mon, 26 Jun 2017 23:03:25 -0400
User-agent: Emacs/25.2 (gnu/linux)


I’ve tried to find a library or some tool to execute Elisp in a running
session while keeping the same environment, but found none.  Some call
it a container or sandbox or even jail.

What I mean by that, is that I would like to execute a body of code and
get the result without actually modifying the variables, functions,
loaded features, etc. of the current session.

I’m fully aware that starting a new session seem to do the same thing,
but I want to execute the piece of code in the *current running

I finally came up with a small library I named _container_[1].  There
are many ways to escape the container (like using `funcall` & `apply`
and also using `eval` on a quoted `eval` form).  It’s more of a proof a
concept than a working library right now.


> (let ((container-ignore-error t)
>   (container
>     (add-to-list 'load-path "~/Documents/")
>     (require 'foo)
>     (setq emacs-version "0.0.0")
>     emacs-version)) ; => "0.0.0"
> emacs-version ; => 26.0.50

The above snippet doesn’t (seem to) have side-effects.

What it does is the following:

* Saves the window configuration and opens a new buffer.

* Overrides the `require` & `load` functions to unload after the
  container finished executing.
* Overrides the `load-theme` function to restore the original theme
  configuration after.

* Overrides the `set`, `setq` & `set-default` functions to make the
  variable buffer local.

* Overrides the `eval` function to apply the above.  This one is
  particularly tricky since we could escape it using a quoted form.  I’m
  considering disabling it altogheter and signal an error.

* (Work in Progress) Overrides the `funcall` & `apply` functions to
  apply the rules above.  This is also tricky since the evaluation
  process doesn’t make much sense to me.  I’m probably not used enough
  with evalutation.  I can’t figure out why:

> (funcall #'setq test 1)

works while:

> (funcall #'setq 'test 1)

doesn’t work.

Of course, I may be totally wrong in my approach and would appreciate
being corrected.  Help and comments are welcomed!

[1] https://github.com/notetiene/emacs-lisp-container

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