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From: <tomas@tuxteam.de>
To: Jean Louis <bugs@gnu.support>
Cc: Help GNU Emacs <help-gnu-emacs@gnu.org>
Subject: Re: How can function know its own name?
Date: Sun, 26 Jun 2022 07:46:24 +0200	[thread overview]
Message-ID: <YrfysMcY0/eNJIof@tuxteam.de> (raw)
In-Reply-To: <courier.0000000062B76E4E.00003F6F@stw1.rcdrun.com>

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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?

Cheers
-- 
t

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  parent reply	other threads:[~2022-06-26  5:46 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-06-25 20:21 How can function know its own name? Jean Louis
2022-06-25 21:37 ` Emanuel Berg
2022-06-26  5:46 ` tomas [this message]
2022-06-26  8:08   ` Jean Louis
2022-06-26  8:54 ` Stefan Monnier via Users list for the GNU Emacs text editor
2022-06-26  9:25   ` tomas
2022-06-26 10:13   ` Jean Louis
2022-06-26 21:25     ` Stefan Monnier
2022-06-27  2:35       ` Jean Louis
2022-06-26  9:43 ` Philip Kaludercic
2022-06-26 10:21   ` Jean Louis
2022-06-26 10:31   ` Jean Louis
2022-06-26 21:13     ` Stefan Monnier via Users list for the GNU Emacs text editor

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