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bug#34975: 26.1.92; In backquote, the comma marker does not work with va

From: Noam Postavsky
Subject: bug#34975: 26.1.92; In backquote, the comma marker does not work with variable name started with dot
Date: Wed, 03 Apr 2019 23:31:24 -0400
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1.91 (gnu/linux)

Michael Heerdegen <address@hidden> writes:

> Drew Adams <address@hidden> writes:
>> > I dunno or have forgotten for what it had been intended, there are no
>> > real uses in the Emacs Elisp sources.
>> >

>> (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."
> Yes, thanks.  I also found that post:
> https://lists.gnu.org/archive/html/emacs-devel/2012-02/msg00330.html
> The state is the same as back then: ,. is a reader macro in Emacs Lisp,
> but the head of the expansion (the symbol named ",.") doesn't have any
> semantics, even not in backquote.

There's also Bug#19790 about this.  I think it makes sense to just
remove this reader macro, as far as I can tell, nobody really wants this
destructive splicing feature.

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