From: Stefan Monnier <monnier@iro.umontreal.ca>
To: Pip Cet <pipcet@gmail.com>
Cc: "Basil L. Contovounesios" <contovob@tcd.ie>,
Lars Ingebrigtsen <larsi@gnus.org>,
emacs-devel@gnu.org
Subject: Re: Always-true predicate?
Date: Sat, 20 Feb 2021 08:58:27 -0500 [thread overview]
Message-ID: <jwv35xq3lau.fsf-monnier+emacs@gnu.org> (raw)
In-Reply-To: <CAOqdjBcPbXvGHWNY-K4UBS=Z=4G=zriEcZFnJgbcATMQz5WO_g@mail.gmail.com> (Pip Cet's message of "Sat, 20 Feb 2021 09:40:38 +0000")
>> Also, I'm not completely sure in which sense it "miscompiles" it,
>> since it can't be compiled correctly, AFAIK. ]
>
> ???
>
> It's perfectly valid ELisp. It should throw. It doesn't.
You're right, technically. But most of the time that code like that
shows up, it's just a bug and the intended semantics is different.
IOW I'd be surprised if there is a piece of code out there that wants
this to signal an error ;-)
[ But, just to clarify: I'm not trying to defend this as "not a bug".
It *is* a bug in the optimizer, no more, no less. ]
> So to avoid having to cons up a new list you have to know about the
> callee to know it doesn't do that, which apply prevents you from
> doing.
I don't see what you mean by "apply prevents you from doing". But in
any case, I'd happy to change my stance to say that the guilt is shared
between `apply` and `&rest`.
And yet another way to look at it is that the real culprit is the fact
that `cons` cells are mutable ;-)
> Looking forward to your patch removing all argument names from defuns
> everywhere ;-)
It's almost ready.
> It seems obvious to me that if f and g are "the same",
Function equality and "obvious" just don't belong in the same sentence, IMO.
> BTW, I made a mistake in my previous email:
>
> (f a &rest b c) should be equivalent to (apply #'f a (append b (list
> c))). No zips, and no spreadification of the last argument.
That reminds me of the macro `gnus--,@` I introduced recently (it's
not the same, since ,@ would splice at macro-expansion time, whereas
your &rest here wants to splice at run time).
Stefan
next prev parent reply other threads:[~2021-02-20 13:58 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-17 12:01 Always-true predicate? Lars Ingebrigtsen
2021-02-17 12:31 ` Andrea Corallo via Emacs development discussions.
2021-02-17 12:40 ` Lars Ingebrigtsen
2021-02-17 16:59 ` Barry Fishman
2021-02-19 15:24 ` Stefan Kangas
2021-02-17 13:16 ` Basil L. Contovounesios
2021-02-17 18:56 ` Pip Cet
2021-02-17 19:19 ` Lars Ingebrigtsen
2021-02-17 19:31 ` Pip Cet
2021-02-17 19:37 ` Lars Ingebrigtsen
2021-02-17 20:18 ` Teemu Likonen
2021-02-17 22:25 ` [External] : " Drew Adams
2021-02-17 23:04 ` Basil L. Contovounesios
2021-02-17 23:13 ` Drew Adams
2021-02-17 23:01 ` Stefan Monnier
2021-02-19 11:27 ` Pip Cet
2021-02-19 15:07 ` Stefan Monnier
2021-02-19 19:04 ` Pip Cet
2021-02-19 20:11 ` Stefan Monnier
2021-02-20 9:40 ` Pip Cet
2021-02-20 13:58 ` Stefan Monnier [this message]
2021-02-19 5:39 ` Richard Stallman
2021-02-19 8:52 ` Robert Pluim
2021-02-19 9:10 ` Eli Zaretskii
2021-02-19 12:12 ` Eli Zaretskii
2021-02-19 12:52 ` Stefan Kangas
2021-02-19 13:00 ` Lars Ingebrigtsen
2021-02-19 13:34 ` Eli Zaretskii
2021-02-19 13:40 ` Lars Ingebrigtsen
2021-02-19 13:53 ` Eli Zaretskii
2021-02-19 14:05 ` Lars Ingebrigtsen
2021-02-19 18:04 ` [External] : " Drew Adams
2021-02-19 14:42 ` Stefan Monnier
2021-02-20 12:47 ` Lars Ingebrigtsen
2021-02-20 12:49 ` Lars Ingebrigtsen
2021-02-20 14:03 ` Stefan Monnier
2021-02-20 14:20 ` Lars Ingebrigtsen
2021-02-20 14:55 ` Stefan Monnier
2021-02-20 15:05 ` Lars Ingebrigtsen
2021-02-20 15:21 ` Stefan Monnier
2021-02-21 12:50 ` Robert Pluim
2021-02-21 13:04 ` Lars Ingebrigtsen
2021-02-19 15:09 ` Stefan Kangas
2021-02-19 15:22 ` Eli Zaretskii
2021-02-19 18:17 ` [External] : " Drew Adams
2021-02-19 18:41 ` Eli Zaretskii
2021-02-22 5:02 ` chad
2021-02-22 15:20 ` Eli Zaretskii
2021-02-22 23:07 ` chad
2021-02-21 6:12 ` Richard Stallman
2021-02-21 15:12 ` Eli Zaretskii
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