From: Lynn Winebarger <owinebar@gmail.com>
To: Stefan Monnier <monnier@iro.umontreal.ca>
Cc: Matthew Trzcinski <matt@excalamus.com>,
emacs-devel <emacs-devel@gnu.org>
Subject: Re: [elpa] externals/org 26ef5e3e5b: org-src: Use `sh-mode' for all the shells it can handle
Date: Mon, 17 Apr 2023 13:24:25 -0400 [thread overview]
Message-ID: <CAM=F=bABP6qLQpcN_a4BWNBO3MLU6wpa5=a6RowXbjjHOMkK4w@mail.gmail.com> (raw)
In-Reply-To: <jwvleiq77z0.fsf-monnier+emacs@gnu.org>
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On Mon, Apr 17, 2023, 1:11 PM Stefan Monnier <monnier@iro.umontreal.ca>
wrote:
> >> ELISP> (macroexpand '`(,@(list 1 2) a b c d))
> >> (append (list 1 2) '(a b c d))
> >> ELISP> (macroexpand '`(a b c d ,@(list 1 2)))
> >> (cons 'a (cons 'b (cons 'c (cons 'd (list 1 2)))))
> >> ELISP>
> > Why is the former more efficient than the latter?
>
> One allocates N₁+N₂ cons cells, then other only allocates N₁ cons-cells.
> This is true regardless of how we macroexpand and byte-compile the code.
> This only makes a diference for code that's executed several times
> (i.e. not at toplevel).
>
I see - what you meant by "such ,@" was when the preceding elements are
constant.
I've seen a veteran Lisp programmer get bitten by side-effecting a list
constructed with that feature of backquote.
Lynn
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prev parent reply other threads:[~2023-04-17 17:24 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <168174708495.14139.12756054653439048176@vcs2.savannah.gnu.org>
[not found] ` <20230417155805.3E200C1391A@vcs2.savannah.gnu.org>
2023-04-17 16:08 ` [elpa] externals/org 26ef5e3e5b: org-src: Use `sh-mode' for all the shells it can handle Stefan Monnier
2023-04-17 16:16 ` Lynn Winebarger
2023-04-17 16:27 ` Philip Kaludercic
2023-04-17 16:37 ` Andreas Schwab
2023-04-17 16:42 ` Philip Kaludercic
2023-04-17 16:39 ` Mattias Engdegård
2023-04-17 16:47 ` Mattias Engdegård
2023-04-17 17:37 ` Stefan Monnier
2023-04-17 18:33 ` Mattias Engdegård
2023-04-17 20:08 ` Stefan Monnier
2023-04-18 9:50 ` Mattias Engdegård
2023-04-17 17:11 ` Stefan Monnier
2023-04-17 17:24 ` Lynn Winebarger [this message]
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