From: Drew Adams <drew.adams@oracle.com>
To: Michael Heerdegen <michael_heerdegen@web.de>,
Xu Chunyang <mail@xuchunyang.me>
Cc: 34975@debbugs.gnu.org
Subject: bug#34975: 26.1.92; In backquote, the comma marker does not work with variable name started with dot
Date: Sun, 24 Mar 2019 17:06:04 -0700 (PDT) [thread overview]
Message-ID: <1430c67b-c447-47b4-92b3-1cba335e8193@default> (raw)
In-Reply-To: <87sgvcxpzh.fsf@web.de>
> AFAIU ,. is a reader macro: (car (read ",.foo"))
> ==> \,\.
>
> I dunno or have forgotten for what it had been intended, there are no
> real uses in the Emacs Elisp sources.
>
> > (let ((.foo 42)) `(,.foo))
Yes, it's intended. It acts the same as ,@
I might use it instead of ,@ to convey (to a human)
a connotation that what follows is not a proper list
(or is not necessarily a proper list), whereas ,@ is
typically thought of as splicing in a list of elements.
(I don't in fact use it, apparently, but I thought I
might have, and if I did use it instead of ,@ then it
would no doubt be for that reason.)
On the other hand, Common Lisp says that ,. has this
difference in meaning from ,@:
"Anywhere ``,@'' may be used, the syntax ``,.'' may
be used instead to indicate that it is permissible
to destroy the list produced by the form following
the ``,.''; this may permit more efficient code,
using nconc instead of append, for example."
https://www.cs.cmu.edu/Groups/AI/util/html/cltl/clm/node190.html#BACKQUOTE
> You would have to write it differently, e.g.
>
> (let ((.foo 42)) `((\, .foo)))
> ==> (42)
Yes.
next prev parent reply other threads:[~2019-03-25 0:06 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-24 14:19 bug#34975: 26.1.92; In backquote, the comma marker does not work with variable name started with dot Xu Chunyang
2019-03-24 15:16 ` Michael Heerdegen
2019-03-25 0:06 ` Drew Adams [this message]
2019-03-25 1:33 ` Michael Heerdegen
2019-03-25 14:21 ` Drew Adams
2019-03-26 0:03 ` Michael Heerdegen
2019-03-26 9:49 ` Andreas Schwab
2019-03-27 1:50 ` Michael Heerdegen
2019-04-04 3:31 ` Noam Postavsky
2019-04-04 13:10 ` Eli Zaretskii
2019-04-04 13:25 ` Noam Postavsky
2019-04-04 22:28 ` Basil L. Contovounesios
2019-04-04 23:37 ` Noam Postavsky
2019-04-05 1:15 ` Basil L. Contovounesios
2019-04-05 6:21 ` Eli Zaretskii
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