From: "João Távora" <joaotavora@gmail.com>
To: Michael Brand <michael.ch.brand@gmail.com>
Cc: emacs-devel <emacs-devel@gnu.org>
Subject: Re: Multidimensional list comprehension with binding
Date: Mon, 11 Jun 2018 17:34:55 +0100 [thread overview]
Message-ID: <CALDnm51nBoOgQTgxLBXwebPKVGx2fLhoLyPzr080AWQLEHaYTQ@mail.gmail.com> (raw)
In-Reply-To: <CALn3zojMktT2eA4nVWGy5t+uM2p9Ae4dOKWkeKABgvm-3KMZ7A@mail.gmail.com>
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Your loop is breaking early because res iterates in
a list of only one value.
You want
for res = (length arg)
to replace the second line, probably.
On Mon, Jun 11, 2018 at 5:25 PM, Michael Brand <michael.ch.brand@gmail.com>
wrote:
> Hi all
>
> I try to replicate the following Python list comprehension with Emacs
> Lisp. It reports the list elements with its length when the length is
> even. The expectation is to calculate the length only once and to not
> use a second and nested list comprehension:
>
> #+begin_src python :results verbatim
> return [[res, arg]
> for arg in ["ab", "c", ""]
> for res in [len(arg)]
> if res % 2 == 0]
> #+end_src
> #+results:
> : [[2, 'ab'], [0, '']]
>
> The above result is as expected (Python 2.7 and 3.6).
>
> In my trial with Emacs Lisp the syntax for the equivalent expression
> seems to be accepted but the result is not the expected ((2 "ab") (0
> "")):
>
> #+begin_src emacs-lisp :results verbatim
> (cl-loop for arg in '("ab" "c" "")
> for res in (list (length arg))
> if (= (% res 2) 0)
> collect (list res arg))
> #+end_src
> #+results:
> : ((0 "ab"))
>
> Am I doing something wrong or is this a bug in
> emacs-26.1-2189-g8377ca6 and 26.1?
>
> Michael
>
> PS: A workaround would be this less elegant version:
>
> #+begin_src emacs-lisp :results verbatim
> (let (res)
> (cl-loop for arg in '("ab" "c" "")
> if (progn (setq res (length arg))
> (= (% res 2) 0))
> collect (list res arg)))
> #+end_src
> #+results:
> : ((2 "ab") (0 ""))
>
>
--
João Távora
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next prev parent reply other threads:[~2018-06-11 16:34 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-11 16:25 Multidimensional list comprehension with binding Michael Brand
2018-06-11 16:34 ` João Távora [this message]
2018-06-11 18:25 ` Michael Brand
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