How to rescind a defun?

How to rescind a defun?

[kj]

If, during an Emacs session, one evaluates a defun that (inadvertently)
redefines an existing function, is it possible to undo this?

Thanks!

RE: How to rescind a defun?

[Drew Adams]

> If, during an Emacs session, one evaluates a defun that 
> (inadvertently) redefines an existing function, is it
> possible to undo this?

See function `fmakunbound'.

Re: How to rescind a defun?

[kj]

In <mailman.1365.1337373409.855.help-gnu-emacs@gnu.org> "Drew Adams" <drew.adams@oracle.com> writes:

>> If, during an Emacs session, one evaluates a defun that 
>> (inadvertently) redefines an existing function, is it
>> possible to undo this?

>See function `fmakunbound'.

Thanks, I would have never found this!

Unfortunately, it seems that the original definition is gone.  (I
had hoped that the new definition was just shadowing the original
one, so that rescinding the former would "resurrect" the latter.)

RE: How to rescind a defun?

[Drew Adams]

> >> If, during an Emacs session, one evaluates a defun that 
> >> (inadvertently) redefines an existing function, is it
> >> possible to undo this?
> 
> > See function `fmakunbound'.
> 
> Thanks, I would have never found this!
> 
> Unfortunately, it seems that the original definition is gone.  (I
> had hoped that the new definition was just shadowing the original
> one, so that rescinding the former would "resurrect" the latter.)

I see now what you meant by "undo".

No, within a given namespace (obarray) and a given program scope (e.g. `flet' or
`labels' binding), a symbol has only one function definition.  

And for a global function definition, assignment is used, not binding.  So there
is no shadowing.

Re: How to rescind a defun?

[Barry Margolin]

In article <mailman.1365.1337373409.855.help-gnu-emacs@gnu.org>,
 "Drew Adams" <drew.adams@oracle.com> wrote:

> > If, during an Emacs session, one evaluates a defun that 
> > (inadvertently) redefines an existing function, is it
> > possible to undo this?
> 
> See function `fmakunbound'.

That will remove the new definition, but not restore the old one.

The only way to do that is to find the old definition and evaluate it.

-- 
Barry Margolin, barmar@alum.mit.edu
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***

Re: How to rescind a defun?

[Pascal J. Bourguignon]

kj <no.email@please.post> writes:

> If, during an Emacs session, one evaluates a defun that (inadvertently)
> redefines an existing function, is it possible to undo this?

If you do that a lot,  you could implement defun to do that.

(require 'cl)

(setf (symbol-function 'emacs-defun) (symbol-function 'defun))

(defmacro defun (name lambda-list &rest body)
   `(progn
       (when (fboundp ',name)
          (push (symbol-function ',name) (get ',name 'old-defuns)))
       (emacs-defun ,name ,lambda-list ,@body)))

(defun pop-defun* (name)
  (setf (symbol-function name) (pop (get name 'old-defuns))))

(defmacro pop-defun (name)
   `(pop-defun* ',name))

(defun f () 42)
(f) --> 42
(defun f () 33)
(f) --> 33
(pop-defun f)
(f) --> 42


Now of course you need to define that early, and load all the libraries
after it, so that they use your defun instead of the native emacs-defun.


-- 
__Pascal Bourguignon__                     http://www.informatimago.com/
A bad day in () is better than a good day in {}.