Re: How can function know its own name?

[Jean Louis <bugs@gnu.support>]

* tomas@tuxteam.de <tomas@tuxteam.de> [2022-06-26 08:46]:
> On Sat, Jun 25, 2022 at 11:21:20PM +0300, Jean Louis wrote:
> > 
> > I would like to invoke logging for specific functions automatically,
> > without specifying what to log, and my function should know which
> > function invoked it.
> 
> This is not completely trivial. In Lisp, a function has no name.
> It is a first-class object which can be bound to (the function
> slot) of a symbol (or to that of two, three... symbols).
> 
> It's like the value 42. Many variables can be bound to that. Or
> none.
> 
> What name has (lambda (x) (if (= (mod x 2) 1) (+ (* 3 x) 1) (/ x 2)))?
> 
> None (yet?).
> 
> Try this:
> 
>   (setf (symbol-function 'foo) (lambda (x) (+ x 1)))
> 
> Now:
> 
>   (foo 13)
> 
>   => 14
> 
> So that function that adds one to its argument is now arguably
> called foo. But:
> 
>   (setf (symbol-function 'bar) (symbol-function 'foo))
> 
> Then:
> 
>   (bar 14)
> 
>   => 15
> 
> ...it can be called bar at the same time. Well, I can be called
> two names too, can't I?
> 
> See 13.3 "Naming a function" and 9.1 "Symbol Components" in our
> beloved Emacs Lisp manual for all the gory details.
> 
> Now to the interesting question: how do debuggers pull it off?

OK.

Maybe one way to give function a capacity to find out its name, the
name of the called function from inside of itself could be to call it
in a wrapper which sets global variable to be symbol of the function.

(defvar rcd-called-function)

(defun rcd-call-function (function &rest args)
  (setq rcd-called-function function)
  (apply function args)
  (setq rcd-called-function nil))

(defun my-fun ()
  (message "My function name is: %s" rcd-called-function))

(rcd-call-function 'my-fun) ⇒ nil


-- 
Jean

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