From: Lars Ingebrigtsen <larsi@gnus.org>
To: "T.V Raman" <raman@google.com>
Cc: emacs-devel@gnu.org
Subject: Re: lists, plain conses and length
Date: Fri, 04 Sep 2020 04:29:47 +0200 [thread overview]
Message-ID: <875z8ugtpg.fsf@gnus.org> (raw)
In-Reply-To: <20200904022334.791EBC2177B@raman-glaptop.localdomain> (T. V. Raman's message of "Thu, 3 Sep 2020 19:23:34 -0700 (PDT)")
"T.V Raman" <raman@google.com> writes:
> (length a)=> Debugger entered--Lisp error: (wrong-type-argument listp 2)
>
> Q: how does one distinguish a cons from a list.
> The error message for length may need fixing since it says the
> argument passed to it is not a list (it's correct) but then listp is wrong?
`length' (and many other functions) require what's called a "proper
list", which simply means that the cdr of the last cons cell is nil.
(length '(1 2 . 3))
-> (wrong-type-argument listp 3)
The predicate to use here is `proper-list-p'.
--
(domestic pets only, the antidote for overdose, milk.)
bloggy blog: http://lars.ingebrigtsen.no
next prev parent reply other threads:[~2020-09-04 2:29 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-04 2:23 lists, plain conses and length T.V Raman
2020-09-04 2:26 ` Stefan Monnier
2020-09-04 14:19 ` T.V Raman
2020-09-04 2:29 ` Lars Ingebrigtsen [this message]
2020-09-04 8:53 ` tomas
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