GNU bug report logs - #11782
24.1; closure is not self-quoting

Previous Next

To add a comment to this bug, you must first unarchive it, by sending
a message to control AT debbugs.gnu.org, with unarchive 11782 in the body.
You can then email your comments to 11782 AT debbugs.gnu.org in the normal way.

Toggle the display of automated, internal messages from the tracker.

Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Christopher Schmidt <christopher <at> ch.ristopher.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 24.1; closure is not self-quoting
Date: Mon, 25 Jun 2012 19:47:02 +0100 (BST)

I am not exactly sure if this is a bug, a feature or something that is
just undefined.

    (funcall (eval (eval '(let ((var)) (lambda ())))))

works fine, whereas

    (funcall (eval (eval '(let ((lex-var)) (lambda ())) t)))

does not work.

Backtrace:

    Debugger entered--Lisp error: (void-function closure)
      (closure ((lex-var) t) nil)
      eval((closure ((lex-var) t) nil))
      (funcall (eval (eval (quote (let ((lex-var)) (lambda nil))) t)))
      eval((funcall (eval (eval (quote (let ((lex-var)) (lambda nil))) t))))

I am on GNU Emacs 24.1.1 (x86_64-unknown-linux-gnu, GTK+ Version
2.24.10).

        Christopher

Message #8 received at 11782 <at> debbugs.gnu.org (full text, mbox):

From: Stefan Monnier <monnier <at> IRO.UMontreal.CA>
To: 11782 <at> debbugs.gnu.org
Subject: Re: bug#11782: 24.1; closure is not self-quoting
Date: Fri, 20 Jul 2012 08:12:41 -0400

>     (funcall (eval (eval '(let ((lex-var)) (lambda ())) t)))
> does not work.

Note that (eval (eval '(cons 1 2))) does not work either.
So I don't consider it a bug.


        Stefan

Message #11 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Christopher Schmidt <christopher <at> ch.ristopher.com>
To: bug-gnu-emacs <at> gnu.org
Subject: Re: bug#11782: 24.1; closure is not self-quoting
Date: Fri, 20 Jul 2012 14:38:07 +0100 (BST)

Stefan Monnier <monnier <at> IRO.UMontreal.CA> writes:

Thanks for your answer.

>>     (funcall (eval (eval '(let ((lex-var)) (lambda ())) t)))
>> does not work.
>
> Note that (eval (eval '(cons 1 2))) does not work either.
> So I don't consider it a bug.

That's true, of course.  Lambdas are an exception in Emacs Lisp and
CL, though.

    (info "(elisp)Lambda Expressions")

    In Emacs Lisp, such a list is valid as an expression--it evaluates
    to itself.  But its main use is not to be evaluated as an
    expression, but to be called as a function.

I stumbled upon this issue a few times already.  So did others.

    http://stackoverflow.com/questions/7913207/how-does-the-definition-for-apply-partially-work-in-emacs-24

IMO the info node I referenced above should mention this.

        Christopher

Message #14 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Christopher Schmidt <christopher <at> ch.ristopher.com>
To: bug-gnu-emacs <at> gnu.org
Subject: Re: bug#11782: 24.1; closure is not self-quoting
Date: Sat, 23 Feb 2013 14:53:15 +0000 (GMT)

Ping?

(I think the issue I describe is a severe bug.)

        Christopher

Message #17 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Stefan Monnier <monnier <at> IRO.UMontreal.CA>
To: bug-gnu-emacs <at> gnu.org
Subject: Re: bug#11782: 24.1; closure is not self-quoting
Date: Tue, 28 May 2013 16:40:44 -0400

> (I think the issue I describe is a severe bug.)

Could you expand on why you think it's severe?


        Stefan

Message #20 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Christopher Schmidt <christopher <at> ch.ristopher.com>
To: bug-gnu-emacs <at> gnu.org
Subject: Re: bug#11782: 24.1; closure is not self-quoting
Date: Tue, 28 May 2013 23:35:08 +0100 (BST)

Stefan Monnier <monnier <at> IRO.UMontreal.CA> writes:

Hi Stefan,

> Could you expand on why you think it's severe?

I think this issue is severe because the behaviour is odd and follows
neither other mature Lispy languages nor the reference manual.

    (info "(elisp)Lambda Expressions")

    In Emacs Lisp, such a list is valid as an expression--it evaluates
    to itself.

As I said 11 month ago, I hit on this issue a few times already.  So did
others.  In most cases I had a lambda form that was eval'ed twice due to
macro expansion.

    ;; -*- lexical-binding: t -*-

    (defmacro a ()
      (let ((l (lambda () )))
        `(funcall ,l)))

    (a)

I realise there is a technical need for lambda's to evaluate to closures
in a lexical environment.  Are there any technical reasons for lexical
closures to not self-quote?

BTW I am perfectly fine with just fixing the docs.

        Christopher

Message #23 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: bug-gnu-emacs <at> gnu.org
Subject: Re: bug#11782: 24.1; closure is not self-quoting
Date: Tue, 28 May 2013 20:25:17 -0400

>> Could you expand on why you think it's severe?
> I think this issue is severe because the behaviour is odd and follows
> neither other mature Lispy languages nor the reference manual.

I see.  So we just disagree on what is considered severe (I expected
something like "this and that common idiom found in those packages fails").

    In Emacs Lisp, such a list is valid as an expression--it evaluates
    to itself.

Clearly this doc needs to be fixed since it confuses lambda expressions
and lambda values and while this conflation mostly worked in dynamic
binding, it does not work any more in the presence of closures.  I just
installed the patch below.


        Stefan


--- doc/lispref/functions.texi	2013-01-01 09:11:05 +0000
+++ doc/lispref/functions.texi	2013-05-29 00:16:58 +0000
@@ -196,9 +196,8 @@
 @end example
 
 @noindent
-In Emacs Lisp, such a list is valid as an expression---it evaluates to
-itself.  But its main use is not to be evaluated as an expression, but
-to be called as a function.
+In Emacs Lisp, such a list is a valid expression which evaluates to
+a function object.
 
   A lambda expression, by itself, has no name; it is an @dfn{anonymous
 function}.  Although lambda expressions can be used this way

Message #28 received at 11782-done <at> debbugs.gnu.org (full text, mbox):

From: Christopher Schmidt <christopher <at> ch.ristopher.com>
To: 11782-done <at> debbugs.gnu.org
Subject: Re: bug#11782: 24.1; closure is not self-quoting
Date: Wed, 29 May 2013 08:05:38 +0100 (BST)

Stefan Monnier <monnier <at> iro.umontreal.ca> writes:
>     In Emacs Lisp, such a list is valid as an expression--it evaluates
>     to itself.
>
> Clearly this doc needs to be fixed since it confuses lambda
> expressions and lambda values and while this conflation mostly worked
> in dynamic binding, it does not work any more in the presence of
> closures.  I just installed the patch below.

Thanks a lot!

        Christopher

Previous Next

GNU bug tracking system
Copyright (C) 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson.