GNU bug report logs - #52063
28.0.60; Confusing presentation of lambda

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From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: larsi <at> gnus.org, 52063 <at> debbugs.gnu.org
Subject: bug#52063: 28.0.60; Confusing presentation of lambda
Date: Wed, 24 Nov 2021 14:06:37 -0500

>> >> > But perhaps others have other opinions here?
>> >> Compile your code and the problem goes away (because you'll never see
>> >> (lambda ...) or (closure ...) values, they'll all be
>> >> byte-code-functions instead ;-)
>> > I don't want to compile my .emacs.
>> > Any other words of wisdom before I write this off as another annoyance
>> > of lexical-binding, and take care to disable that wherever I can?
>> The other word of wisdom is:
>> Don't add lambdas to hook.  Always name those functions.
> So this issue is specific to hooks?

No, but in 99% of the cases you won't actually *see* a function value
(unless you specifically go looking for it, e.g. with `symbol-function`).

One of the cases where you are more likely to see one is if you look at
the value of a hook.

> I thought add-hook is just a fancy way of consing a list,

It is.

> but you seem to say that it has some side effects that other
> constructs don't?

Not really, no.

> IOW, would manually consing a list with a lambda-function produce the
> same results,

Yes.

> or would it leave the lambda-function intact?

No.  A *value* of the form (lambda ARGS . BODY) is a (non-compiled)
dynamically-scoped function.  Non-compiled statically-scoped function
values use the form (closure ENV ARGS . BODY...).

So you'll only get a value of the form (lambda ARGS . BODY) if you use
the dynamically scoped dialect of ELisp (or if you manually create such
a list, e.g. with '(lambda ...) or `(lambda ...) or (list 'lambda ...),
etc...).


        Stefan

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