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bug#24875: 26.0.50; In Dotted Pair Notation, the read function returns C
From: |
Lars Ingebrigtsen |
Subject: |
bug#24875: 26.0.50; In Dotted Pair Notation, the read function returns CDR if CAR is absent |
Date: |
Tue, 06 Jul 2021 19:15:09 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/28.0.50 (gnu/linux) |
Stefan Monnier <monnier@iro.umontreal.ca> writes:
> It's the "natural" behavior if you start from
>
> (Ea . Ed)
>
> as the notation for cons cells and extend it to
>
> (E1 E2 E3 .. . Ed)
>
> such that
>
> (E1 {foo} . Ed) = (E1 . ({foo} . Ed))
>
> because then you replace `{foo}` with the empty sequence and you get:
>
> (E1 . Ed) = (E1 . ( . Ed))
>
> and hence
>
> Ed = ( . Ed)
>
> It's not used very often, so in theory we could potentially change it,
> but I haven't seen any good alternative interpretation for it, and
> I don't see the benefit of signaling an error.
Ah, I see! Thanks for the explanation -- I now taken a stab at finding
a place in the Lisp manual to explain this (and explaining it slightly
shorter). Feel free to adjust as required.
--
(domestic pets only, the antidote for overdose, milk.)
bloggy blog: http://lars.ingebrigtsen.no